Toxicology – Class IB Antidysrhythmic Agents

Core Concept

Class IB antidysrhythmic drugs are fast sodium-channel blockers. Historically important examples include:

• Lidocaine
• Mexiletine
• Tocainide — now largely obsolete/discontinued in many regions

Phenytoin also has Class IB-like electrophysiologic properties but is better considered separately.

The most important modern toxicology distinction is that lidocaine toxicity is also local anesthetic systemic toxicity (LAST).

Major manifestations include:

• Early neurologic excitation
• Circumoral or tongue paresthesia
• Tinnitus
• Dizziness
• Seizures
• CNS depression/coma
• Hypotension
• Bradycardia
• Conduction disturbances
• Ventricular dysrhythmias
• Cardiovascular collapse

Severe local-anesthetic toxicity has an important modern rescue treatment:

Intravenous lipid emulsion (ILE)

Thus, the historical statement that there is “no specific antidote” requires qualification for severe lidocaine-associated LAST.

Mechanism

Class IB drugs block fast voltage-gated sodium channels.

Their effects are particularly prominent in:

• Depolarized tissue
• Ischemic myocardium
• Rapidly firing sodium channels

At therapeutic concentrations they can suppress abnormal ventricular automaticity.

With excessive exposure, sodium-channel blockade extends to normal cardiac and nervous tissue.

CNS Sodium-Channel Toxicity

Local anesthetics inhibit neuronal sodium channels.

As concentrations rise, inhibitory CNS pathways may be affected first, producing an initial excitatory phase.

Early symptoms may include:

• Circumoral numbness
• Tongue paresthesia
• Metallic or abnormal taste
• Tinnitus
• Dizziness
• Lightheadedness
• Visual disturbance
• Restlessness
• Tremor
• Confusion

This can progress to:

Agitation → seizure → CNS depression → coma → respiratory arrest

Cardiac Sodium-Channel Toxicity

At higher concentrations:

Na⁺-channel blockade → impaired conduction + reduced myocardial excitability/contractility

Possible consequences include:

• PR prolongation
• QRS widening
• AV block
• Bradycardia
• Ventricular dysrhythmias
• Hypotension
• Cardiogenic shock
• Asystole

Lidocaine

Lidocaine is used as:

• Local anesthetic
• Regional anesthetic
• Topical anesthetic
• Selected ventricular antiarrhythmic therapy

Toxicity may follow:

• Excessive injection
• Accidental intravascular administration
• Rapid systemic absorption
• Excessive topical exposure
• Impaired metabolism
• Medication error
• Rare oral exposure

Acute intravascular exposure can produce toxicity within minutes.

Local Anesthetic Systemic Toxicity – LAST

The modern syndrome of serious systemic toxicity from lidocaine or another local anesthetic is termed:

Local Anesthetic Systemic Toxicity (LAST)

LAST can produce both:

Neurologic toxicity

• Paresthesia
• Tinnitus
• Agitation
• Seizure
• Coma

Cardiovascular toxicity

• Hypotension
• Bradycardia
• Conduction block
• Ventricular dysrhythmia
• Cardiovascular collapse

The traditional progression from neurologic symptoms to cardiovascular toxicity is useful but not universal.

Some patients can present primarily with cardiovascular collapse.

Why Toxicity May Occur at Therapeutic Use

Risk depends on more than the total administered dose.

Important factors include:

• Injection site vascularity
• Accidental intravascular administration
• Rate of administration
• Patient size
• Age
• Cardiac output
• Hepatic function
• Protein binding
• Acid–base status
• Concomitant drugs

Therefore, a single rigid “toxic dose” cannot reliably predict LAST.

Lidocaine Metabolism

Lidocaine is predominantly metabolized in the liver.

Reduced clearance can occur with:

• Severe hepatic dysfunction
• Reduced hepatic blood flow
• Heart failure
• Shock

Repeated dosing or prolonged infusion can therefore cause accumulation.

Acidemia

Acidemia is particularly undesirable in severe local-anesthetic toxicity.

It may increase the active drug fraction and worsen:

• CNS toxicity
• Sodium-channel blockade
• Myocardial depression

Therefore, adequate oxygenation and ventilation are important during resuscitation.

Mexiletine

Mexiletine is an orally active Class IB sodium-channel blocker structurally and pharmacologically related to lidocaine.

Toxicity may produce:

• Nausea/vomiting
• Tremor
• Dizziness
• Ataxia
• Confusion
• Seizures
• Bradycardia
• Hypotension
• Conduction abnormalities
• Ventricular dysrhythmias

Neurologic toxicity may be prominent.

Tocainide

Tocainide is an older orally active lidocaine-like drug.

It has largely disappeared from contemporary clinical practice because of safety concerns and availability of alternatives.

Older toxicology descriptions remain historically relevant but are less important for current practice.

Neurologic Warning Signs

One of the important characteristics of Class IB toxicity is that neurologic symptoms may precede cardiovascular deterioration.

Early findings can include:

• Restlessness
• Dizziness
• Paresthesias
• Tinnitus
• Tremor
• Confusion
• Visual disturbances

These symptoms should not automatically be attributed to anxiety or hyperventilation when systemic local-anesthetic exposure is possible.

Seizures

Seizures are a major manifestation of severe lidocaine/LAST toxicity.

Seizures worsen toxicity by producing:

• Hypoxemia
• Hypercarbia
• Lactic acidosis
• Increased metabolic demand

These changes can intensify cardiovascular toxicity.

Therefore:

Rapid seizure control + oxygenation + ventilation are critical.

Seizure Treatment

Benzodiazepines are generally first-line therapy.

Persistent seizures may require escalation with appropriate anticonvulsant/anesthetic therapy.

Large doses of medications that significantly depress myocardial function should be used cautiously in a patient already developing cardiovascular collapse.

CNS Depression

As toxicity progresses, initial CNS excitation may transition to:

• Drowsiness
• Respiratory depression
• Coma
• Apnea

Airway and ventilation support may therefore become necessary rapidly.

Cardiovascular Findings

Severe toxicity may produce:

• Hypotension
• Bradycardia
• AV block
• QRS widening
• Ventricular dysrhythmias
• Cardiac arrest

Unlike Class IA agents, therapeutic Class IB drugs do not characteristically produce major QT prolongation.

Marked QT prolongation should therefore prompt consideration of:

• Coingestants
• Electrolyte abnormalities
• Another drug mechanism

ECG

Obtain an ECG in significant systemic toxicity.

Assess:

• Rate
• Rhythm
• PR interval
• QRS duration
• QT/QTc
• AV conduction
• Ventricular ectopy

However:

A normal ECG does not exclude early lidocaine toxicity.

Neurologic symptoms may occur before obvious ECG abnormalities.

Methemoglobinemia – Important Clarification

Methemoglobinemia is classically associated with certain local anesthetics, especially:

• Benzocaine
• Prilocaine

Lidocaine can cause methemoglobinemia, but it is substantially less characteristic than with benzocaine or prilocaine.

Consider it when there is:

• Cyanosis disproportionate to respiratory findings
• Low pulse-oximetry readings that do not normalize as expected with oxygen
• Chocolate-brown blood
• An exposure capable of oxidizing hemoglobin

Confirm with co-oximetry.

Laboratory Evaluation

Significant poisoning may warrant:

• Glucose
• Electrolytes
• Potassium
• Magnesium
• Calcium
• Bicarbonate
• Creatinine

Severe poisoning may additionally require:

• Blood gas
• Lactate
• Serial acid–base assessment

Co-oximetry is appropriate if methemoglobinemia is suspected.

Serum Drug Concentrations

Lidocaine or mexiletine concentrations can occasionally support a diagnosis but should not delay treatment.

Clinical toxicity correlates imperfectly with an isolated serum concentration.

Management should be based primarily on:

• Neurologic findings
• ECG
• Hemodynamics
• Respiratory status
• Exposure history

Routine serial drug levels are generally not required to determine recovery in most poisoning cases.

Initial Management

Priorities are:

Stop exposure → airway/oxygenation → control seizures → ECG/circulation → treat cardiovascular toxicity

For suspected LAST, preparation for lipid-emulsion therapy should occur early when severe neurologic or cardiovascular toxicity develops.

Stop Local Anesthetic Administration

If toxicity develops during local or regional anesthesia:

Immediately stop administration of the local anesthetic.

Preventing further systemic exposure is the first intervention.

Oxygenation and Ventilation

Avoid:

• Hypoxemia
• Hypercarbia
• Severe acidemia

These physiologic abnormalities can worsen local-anesthetic cardiotoxicity.

Early airway support may be necessary with:

• Recurrent seizures
• Coma
• Apnea
• Severe cardiovascular collapse

Intravenous Lipid Emulsion

This is the major modern addition missing from the older source.

IV lipid emulsion is an established rescue therapy for severe local anesthetic systemic toxicity, particularly when cardiovascular instability is present.

Its proposed mechanisms include:

• Sequestration/redistribution of lipophilic local anesthetic
• Improved myocardial substrate availability
• Direct beneficial effects on myocardial function

It is especially relevant to severe toxicity from highly lipophilic local anesthetics, but it is also used for severe lidocaine-associated LAST.

Exact administration should follow a current LAST resuscitation protocol.

Cardiac Arrest in LAST

Resuscitation differs somewhat from ordinary cardiac arrest because the myocardium is profoundly affected by the local anesthetic.

Priorities include:

• High-quality CPR
• Adequate oxygenation and ventilation
• Seizure control
• Correction of acidemia
• Early lipid emulsion for severe LAST
• Appropriate defibrillation when indicated

Resuscitation may need to be prolonged because severe local-anesthetic cardiotoxicity can be reversible as the drug redistributes and is metabolized.

Vasopressors

Vasopressor therapy may be required for severe hypotension.

In LAST, standard resuscitation drugs may need modification because excessive catecholamine exposure can worsen arrhythmogenicity and interfere with successful resuscitation.

Current LAST-specific resuscitation guidance should therefore be followed rather than simply applying an old dopamine-first algorithm.

Trendelenburg – Obsolete

Routine Trendelenburg positioning is not recommended as treatment for hypotension.

It does not provide reliable sustained improvement in perfusion and may worsen respiratory mechanics.

Sodium Bicarbonate

Sodium bicarbonate may be considered when significant sodium-channel-blocker physiology is present, particularly with:

• QRS widening
• Severe conduction slowing
• Acidemia

However, in severe LAST it does not replace lipid emulsion and comprehensive resuscitation.

Bradycardia and AV Block

Management centers on:

• Correcting hypoxemia/acidemia
• Treating systemic local-anesthetic toxicity
• Hemodynamic support

Temporary pacing may be considered for refractory severe bradycardia or high-grade block.

However, electrical pacing may be ineffective when myocardial sodium-channel blockade and contractile depression are profound.

Ventricular Dysrhythmias

Management includes:

• Correction of hypoxemia
• Correction of acidemia
• Treatment of electrolyte abnormalities
• Defibrillation/cardioversion when clinically indicated
• LAST-specific resuscitation

Avoid reflexively adding additional sodium-channel-blocking antiarrhythmics because they may worsen the underlying toxicity.

Antiarrhythmics in LAST

The older recommendation to treat lidocaine-induced dysrhythmia with additional Class I drugs should be approached cautiously.

Agents that further impair myocardial conduction can aggravate toxicity.

Treatment should instead focus on reversing the toxic physiology and following contemporary LAST resuscitation guidance.

Torsades de Pointes

Torsades is not the defining dysrhythmia of typical Class IB poisoning.

If polymorphic VT with prolonged QT occurs:

• Correct potassium
• Correct magnesium
• Remove QT-prolonging agents
• Give IV magnesium
• Electrically treat unstable dysrhythmia

Consider another drug or electrolyte abnormality if major QT prolongation dominates the presentation.

GI Decontamination

GI decontamination applies primarily to oral drugs such as mexiletine.

Do not induce vomiting.

Routine gastric lavage is obsolete.

Activated charcoal may occasionally be considered after a substantial recent oral ingestion when:

• The substance is adsorbable
• The airway is safe
• Aspiration risk is acceptable

It has no role in an already absorbed parenteral lidocaine exposure.

Extracorporeal Removal

Routine:

• Hemodialysis
• Hemoperfusion
• Hemofiltration
• Forced diuresis
• Urinary manipulation

do not represent standard toxin-removal strategies for lidocaine poisoning.

In catastrophic refractory cardiovascular collapse, the relevant extracorporeal intervention is circulatory support, not conventional dialysis.

VA-ECMO

Severe LAST is potentially reversible.

When cardiovascular collapse remains refractory despite appropriate resuscitation and lipid therapy, VA-ECMO may be considered at an experienced center.

This modernizes the older concept of emergency cardiopulmonary bypass.

ECMO supports circulation while the local anesthetic redistributes and is metabolized.

Differential Diagnosis

The combination of neurologic toxicity, seizures, and cardiovascular abnormalities can also occur with:

• Other Class I antiarrhythmics
• Tricyclic antidepressants
• Diphenhydramine
• Cocaine
• Chloroquine
• β-blockers
• Calcium-channel blockers
• Other local anesthetics

Nontoxicologic causes include:

• Hypoglycemia
• Electrolyte abnormalities
• Intracranial pathology
• CNS infection
• Primary seizure disorders

Monitoring

Significant toxicity requires monitoring of:

• Mental status
• Respiratory function
• Oxygenation
• Heart rate
• Blood pressure
• Continuous ECG
• Acid–base status when severe

Monitor severe cases for recurrent:

• Seizures
• Dysrhythmias
• Hypotension
• Respiratory failure

Observation

The historical universal 6-hour observation rule should not be applied mechanically.

Observation depends on:

• Drug
• Route
• Formulation
• Amount
• Timing
• Neurologic findings
• ECG
• Hemodynamics
• Coingestants

Parenteral intravascular lidocaine toxicity generally develops rapidly, whereas oral Class IB agents may have a different time course.

Admission

Monitored admission is appropriate for:

• Seizures
• Significant altered mental status
• Respiratory depression
• Hypotension
• Bradycardia
• AV block
• QRS widening
• Ventricular dysrhythmia
• Any clinically significant LAST

Severe cardiovascular or neurologic toxicity warrants intensive care.

Pregnancy

The historical FDA pregnancy letter categories are obsolete.

Management of severe poisoning during pregnancy prioritizes maternal:

• Airway
• Oxygenation
• Ventilation
• Seizure control
• Hemodynamics

Maternal stabilization is also fundamental to fetal oxygenation and perfusion.

Safeguarding

Rigid historical age cutoffs for neglect, abuse, or intentional poisoning are outdated.

Pediatric exposures should instead be assessed according to:

• Developmental capability
• Access
• Circumstances
• Consistency of history
• Recurrent unexplained exposure
• Broader safeguarding concerns

Prognosis

Early neurologic toxicity is often completely reversible when recognized and treated promptly.

Poor outcomes are associated with:

• Prolonged seizures
• Severe hypoxemia
• Acidemia
• Refractory ventricular dysrhythmia
• Prolonged cardiovascular collapse
• Hypoxic brain injury

Even severe LAST can be reversible with prolonged, aggressive resuscitation.

Important Modernization of the Older Source

• Lidocaine toxicity should be recognized within the modern syndrome of local anesthetic systemic toxicity (LAST).
• Neurologic manifestations often precede cardiovascular toxicity, but this sequence is not universal.
• A normal early ECG does not exclude LAST.
• Severe toxicity can cause seizures, conduction block, ventricular dysrhythmias, and cardiovascular collapse.
• IV lipid emulsion is a major modern rescue treatment for severe LAST and is absent from the historical source.
• Avoid hypoxemia, hypercarbia, and acidemia because they worsen toxicity.
• Benzodiazepines are first-line for seizures.
• Sodium bicarbonate may have a role in significant conduction toxicity but does not replace LAST-specific resuscitation.
• Additional sodium-channel-blocking antiarrhythmics can worsen toxicity.
• Major QT prolongation/torsades is less characteristic of Class IB poisoning than Class IA poisoning.
• Methemoglobinemia is much more strongly associated with benzocaine/prilocaine than with lidocaine.
• Routine gastric lavage is obsolete.
• Dialysis is not a useful primary toxin-removal strategy.
• Trendelenburg and dopamine-first hypotension management are outdated.
• “Cardiac bypass” is better conceptualized today as VA-ECMO for selected refractory, potentially reversible cardiovascular collapse.
• Fixed observation periods should be replaced by agent-, route-, formulation-, and symptom-based monitoring.

Key Points

• Class IB drugs block fast Na⁺ channels.
• Major examples are lidocaine and mexiletine; tocainide is largely historical.
• Lidocaine systemic toxicity = LAST.
• Early LAST may cause circumoral paresthesia, tinnitus, dizziness, agitation, and tremor.
• Severe toxicity progresses to seizures, coma, respiratory depression, bradycardia, conduction block, ventricular dysrhythmias, and cardiovascular collapse.
• Control seizures rapidly and prevent hypoxemia, hypercarbia, and acidemia.
• IV lipid emulsion is an important rescue therapy for severe LAST.
• ECG abnormalities may occur late; a normal ECG does not exclude early neurologic toxicity.
• Avoid adding drugs that worsen sodium-channel blockade.
• Severe refractory cardiovascular collapse may require VA-ECMO.

Toxicology – Class IA Antidysrhythmics: Quinidine and Disopyramide

Core Concept

Quinidine and disopyramide are Class IA sodium-channel-blocking antidysrhythmics. Their use has declined substantially because safer or more effective alternatives are available for many arrhythmias.

In overdose, the major dangers are:

• Fast sodium-channel blockade → QRS widening
• Potassium-channel blockade → QT prolongation
• Ventricular dysrhythmias
• Torsades de pointes
• Hypotension
• Bradycardia/AV block
• Seizures and CNS depression

Quinidine additionally produces cinchonism, while disopyramide has particularly prominent antimuscarinic and negative-inotropic effects.

There is no specific antidote.

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Mechanism – Class IA

Class IA agents block fast myocardial sodium channels.

This slows phase-0 depolarization:

Na⁺-channel blockade → slowed conduction → QRS widening

They also inhibit repolarizing potassium currents:

K⁺-channel blockade → prolonged repolarization → QT prolongation

Thus, Class IA poisoning can produce the dangerous combination of:

Wide QRS + prolonged QT

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Electrophysiologic Effects

Toxicity may cause:

• Slowed atrial conduction
• Slowed AV/intraventricular conduction
• QRS widening
• QT prolongation
• Bradyarrhythmias
• Ventricular tachycardia
• Ventricular fibrillation
• Torsades de pointes

These abnormalities may deteriorate rapidly.

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Quinidine

Quinidine is closely related to quinine.

In addition to sodium- and potassium-channel effects, it can produce:

• α-adrenergic blockade
• Hypotension
• GI symptoms
• Cinchonism

Its role in contemporary rhythm management is much narrower than suggested by older toxicology texts.

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Disopyramide

Disopyramide has important:

• Sodium-channel-blocking activity
• Potassium-channel effects
• Antimuscarinic activity
• Negative inotropic effects

Consequently, toxicity can include:

• Dry mouth
• Mydriasis
• Urinary retention
• Ileus
• Tachycardia
• Delirium
• Hypotension
• Heart failure/cardiogenic shock
• Conduction abnormalities

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Toxic Dose

There is no reliable universal toxic-dose threshold.

Toxicity can occur relatively close to therapeutic concentrations, especially when clearance is impaired or interacting medications are present.

Risk depends on:

• Agent
• Formulation
• Amount
• Renal/hepatic function
• Baseline conduction disease
• Electrolytes
• Drug interactions
• Coingestants

Clinical status and serial ECG findings are more important than the reported dose alone.

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Sustained-Release Preparations

Modified-release formulations can produce:

• Delayed absorption
• Delayed peak toxicity
• Prolonged cardiotoxicity

Antimuscarinic slowing of GI motility may further delay absorption.

An initially normal ECG therefore does not necessarily exclude later deterioration after a substantial sustained-release exposure.

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Cinchonism

Quinidine can produce a syndrome known as cinchonism.

Possible manifestations include:

• Tinnitus
• Hearing disturbance
• Headache
• Dizziness
• Nausea/vomiting
• Visual disturbance
• Confusion

More severe toxicity may cause marked visual impairment and serious neurologic or cardiovascular abnormalities.

Sudden tinnitus or visual symptoms in a patient taking quinidine should raise concern for toxicity.

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Neurologic Toxicity

Severe poisoning may produce:

• Confusion
• Somnolence
• Seizures
• Coma
• Respiratory depression

Seizures can worsen cardiotoxicity through:

Seizure → lactic acidosis → acidemia → increased sodium-channel toxicity

Rapid seizure control is therefore important.

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Cardiovascular Toxicity

Major manifestations include:

• QRS widening
• QT prolongation
• AV conduction delay
• Bradycardia
• Hypotension
• Ventricular tachycardia
• Ventricular fibrillation
• Torsades de pointes

Severe poisoning can progress to shock or cardiac arrest.

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Why Hypotension Occurs

Hypotension may result from several simultaneous mechanisms:

• Myocardial depression
• Sodium-channel blockade
• Dysrhythmia
• α-adrenergic blockade, particularly with quinidine
• Negative inotropy, particularly with disopyramide
• Acidemia

Therefore, treatment must address both circulation and the underlying electrical toxicity.

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ECG – Essential Test

Obtain an ECG promptly in suspected significant poisoning.

Assess:

• Heart rate
• Rhythm
• PR interval
• QRS duration
• QT/QTc
• AV conduction
• Ventricular ectopy

Symptomatic or significant exposures require continuous cardiac monitoring.

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QRS Widening

QRS widening reflects myocardial sodium-channel blockade.

Increasing QRS duration suggests increasing conduction toxicity and greater risk of ventricular dysrhythmia.

The ECG and clinical trajectory are more useful than a serum drug concentration for acute management.

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QT Prolongation

Class IA agents delay ventricular repolarization.

This produces:

QT prolongation → early afterdepolarizations → polymorphic VT → torsades de pointes

Risk increases with:

• Hypokalemia
• Hypomagnesemia
• Bradycardia
• Other QT-prolonging drugs
• Congenital long-QT susceptibility

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Quinidine and Diarrhea

Quinidine commonly causes gastrointestinal adverse effects, including diarrhea.

Significant diarrhea can cause:

K⁺ loss → hypokalemia → increased QT-related dysrhythmia risk

Thus electrolyte abnormalities can convert otherwise modest drug exposure into a more dangerous electrophysiologic situation.

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Syncope

Syncope in a patient receiving a QT-prolonging Class IA agent should prompt urgent consideration of a transient ventricular dysrhythmia, including torsades.

However, it should not be assumed automatically; other causes of syncope still require evaluation.

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Laboratory Evaluation

Important tests in significant poisoning include:

• Potassium
• Magnesium
• Calcium
• Bicarbonate
• Creatinine
• Glucose

Severe cases may additionally require:

• Blood gas
• Lactate
• Renal and hepatic assessment

Renal function is particularly relevant to drugs with substantial renal elimination.

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Serum Drug Concentrations

Quinidine or disopyramide concentrations may occasionally provide supportive information, but they generally do not determine emergency treatment.

Management should be guided by:

• ECG
• Blood pressure
• Mental status
• Seizures
• Perfusion
• Electrolytes

Do not delay treatment while awaiting a drug level.

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Initial Management

Priorities are:

Airway/breathing → ECG → circulation → correct electrolytes → control seizures → treat conduction abnormalities/torsades

Continuous monitoring is important because deterioration can be abrupt.

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Sodium Bicarbonate

Sodium bicarbonate is an important treatment when significant sodium-channel blockade is present.

Clinical indications include:

• Significant QRS widening
• Ventricular conduction toxicity
• Ventricular dysrhythmia associated with sodium-channel blockade
• Cardiovascular instability in the appropriate toxicologic context

Its effects come from:

• Sodium loading
• Alkalinization
• Reduced drug interaction with myocardial sodium channels

Treatment is guided by ECG response, hemodynamics, and acid–base/electrolyte status rather than blindly targeting a fixed dose.

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Avoid Acidemia

Acidemia can intensify sodium-channel-blocker cardiotoxicity.

Therefore:

• Treat seizures promptly
• Maintain adequate ventilation
• Correct hypoperfusion
• Address severe metabolic abnormalities

Excessive alkalinization should also be avoided because it can cause clinically important electrolyte disturbances.

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Torsades de Pointes

Management priorities include:

• Stop QT-prolonging drugs
• Correct hypokalemia
• Correct hypomagnesemia
• Correct other important electrolyte abnormalities
• IV magnesium
• Electrical defibrillation/cardioversion if unstable

For recurrent pause-dependent torsades associated with bradycardia, increasing the heart rate with overdrive pacing may be appropriate.

Isoproterenol has selected roles in acquired bradycardia-dependent torsades but is not appropriate for every prolonged-QT situation.

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Drugs to Avoid in Torsades

Avoid adding medications that further prolong repolarization.

In particular, additional Class IA drugs are inappropriate.

Other QT-prolonging antiarrhythmics may also worsen acquired long-QT-associated torsades.

The older recommendation lists should therefore be interpreted according to the mechanism rather than memorized as isolated drug names.

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Bradycardia and AV Block

Severe sodium-channel toxicity can produce:

• Bradycardia
• AV block
• Intraventricular conduction delay

Standard bradycardia measures may be attempted as clinically appropriate, but severe toxicologic conduction blockade may respond poorly.

Temporary pacing may be considered when clinically significant bradycardia or high-grade block persists despite correction of the toxicologic abnormalities.

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Important Pacing Limitation

Electrical capture does not guarantee effective mechanical cardiac output in profound sodium-channel-blocker poisoning.

Therefore, pacing should not distract from:

• Sodium bicarbonate therapy
• Correction of acidemia
• Electrolyte correction
• Hemodynamic support

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Hypotension

Management includes:

• Appropriate isotonic crystalloid when volume responsive
• Treatment of the dysrhythmia
• Sodium bicarbonate when sodium-channel cardiotoxicity is present
• Correction of acidemia

Persistent shock may require vasopressor therapy.

Norepinephrine is generally more appropriate than the historical routine dopamine-first approach for persistent vasodilatory hypotension.

Disopyramide-associated myocardial depression may complicate the hemodynamic picture.

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Seizures

Benzodiazepines are first-line therapy.

Persistent seizures may require:

• Additional benzodiazepines
• Phenobarbital
• Appropriate anesthetic therapy for refractory status epilepticus

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Phenytoin – Modern Correction

The historical recommendation to use phenytoin/fosphenytoin for refractory ventricular dysrhythmias is not part of routine modern management of Class IA poisoning.

Phenytoin itself interacts with sodium channels and can produce cardiovascular toxicity during IV administration.

It is also generally not preferred for toxicant-induced seizures.

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Lidocaine

Lidocaine may have a specialist-guided role in refractory ventricular dysrhythmias caused by sodium-channel blockers after appropriate sodium bicarbonate therapy.

It should not replace bicarbonate as the fundamental treatment of significant Class IA sodium-channel toxicity.

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Other Class I Antiarrhythmics

Avoid using additional Class IA agents because they can worsen:

• Sodium-channel blockade
• QRS widening
• QT prolongation
• Hypotension

Class IC sodium-channel blockers can likewise worsen conduction toxicity.

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GI Decontamination

Do not induce vomiting.

Seizures, dysrhythmias, or altered consciousness may develop abruptly.

Routine gastric lavage is obsolete.

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Activated Charcoal

A single dose of activated charcoal may be considered after a substantial recent oral exposure when:

• The drug is adsorbable
• The airway is safe
• Aspiration risk is acceptable

It should never delay cardiovascular stabilization.

Routine repeat-dose charcoal solely because GI motility is slowed is not established.

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Whole-Bowel Irrigation

Whole-bowel irrigation is not routine.

It may occasionally be considered after a substantial sustained-release ingestion when:

• The patient is sufficiently stable
• Bowel function is adequate
• The airway is protected
• There is no obstruction, ileus, or perforation

Because antimuscarinic effects can impair GI motility, WBI may sometimes be impractical or inappropriate.

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Extracorporeal Removal

Quinidine is generally poorly suited to routine extracorporeal removal because of its pharmacokinetic characteristics.

Historical suggestions that disopyramide should routinely undergo hemodialysis should also be interpreted cautiously.

Extracorporeal treatment is not the primary strategy for Class IA cardiotoxicity and should not delay:

• Sodium bicarbonate
• Dysrhythmia treatment
• Vasopressor support
• Electrolyte correction

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Refractory Cardiovascular Collapse

Massive sodium-channel-blocker poisoning may rarely cause shock or dysrhythmia refractory to conventional therapy.

Selected severe cases may require advanced rescue measures such as VA-ECMO at an experienced center.

The older reference to “cardiac bypass” is better understood in modern practice as temporary extracorporeal circulatory support for potentially reversible poisoning.

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Chronic Quinidine Adverse Effects

Therapeutic quinidine can rarely cause immune-mediated complications such as:

• Thrombocytopenia
• Hemolytic anemia
• Drug-induced lupus-like reactions

These are distinct from the acute electrophysiologic toxicity of overdose.

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Drug Interactions

Risk increases when Class IA agents are combined with:

• Other QT-prolonging medications
• Other sodium-channel blockers
• Drugs altering their metabolism
• Drugs causing hypokalemia or hypomagnesemia

A medication review is therefore particularly important when toxicity occurs at apparently therapeutic dosing.

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Differential Diagnosis

The combination of:

CNS toxicity + seizure + QRS widening

can also occur with:

• Tricyclic antidepressants
• Diphenhydramine and some other antihistamines
• Cocaine
• Flecainide/propafenone
• Chloroquine
• Other sodium-channel-blocking xenobiotics

QT prolongation and torsades have their own broad drug and electrolyte differential.

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Monitoring

Significant poisoning requires:

• Continuous ECG
• Blood pressure monitoring
• Respiratory monitoring
• Serial electrolytes
• Renal function
• Serial assessment of QRS and QT

Severe cases also require monitoring for:

• Seizures
• Acidemia
• Shock
• End-organ hypoperfusion

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Observation

A fixed 6-hour rule should not be applied universally.

Observation depends on:

• Agent
• Immediate- vs sustained-release formulation
• Amount
• ECG findings
• Symptoms
• Electrolytes
• Coingestants
• Clinical trajectory

Sustained-release products can produce delayed and prolonged toxicity.

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Admission

Monitored inpatient care is appropriate for:

• QRS widening
• Significant QT prolongation
• Dysrhythmia
• Syncope concerning for dysrhythmia
• Hypotension
• Bradycardia/high-grade AV block
• Seizures
• Altered mental status
• Significant cinchonism
• Large sustained-release exposure

Severe cardiovascular instability warrants ICU care.

⸻

Pregnancy

Historical FDA pregnancy letter categories are obsolete.

Clinically significant poisoning during pregnancy should be managed according to maternal physiology, with priority given to:

• Airway
• Oxygenation
• Cardiac rhythm
• Blood pressure
• Seizure control

Maternal dysrhythmia and shock also threaten fetal perfusion.

⸻

Safeguarding

Rigid historical age cutoffs for neglect, abuse, or intentional poisoning are outdated.

Pediatric exposure should instead be assessed according to developmental capability, access, circumstances, history consistency, recurrent events, and other safeguarding concerns.

⸻

Prognosis

Mild poisoning may resolve with monitoring and supportive treatment.

Severe poisoning carries risk of:

• Ventricular dysrhythmia
• Torsades
• Cardiogenic/vasodilatory shock
• Seizures
• Respiratory failure
• Cardiac arrest
• Hypoxic brain injury

Outcome is strongly influenced by early recognition and correction of electrophysiologic toxicity.

⸻

Important Modernization of the Older Source

• Quinidine and disopyramide are now used much less commonly than historically.
• Class IA = sodium-channel blockade + potassium-channel blockade.
• Therefore, poisoning can produce both QRS widening and QT prolongation.
• Quinidine can cause cinchonism.
• Disopyramide has prominent antimuscarinic and negative-inotropic effects.
• Sodium bicarbonate is central when clinically important sodium-channel blockade is present.
• Correct K⁺ and Mg²⁺ aggressively when QT-related dysrhythmia risk is present.
• IV magnesium is central to torsades management.
• Overdrive pacing may help selected recurrent bradycardia-dependent torsades.
• Phenytoin/fosphenytoin is not routine modern therapy for Class IA cardiotoxicity or toxicologic seizures.
• Additional Class IA/IC sodium-channel blockers should generally be avoided.
• Norepinephrine is generally favored over routine dopamine-first treatment for persistent vasodilatory shock.
• Routine gastric lavage is obsolete.
• Repeated charcoal is not automatically indicated because of slowed GI motility.
• WBI has only a selective role in substantial sustained-release exposure.
• Drug concentrations should not delay ECG-directed treatment.
• Severe refractory cardiovascular collapse may warrant advanced extracorporeal circulatory support.

Key Points

• Class IA toxicity = Na⁺ blockade + K⁺ blockade.
• Na⁺ blockade → QRS widening and conduction slowing.
• K⁺ blockade → QT prolongation and torsades risk.
• Quinidine additionally causes cinchonism.
• Disopyramide has strong antimuscarinic and myocardial-depressant effects.
• Obtain an early ECG and continuously monitor significant poisoning.
• Sodium bicarbonate is first-line for important sodium-channel cardiotoxicity.
• Magnesium and electrolyte correction are central for torsades.
• Benzodiazepines are first-line for seizures.
• Avoid additional Class IA/IC agents that worsen conduction.
• Sustained-release formulations may cause delayed toxicity.
• There is no specific antidote.

Toxicology – Tricyclic Antidepressants (TCAs)

Core Concept

Tricyclic antidepressants are highly important toxicologic drugs because substantial overdose can rapidly produce:

• Myocardial sodium-channel blockade
• Hypotension
• Ventricular dysrhythmias
• Seizures
• CNS depression/coma
• Antimuscarinic effects

A patient who initially appears relatively stable can deteriorate abruptly.

The central treatment principle is:

Suspected TCA cardiotoxicity + QRS widening/hypotension/ventricular dysrhythmia → sodium bicarbonate

There is no single specific antidote that reverses all TCA toxicity.

Important TCAs

Examples include:

• Amitriptyline
• Nortriptyline
• Imipramine
• Desipramine
• Clomipramine
• Doxepin
• Trimipramine
• Protriptyline

Some older agents such as dosulepin/dothiepin remain relevant in certain regions but are used less widely.

Therapeutic Uses

Although TCAs were developed as antidepressants, modern uses can include:

• Depression
• Neuropathic pain
• Migraine/headache prevention
• Selected chronic pain syndromes
• Sleep-related/off-label indications
• Enuresis with selected agents

Their narrow therapeutic index makes overdose substantially more dangerous than overdose with many newer antidepressants.

Mechanisms of Toxicity

TCA poisoning is not caused by a single receptor effect.

Important mechanisms include:

1. Fast sodium-channel blockade
2. Muscarinic receptor antagonism
3. α₁-Adrenergic blockade
4. Norepinephrine and serotonin reuptake inhibition
5. Potassium-channel effects contributing to repolarization abnormalities

The most immediately life-threatening mechanism is usually cardiac sodium-channel blockade.

Sodium-Channel Blockade

TCAs inhibit fast sodium channels in myocardial tissue.

This slows phase-0 depolarization:

Na⁺ channel blockade → slowed conduction → QRS widening → ventricular dysrhythmia/cardiovascular collapse

Sodium-channel blockade also contributes to neurologic toxicity.

Importantly, TCA binding to sodium channels becomes more problematic with acidemia.

Why Acidemia Is Dangerous

Acidemia can:

• Increase the pharmacologically active fraction of TCA
• Enhance sodium-channel binding
• Worsen conduction slowing
• Increase hypotension and dysrhythmia risk

This creates a dangerous cycle:

Seizure/shock → lactic acidosis → greater TCA cardiotoxicity → worsening shock

Rapid control of seizures, adequate ventilation, and correction of clinically important acidemia are therefore critical.

Antimuscarinic Effects

TCAs may produce:

• Mydriasis
• Dry mouth
• Tachycardia
• Flushing
• Reduced bowel sounds
• Urinary retention
• Delirium

However, the full classic antimuscarinic toxidrome is not required.

Life-threatening sodium-channel toxicity can occur whether or not peripheral antimuscarinic findings are dramatic.

α₁-Adrenergic Blockade

Peripheral α₁ blockade causes vasodilation and contributes to:

• Orthostatic hypotension
• Severe hypotension in overdose

TCA-related shock may therefore combine:

• Vasodilation
• Myocardial depression
• Dysrhythmia
• Acidemia

Toxic Dose

There is no perfectly reliable dose threshold for an individual patient.

Risk generally increases with:

• Larger mg/kg exposure
• Potent cardiotoxic TCAs
• Coingestants
• Delayed treatment
• Acidemia
• Underlying cardiac disease

Because the consequences can be severe, suspected significant pediatric ingestion deserves particular caution.

Clinical findings and the ECG are more important than the reported dose alone.

Clinical Presentation

A useful way to remember serious TCA poisoning is:

“3 Cs”

• Coma
• Convulsions
• Cardiotoxicity

Additional findings include:

• Tachycardia
• Hypotension
• Antimuscarinic findings
• Respiratory depression
• Hyperthermia
• Metabolic acidosis

Neurologic Toxicity

Possible manifestations include:

• Drowsiness
• Confusion
• Agitation
• Delirium
• Seizures
• Coma

Neurologic and cardiovascular toxicity often occur together because sodium-channel blockade affects both tissues.

Seizures

TCA-associated seizures may occur abruptly.

Complications include:

• Hypoxemia
• Aspiration
• Lactic acidosis
• Hyperthermia
• Rhabdomyolysis
• Worsening cardiotoxicity

Because acidosis increases TCA cardiotoxicity, seizure control has direct cardiovascular importance.

Seizure Treatment

Benzodiazepines are first-line therapy.

Persistent toxicologic seizures may require:

• Additional benzodiazepines
• Phenobarbital
• Appropriate anesthetic therapy for refractory status epilepticus

The historical recommendation for phenytoin is outdated.

Phenytoin is generally not preferred in TCA-induced seizures, particularly because it has sodium-channel-blocking properties and does not address the toxicologic mechanism effectively.

Cardiovascular Toxicity

Common findings include:

• Sinus tachycardia
• QRS widening
• Hypotension

Severe poisoning can progress to:

• AV/intraventricular conduction disturbances
• Ventricular tachycardia
• Ventricular fibrillation
• Profound shock
• Cardiac arrest

Abrupt deterioration is characteristic of serious TCA poisoning.

ECG – One of the Most Important Tests

Obtain an ECG promptly after suspected significant TCA poisoning.

Assess:

• Heart rate and rhythm
• QRS duration
• QT/QTc
• Terminal QRS morphology
• Lead aVR

Continuous cardiac monitoring is appropriate for clinically important poisoning.

QRS Widening

A QRS around or above 100 ms increases concern for clinically meaningful sodium-channel blockade.

Increasing QRS duration generally correlates with increasing toxicity.

Historical studies associated progressively wider QRS complexes with greater risks of:

• Seizures
• Ventricular dysrhythmias

However, old thresholds such as 100, 120, or 160 ms should not be interpreted as absolute biological cutoffs.

Treat the ECG, clinical condition, and trajectory, not a single number.

Lead aVR

TCA sodium-channel blockade may produce:

• Prominent terminal R wave in aVR
• Increased R/S ratio in aVR

These findings support sodium-channel toxicity but should not be interpreted in isolation.

QRS duration and the overall clinical syndrome remain important.

QT Prolongation

TCAs can also prolong ventricular repolarization.

QT prolongation may reflect potassium-channel effects and can increase dysrhythmia risk.

Correct important:

• Hypokalemia
• Hypomagnesemia
• Hypocalcemia

and avoid additional QT-prolonging drugs when possible.

Sodium Bicarbonate

Sodium bicarbonate is the cornerstone of treatment for significant TCA cardiotoxicity.

Important indications include:

• Clinically significant QRS widening
• Ventricular dysrhythmia due to sodium-channel blockade
• Hypotension associated with TCA cardiotoxicity
• Other convincing evidence of serious myocardial sodium-channel blockade

It should not be reserved only for cardiac arrest.

How Sodium Bicarbonate Works

Two major mechanisms are important:

1. Sodium loading

Increasing extracellular sodium helps overcome sodium-channel blockade.

2. Alkalemia

Increasing serum pH reduces the active free fraction and decreases drug interaction with myocardial sodium channels.

Clinical effects may include:

• QRS narrowing
• Improved blood pressure
• Reduced ventricular ectopy
• Improved conduction

Bicarbonate Endpoints

Treatment is guided by:

• QRS narrowing
• Rhythm
• Blood pressure
• Perfusion
• Acid–base status
• Serum sodium and potassium

Excessive treatment can cause:

• Severe alkalemia
• Hypernatremia
• Hypokalemia
• Reduced ionized calcium
• Volume overload

Therefore, therapy requires repeated ECG and laboratory reassessment.

Ventilation

Adequate ventilation is especially important because hypercapnia produces respiratory acidosis and may worsen TCA cardiotoxicity.

If intubation is required, avoid unnecessary hypoventilation and abrupt development of acidemia.

At the same time, excessive combined hyperventilation and bicarbonate can produce dangerous alkalemia.

Hypotension

TCA-associated hypotension can result from:

• α₁ blockade
• Myocardial depression
• Sodium-channel blockade
• Dysrhythmia
• Acidemia
• Relative volume depletion

Management must therefore address more than simple fluid loss.

Management of TCA Hypotension

Initial measures include:

• Airway and oxygenation support
• Appropriate isotonic crystalloid
• Sodium bicarbonate when cardiotoxicity is present
• Correction of seizures and acidemia

Persistent hypotension may require a vasopressor.

Norepinephrine is generally favored for persistent TCA-associated vasodilatory shock.

Routine dopamine-first therapy is outdated.

Routine Trendelenburg positioning is also obsolete.

Ventricular Dysrhythmias

First priorities include:

• Sodium bicarbonate
• Correction of hypoxemia
• Correction of acidemia
• Control of seizures
• Correction of major electrolyte abnormalities

If serious ventricular dysrhythmia persists despite appropriate alkalinization/sodium therapy, specialist-guided additional antiarrhythmic therapy may be considered.

Antiarrhythmics to Avoid

Drugs that further inhibit cardiac sodium channels can worsen TCA toxicity.

Particularly avoid routine use of:

• Class IA agents
• Class IC agents

Examples include:

• Quinidine
• Procainamide
• Flecainide
• Propafenone

Lidocaine

Lidocaine has historically been used for refractory ventricular dysrhythmias after adequate sodium bicarbonate treatment.

Its use is secondary to correction of the underlying sodium-channel toxicity and should be guided by toxicology/cardiology expertise.

The historical antiarrhythmic algorithms in older references should not replace current toxicologic resuscitation practice.

Physostigmine – Avoid

Despite antimuscarinic findings, physostigmine should generally not be used in significant TCA poisoning.

TCA overdose carries risks of:

• QRS widening
• Conduction block
• Ventricular dysrhythmia
• Seizures

Increasing cholinergic activity in this setting can produce dangerous bradyarrhythmia or other complications.

Antimuscarinic delirium in a suspected TCA overdose should therefore not be treated as though it were a pure atropine-like poisoning.

Flumazenil – Avoid

Flumazenil should generally be avoided in suspected TCA or mixed antidepressant overdose.

If a benzodiazepine has been coingested, its anticonvulsant activity may actually be protective.

Flumazenil can remove this protection and precipitate:

• Seizures
• Severe withdrawal
• Increased cardiotoxic complications

Pulmonary Complications

Severe poisoning can cause:

• Respiratory depression
• Loss of airway reflexes
• Aspiration pneumonitis
• Acute lung injury

Early airway control may be appropriate when severe CNS depression or recurrent seizures compromise ventilation or airway protection.

Rhabdomyolysis

Rhabdomyolysis can follow:

• Recurrent seizures
• Hyperthermia
• Prolonged coma
• Severe agitation

Monitor selected severe cases with:

• CK
• Potassium
• Creatinine
• Urinalysis
• Urine output

Metabolic Acidosis

Lactic acidosis can result from:

• Seizures
• Shock
• Hypoxemia

Because acidemia potentiates sodium-channel toxicity, it is especially dangerous in TCA overdose.

Treatment focuses on correcting the underlying seizure, ventilation, and circulatory failure while using sodium bicarbonate when indicated for TCA cardiotoxicity.

Diagnosis

Diagnosis is based on:

• Medication history
• Clinical syndrome
• ECG
• Coingestant assessment

A quantitative serum TCA concentration is generally not useful for guiding acute treatment.

A severely toxic patient can require aggressive treatment regardless of the measured serum concentration.

Laboratory Evaluation

Significant poisoning may require:

• Electrolytes
• Bicarbonate
• Glucose
• Creatinine
• Blood gas
• CK after prolonged seizure/coma
• Lactate in severe shock or seizures

Serial testing is more useful than isolated values when severe toxicity is evolving.

Occult Coingestion

Intentional TCA overdose commonly requires evaluation for additional substances.

Acetaminophen testing is often appropriate because early acetaminophen poisoning may be clinically silent.

Other testing should be directed by history and clinical findings.

Neuroimaging and Lumbar Puncture

Head CT, lumbar puncture, cultures, and other neurologic investigations are not automatically required simply because TCA poisoning causes coma or seizures.

They are appropriate when:

• Diagnosis remains uncertain
• Trauma is possible
• Focal findings are present
• Infection is suspected
• Clinical course is inconsistent with poisoning

GI Decontamination

Do not induce vomiting.

Abrupt seizures and coma make emesis particularly dangerous.

Gastric Lavage

Routine gastric lavage is obsolete and should not be performed simply because the ingestion is large.

Potential harms include:

• Aspiration
• Mechanical injury
• Delays in resuscitation

Airway, ECG, seizures, and circulation take priority.

Activated Charcoal

A single dose of activated charcoal may be considered after a substantial recent ingestion when:

• The airway is protected or reliably intact
• Aspiration risk is acceptable
• The drug remains potentially available for adsorption

TCAs slow gastric motility, so delayed absorption may occur.

However, this does not justify routine repeated charcoal administration.

Extracorporeal Removal

Hemodialysis and hemoperfusion do not meaningfully enhance TCA elimination because TCAs generally have:

• Large volumes of distribution
• Extensive tissue distribution
• High protein binding

Extracorporeal therapy should therefore not delay proven supportive and sodium-bicarbonate-based treatment.

Refractory Cardiovascular Collapse

Rare massive TCA poisoning can produce profound shock or cardiac arrest despite conventional therapy.

Selected refractory cases may involve specialist consideration of:

• Intravenous lipid emulsion as rescue therapy
• VA-ECMO or other extracorporeal circulatory support

Evidence for lipid emulsion outside established indications is limited, so it is not routine first-line treatment.

ECMO provides temporary cardiopulmonary support while the toxin redistributes and is metabolized; it does not directly remove the TCA.

Monitoring

Clinically significant TCA poisoning requires close monitoring of:

• Airway and ventilation
• Mental status
• Heart rate
• Blood pressure
• Continuous ECG
• QRS duration
• Temperature
• Acid–base status
• Electrolytes

Severe cases also require monitoring for:

• Rhabdomyolysis
• Renal injury
• Recurrent seizures
• Shock

Observation

Most serious TCA toxicity becomes evident relatively early after a substantial immediate-release ingestion, but the older universal “6-hour rule” should not be treated as absolute.

Disposition depends on:

• Agent and formulation
• Estimated exposure
• Symptoms
• Serial ECGs
• Hemodynamics
• Mental status
• Coingestants
• Clinical trajectory

Persistent tachycardia alone should be interpreted in the overall clinical context rather than automatically defining severe poisoning.

Admission

ICU-level care is appropriate for:

• QRS widening
• Significant hypotension
• Ventricular dysrhythmia
• Recurrent seizures
• Coma
• Respiratory failure
• Severe acidemia
• Other evidence of major cardiotoxicity

Pregnancy

Historical FDA pregnancy letter categories are obsolete.

In maternal TCA poisoning, priorities remain:

• Airway and ventilation
• Seizure control
• Hemodynamic stabilization
• Correction of cardiotoxicity

Maternal hypoxemia, hypotension, seizures, and dysrhythmias also threaten fetal perfusion and oxygenation.

Life-saving sodium bicarbonate and resuscitative treatment should not be withheld because of pregnancy.

Safeguarding

Rigid historical age thresholds for assuming neglect, abuse, or intentional ingestion are inappropriate.

Pediatric poisoning should instead be assessed according to:

• Developmental capability
• Medication accessibility
• Exposure circumstances
• Consistency of the history
• Recurrent unexplained events
• Broader safeguarding concerns

Intentional self-poisoning requires appropriate safety assessment after medical stabilization.

Prognosis

Patients who survive the acute cardiotoxic phase without major hypoxic or ischemic complications can recover completely.

Poor outcomes are generally associated with:

• Prolonged hypotension
• Refractory ventricular dysrhythmia
• Cardiac arrest
• Recurrent/prolonged seizures
• Severe acidemia
• Hypoxic brain injury

Important Modernization of the Older Source

• TCA lethality is driven particularly by fast myocardial sodium-channel blockade, not simply monoamine-reuptake inhibition.
• QRS widening is one of the most useful bedside markers of serious toxicity.
• Historical QRS thresholds predict increasing risk but are not absolute treatment boundaries.
• Lead aVR abnormalities support the diagnosis but should not be interpreted alone.
• Acidemia potentiates TCA cardiotoxicity.
• Sodium bicarbonate is first-line for significant QRS widening, ventricular conduction toxicity, and TCA-associated hypotension/cardiotoxicity.
• Phenytoin is generally not preferred for TCA-induced seizures.
• Class IA and IC antiarrhythmics can worsen sodium-channel blockade and should generally be avoided.
• Physostigmine should generally be avoided in significant TCA poisoning.
• Flumazenil is hazardous in TCA/mixed overdose because it may precipitate seizures.
• Norepinephrine is generally preferred over the historical dopamine-first strategy for persistent shock.
• Trendelenburg positioning is obsolete.
• Ipecac and routine gastric lavage have no modern role.
• Routine repeated activated charcoal is not established.
• Hemodialysis and hemoperfusion do not meaningfully remove TCAs.
• Selected refractory cardiovascular collapse may require rescue therapies such as ECMO.
• Serum TCA concentrations do not guide acute treatment.

Key Points

• TCA overdose = coma + convulsions + cardiotoxicity.
• Na⁺-channel blockade → QRS widening → ventricular dysrhythmia and shock.
• Acidemia worsens sodium-channel blockade.
• Sodium bicarbonate is the cornerstone of cardiotoxicity treatment.
• Benzodiazepines are first-line for seizures.
• Avoid phenytoin as routine seizure therapy, physostigmine, flumazenil, and class IA/IC antiarrhythmics in significant TCA toxicity.
• Obtain an early ECG and follow serial QRS/rhythm changes.
• Significant hypotension, QRS widening, seizure, coma, or dysrhythmia warrants intensive monitoring.
• Serum TCA levels are not useful for bedside treatment decisions.
• Patients can deteriorate abruptly, so early recognition and aggressive supportive care are critical.

241. Toxicology – Tricyclic Antidepressants (TCAs)

Core Concept

Tricyclic antidepressants are highly important toxicologic drugs because substantial overdose can rapidly produce:

Myocardial sodium-channel blockade   Hypotension   Ventricular dysrhythmias   Seizures   CNS depression/coma   Antimuscarinic effects

A patient who initially appears relatively stable can deteriorate abruptly.

The central treatment principle is:

Suspected TCA cardiotoxicity + QRS widening/hypotension/ventricular dysrhythmia → sodium bicarbonate

There is no single specific antidote that reverses all TCA toxicity.

⸻

Important TCAs

Examples include:

Amitriptyline   Nortriptyline   Imipramine   Desipramine   Clomipramine   Doxepin   Trimipramine   Protriptyline

Some older agents such as dosulepin/dothiepin remain relevant in certain regions but are used less widely.

⸻

Therapeutic Uses

Although TCAs were developed as antidepressants, modern uses can include:

Depression   Neuropathic pain   Migraine/headache prevention   Selected chronic pain syndromes   Sleep-related/off-label indications   Enuresis with selected agents

Their narrow therapeutic index makes overdose substantially more dangerous than overdose with many newer antidepressants.

⸻

Mechanisms of Toxicity

TCA poisoning is not caused by a single receptor effect.

Important mechanisms include:

Fast sodium-channel blockade   Muscarinic receptor antagonism   α₁-Adrenergic blockade   Norepinephrine and serotonin reuptake inhibition   Potassium-channel effects contributing to repolarization abnormalities

The most immediately life-threatening mechanism is usually cardiac sodium-channel blockade.

⸻

Sodium-Channel Blockade

TCAs inhibit fast sodium channels in myocardial tissue.

This slows phase-0 depolarization:

Na⁺ channel blockade → slowed conduction → QRS widening → ventricular dysrhythmia/cardiovascular collapse

Sodium-channel blockade also contributes to neurologic toxicity.

Importantly, TCA binding to sodium channels becomes more problematic with acidemia.

⸻

Why Acidemia Is Dangerous

Acidemia can:

Increase the pharmacologically active fraction of TCA   Enhance sodium-channel binding   Worsen conduction slowing   Increase hypotension and dysrhythmia risk

This creates a dangerous cycle:

Seizure/shock → lactic acidosis → greater TCA cardiotoxicity → worsening shock

Rapid control of seizures, adequate ventilation, and correction of clinically important acidemia are therefore critical.

⸻

Antimuscarinic Effects

TCAs may produce:

Mydriasis   Dry mouth   Tachycardia   Flushing   Reduced bowel sounds   Urinary retention   Delirium

However, the full classic antimuscarinic toxidrome is not required.

Life-threatening sodium-channel toxicity can occur whether or not peripheral antimuscarinic findings are dramatic.

⸻

α₁-Adrenergic Blockade

Peripheral α₁ blockade causes vasodilation and contributes to:

Orthostatic hypotension   Severe hypotension in overdose

TCA-related shock may therefore combine:

Vasodilation   Myocardial depression   Dysrhythmia   Acidemia

⸻

Toxic Dose

There is no perfectly reliable dose threshold for an individual patient.

Risk generally increases with:

Larger mg/kg exposure   Potent cardiotoxic TCAs   Coingestants   Delayed treatment   Acidemia   Underlying cardiac disease

Because the consequences can be severe, suspected significant pediatric ingestion deserves particular caution.

Clinical findings and the ECG are more important than the reported dose alone.

⸻

Clinical Presentation

A useful way to remember serious TCA poisoning is:

“3 Cs”

Coma   Convulsions   Cardiotoxicity

Additional findings include:

Tachycardia   Hypotension   Antimuscarinic findings   Respiratory depression   Hyperthermia   Metabolic acidosis

⸻

Neurologic Toxicity

Possible manifestations include:

Drowsiness   Confusion   Agitation   Delirium   Seizures   Coma

Neurologic and cardiovascular toxicity often occur together because sodium-channel blockade affects both tissues.

⸻

Seizures

TCA-associated seizures may occur abruptly.

Complications include:

Hypoxemia   Aspiration   Lactic acidosis   Hyperthermia   Rhabdomyolysis   Worsening cardiotoxicity

Because acidosis increases TCA cardiotoxicity, seizure control has direct cardiovascular importance.

⸻

Seizure Treatment

Benzodiazepines are first-line therapy.

Persistent toxicologic seizures may require:

Additional benzodiazepines   Phenobarbital   Appropriate anesthetic therapy for refractory status epilepticus

The historical recommendation for phenytoin is outdated.

Phenytoin is generally not preferred in TCA-induced seizures, particularly because it has sodium-channel-blocking properties and does not address the toxicologic mechanism effectively.

⸻

Cardiovascular Toxicity

Common findings include:

Sinus tachycardia   QRS widening   Hypotension

Severe poisoning can progress to:

AV/intraventricular conduction disturbances   Ventricular tachycardia   Ventricular fibrillation   Profound shock   Cardiac arrest

Abrupt deterioration is characteristic of serious TCA poisoning.

⸻

ECG – One of the Most Important Tests

Obtain an ECG promptly after suspected significant TCA poisoning.

Assess:

Heart rate and rhythm   QRS duration   QT/QTc   Terminal QRS morphology   Lead aVR

Continuous cardiac monitoring is appropriate for clinically important poisoning.

⸻

QRS Widening

A QRS around or above 100 ms increases concern for clinically meaningful sodium-channel blockade.

Increasing QRS duration generally correlates with increasing toxicity.

Historical studies associated progressively wider QRS complexes with greater risks of:

Seizures   Ventricular dysrhythmias

However, old thresholds such as 100, 120, or 160 ms should not be interpreted as absolute biological cutoffs.

Treat the ECG, clinical condition, and trajectory, not a single number.

⸻

Lead aVR

TCA sodium-channel blockade may produce:

Prominent terminal R wave in aVR   Increased R/S ratio in aVR

These findings support sodium-channel toxicity but should not be interpreted in isolation.

QRS duration and the overall clinical syndrome remain important.

⸻

QT Prolongation

TCAs can also prolong ventricular repolarization.

QT prolongation may reflect potassium-channel effects and can increase dysrhythmia risk.

Correct important:

Hypokalemia   Hypomagnesemia   Hypocalcemia

and avoid additional QT-prolonging drugs when possible.

⸻

Sodium Bicarbonate

Sodium bicarbonate is the cornerstone of treatment for significant TCA cardiotoxicity.

Important indications include:

Clinically significant QRS widening   Ventricular dysrhythmia due to sodium-channel blockade   Hypotension associated with TCA cardiotoxicity   Other convincing evidence of serious myocardial sodium-channel blockade

It should not be reserved only for cardiac arrest.

⸻

How Sodium Bicarbonate Works

Two major mechanisms are important:

1. Sodium loading

Increasing extracellular sodium helps overcome sodium-channel blockade.

2. Alkalemia

Increasing serum pH reduces the active free fraction and decreases drug interaction with myocardial sodium channels.

Clinical effects may include:

QRS narrowing   Improved blood pressure   Reduced ventricular ectopy   Improved conduction

⸻

Bicarbonate Endpoints

Treatment is guided by:

QRS narrowing   Rhythm   Blood pressure   Perfusion   Acid–base status   Serum sodium and potassium

Excessive treatment can cause:

Severe alkalemia   Hypernatremia   Hypokalemia   Reduced ionized calcium   Volume overload

Therefore, therapy requires repeated ECG and laboratory reassessment.

⸻

Ventilation

Adequate ventilation is especially important because hypercapnia produces respiratory acidosis and may worsen TCA cardiotoxicity.

If intubation is required, avoid unnecessary hypoventilation and abrupt development of acidemia.

At the same time, excessive combined hyperventilation and bicarbonate can produce dangerous alkalemia.

⸻

Hypotension

TCA-associated hypotension can result from:

α₁ blockade   Myocardial depression   Sodium-channel blockade   Dysrhythmia   Acidemia   Relative volume depletion

Management must therefore address more than simple fluid loss.

⸻

Management of TCA Hypotension

Initial measures include:

Airway and oxygenation support   Appropriate isotonic crystalloid   Sodium bicarbonate when cardiotoxicity is present   Correction of seizures and acidemia

Persistent hypotension may require a vasopressor.

Norepinephrine is generally favored for persistent TCA-associated vasodilatory shock.

Routine dopamine-first therapy is outdated.

Routine Trendelenburg positioning is also obsolete.

⸻

Ventricular Dysrhythmias

First priorities include:

Sodium bicarbonate   Correction of hypoxemia   Correction of acidemia   Control of seizures   Correction of major electrolyte abnormalities

If serious ventricular dysrhythmia persists despite appropriate alkalinization/sodium therapy, specialist-guided additional antiarrhythmic therapy may be considered.

⸻

Antiarrhythmics to Avoid

Drugs that further inhibit cardiac sodium channels can worsen TCA toxicity.

Particularly avoid routine use of:

Class IA agents   Class IC agents

Examples include:

Quinidine   Procainamide   Flecainide   Propafenone

⸻

Lidocaine

Lidocaine has historically been used for refractory ventricular dysrhythmias after adequate sodium bicarbonate treatment.

Its use is secondary to correction of the underlying sodium-channel toxicity and should be guided by toxicology/cardiology expertise.

The historical antiarrhythmic algorithms in older references should not replace current toxicologic resuscitation practice.

⸻

Physostigmine – Avoid

Despite antimuscarinic findings, physostigmine should generally not be used in significant TCA poisoning.

TCA overdose carries risks of:

QRS widening   Conduction block   Ventricular dysrhythmia   Seizures

Increasing cholinergic activity in this setting can produce dangerous bradyarrhythmia or other complications.

Antimuscarinic delirium in a suspected TCA overdose should therefore not be treated as though it were a pure atropine-like poisoning.

⸻

Flumazenil – Avoid

Flumazenil should generally be avoided in suspected TCA or mixed antidepressant overdose.

If a benzodiazepine has been coingested, its anticonvulsant activity may actually be protective.

Flumazenil can remove this protection and precipitate:

Seizures   Severe withdrawal   Increased cardiotoxic complications

⸻

Pulmonary Complications

Severe poisoning can cause:

Respiratory depression   Loss of airway reflexes   Aspiration pneumonitis   Acute lung injury

Early airway control may be appropriate when severe CNS depression or recurrent seizures compromise ventilation or airway protection.

⸻

Rhabdomyolysis

Rhabdomyolysis can follow:

Recurrent seizures   Hyperthermia   Prolonged coma   Severe agitation

Monitor selected severe cases with:

CK   Potassium   Creatinine   Urinalysis   Urine output

⸻

Metabolic Acidosis

Lactic acidosis can result from:

Seizures   Shock   Hypoxemia

Because acidemia potentiates sodium-channel toxicity, it is especially dangerous in TCA overdose.

Treatment focuses on correcting the underlying seizure, ventilation, and circulatory failure while using sodium bicarbonate when indicated for TCA cardiotoxicity.

⸻

Diagnosis

Diagnosis is based on:

Medication history   Clinical syndrome   ECG   Coingestant assessment

A quantitative serum TCA concentration is generally not useful for guiding acute treatment.

A severely toxic patient can require aggressive treatment regardless of the measured serum concentration.

⸻

Laboratory Evaluation

Significant poisoning may require:

Electrolytes   Bicarbonate   Glucose   Creatinine   Blood gas   CK after prolonged seizure/coma   Lactate in severe shock or seizures

Serial testing is more useful than isolated values when severe toxicity is evolving.

⸻

Occult Coingestion

Intentional TCA overdose commonly requires evaluation for additional substances.

Acetaminophen testing is often appropriate because early acetaminophen poisoning may be clinically silent.

Other testing should be directed by history and clinical findings.

⸻

Neuroimaging and Lumbar Puncture

Head CT, lumbar puncture, cultures, and other neurologic investigations are not automatically required simply because TCA poisoning causes coma or seizures.

They are appropriate when:

Diagnosis remains uncertain   Trauma is possible   Focal findings are present   Infection is suspected   Clinical course is inconsistent with poisoning

⸻

GI Decontamination

Do not induce vomiting.

Abrupt seizures and coma make emesis particularly dangerous.

⸻

Gastric Lavage

Routine gastric lavage is obsolete and should not be performed simply because the ingestion is large.

Potential harms include:

Aspiration   Mechanical injury   Delays in resuscitation

Airway, ECG, seizures, and circulation take priority.

⸻

Activated Charcoal

A single dose of activated charcoal may be considered after a substantial recent ingestion when:

The airway is protected or reliably intact   Aspiration risk is acceptable   The drug remains potentially available for adsorption

TCAs slow gastric motility, so delayed absorption may occur.

However, this does not justify routine repeated charcoal administration.

⸻

Extracorporeal Removal

Hemodialysis and hemoperfusion do not meaningfully enhance TCA elimination because TCAs generally have:

Large volumes of distribution   Extensive tissue distribution   High protein binding

Extracorporeal therapy should therefore not delay proven supportive and sodium-bicarbonate-based treatment.

⸻

Refractory Cardiovascular Collapse

Rare massive TCA poisoning can produce profound shock or cardiac arrest despite conventional therapy.

Selected refractory cases may involve specialist consideration of:

Intravenous lipid emulsion as rescue therapy   VA-ECMO or other extracorporeal circulatory support

Evidence for lipid emulsion outside established indications is limited, so it is not routine first-line treatment.

ECMO provides temporary cardiopulmonary support while the toxin redistributes and is metabolized; it does not directly remove the TCA.

⸻

Monitoring

Clinically significant TCA poisoning requires close monitoring of:

Airway and ventilation   Mental status   Heart rate   Blood pressure   Continuous ECG   QRS duration   Temperature   Acid–base status   Electrolytes

Severe cases also require monitoring for:

Rhabdomyolysis   Renal injury   Recurrent seizures   Shock

⸻

Observation

Most serious TCA toxicity becomes evident relatively early after a substantial immediate-release ingestion, but the older universal “6-hour rule” should not be treated as absolute.

Disposition depends on:

Agent and formulation   Estimated exposure   Symptoms   Serial ECGs   Hemodynamics   Mental status   Coingestants   Clinical trajectory

Persistent tachycardia alone should be interpreted in the overall clinical context rather than automatically defining severe poisoning.

⸻

Admission

ICU-level care is appropriate for:

QRS widening   Significant hypotension   Ventricular dysrhythmia   Recurrent seizures   Coma   Respiratory failure   Severe acidemia   Other evidence of major cardiotoxicity

⸻

Pregnancy

Historical FDA pregnancy letter categories are obsolete.

In maternal TCA poisoning, priorities remain:

Airway and ventilation   Seizure control   Hemodynamic stabilization   Correction of cardiotoxicity

Maternal hypoxemia, hypotension, seizures, and dysrhythmias also threaten fetal perfusion and oxygenation.

Life-saving sodium bicarbonate and resuscitative treatment should not be withheld because of pregnancy.

⸻

Safeguarding

Rigid historical age thresholds for assuming neglect, abuse, or intentional ingestion are inappropriate.

Pediatric poisoning should instead be assessed according to:

Developmental capability   Medication accessibility   Exposure circumstances   Consistency of the history   Recurrent unexplained events   Broader safeguarding concerns

Intentional self-poisoning requires appropriate safety assessment after medical stabilization.

⸻

Prognosis

Patients who survive the acute cardiotoxic phase without major hypoxic or ischemic complications can recover completely.

Poor outcomes are generally associated with:

Prolonged hypotension   Refractory ventricular dysrhythmia   Cardiac arrest   Recurrent/prolonged seizures   Severe acidemia   Hypoxic brain injury

⸻

Important Modernization of the Older Source

TCA lethality is driven particularly by fast myocardial sodium-channel blockade, not simply monoamine-reuptake inhibition.   QRS widening is one of the most useful bedside markers of serious toxicity.   Historical QRS thresholds predict increasing risk but are not absolute treatment boundaries.   Lead aVR abnormalities support the diagnosis but should not be interpreted alone.   Acidemia potentiates TCA cardiotoxicity.   Sodium bicarbonate is first-line for significant QRS widening, ventricular conduction toxicity, and TCA-associated hypotension/cardiotoxicity.   Phenytoin is generally not preferred for TCA-induced seizures.   Class IA and IC antiarrhythmics can worsen sodium-channel blockade and should generally be avoided.   Physostigmine should generally be avoided in significant TCA poisoning.   Flumazenil is hazardous in TCA/mixed overdose because it may precipitate seizures.   Norepinephrine is generally preferred over the historical dopamine-first strategy for persistent shock.   Trendelenburg positioning is obsolete.   Ipecac and routine gastric lavage have no modern role.   Routine repeated activated charcoal is not established.   Hemodialysis and hemoperfusion do not meaningfully remove TCAs.   Selected refractory cardiovascular collapse may require rescue therapies such as ECMO.   Serum TCA concentrations do not guide acute treatment.

Key Points

TCA overdose = coma + convulsions + cardiotoxicity.   Na⁺-channel blockade → QRS widening → ventricular dysrhythmia and shock.   Acidemia worsens sodium-channel blockade.   Sodium bicarbonate is the cornerstone of cardiotoxicity treatment.   Benzodiazepines are first-line for seizures.   Avoid phenytoin as routine seizure therapy, physostigmine, flumazenil, and class IA/IC antiarrhythmics in significant TCA toxicity.   Obtain an early ECG and follow serial QRS/rhythm changes.   Significant hypotension, QRS widening, seizure, coma, or dysrhythmia warrants intensive monitoring.   Serum TCA levels are not useful for bedside treatment decisions.   Patients can deteriorate abruptly, so early recognition and aggressive supportive care are critical.

Toxicology – Venlafaxine and Related SNRIs

Core Concept

The historical term “bicyclic antidepressants” is no longer a useful modern toxicology classification for venlafaxine.

Venlafaxine is now classified as a serotonin–norepinephrine reuptake inhibitor (SNRI). Its active metabolite, desvenlafaxine, is also marketed as an antidepressant.

Venlafaxine overdose is clinically important because substantial poisoning can cause:

• Seizures
• Serotonin toxicity
• Tachycardia and hypertension
• CNS depression
• QRS or QT abnormalities
• Ventricular dysrhythmias
• Hypotension and cardiogenic shock in severe cases

The older description of venlafaxine overdose as predominantly “mild CNS depression” substantially understates its potential severity.

There is no specific antidote.

Historical Drugs

Older literature grouped several structurally related drugs together.

Venlafaxine

Remains widely used and is the principal clinically relevant drug in this older chapter.

Viloxazine

The source describes viloxazine as investigational. This is outdated.

Viloxazine has subsequently been used clinically in some jurisdictions, including as a nonstimulant treatment for ADHD. Its modern pharmacology and overdose profile should not simply be assumed to be identical to venlafaxine.

Zimelidine

Withdrawn decades ago after association with serious neurologic adverse effects, including Guillain–Barré syndrome. It is primarily of historical interest.

Mechanism of Venlafaxine

Venlafaxine inhibits reuptake of:

• Serotonin (5-HT)
• Norepinephrine (NE)

This increases synaptic monoamine concentrations.

At lower therapeutic exposure, serotonergic effects predominate; noradrenergic effects become more prominent as exposure increases.

It has relatively little direct muscarinic, histamine, or α₁-antagonist activity compared with classic TCAs.

Metabolism

Venlafaxine undergoes hepatic metabolism, importantly through CYP2D6, producing the active metabolite:

O-desmethylvenlafaxine = desvenlafaxine

Both parent drug and active metabolite contribute to clinical effects.

Renal elimination is important for the drug and its metabolites, so renal impairment can prolong exposure.

Immediate-Release vs Extended-Release

Venlafaxine is available in immediate- and extended-release formulations.

This distinction matters in overdose because modified-release products can produce:

• Delayed absorption
• Delayed peak toxicity
• Prolonged symptoms
• Delayed seizures

Therefore, a patient who initially appears well may not necessarily remain asymptomatic after a substantial extended-release ingestion.

Toxic Dose

There is no single reliable dose threshold that predicts an individual’s course.

In general:

Increasing exposure → increasing risk of seizures and cardiovascular toxicity

Very large overdoses can cause severe or fatal poisoning.

The historical statement that death had not been reported is obsolete.

Modern experience confirms that venlafaxine overdose can be fatal, particularly after massive ingestion or severe cardiovascular toxicity.

Neurologic Toxicity

Possible manifestations include:

• Dizziness
• Tremor
• Agitation
• Confusion
• Somnolence
• Myoclonus
• Seizures
• Coma

Seizures are one of the hallmark complications of significant venlafaxine overdose.

They may occur after an initially relatively benign period.

Seizures

Venlafaxine lowers the seizure threshold.

Seizures may be:

• Generalized
• Recurrent
• Delayed, especially with modified-release formulations

Complications include:

• Hypoxemia
• Aspiration
• Lactic acidosis
• Hyperthermia
• Rhabdomyolysis
• Acute kidney injury

Seizure Management

Benzodiazepines are first-line treatment for toxicant-induced seizures.

Persistent seizures may require:

• Additional benzodiazepines
• Phenobarbital
• Appropriate anesthetic therapy for refractory status epilepticus

Phenytoin is generally not preferred for toxicologic seizures.

Serotonin Toxicity

Venlafaxine can produce serotonin syndrome, particularly after substantial overdose or combination with other serotonergic drugs.

Important findings include:

• Agitation
• Diaphoresis
• Tremor
• Hyperreflexia
• Inducible or spontaneous clonus
• Ocular clonus
• Increased bowel activity
• Hyperthermia in severe cases

Severe toxicity may cause:

• Marked hyperthermia
• Rhabdomyolysis
• Coagulopathy
• Metabolic acidosis
• Multiorgan failure

Important Drug Interactions

Serotonin toxicity risk increases with other serotonergic agents, including:

• MAO inhibitors
• SSRIs
• Other SNRIs
• Certain serotonergic analgesics
• Some other serotonergic medications

Combination with an MAO inhibitor is particularly hazardous.

Sedative coingestants may increase CNS and respiratory depression.

Cardiovascular Effects

Mild or moderate poisoning commonly produces:

• Sinus tachycardia
• Mild hypertension

Increasing toxicity may produce:

• Hypotension
• QRS prolongation
• QT prolongation
• Ventricular dysrhythmias
• Myocardial dysfunction

Massive poisoning can produce profound cardiovascular collapse.

Severe Cardiovascular Toxicity

In very large overdose, venlafaxine may produce:

• Reduced myocardial contractility
• Cardiogenic shock
• Ventricular dysrhythmias
• Severe hypotension

This is clinically distinct from the usually mild cardiovascular effects of many SSRI overdoses.

ECG

An ECG is important after significant venlafaxine overdose.

Assess:

• Heart rate
• Rhythm
• QRS duration
• QT/QTc
• Conduction abnormalities

Continuous cardiac monitoring is appropriate for symptomatic or substantial poisoning.

QRS Widening

Marked QRS widening after venlafaxine overdose suggests clinically significant myocardial conduction toxicity.

Sodium bicarbonate has been used when substantial sodium-channel-like conduction toxicity is present, particularly with:

• Significant QRS widening
• Ventricular dysrhythmia associated with conduction slowing

However, venlafaxine cardiotoxicity can involve more than a simple TCA-like sodium-channel mechanism, so bicarbonate should not be assumed to reverse every cardiovascular manifestation.

QT Prolongation

QT prolongation may occur, particularly in severe poisoning or when additional risk factors are present.

Correct:

• Hypokalemia
• Hypomagnesemia
• Hypocalcemia when clinically significant

Avoid additional QT-prolonging medications when possible.

Torsades de pointes is managed according to standard toxicologic resuscitation principles.

Blood Pressure

Early findings may include hypertension because of increased noradrenergic activity.

Severe poisoning may instead progress to:

• Vasodilatory hypotension
• Myocardial dysfunction
• Cardiogenic shock

Thus, the blood-pressure pattern can change as toxicity becomes more severe.

Hypotension

Management includes assessment of:

• Volume status
• Cardiac function
• Rhythm
• Acid–base status
• Coingestants

Appropriate isotonic crystalloid may be used when indicated.

Persistent shock may require vasopressor support, commonly with norepinephrine, while severe myocardial dysfunction may require more advanced hemodynamic support.

Routine Trendelenburg positioning and a dopamine-first approach are outdated.

Refractory Cardiogenic Shock

Massive venlafaxine poisoning can occasionally cause profound reversible myocardial failure.

Severe refractory cases may require advanced critical-care support, including consideration of mechanical circulatory support such as VA-ECMO in appropriately selected patients.

ECMO supports circulation while the drug is metabolized; it does not function as a venlafaxine antidote.

Hyperthermia

Hyperthermia should raise concern for:

• Serotonin toxicity
• Recurrent seizures
• Severe agitation

Marked hyperthermia is an emergency because it can rapidly cause:

• Rhabdomyolysis
• Hepatic injury
• Coagulopathy
• Renal failure
• CNS injury

Management emphasizes sedation, control of muscular activity, and active cooling.

Antipyretics are not useful for serotonin-mediated hyperthermia.

Hyponatremia / SIADH

SNRIs can be associated with:

• SIADH
• Hyponatremia

This is particularly relevant during therapeutic use in susceptible patients, such as older adults or those taking other medications that promote hyponatremia.

Severe hyponatremia can itself produce:

• Confusion
• Seizures
• Coma

Therefore, electrolytes are important when neurologic findings are present.

Gastrointestinal Effects

Possible findings include:

• Nausea
• Vomiting
• Dry mouth
• Abdominal discomfort

These are generally secondary concerns compared with neurologic and cardiovascular toxicity.

Diagnosis

Diagnosis is primarily based on:

• Drug and formulation
• Amount
• Time of ingestion
• Symptoms
• ECG
• Coingestants

Serum venlafaxine concentrations are not routinely useful for emergency management.

Laboratory Evaluation

Mild uncomplicated exposure may require limited testing.

Significant poisoning may warrant:

• Electrolytes
• Sodium
• Potassium
• Bicarbonate
• Creatinine
• Glucose
• CK if seizures/hyperthermia occur
• Blood gas and lactate in severe poisoning

Severe hyperthermia or shock may additionally require:

• Liver tests
• Coagulation studies
• Serial renal assessment

Occult Coingestion

Intentional antidepressant overdose should prompt assessment for important coingestants.

Acetaminophen testing is often appropriate because clinically important early poisoning can be asymptomatic.

Salicylate testing should be based on the circumstances and clinical/acid–base findings rather than used mechanically in every case.

Imaging and Lumbar Puncture

Head CT, lumbar puncture, and cultures are not routinely required merely because venlafaxine causes altered mental status or a seizure.

They should be considered when:

• The diagnosis remains uncertain
• Focal neurologic deficits occur
• Trauma is possible
• CNS infection is suspected
• Mental status fails to follow the expected toxicologic course

Initial Management

Priorities are:

Airway/breathing → seizure control → temperature → ECG/circulation → identify serotonin toxicity → monitor for delayed deterioration

Supportive care remains the foundation of treatment.

Physostigmine

Physostigmine has no routine role in venlafaxine poisoning.

Venlafaxine does not produce a classic pure antimuscarinic syndrome, and significant poisoning carries seizure and cardiovascular risks.

GI Decontamination

Do not induce vomiting.

Routine gastric lavage is obsolete.

A single dose of activated charcoal may be considered after a substantial recent ingestion when:

• The airway is reliably protected
• Aspiration risk is acceptable
• Expected benefit justifies treatment

It should never delay stabilization of seizures, hyperthermia, or cardiovascular toxicity.

Extended-Release Ingestion

Because extended-release venlafaxine can remain within the GI tract for prolonged periods, substantial ingestion may require longer monitoring than an immediate-release exposure.

Selected very large modified-release ingestions may warrant specialist discussion regarding additional GI decontamination strategies, but these are not routine measures for every overdose.

Hemodialysis and Hemoperfusion

Conventional hemodialysis and hemoperfusion do not provide useful routine venlafaxine elimination because of its pharmacokinetic characteristics.

Dialysis may still be required for a separate indication such as severe renal failure, but it should not be viewed as the primary antidotal treatment.

Monitoring

Significant poisoning requires monitoring of:

• Mental status
• Respiratory function
• Heart rate
• Blood pressure
• ECG
• Core temperature
• Seizure activity

Severe cases additionally require monitoring of:

• CK
• Electrolytes
• Renal function
• Lactate/acid–base status
• Liver function
• Coagulation

Observation

The older assumption that toxicity simply appears within a few hours and resolves within 24–48 hours is too rigid.

Observation should consider:

• Immediate- vs extended-release preparation
• Estimated exposure
• Symptoms
• ECG
• Seizures
• Serotonin toxicity
• Coingestants
• Clinical trajectory

Delayed seizures are particularly important after extended-release venlafaxine.

Admission

Hospital admission is appropriate for:

• Seizure
• Persistent altered mental status
• Serotonin toxicity
• Hyperthermia
• Significant QRS or QT abnormality
• Dysrhythmia
• Persistent hypotension
• Evidence of myocardial dysfunction
• Significant metabolic or end-organ injury

Severe cardiovascular toxicity, recurrent seizures, or marked hyperthermia warrants intensive care.

Pregnancy

The historical FDA pregnancy letter category is obsolete.

Management of significant overdose during pregnancy prioritizes maternal:

• Airway
• Oxygenation
• Blood pressure
• Temperature
• Seizure control

Severe maternal hypoxemia, shock, hyperthermia, or seizures also threaten fetal well-being.

Safeguarding

The historical rigid age thresholds for neglect or intentional poisoning are inappropriate.

Pediatric exposures should instead be evaluated according to:

• Developmental capability
• Medication accessibility
• Circumstances
• Consistency of history
• Recurrent unexplained exposures
• Broader safeguarding concerns

Intentional self-poisoning requires appropriate safety assessment after medical stabilization.

Prognosis

Most mild venlafaxine overdoses recover with supportive treatment.

Increasingly severe poisoning carries risk of:

• Recurrent seizures
• Serotonin toxicity
• Hyperthermia
• Rhabdomyolysis
• Ventricular dysrhythmias
• Cardiogenic shock
• Multiorgan injury

Massive venlafaxine overdose can be fatal, contrary to the historical source.

Important Modernization of the Older Source

• “Bicyclic antidepressant” is an outdated classification for venlafaxine; it is an SNRI.
• Desvenlafaxine is its pharmacologically active metabolite and also a marketed drug.
• Venlafaxine overdose is not simply a mild CNS-depressant syndrome.
• Seizures are a major hallmark of significant poisoning.
• Extended-release preparations can cause delayed seizures and prolonged toxicity.
• Serotonin syndrome is an important complication, especially with serotonergic coexposure.
• Massive overdose can cause QRS/QT abnormalities, ventricular dysrhythmias, myocardial dysfunction, cardiogenic shock, and death.
• Zimelidine is historical; viloxazine should not simply be treated as interchangeable with venlafaxine.
• Phenytoin is generally not preferred for toxicologic seizures.
• Trendelenburg and routine dopamine-first shock treatment are outdated.
• Severe reversible cardiogenic shock may occasionally require advanced mechanical circulatory support.
• Routine gastric lavage is obsolete.
• Activated charcoal has a selective role when the airway is safe.
• Hemodialysis does not meaningfully enhance venlafaxine elimination.
• Observation should account for formulation and delayed toxicity rather than follow a fixed short period.
• There is no specific antidote.

Key Points

• Venlafaxine = SNRI, not a clinically useful “bicyclic” category.
• Major overdose risks = seizures + serotonin toxicity + cardiovascular toxicity.
• Mild poisoning often causes tachycardia, hypertension, tremor, and CNS symptoms.
• Severe poisoning can progress to hyperthermia, QRS/QT abnormalities, dysrhythmias, hypotension, and cardiogenic shock.
• Extended-release venlafaxine can produce delayed toxicity.
• Benzodiazepines are first-line for seizures.
• Significant hyperthermia requires control of muscular activity and active cooling.
• Obtain ECG monitoring after substantial or symptomatic overdose.
• Dialysis is not useful for routine toxin removal.
• No specific antidote exists.

Toxicology – Anticholinergic (Antimuscarinic) Compounds

Core Concept

A wide range of prescription drugs, OTC medications, plants, and other substances can produce antimuscarinic toxicity, traditionally called the anticholinergic syndrome.

The classic toxidrome consists of:

Delirium + mydriasis + dry skin/mucosa + tachycardia + hyperthermia + decreased bowel activity + urinary retention

Severe poisoning may cause:

• Extreme agitation
• Hallucinations
• Seizures
• Coma
• Hyperthermia
• Rhabdomyolysis
• Cardiovascular toxicity

Most cases are diagnosed clinically from the toxidrome, rather than by serum drug concentrations.

Terminology

“Anticholinergic” is commonly used, but antimuscarinic is more pharmacologically precise for this syndrome.

These drugs competitively antagonize acetylcholine primarily at muscarinic receptors.

They do not simply block every cholinergic receptor.

Common Causes

Important antimuscarinic drugs include:

• Atropine
• Scopolamine
• Benztropine
• Trihexyphenidyl
• Oxybutynin
• Tolterodine
• Solifenacin
• Trospium
• Dicyclomine
• Glycopyrrolate
• Cyclopentolate
• Tropicamide
• Ipratropium

Many other medications have clinically important antimuscarinic properties, including:

• Diphenhydramine
• Doxylamine
• Tricyclic antidepressants
• Some antipsychotics
• Some skeletal-muscle relaxants
• Some antiparkinsonian drugs

Certain plants containing atropine-like alkaloids can produce the same syndrome.

Muscarinic Physiology

Acetylcholine acting at muscarinic receptors normally contributes to:

• Salivation
• Lacrimation
• Sweating
• Pupillary constriction
• Accommodation
• GI motility
• Bladder contraction
• Parasympathetic cardiac regulation

Blocking these actions produces the characteristic toxidrome.

Central vs Peripheral Effects

Antimuscarinic toxicity can be divided conceptually into:

Central effects

• Agitation
• Confusion
• Delirium
• Hallucinations
• Disorganized behavior
• Seizures
• Coma

Peripheral effects

• Mydriasis
• Blurred vision
• Dry mouth
• Dry skin
• Flushing
• Tachycardia
• Reduced bowel sounds
• Ileus
• Urinary retention
• Hyperthermia

Not every patient develops every finding.

Classic Clinical Mnemonic

The traditional descriptions remain useful:

• “Mad as a hatter” → delirium
• “Blind as a bat” → mydriasis/cycloplegia
• “Dry as a bone” → dry skin and mucosa
• “Red as a beet” → flushing
• “Hot as a hare” → hyperthermia
• “Full as a flask” → urinary retention

These are memory aids rather than diagnostic criteria.

Mental Status

Central antimuscarinic toxicity commonly produces a distinctive agitated delirium.

Features can include:

• Confusion
• Disorientation
• Inattention
• Picking at imaginary objects
• Visual hallucinations
• Paranoia
• Incoherent speech
• Restlessness
• Attempting to climb from bed

The patient may interact with objects or people that are not present.

Severe poisoning may progress from agitation to:

• Somnolence
• Seizures
• Coma

Tachycardia

Sinus tachycardia is common because vagal muscarinic influence on the heart is reduced.

However, the older statement that absence of tachycardia should strongly call the diagnosis into question is too rigid.

Heart rate can be influenced by:

• Age
• Coingestants
• β-blockers
• Baseline conduction disease
• Specific antimuscarinic agent
• Timing of examination

Diagnosis should be based on the entire syndrome.

Eyes

Typical findings include:

• Mydriasis
• Reduced pupillary response
• Cycloplegia
• Blurred near vision
• Photophobia

Ophthalmic antimuscarinic medications can occasionally cause systemic toxicity, particularly in susceptible patients.

Unilateral Mydriasis

Accidental exposure of only one eye to:

• Atropine
• Tropicamide
• Cyclopentolate
• Scopolamine-like substances

can produce unilateral pharmacologic mydriasis.

This can mimic a neurologic emergency.

However, unexplained new anisocoria should not automatically be attributed to a medication unless the exposure history and examination are convincing.

Skin and Secretions

Typical findings include:

• Warm skin
• Dry skin
• Flushing
• Dry mouth
• Reduced salivation

Sweating is impaired because eccrine sweat glands use muscarinic cholinergic signaling, despite belonging anatomically to the sympathetic nervous system.

This is an important physiologic exception.

Hyperthermia

Hyperthermia can result from:

• Impaired sweating
• Reduced heat dissipation
• Agitation
• Excessive muscular activity

Severe hyperthermia can cause:

• Rhabdomyolysis
• Acute kidney injury
• Coagulopathy
• Hepatic injury
• CNS injury

Children may be particularly susceptible to impaired heat dissipation.

Gastrointestinal Effects

Muscarinic blockade reduces GI motility.

Possible findings include:

• Reduced bowel sounds
• Constipation
• Abdominal distension
• Ileus

Slowed GI motility can also delay absorption of an ingested drug, contributing to prolonged or delayed toxicity.

Urinary Retention

Muscarinic blockade interferes with detrusor contraction and may cause:

• Difficulty voiding
• Bladder distension
• Urinary retention

A distended bladder can itself worsen agitation and delirium.

Bladder assessment is therefore useful in a persistently agitated patient.

Sympathomimetic vs Antimuscarinic Toxicity

Both syndromes can cause:

• Agitation
• Tachycardia
• Hypertension
• Mydriasis
• Hyperthermia

A useful distinction is:

Sympathomimetic toxicity → usually sweaty

Antimuscarinic toxicity → usually dry

Sympathomimetic poisoning also tends to preserve or increase bowel activity, whereas antimuscarinic toxicity tends to reduce it.

No single finding is perfectly diagnostic.

Cardiovascular Toxicity

Pure antimuscarinic poisoning usually produces:

• Sinus tachycardia

Major dysrhythmias are uncommon with drugs whose only important mechanism is muscarinic blockade.

Therefore:

QRS widening, major QT abnormalities, ventricular dysrhythmias, or severe hypotension should raise concern for additional toxic mechanisms or coingestants.

Diphenhydramine – Important Exception

Large diphenhydramine overdoses can cause both:

• Antimuscarinic delirium
• Myocardial sodium-channel blockade

This can produce:

• QRS widening
• Ventricular dysrhythmias
• Seizures

Therefore, a patient may appear strongly antimuscarinic while simultaneously having potentially dangerous cardiotoxicity.

Tricyclic Antidepressants

TCAs can cause:

• Antimuscarinic findings
• CNS toxicity
• Seizures
• α₁ blockade
• Sodium-channel blockade

A patient with antimuscarinic delirium plus:

• QRS widening
• Hypotension
• Ventricular dysrhythmia
• Significant terminal R-wave abnormalities in aVR

should be evaluated for TCA or another sodium-channel-blocking drug.

Seizures

Seizures can occur in severe poisoning or when the causative drug has additional proconvulsant properties.

Management includes:

• Airway and oxygenation assessment
• Benzodiazepines as first-line anticonvulsant therapy
• Correction of glucose and important metabolic abnormalities
• Escalation according to toxicologic status-epilepticus management if persistent

Rhabdomyolysis

Severe agitation, hyperthermia, or seizures can produce rhabdomyolysis.

Evaluate significant cases with:

• CK
• Potassium
• Creatinine
• Urinalysis
• Urine output

Prompt control of agitation and temperature helps prevent this complication.

Diagnosis

Antimuscarinic poisoning is primarily a clinical diagnosis.

Important clues include:

• Characteristic toxidrome
• Medication history
• Plant exposure
• OTC medication access
• Prescription medications
• Coingestants

Routine measurement of serum concentrations is usually unnecessary for pure antimuscarinic agents.

Laboratory Evaluation

Mild uncomplicated cases may require little testing.

In significant toxicity, useful studies may include:

• Glucose
• Electrolytes
• Bicarbonate
• Creatinine
• CK
• Urinalysis
• Temperature measurement

Additional testing depends on the differential diagnosis and suspected drug.

ECG

An ECG is particularly important when:

• The exact drug is uncertain
• Intentional overdose occurred
• Diphenhydramine is suspected
• TCA exposure is possible
• Seizures occur
• Significant tachycardia or hypotension is present

Look for:

• QRS widening
• QT prolongation
• Conduction abnormalities
• Ventricular dysrhythmias

The ECG is also critical when considering physostigmine.

Occult Coingestion

Intentional poisoning should prompt evaluation for clinically important coingestants.

Acetaminophen screening is often relevant because early acetaminophen poisoning may be asymptomatic.

Other testing should be directed by history, examination, ECG, and acid–base findings rather than performed indiscriminately.

Initial Management

The priorities are:

Airway/breathing → control dangerous agitation → core temperature → ECG → circulation → complications

Most patients improve with supportive care.

Environmental Management

Patients with delirium benefit from:

• A calm environment
• Reduced unnecessary stimulation
• Close observation
• Protection from falls and trauma

Physical restraints alone can increase:

• Muscular activity
• Hyperthermia
• Acidosis
• Rhabdomyolysis

If restraints are temporarily necessary for immediate safety, adequate chemical sedation and continuous reassessment are important.

Agitation

Benzodiazepines can be used for significant agitation, particularly when:

• The diagnosis is uncertain
• Seizures are possible
• Physostigmine is inappropriate
• Mixed poisoning is suspected

Excessive nonspecific sedation should be avoided when a more targeted and appropriate treatment is available.

Physostigmine

Physostigmine is a reversible acetylcholinesterase inhibitor that crosses the blood–brain barrier.

It increases acetylcholine in both the CNS and peripheral nervous system.

In a carefully selected patient, it can rapidly reverse:

• Delirium
• Hallucinations
• Agitation
• Confusion

and may improve peripheral antimuscarinic findings.

Modern Role of Physostigmine

The older description of physostigmine primarily as a diagnostic test is outdated.

Its modern role is mainly therapeutic in selected patients with severe, predominantly pure antimuscarinic delirium.

It should not be used merely to prove the diagnosis or to avoid otherwise clinically necessary diagnostic evaluation.

When Physostigmine May Be Appropriate

Consider it when there is:

• Convincing antimuscarinic delirium
• Significant agitation or hallucinations
• A predominantly pure antimuscarinic exposure
• No important ECG evidence of sodium-channel blockade
• No major contraindicating coingestion

Selection should be cautious and ideally involve toxicology/poison-center guidance.

When Physostigmine Should Be Avoided

Avoid or use extreme caution when there is:

• Significant QRS widening
• Suspected TCA poisoning
• Significant sodium-channel blockade
• Important conduction disease
• Bradycardia
• High-risk proconvulsant coingestion
• Uncertain mixed overdose where dangerous cardiotoxicity is plausible

The older blanket contraindication lists involving conditions such as diabetes or all asthma are not the main modern toxicologic decision points.

Physostigmine Adverse Effects

Excessive acetylcholinesterase inhibition can produce cholinergic toxicity.

Possible effects include:

• Bradycardia
• Bronchorrhea
• Bronchospasm
• Sweating
• Salivation
• Nausea
• Vomiting
• Diarrhea
• Hypotension
• Seizures

Administration should therefore occur in an appropriately monitored setting with resuscitation capability.

Recurrence After Physostigmine

Physostigmine may have a shorter duration than the causative drug.

Therefore:

Initial improvement does not necessarily mean the poisoning has resolved.

Antimuscarinic delirium may recur and require continued observation and reassessment.

Sodium Bicarbonate

If an antimuscarinic-appearing overdose also produces significant sodium-channel blockade, sodium bicarbonate may be indicated.

Examples include severe poisoning with:

• Diphenhydramine
• Tricyclic antidepressants
• Other sodium-channel-blocking agents

Treatment is directed at the conduction toxicity, not at muscarinic blockade itself.

GI Decontamination

Ipecac is obsolete and should not be used.

Inducing vomiting is particularly dangerous because delirium, seizures, and CNS depression can develop unexpectedly.

Gastric Lavage

Routine gastric lavage is not recommended.

The historical idea that antimuscarinic-induced delayed gastric emptying automatically justifies lavage many hours after ingestion is not supported as a routine modern strategy.

Risks include:

• Aspiration
• Airway complications
• Mechanical injury

Activated Charcoal

A single dose of activated charcoal may be considered after a substantial recent ingestion when:

• The substance is adsorbable
• The airway is safe
• Expected benefit outweighs aspiration risk

Because antimuscarinic drugs may slow gastric emptying, useful drug may occasionally remain in the stomach longer than expected, but this does not justify routine late charcoal.

Repeat-dose charcoal is not routinely indicated simply because a drug is antimuscarinic.

Hyperthermia Management

Management includes:

• Control of agitation
• Removal of excess clothing
• External cooling
• Appropriate IV fluids
• Treatment of seizures

Antipyretics are not effective because antimuscarinic hyperthermia is not caused by an elevated hypothalamic fever set point.

Urinary Retention

Clinically significant bladder distension may require bladder decompression.

This can sometimes substantially improve agitation and discomfort.

Monitoring

Significant poisoning warrants monitoring of:

• Mental status
• Heart rate
• Blood pressure
• Core temperature
• ECG when appropriate
• Hydration
• Urine output

Severe cases additionally require monitoring for:

• CK elevation
• Renal injury
• Electrolyte abnormalities
• Hyperthermic complications

Observation

Antimuscarinic toxicity may persist longer than expected because:

• Some causative drugs have long half-lives
• GI motility is reduced
• Absorption may be delayed
• Active metabolites may persist

The older universal 6–12-hour observation rule should not be applied mechanically.

Observation should depend on:

• Agent
• Formulation
• Amount
• Symptoms
• Mental status trajectory
• ECG
• Coingestants
• Need for sedatives or physostigmine

Differential Diagnosis

Other causes of delirium, tachycardia, mydriasis, or hyperthermia include:

• Sympathomimetic poisoning
• Serotonin syndrome
• Alcohol or sedative withdrawal
• Mania or psychosis
• Hyperthyroidism/thyroid storm
• CNS infection
• Sepsis
• Hypoglycemia
• Intracranial hemorrhage
• Postictal states

The toxidrome should guide evaluation, but alternative dangerous diagnoses should not be ignored.

Pregnancy

The historical FDA pregnancy letter categories are obsolete.

Management of clinically significant poisoning during pregnancy focuses on:

• Maternal airway
• Oxygenation
• Temperature
• Hemodynamics
• Seizure control

Medication-specific fetal considerations can then be addressed according to the actual causative drug.

Safeguarding

Rigid age cutoffs for presumed neglect, abuse, or intentional poisoning are outdated.

Pediatric exposure should instead be evaluated according to:

• Developmental capability
• Access to medications
• Circumstances
• Consistency of the history
• Recurrent unexplained exposures
• Broader safeguarding concerns

Prognosis

Most uncomplicated antimuscarinic poisonings resolve completely with supportive care.

Severe outcomes are more likely when there is:

• Extreme hyperthermia
• Refractory agitation
• Seizures
• Rhabdomyolysis
• Aspiration
• Trauma during delirium
• Sodium-channel cardiotoxicity from the particular drug
• Significant coingestion

Important Modernization of the Older Source

• Antimuscarinic is the more precise term for the classic “anticholinergic” toxidrome.
• Diagnosis is clinical and does not require every classic feature.
• Absence of tachycardia does not absolutely exclude the syndrome.
• Sympathomimetic toxicity usually causes diaphoresis, whereas antimuscarinic poisoning usually produces dry skin and mucosa.
• Major QRS widening or ventricular dysrhythmia suggests an additional mechanism such as sodium-channel blockade.
• Diphenhydramine and TCAs can produce both antimuscarinic findings and dangerous cardiotoxicity.
• Physostigmine is no longer viewed merely as a diagnostic challenge; it can be a targeted therapeutic antidote in carefully selected pure antimuscarinic delirium.
• Avoid physostigmine when significant sodium-channel blockade, TCA toxicity, or another major contraindicating mechanism is suspected.
• Benzodiazepines remain important for seizures and selected agitation.
• Ipecac is obsolete.
• Routine gastric lavage is inappropriate.
• Delayed gastric emptying does not automatically justify late lavage or repeated charcoal.
• Physical restraint alone can worsen hyperthermia and rhabdomyolysis.
• Antipyretics do not treat antimuscarinic hyperthermia.
• Observation should be based on the specific drug, formulation, symptoms, ECG, and clinical course rather than a fixed time.

Key Points

• Muscarinic blockade → dry, dilated, tachycardic, delirious, hot, urinary-retaining patient.
• Central toxicity produces delirium, hallucinations, agitation, seizures, and occasionally coma.
• Peripheral toxicity produces mydriasis, dry mucosa/skin, tachycardia, ileus, urinary retention, and impaired sweating.
• Dry skin helps distinguish antimuscarinic from sympathomimetic toxicity.
• Obtain an ECG when the drug is uncertain or cardiotoxic coeffects are possible.
• QRS widening suggests sodium-channel blockade, not simple muscarinic antagonism.
• Benzodiazepines are first-line for toxicologic seizures.
• Physostigmine can reverse severe pure antimuscarinic delirium in appropriately selected patients.
• Hyperthermia requires sedation, cooling, and supportive care—not antipyretics.
• Ipecac and routine gastric lavage have no modern role.

Toxicology – Angiotensin-Converting Enzyme (ACE) Inhibitors

Core Concept

ACE inhibitors are widely used cardiovascular and renal medications. Important examples include:

• Captopril
• Enalapril
• Lisinopril
• Ramipril
• Benazepril
• Fosinopril
• Perindopril
• Quinapril
• Trandolapril

They are used for conditions such as:

• Hypertension
• Heart failure with reduced ejection fraction
• Post-myocardial-infarction ventricular dysfunction
• Selected chronic kidney disease, particularly with albuminuria
• Other conditions involving the renin–angiotensin–aldosterone system (RAAS)

Most isolated ACE-inhibitor overdoses produce mild or moderate hypotension, but severe vasodilatory shock can occur after a very large exposure or when important coingestants or comorbidities are present.

There is no routinely required specific antidote.

⸻

Renin–Angiotensin–Aldosterone System

The RAAS helps maintain:

• Blood pressure
• Vascular tone
• Sodium balance
• Extracellular fluid volume
• Renal perfusion

Reduced renal perfusion stimulates renin release.

The sequence is:

Angiotensinogen → angiotensin I → ACE → angiotensin II

Angiotensin II then:

• Produces vasoconstriction
• Stimulates aldosterone secretion
• Promotes sodium retention
• Supports blood pressure and renal hemodynamics

⸻

Mechanism of ACE Inhibition

ACE inhibitors block conversion of:

Angiotensin I → Angiotensin II

Consequences include:

• Reduced vasoconstriction
• Reduced aldosterone secretion
• Reduced sodium retention
• Reduced systemic vascular resistance
• Lower blood pressure

In overdose, excessive loss of angiotensin-II-mediated vascular tone can cause significant hypotension.

⸻

Bradykinin

ACE also normally degrades bradykinin.

ACE inhibition therefore increases bradykinin activity.

This contributes to:

• Vasodilation
• Dry cough
• ACE-inhibitor-associated angioedema

This mechanism is clinically important because ACE-inhibitor angioedema is bradykinin-mediated, rather than a conventional histamine-mediated allergic reaction.

⸻

Toxic Dose

There is no reliable universal toxic dose.

Many isolated ingestions, including some apparently large ones, produce only limited hypotension.

Severity depends on:

• Specific ACE inhibitor
• Amount and formulation
• Baseline blood pressure
• Hydration status
• Renal function
• Age and frailty
• Coingestants
• Concurrent antihypertensive therapy

Clinical findings are more useful than the reported dose alone.

⸻

Principal Acute Toxicity – Hypotension

The major manifestation of acute overdose is:

Reduced angiotensin II → vasodilation → decreased systemic vascular resistance → hypotension

Possible symptoms include:

• Dizziness
• Weakness
• Lightheadedness
• Orthostatic symptoms
• Syncope

Severe poisoning may produce:

• Persistent hypotension
• Altered mental status
• Oliguria
• Acute kidney injury
• Shock

⸻

Heart Rate

Tachycardia may accompany hypotension, but the response is variable.

Bradycardia is not usually the defining feature of isolated ACE-inhibitor overdose.

If substantial bradycardia occurs, consider:

• β-blocker coingestion
• Calcium-channel blocker coingestion
• Digoxin
• Clonidine
• Conduction disease
• Hyperkalemia
• Other causes

⸻

Hyperkalemia

ACE inhibition reduces aldosterone activity.

This decreases renal potassium excretion and can produce:

Hyperkalemia

Risk is greatest with:

• Chronic kidney disease
• Acute kidney injury
• Potassium supplements
• Potassium-sparing diuretics
• Other RAAS inhibitors
• Significant dehydration or renal hypoperfusion

Hyperkalemia may be more clinically important than the initial blood-pressure abnormality in susceptible patients.

⸻

Renal Effects

Angiotensin II normally constricts the efferent arteriole, helping maintain glomerular filtration when renal perfusion falls.

ACE inhibition reduces this compensatory effect.

Consequently, renal function may deteriorate in settings such as:

• Severe volume depletion
• Renal hypoperfusion
• Bilateral renal artery stenosis
• Advanced kidney disease
• Severe hypotension

Monitor creatinine and urine output in clinically significant poisoning.

⸻

ACE-Inhibitor Angioedema

One of the most important adverse effects is bradykinin-mediated angioedema.

It can involve:

• Lips
• Tongue
• Floor of mouth
• Oropharynx
• Larynx

Severe swelling can cause life-threatening airway obstruction.

⸻

Clinical Pattern of Angioedema

Typical findings include:

• Nonpitting swelling
• Lip or tongue enlargement
• Voice change
• Dysphagia
• Drooling
• Throat tightness
• Stridor in advanced disease

Unlike histamine-mediated anaphylaxis, ACE-inhibitor angioedema often occurs without urticaria or generalized pruritus.

⸻

Timing of Angioedema

Angioedema can occur:

• Soon after starting therapy
• Months later
• Even after years of previously tolerated treatment

Therefore, long-term uneventful use does not exclude an ACE inhibitor as the cause.

Angioedema is an adverse drug reaction and does not require an overdose.

⸻

Airway Management

Airway assessment is the highest priority in significant ACE-inhibitor angioedema.

Concerning findings include:

• Progressive tongue swelling
• Floor-of-mouth swelling
• Voice change
• Drooling
• Dysphagia
• Stridor
• Respiratory distress

If airway compromise is developing:

Secure the airway before swelling progresses to the point that intubation becomes extremely difficult.

Severe cases may require advanced airway expertise and preparation for a surgical airway.

⸻

Epinephrine, Antihistamines, and Steroids

A critical distinction is that ACE-inhibitor angioedema is primarily bradykinin-mediated.

Therefore:

• Antihistamines
• Corticosteroids
• Epinephrine

do not directly reverse the underlying bradykinin mechanism and may have limited benefit in isolated ACE-inhibitor angioedema.

However, if the diagnosis is uncertain and anaphylaxis is possible, epinephrine should not be withheld from a patient with a compatible life-threatening allergic reaction.

⸻

Bradykinin-Targeted Therapies

Several therapies have been studied or used for severe ACE-inhibitor angioedema, including agents that target bradykinin pathways and, in some settings, plasma-derived products.

Evidence has been mixed, and no pharmacologic treatment should delay definitive airway management.

The key principle is:

Airway protection takes precedence over medication.

⸻

ACE-Inhibitor Cough

A persistent dry cough can occur during therapeutic treatment.

This is associated with increased bradykinin and related mediators.

The cough is:

• Usually nonproductive
• Not evidence of pulmonary edema by itself
• Reversible after discontinuation, although resolution may take longer than only a few days in some patients

⸻

Other Chronic Adverse Effects

Less common adverse effects include:

• Dysgeusia, particularly with captopril
• Rash
• Renal dysfunction
• Rare hepatic injury
• Rare hematologic abnormalities

These are not the defining findings of acute overdose.

⸻

Diagnosis

ACE-inhibitor poisoning is usually a clinical diagnosis based on:

• Medication history
• Amount and timing
• Vital signs
• Renal function
• Potassium
• Coingestants

Serum ACE-inhibitor concentrations are not useful for routine emergency management.

⸻

Laboratory Evaluation

A small, asymptomatic isolated exposure may require little testing.

For symptomatic or substantial poisoning, useful tests include:

• Electrolytes
• Potassium
• Bicarbonate
• Creatinine
• Glucose

Additional testing depends on clinical severity and suspected coingestants.

⸻

ECG

An ECG is appropriate when there is:

• Significant hypotension
• Hyperkalemia
• Syncope
• Intentional overdose
• Suspected cardiovascular coingestion

Marked conduction abnormalities are not typical of isolated ACE-inhibitor poisoning and should prompt investigation for:

• Hyperkalemia
• β-blockers
• Calcium-channel blockers
• Sodium-channel blockers
• Other coingestants

⸻

Differential Diagnosis of Hypotension

Toxicologic possibilities include:

• β-blockers
• Calcium-channel blockers
• α₁ antagonists
• Clonidine and other imidazolines
• Nitrates
• Tricyclic antidepressants
• Other vasodilators

Nontoxicologic possibilities include:

• Dehydration
• Sepsis
• Hemorrhage
• Cardiogenic shock
• Adrenal crisis
• Anaphylaxis
• Autonomic dysfunction

Severe or unusual findings should not automatically be attributed to the ACE inhibitor.

⸻

Initial Management

Management centers on:

Airway assessment → circulation/perfusion → renal and potassium evaluation → supportive care

For uncomplicated isolated overdose, supportive treatment is usually sufficient.

⸻

IV Fluids

Hypotension may respond to appropriate isotonic crystalloid, especially when volume depletion is contributing.

However, fluid administration should be individualized in patients with:

• Heart failure
• Renal impairment
• Pulmonary edema

The goal is restoration of adequate perfusion rather than administration of a fixed volume.

⸻

Trendelenburg – Modern Correction

Routine Trendelenburg positioning is obsolete for treatment of hypotension.

It provides no reliable sustained improvement in organ perfusion and may worsen respiratory mechanics.

⸻

Vasopressors

Persistent shock despite appropriate initial fluid resuscitation may require vasopressor therapy.

Norepinephrine is generally a reasonable first-line vasopressor for persistent vasodilatory shock.

The historical dopamine-first approach is no longer routinely preferred.

⸻

Refractory ACE-Inhibitor Shock

Rare severe overdose can produce hypotension that is unusually resistant to conventional vasopressors because the RAAS pathway itself is blocked.

Angiotensin II has been used in selected cases of severe refractory ACE-inhibitor-associated vasodilatory shock.

This is a specialist/critical-care intervention rather than routine therapy for ordinary ACE-inhibitor ingestion.

⸻

Atropine

Atropine is useful only when clinically significant bradycardia contributes to poor perfusion.

It is not an antidote to ACE inhibition and should not be routinely administered simply because the patient is hypotensive.

⸻

Hyperkalemia Management

Clinically important hyperkalemia should be managed according to severity.

Principles include:

• ECG assessment
• Cardiac membrane stabilization when indicated
• Intracellular potassium shifting
• Correction of contributing abnormalities
• Potassium removal when required
• Dialysis in selected severe cases, particularly with renal failure

Treatment is based on the potassium level, ECG, clinical condition, renal function, and trajectory.

⸻

GI Decontamination

Do not induce vomiting.

Routine gastric lavage is obsolete.

Activated charcoal may occasionally be considered after a substantial recent ingestion when:

• Presentation is sufficiently early
• The airway is safe
• Expected benefit outweighs aspiration risk

Most uncomplicated ACE-inhibitor exposures do not require aggressive GI decontamination.

⸻

No Routine Specific Antidote

There is no standard antidote required for ordinary ACE-inhibitor poisoning.

Management consists primarily of:

• Hemodynamic support
• Renal monitoring
• Hyperkalemia treatment when necessary
• Airway management for angioedema
• Treatment of coingestants

⸻

Observation

The older universal 4–6-hour observation rule should not be applied mechanically.

Observation depends on:

• Specific agent
• Amount
• Formulation
• Symptoms
• Blood-pressure trajectory
• Renal function
• Potassium
• Coingestants

Clinically important hypotension usually develops relatively early after immediate-release ingestion, but persistent toxicity can occur after substantial exposures or in patients with impaired physiology.

⸻

Admission

Hospital management is appropriate for:

• Persistent hypotension
• Shock
• Significant hyperkalemia
• Acute kidney injury
• Altered mental status
• Significant coingestion
• Angioedema involving the tongue, floor of mouth, pharynx, or larynx
• Any threatened airway

Severe shock or airway compromise warrants intensive care.

⸻

Pregnancy – Major Modern Correction

The historical FDA pregnancy letter categories are obsolete.

ACE inhibitors are generally avoided during pregnancy, particularly because fetal RAAS blockade later in pregnancy can cause serious fetal toxicity.

Potential complications include:

• Fetal renal dysfunction
• Oligohydramnios
• Impaired skull ossification
• Pulmonary developmental complications secondary to oligohydramnios
• Neonatal renal failure
• Fetal or neonatal death in severe exposure

Pregnancy exposure should prompt obstetric and medication review rather than reliance on the old “Category D” designation.

⸻

Pregnancy Testing

The older statement that every woman of childbearing age must undergo pregnancy testing before ACE-inhibitor therapy is overly rigid as a universal toxicology rule.

Medication counseling and pregnancy assessment should be individualized according to clinical circumstances and current prescribing guidance.

⸻

Safeguarding

Rigid historical age cutoffs for neglect, abuse, or intentional poisoning are inappropriate.

Pediatric exposure should instead be evaluated according to:

• Developmental ability
• Medication accessibility
• Circumstances
• Consistency of the history
• Recurrent unexplained poisoning
• Other safeguarding concerns

⸻

Prognosis

Most isolated ACE-inhibitor overdoses have a favorable outcome with supportive care.

Poor outcomes are more likely with:

• Massive exposure
• Severe persistent hypotension
• Significant hyperkalemia
• Acute kidney injury
• Serious cardiovascular coingestants
• Prolonged hypoperfusion
• Airway compromise from angioedema

⸻

Important Modernization of the Older Source

• ACE inhibitors reduce angiotensin II and aldosterone while increasing bradykinin activity.
• Acute overdose primarily causes vasodilatory hypotension.
• Hyperkalemia and renal dysfunction are especially important in susceptible patients.
• ACE-inhibitor angioedema is predominantly bradykinin-mediated, not classic histamine-mediated allergy.
• Angioedema may develop even after years of therapy.
• Airway management is the priority in progressive tongue/pharyngeal/laryngeal swelling.
• Antihistamines and corticosteroids do not directly reverse bradykinin-mediated angioedema.
• If true anaphylaxis remains possible, epinephrine should still be used appropriately.
• Routine serum ACE-inhibitor concentrations have no clinical role.
• Trendelenburg positioning is obsolete.
• Norepinephrine is generally favored over dopamine for persistent vasodilatory shock.
• Angiotensin II has a specialized role in selected refractory shock.
• Atropine is useful only when clinically important bradycardia is actually present.
• Ipecac and routine gastric lavage are obsolete.
• Activated charcoal has only a selective early role.
• Fixed observation periods should be replaced by symptom-, renal-, potassium-, and exposure-based assessment.
• Historical FDA pregnancy letter categories are obsolete.

Key Points

• ACE inhibition → ↓ angiotensin II → vasodilation and hypotension.
• ↓ aldosterone → risk of hyperkalemia.
• Reduced efferent arteriolar constriction can worsen renal function in susceptible patients.
• ↑ bradykinin → cough and angioedema.
• Most isolated overdoses are relatively mild, but severe vasodilatory shock can occur.
• Monitor blood pressure, potassium, creatinine, and ECG when clinically indicated.
• Treat hypotension supportively; persistent vasodilatory shock may require a vasopressor.
• Progressive ACE-inhibitor angioedema is primarily an airway emergency.
• There is no routinely required specific antidote for uncomplicated ACE-inhibitor overdose.

Toxicology – Amrinone (Inamrinone) and Milrinone

Core Concept

Amrinone, now generally called inamrinone, and milrinone are phosphodiesterase-3 (PDE3) inhibitors with combined:

• Positive inotropic effects – increase cardiac contractility
• Vasodilator effects – decrease systemic and pulmonary vascular resistance

For this reason they are sometimes called inodilators.

Milrinone has largely replaced inamrinone in contemporary clinical practice because of more favorable pharmacologic and adverse-effect characteristics.

The major acute toxic effects are:

Excessive vasodilation → hypotension

and

Increased myocardial excitability → tachyarrhythmias/ventricular dysrhythmias

There is no specific antidote.

Modern Clinical Role

Milrinone may be used for short-term hemodynamic support in selected patients with:

• Acute decompensated heart failure with low cardiac output
• Severe ventricular dysfunction
• Post-cardiac-surgery low-output states
• Selected right ventricular failure
• Selected pulmonary hypertension situations

Its use requires careful hemodynamic assessment because increased contractility may be offset by substantial vasodilation.

Inamrinone is now rarely used compared with milrinone.

PDE3 Physiology

Normally:

Adenylyl cyclase → cAMP

while:

PDE3 breaks down cAMP

PDE3 inhibition therefore increases intracellular cAMP.

Cardiac Mechanism

In cardiac myocytes:

PDE3 inhibition → ↑ cAMP → ↑ protein kinase A activity → ↑ intracellular Ca²⁺ availability → stronger contraction

The result is:

• Increased myocardial contractility
• Increased stroke volume
• Increased cardiac output in appropriately selected patients

Unlike catecholamines, the drug does not require direct β-receptor stimulation to generate its primary inotropic effect.

Vascular Mechanism

In vascular smooth muscle, increased cAMP promotes relaxation.

Therefore:

PDE3 inhibition → vasodilation → ↓ systemic vascular resistance

It can also decrease pulmonary vascular resistance.

Thus the overall pharmacologic profile is:

↑ Contractility + ↓ afterload = inodilation

Why Hypotension Occurs

The same vasodilating action that may improve forward cardiac output can become excessive.

In toxicity:

Excessive vasodilation → ↓ SVR → hypotension → impaired organ perfusion

This is especially important in patients who already have:

• Low blood pressure
• Volume depletion
• Severe heart failure
• Other vasodilating medications

Toxic Dose

A reliable universal toxic threshold has not been established.

Most clinically important toxicity historically occurred through:

• Therapeutic dosing errors
• Excessive IV administration
• Drug accumulation

Clinical severity is more useful than a reported amount.

Milrinone and Renal Function

Milrinone is substantially dependent on renal elimination.

Therefore:

Renal impairment → reduced clearance → prolonged exposure → greater risk of hypotension and dysrhythmias

Renal function is consequently an important consideration during both therapeutic use and suspected toxicity.

Dose accumulation may occur even without a single dramatic overdose.

Acute Cardiovascular Toxicity

The major findings are:

• Hypotension
• Tachycardia
• Palpitations
• Ventricular ectopy
• Supraventricular dysrhythmias
• Ventricular dysrhythmias

Severe hypotension can lead to:

• Altered mental status
• Myocardial ischemia
• Acute kidney injury
• Shock

Dysrhythmias

PDE3 inhibition can increase myocardial excitability.

Possible rhythm disturbances include:

• Premature ventricular complexes
• Atrial tachyarrhythmias
• Ventricular tachycardia
• Other ventricular dysrhythmias

Risk may be increased by:

• Hypokalemia
• Hypomagnesemia
• Structural heart disease
• Myocardial ischemia
• Other proarrhythmic medications

Electrolytes

Electrolyte abnormalities can increase dysrhythmia risk.

Particular attention should be given to:

• Potassium
• Magnesium
• Calcium

Hypokalemia may occur in patients receiving intensive heart-failure treatment, particularly when concurrent diuretics are being used.

Gastrointestinal Effects

Reported adverse effects include:

• Nausea
• Vomiting
• Diarrhea
• Abdominal discomfort

These are generally less important than cardiovascular toxicity during acute poisoning.

Thrombocytopenia

Inamrinone has historically been associated with thrombocytopenia, particularly during sustained therapy.

It is generally:

• Dose/exposure related
• Reversible after dose reduction or discontinuation

This adverse effect was one factor limiting long-term use.

Milrinone has a substantially lower tendency to produce this complication.

Hepatic Effects

Inamrinone has also been associated with:

• Aminotransferase abnormalities
• Rare clinically significant hepatotoxicity

This is more relevant to prolonged exposure than a brief acute overdose.

Why Chronic Oral PDE3 Therapy Fell Out of Favor

An important modern point is that chronic oral PDE3 inhibitor therapy for heart failure did not improve long-term survival and was associated with adverse outcomes.

Therefore, contemporary milrinone use is primarily short-term IV therapy in selected patients, rather than routine chronic oral heart-failure treatment.

Diagnosis

Diagnosis is based primarily on:

• Medication history
• Infusion history
• Hemodynamic findings
• ECG
• Renal function
• Electrolytes

There is no routinely useful serum inamrinone or milrinone concentration for emergency toxicologic decision-making.

Essential Assessment

In clinically important toxicity, evaluate:

• Blood pressure
• Heart rate
• Mental status
• Peripheral perfusion
• ECG
• Continuous cardiac rhythm

Laboratory evaluation may include:

• Electrolytes
• Potassium
• Magnesium
• Calcium
• Creatinine
• Glucose

Additional tests depend on severity.

Chronic-Therapy Evaluation

If adverse effects develop during prolonged inamrinone exposure, additional evaluation can include:

• CBC with platelet count
• Liver enzymes
• Renal function
• Electrolytes

For milrinone, renal function is especially important because impaired clearance can substantially prolong its effects.

Initial Management of IV Overdose

The first step in excessive IV administration is straightforward:

Stop the infusion.

Then assess:

• Airway and breathing
• Blood pressure and perfusion
• Cardiac rhythm
• Renal function
• Electrolytes

Significant hypotension or dysrhythmia warrants monitored critical care.

Hypotension Management

Treatment depends on both volume status and cardiac function.

Appropriate isotonic crystalloid may be useful if the patient is volume depleted.

However, many patients receiving PDE3 inhibitors already have severe heart failure, so indiscriminate fluid loading may cause:

• Pulmonary edema
• Worsening congestion
• Respiratory compromise

Fluid therapy should therefore be individualized.

Trendelenburg – Modern Correction

Routine Trendelenburg positioning is obsolete as treatment for hypotension.

It does not provide reliable sustained improvement in organ perfusion and may worsen respiratory mechanics in some patients.

Vasopressors

Persistent vasodilatory hypotension may require a vasopressor.

A vasoconstricting agent such as norepinephrine is commonly appropriate when significant vasodilatory shock persists.

Selection should account for:

• Cardiac function
• Rhythm
• Degree of vasodilation
• Perfusion
• Other medications

Atropine

The historical source recommends atropine if hypotension is caused by bradycardia.

Atropine may be appropriate for clinically important symptomatic bradycardia, but bradycardia is not the characteristic toxicity of PDE3 inhibition.

Hypotension should not automatically be treated with atropine unless the heart-rate disturbance is actually contributing to poor perfusion.

Dysrhythmia Management

Management includes:

• Stop the offending drug
• Correct hypoxemia
• Correct significant potassium abnormalities
• Correct magnesium abnormalities
• Treat acid–base disturbances
• Evaluate myocardial ischemia
• Follow contemporary resuscitation principles for unstable dysrhythmias

Electrical cardioversion/defibrillation is used when indicated by the rhythm and hemodynamic state.

Drug Interactions

Concomitant medications may amplify toxicity.

Examples include:

• Other vasodilators → greater hypotension
• Other positive inotropes → greater myocardial oxygen demand or arrhythmia risk
• Diuretics → electrolyte depletion
• Other proarrhythmic drugs → greater dysrhythmia risk

Medication compatibility is also important for IV therapy; drugs should not be mixed in the same line unless compatibility is established.

Outflow Obstruction

Increasing contractility while reducing vascular resistance can be undesirable in some forms of dynamic ventricular outflow obstruction.

Therefore, PDE3 inhibitors require caution in conditions where stronger contraction may worsen an obstructive pressure gradient.

Sulfite Hypersensitivity – Modern Nuance

Some older inamrinone formulations contained sulfite preservatives.

The historical statement that asthma itself is an absolute contraindication is too broad.

Sulfite-sensitive individuals, particularly some patients with asthma, may be at greater risk of hypersensitivity reactions depending on the formulation.

Current product ingredients should be checked rather than assuming all PDE3 inhibitor preparations carry the same risk.

GI Decontamination

Modern milrinone and inamrinone toxicity is usually related to parenteral therapy, making gastrointestinal decontamination irrelevant in most cases.

For an unusual oral exposure:

• Do not induce vomiting.
• Routine gastric lavage is obsolete.

Activated charcoal might be considered only in selected recent clinically significant oral exposures when the airway is safe.

It should not delay cardiovascular stabilization.

No Specific Antidote

There is no specific reversal agent for inamrinone or milrinone toxicity.

Treatment consists of:

• Discontinuing exposure
• Hemodynamic support
• Correction of electrolytes
• Dysrhythmia treatment
• Management of complications

Extracorporeal Removal

Extracorporeal removal is not a routine antidotal strategy for PDE3 inhibitor toxicity.

In severe milrinone toxicity with renal dysfunction, management should involve toxicology, cardiology, and critical-care specialists because prolonged pharmacologic effects may occur.

Monitoring

Significant toxicity requires monitoring of:

• Blood pressure
• Heart rate
• ECG/rhythm
• Oxygenation
• Mental status
• Urine output
• Renal function
• Potassium
• Magnesium

Additional monitoring is guided by the clinical course.

Observation

The historical fixed 6-hour observation period should not be applied universally.

Duration depends on:

• Agent
• Route
• Magnitude of exposure
• Renal function
• Symptoms
• ECG findings
• Hemodynamic stability

Milrinone toxicity may be prolonged when renal clearance is impaired.

Admission

Monitored inpatient care is appropriate for:

• Persistent hypotension
• Significant dysrhythmia
• Evidence of poor organ perfusion
• Significant electrolyte abnormalities
• Renal dysfunction with suspected drug accumulation

Severe hemodynamic instability generally warrants intensive-care management.

Pregnancy

The historical FDA pregnancy letter category is obsolete.

Clinically significant toxicity during pregnancy should be treated according to maternal physiology.

Particularly important goals are maintaining:

• Maternal blood pressure
• Oxygenation
• Cardiac output
• Uteroplacental perfusion

Necessary treatment should not be withheld solely because of pregnancy.

Prognosis

Mild toxicity usually improves after:

• Drug discontinuation
• Clearance of the medication
• Correction of hemodynamic and electrolyte abnormalities

Prognosis becomes more serious when there is:

• Refractory shock
• Sustained ventricular dysrhythmia
• Severe underlying cardiac disease
• Renal failure causing prolonged milrinone exposure
• Multiorgan hypoperfusion

Important Modernization of the Older Source

• Amrinone is now generally called inamrinone.
• Inamrinone and milrinone are PDE3 inhibitors/inodilators.
• Milrinone has largely replaced inamrinone in contemporary practice.
• PDE3 inhibition → ↑ cAMP → increased cardiac contractility plus vascular relaxation.
• Acute toxicity is dominated by hypotension and dysrhythmias.
• Milrinone depends substantially on renal clearance; renal impairment can prolong toxicity.
• Inamrinone is more strongly associated with thrombocytopenia during prolonged exposure.
• Chronic oral PDE3 inhibitor therapy is not routine modern heart-failure treatment because long-term outcome data were unfavorable.
• Asthma alone is not a universal absolute contraindication; sulfite sensitivity depends partly on formulation.
• Routine Trendelenburg positioning is obsolete.
• Fluid resuscitation must be cautious in patients with heart failure.
• Persistent vasodilatory shock may require norepinephrine or another appropriately selected vasopressor.
• Atropine is relevant only when clinically important bradycardia is actually present.
• Routine gastric lavage is obsolete.
• There is no specific antidote.
• Observation should account for renal function and clinical trajectory rather than follow a fixed 6-hour rule.

Key Points

• Inamrinone/milrinone = PDE3 inhibitors.
• ↑ cAMP in myocardium → ↑ intracellular Ca²⁺ → positive inotropy.
• ↑ cAMP in vascular smooth muscle → vasodilation.
• Together these effects make them inodilators.
• Main acute toxicities: hypotension + dysrhythmias.
• Check and correct K⁺, Mg²⁺, and other relevant electrolyte abnormalities.
• Milrinone toxicity can be prolonged in renal impairment.
• Inamrinone can cause thrombocytopenia, especially with prolonged exposure.
• Stop an excessive infusion immediately and provide hemodynamic and rhythm support.
• No specific antidote exists.

237. Toxicology – Amrinone (Inamrinone) and Milrinone

Core Concept

Amrinone, now generally called inamrinone, and milrinone are phosphodiesterase-3 (PDE3) inhibitors with combined:

Positive inotropic effects – increase cardiac contractility   Vasodilator effects – decrease systemic and pulmonary vascular resistance

For this reason they are sometimes called inodilators.

Milrinone has largely replaced inamrinone in contemporary clinical practice because of more favorable pharmacologic and adverse-effect characteristics.

The major acute toxic effects are:

Excessive vasodilation → hypotension

and

Increased myocardial excitability → tachyarrhythmias/ventricular dysrhythmias

There is no specific antidote.

⸻

Modern Clinical Role

Milrinone may be used for short-term hemodynamic support in selected patients with:

Acute decompensated heart failure with low cardiac output   Severe ventricular dysfunction   Post-cardiac-surgery low-output states   Selected right ventricular failure   Selected pulmonary hypertension situations

Its use requires careful hemodynamic assessment because increased contractility may be offset by substantial vasodilation.

Inamrinone is now rarely used compared with milrinone.

⸻

PDE3 Physiology

Normally:

Adenylyl cyclase → cAMP

while:

PDE3 breaks down cAMP

PDE3 inhibition therefore increases intracellular cAMP.

⸻

Cardiac Mechanism

In cardiac myocytes:

PDE3 inhibition → ↑ cAMP → ↑ protein kinase A activity → ↑ intracellular Ca²⁺ availability → stronger contraction

The result is:

Increased myocardial contractility   Increased stroke volume   Increased cardiac output in appropriately selected patients

Unlike catecholamines, the drug does not require direct β-receptor stimulation to generate its primary inotropic effect.

⸻

Vascular Mechanism

In vascular smooth muscle, increased cAMP promotes relaxation.

Therefore:

PDE3 inhibition → vasodilation → ↓ systemic vascular resistance

It can also decrease pulmonary vascular resistance.

Thus the overall pharmacologic profile is:

↑ Contractility + ↓ afterload = inodilation

⸻

Why Hypotension Occurs

The same vasodilating action that may improve forward cardiac output can become excessive.

In toxicity:

Excessive vasodilation → ↓ SVR → hypotension → impaired organ perfusion

This is especially important in patients who already have:

Low blood pressure   Volume depletion   Severe heart failure   Other vasodilating medications

⸻

Toxic Dose

A reliable universal toxic threshold has not been established.

Most clinically important toxicity historically occurred through:

Therapeutic dosing errors   Excessive IV administration   Drug accumulation

Clinical severity is more useful than a reported amount.

⸻

Milrinone and Renal Function

Milrinone is substantially dependent on renal elimination.

Therefore:

Renal impairment → reduced clearance → prolonged exposure → greater risk of hypotension and dysrhythmias

Renal function is consequently an important consideration during both therapeutic use and suspected toxicity.

Dose accumulation may occur even without a single dramatic overdose.

⸻

Acute Cardiovascular Toxicity

The major findings are:

Hypotension   Tachycardia   Palpitations   Ventricular ectopy   Supraventricular dysrhythmias   Ventricular dysrhythmias

Severe hypotension can lead to:

Altered mental status   Myocardial ischemia   Acute kidney injury   Shock

⸻

Dysrhythmias

PDE3 inhibition can increase myocardial excitability.

Possible rhythm disturbances include:

Premature ventricular complexes   Atrial tachyarrhythmias   Ventricular tachycardia   Other ventricular dysrhythmias

Risk may be increased by:

Hypokalemia   Hypomagnesemia   Structural heart disease   Myocardial ischemia   Other proarrhythmic medications

⸻

Electrolytes

Electrolyte abnormalities can increase dysrhythmia risk.

Particular attention should be given to:

Potassium   Magnesium   Calcium

Hypokalemia may occur in patients receiving intensive heart-failure treatment, particularly when concurrent diuretics are being used.

⸻

Gastrointestinal Effects

Reported adverse effects include:

Nausea   Vomiting   Diarrhea   Abdominal discomfort

These are generally less important than cardiovascular toxicity during acute poisoning.

⸻

Thrombocytopenia

Inamrinone has historically been associated with thrombocytopenia, particularly during sustained therapy.

It is generally:

Dose/exposure related   Reversible after dose reduction or discontinuation

This adverse effect was one factor limiting long-term use.

Milrinone has a substantially lower tendency to produce this complication.

⸻

Hepatic Effects

Inamrinone has also been associated with:

Aminotransferase abnormalities   Rare clinically significant hepatotoxicity

This is more relevant to prolonged exposure than a brief acute overdose.

⸻

Why Chronic Oral PDE3 Therapy Fell Out of Favor

An important modern point is that chronic oral PDE3 inhibitor therapy for heart failure did not improve long-term survival and was associated with adverse outcomes.

Therefore, contemporary milrinone use is primarily short-term IV therapy in selected patients, rather than routine chronic oral heart-failure treatment.

⸻

Diagnosis

Diagnosis is based primarily on:

Medication history   Infusion history   Hemodynamic findings   ECG   Renal function   Electrolytes

There is no routinely useful serum inamrinone or milrinone concentration for emergency toxicologic decision-making.

⸻

Essential Assessment

In clinically important toxicity, evaluate:

Blood pressure   Heart rate   Mental status   Peripheral perfusion   ECG   Continuous cardiac rhythm

Laboratory evaluation may include:

Electrolytes   Potassium   Magnesium   Calcium   Creatinine   Glucose

Additional tests depend on severity.

⸻

Chronic-Therapy Evaluation

If adverse effects develop during prolonged inamrinone exposure, additional evaluation can include:

CBC with platelet count   Liver enzymes   Renal function   Electrolytes

For milrinone, renal function is especially important because impaired clearance can substantially prolong its effects.

⸻

Initial Management of IV Overdose

The first step in excessive IV administration is straightforward:

Stop the infusion.

Then assess:

Airway and breathing   Blood pressure and perfusion   Cardiac rhythm   Renal function   Electrolytes

Significant hypotension or dysrhythmia warrants monitored critical care.

⸻

Hypotension Management

Treatment depends on both volume status and cardiac function.

Appropriate isotonic crystalloid may be useful if the patient is volume depleted.

However, many patients receiving PDE3 inhibitors already have severe heart failure, so indiscriminate fluid loading may cause:

Pulmonary edema   Worsening congestion   Respiratory compromise

Fluid therapy should therefore be individualized.

⸻

Trendelenburg – Modern Correction

Routine Trendelenburg positioning is obsolete as treatment for hypotension.

It does not provide reliable sustained improvement in organ perfusion and may worsen respiratory mechanics in some patients.

⸻

Vasopressors

Persistent vasodilatory hypotension may require a vasopressor.

A vasoconstricting agent such as norepinephrine is commonly appropriate when significant vasodilatory shock persists.

Selection should account for:

Cardiac function   Rhythm   Degree of vasodilation   Perfusion   Other medications

⸻

Atropine

The historical source recommends atropine if hypotension is caused by bradycardia.

Atropine may be appropriate for clinically important symptomatic bradycardia, but bradycardia is not the characteristic toxicity of PDE3 inhibition.

Hypotension should not automatically be treated with atropine unless the heart-rate disturbance is actually contributing to poor perfusion.

⸻

Dysrhythmia Management

Management includes:

Stop the offending drug   Correct hypoxemia   Correct significant potassium abnormalities   Correct magnesium abnormalities   Treat acid–base disturbances   Evaluate myocardial ischemia   Follow contemporary resuscitation principles for unstable dysrhythmias

Electrical cardioversion/defibrillation is used when indicated by the rhythm and hemodynamic state.

⸻

Drug Interactions

Concomitant medications may amplify toxicity.

Examples include:

Other vasodilators → greater hypotension   Other positive inotropes → greater myocardial oxygen demand or arrhythmia risk   Diuretics → electrolyte depletion   Other proarrhythmic drugs → greater dysrhythmia risk

Medication compatibility is also important for IV therapy; drugs should not be mixed in the same line unless compatibility is established.

⸻

Outflow Obstruction

Increasing contractility while reducing vascular resistance can be undesirable in some forms of dynamic ventricular outflow obstruction.

Therefore, PDE3 inhibitors require caution in conditions where stronger contraction may worsen an obstructive pressure gradient.

⸻

Sulfite Hypersensitivity – Modern Nuance

Some older inamrinone formulations contained sulfite preservatives.

The historical statement that asthma itself is an absolute contraindication is too broad.

Sulfite-sensitive individuals, particularly some patients with asthma, may be at greater risk of hypersensitivity reactions depending on the formulation.

Current product ingredients should be checked rather than assuming all PDE3 inhibitor preparations carry the same risk.

⸻

GI Decontamination

Modern milrinone and inamrinone toxicity is usually related to parenteral therapy, making gastrointestinal decontamination irrelevant in most cases.

For an unusual oral exposure:

Do not induce vomiting.   Routine gastric lavage is obsolete.

Activated charcoal might be considered only in selected recent clinically significant oral exposures when the airway is safe.

It should not delay cardiovascular stabilization.

⸻

No Specific Antidote

There is no specific reversal agent for inamrinone or milrinone toxicity.

Treatment consists of:

Discontinuing exposure   Hemodynamic support   Correction of electrolytes   Dysrhythmia treatment   Management of complications

⸻

Extracorporeal Removal

Extracorporeal removal is not a routine antidotal strategy for PDE3 inhibitor toxicity.

In severe milrinone toxicity with renal dysfunction, management should involve toxicology, cardiology, and critical-care specialists because prolonged pharmacologic effects may occur.

⸻

Monitoring

Significant toxicity requires monitoring of:

Blood pressure   Heart rate   ECG/rhythm   Oxygenation   Mental status   Urine output   Renal function   Potassium   Magnesium

Additional monitoring is guided by the clinical course.

⸻

Observation

The historical fixed 6-hour observation period should not be applied universally.

Duration depends on:

Agent   Route   Magnitude of exposure   Renal function   Symptoms   ECG findings   Hemodynamic stability

Milrinone toxicity may be prolonged when renal clearance is impaired.

⸻

Admission

Monitored inpatient care is appropriate for:

Persistent hypotension   Significant dysrhythmia   Evidence of poor organ perfusion   Significant electrolyte abnormalities   Renal dysfunction with suspected drug accumulation

Severe hemodynamic instability generally warrants intensive-care management.

⸻

Pregnancy

The historical FDA pregnancy letter category is obsolete.

Clinically significant toxicity during pregnancy should be treated according to maternal physiology.

Particularly important goals are maintaining:

Maternal blood pressure   Oxygenation   Cardiac output   Uteroplacental perfusion

Necessary treatment should not be withheld solely because of pregnancy.

⸻

Prognosis

Mild toxicity usually improves after:

Drug discontinuation   Clearance of the medication   Correction of hemodynamic and electrolyte abnormalities

Prognosis becomes more serious when there is:

Refractory shock   Sustained ventricular dysrhythmia   Severe underlying cardiac disease   Renal failure causing prolonged milrinone exposure   Multiorgan hypoperfusion

⸻

Important Modernization of the Older Source

Amrinone is now generally called inamrinone.   Inamrinone and milrinone are PDE3 inhibitors/inodilators.   Milrinone has largely replaced inamrinone in contemporary practice.   PDE3 inhibition → ↑ cAMP → increased cardiac contractility plus vascular relaxation.   Acute toxicity is dominated by hypotension and dysrhythmias.   Milrinone depends substantially on renal clearance; renal impairment can prolong toxicity.   Inamrinone is more strongly associated with thrombocytopenia during prolonged exposure.   Chronic oral PDE3 inhibitor therapy is not routine modern heart-failure treatment because long-term outcome data were unfavorable.   Asthma alone is not a universal absolute contraindication; sulfite sensitivity depends partly on formulation.   Routine Trendelenburg positioning is obsolete.   Fluid resuscitation must be cautious in patients with heart failure.   Persistent vasodilatory shock may require norepinephrine or another appropriately selected vasopressor.   Atropine is relevant only when clinically important bradycardia is actually present.   Routine gastric lavage is obsolete.   There is no specific antidote.   Observation should account for renal function and clinical trajectory rather than follow a fixed 6-hour rule.

Key Points

Inamrinone/milrinone = PDE3 inhibitors.   ↑ cAMP in myocardium → ↑ intracellular Ca²⁺ → positive inotropy.   ↑ cAMP in vascular smooth muscle → vasodilation.   Together these effects make them inodilators.   Main acute toxicities: hypotension + dysrhythmias.   Check and correct K⁺, Mg²⁺, and other relevant electrolyte abnormalities.   Milrinone toxicity can be prolonged in renal impairment.   Inamrinone can cause thrombocytopenia, especially with prolonged exposure.   Stop an excessive infusion immediately and provide hemodynamic and rhythm support.   No specific antidote exists.

Toxicology – Amphetamines

Core Concept

Amphetamines are central nervous system stimulants and sympathomimetic drugs. They include prescription medications as well as illicitly manufactured stimulants.

Therapeutic amphetamine preparations are used mainly for:

• Attention-deficit/hyperactivity disorder (ADHD)
• Narcolepsy
• Selected other indications

The characteristic overdose syndrome is a sympathomimetic toxidrome:

Agitation + tachycardia + hypertension + mydriasis + diaphoresis + hyperthermia

Severe toxicity can progress to:

• Seizures
• Dangerous hyperthermia
• Rhabdomyolysis
• Dysrhythmias
• Myocardial ischemia
• Intracranial hemorrhage
• Shock
• Multiorgan failure

There is no specific antidote. Benzodiazepine-based sedation and aggressive supportive care are central to treatment.

Amphetamine-Type Stimulants

Clinically relevant agents include:

• Amphetamine
• Dextroamphetamine
• Mixed amphetamine salts
• Lisdexamfetamine
• Methamphetamine

Several drugs listed as “amphetamines” in older references are actually chemically or pharmacologically distinct stimulants or anorectic agents.

Many historical appetite suppressants listed in the source are also no longer commonly used because of safety concerns or regulatory changes.

Mechanism of Action

Amphetamines increase central and peripheral monoaminergic signaling.

Important mechanisms include:

• Increased presynaptic release of norepinephrine
• Increased release of dopamine
• Effects on serotonin at higher exposures or with particular agents
• Reversal/disruption of monoamine transport processes
• Intracellular effects involving vesicular monoamine storage

The older description of amphetamines as primarily direct α- and β-receptor agonists is incomplete.

Their major sympathomimetic effects arise predominantly from increased catecholamine availability.

Sympathomimetic Toxidrome

Typical findings include:

• Agitation
• Anxiety
• Restlessness
• Tachycardia
• Hypertension
• Mydriasis
• Diaphoresis
• Tremor
• Hyperreflexia
• Hyperthermia

Increasing toxicity can produce:

• Severe agitation
• Psychosis
• Seizures
• Cardiovascular complications
• Multiorgan injury

Amphetamine vs Antimuscarinic Toxicity

Both can produce:

• Agitation
• Tachycardia
• Mydriasis
• Hyperthermia

A useful distinction is:

Sympathomimetic → usually sweaty

Antimuscarinic → usually dry

Sympathomimetic patients often have marked diaphoresis and active bowel sounds, although no single physical finding is completely reliable.

Toxic Dose

There is no dependable universal toxic-dose threshold.

Severity varies with:

• Specific drug
• Formulation
• Route
• Patient size
• Individual sensitivity
• Chronic tolerance
• Coingestants
• Underlying cardiovascular disease

Therefore, management should be based on clinical toxicity rather than reported dose alone.

Tolerance in chronic users does not protect against catastrophic cardiovascular or hyperthermic complications.

Routes of Exposure

Amphetamine-type stimulants may be:

• Swallowed
• Insufflated
• Smoked
• Injected

The route influences:

• Speed of onset
• Peak concentration
• Duration
• Complication profile

Rapid-delivery routes can produce abrupt severe toxicity.

Neurologic Effects

Common manifestations include:

• Anxiety
• Agitation
• Tremor
• Headache
• Insomnia
• Hypervigilance
• Confusion

Severe toxicity can cause:

• Delirium
• Seizures
• Coma
• Intracranial hemorrhage
• Ischemic stroke

Psychiatric Effects

Amphetamine intoxication may produce:

• Paranoia
• Hallucinations
• Delusions
• Aggression
• Severe anxiety
• Stimulant-induced psychosis

Psychiatric symptoms may persist after peripheral sympathomimetic findings have improved.

Persistent psychosis requires reassessment for:

• Continued intoxication
• Sleep deprivation
• Coingestants
• Underlying psychiatric illness
• Other neurologic or metabolic disorders

Seizures

Seizures can result from intense CNS stimulation.

Complications include:

• Hypoxemia
• Lactic acidosis
• Hyperthermia
• Rhabdomyolysis
• Hyperkalemia
• Aspiration
• Acute kidney injury

Prompt control is essential.

Cardiovascular Effects

Common findings are:

• Sinus tachycardia
• Hypertension
• Palpitations

Severe toxicity may produce:

• Myocardial ischemia or infarction
• Coronary vasospasm
• Ventricular dysrhythmias
• Acute cardiomyopathy
• Acute heart failure
• Aortic dissection
• Shock

Young age does not exclude serious stimulant-associated cardiovascular disease.

Hypertension

Hypertension results from:

• Catecholamine excess
• Vasoconstriction
• Increased cardiac output
• Agitation

A major principle is:

Treat the hyperadrenergic state, not merely the blood-pressure number.

Sedation often improves both agitation and hypertension.

Severe Hypertensive Complications

Marked hypertension may contribute to:

• Intracranial hemorrhage
• Aortic dissection
• Myocardial ischemia
• Pulmonary edema
• Other end-organ injury

Persistent severe hypertension with acute organ injury requires titratable cardiovascular treatment in addition to sedation.

Hyperthermia

Severe hyperthermia is one of the most dangerous features of stimulant poisoning.

It can result from:

• Excessive motor activity
• Agitation
• Seizures
• Increased metabolic activity
• Catecholamine excess
• Impaired heat dissipation

Severe hyperthermia can rapidly produce:

• Rhabdomyolysis
• Hepatic injury
• Acute kidney injury
• Coagulopathy
• Cerebral injury
• Multiorgan failure

Hyperthermia Treatment

Management centers on:

• Rapid control of agitation
• External cooling
• Appropriate IV fluids
• Treatment of seizures
• Correction of physiologic abnormalities

Antipyretics such as acetaminophen do not correct stimulant hyperthermia because the problem is not an elevated hypothalamic fever set point.

Severe Agitation

Agitation itself can perpetuate:

Muscular activity → heat production → acidosis → rhabdomyolysis → worsening toxicity

Prompt sedation therefore has physiologic as well as behavioral importance.

Benzodiazepines

Benzodiazepines are generally first-line treatment for:

• Significant agitation
• Sympathomimetic excitation
• Seizures

They can also indirectly improve:

• Tachycardia
• Hypertension
• Hyperthermia caused by excessive muscular activity

Exact dosing should be titrated according to current emergency protocols and clinical response.

Refractory Agitation

Severe stimulant toxicity may require escalating sedation and intensive supportive management.

If dangerous agitation or hyperthermia cannot otherwise be controlled, advanced airway management and deep sedation may become necessary.

If neuromuscular paralysis is used:

Paralysis stops muscular activity but does not provide sedation or terminate cerebral seizure activity.

Adequate sedation and seizure treatment must continue.

Seizure Management

Benzodiazepines are first-line.

Refractory toxicologic seizures may require:

• Additional benzodiazepines
• Phenobarbital
• Appropriate anesthetic therapy for status epilepticus

Phenytoin – Modern Correction

The older recommendation to add phenytoin routinely is outdated.

Phenytoin is generally not preferred for toxin-induced seizures, because it does not effectively address many toxicologic seizure mechanisms.

Rhabdomyolysis

Rhabdomyolysis can result from:

• Hyperthermia
• Severe agitation
• Prolonged muscular activity
• Seizures
• Prolonged immobilization

Evaluate significant cases with:

• CK
• Potassium
• Creatinine
• Urinalysis
• Serial renal function

Treatment emphasizes appropriate fluid therapy and correction of electrolyte abnormalities.

Urinary Alkalinization

Routine urinary alkalinization is not recommended for stimulant-associated rhabdomyolysis.

It has not demonstrated clear benefit over appropriate supportive fluid management and can produce electrolyte and acid–base complications.

Renal Injury

Acute kidney injury may result from:

• Rhabdomyolysis
• Hyperthermia
• Hypotension
• Dehydration
• Severe systemic toxicity

Urine output and renal function should be monitored in severe poisoning.

Hepatic Injury

Severe hyperthermia and systemic toxicity can cause:

• Marked aminotransferase elevation
• Hepatic necrosis
• Acute liver failure

Liver injury is particularly concerning when accompanied by:

• Coagulopathy
• Hypoglycemia
• Lactic acidosis
• Encephalopathy

Coagulopathy

Extreme hyperthermia can trigger systemic coagulation abnormalities, including a DIC-like syndrome.

Monitor coagulation studies when severe hyperthermia or multiorgan injury develops.

Pulmonary Complications

Severe stimulant poisoning may cause:

• Aspiration
• Pulmonary edema
• Acute lung injury
• Respiratory failure

Respiratory compromise may also occur secondary to:

• Seizures
• CNS deterioration
• Severe cardiovascular toxicity

Acid–Base Disturbances

Lactic acidosis can result from:

• Severe agitation
• Seizures
• Hyperthermia
• Tissue hypoperfusion

Improvement often follows control of muscular activity, cooling, and restoration of perfusion.

Persistent severe acidosis should prompt investigation for shock, ongoing seizures, hyperthermia, or coingestants.

Electrolyte Abnormalities

Possible abnormalities include:

• Potassium disturbances
• Sodium disturbances
• Dehydration-related abnormalities

Electrolytes should be monitored closely in severe hyperthermia, seizures, or rhabdomyolysis.

Diagnosis

Amphetamine toxicity is primarily a clinical diagnosis.

Important information includes:

• Substance used
• Route
• Approximate timing
• Formulation
• Coingestants
• Prescription versus illicit source
• Duration of symptoms

Treatment should not wait for a urine drug screen when the clinical syndrome is convincing.

Urine Amphetamine Screening

Immunoassay drug screens have important limitations.

Possible problems include:

• False-positive results
• False-negative results
• Cross-reactivity with medications
• Inability to establish degree of intoxication
• Inability to prove that detected drug caused the current syndrome

A positive urine result indicates exposure within the detection window, not necessarily current clinical toxicity.

Confirmatory mass-spectrometric testing may be used when definitive identification matters.

Laboratory Evaluation

Minor uncomplicated intoxication may require limited testing.

Significant toxicity may warrant:

• Electrolytes
• Bicarbonate
• Creatinine
• Glucose
• CK
• Liver tests
• Blood gas and/or lactate
• Coagulation studies in severe hyperthermia
• Urinalysis

Intentional overdose may also require evaluation for important occult coingestants.

ECG and Cardiac Evaluation

Obtain an ECG when clinically significant toxicity is present.

Continuous monitoring is appropriate for:

• Severe tachycardia
• Chest pain
• Significant hypertension
• Dysrhythmia
• Hyperthermia
• Severe intoxication

Chest pain or ischemic findings should prompt appropriate evaluation for acute coronary injury.

Neurologic Imaging

Head CT is not required simply because a patient used amphetamines.

It becomes important when there is:

• Severe or unusual headache
• Focal neurologic deficit
• Persistent altered consciousness
• Suspected intracranial hemorrhage
• Trauma
• Seizure with concerning features

Lumbar puncture is likewise based on the differential diagnosis rather than routinely performed for stimulant intoxication.

Initial Management

Priorities are:

Airway/breathing → control agitation/seizures → measure core temperature → assess circulation → rapidly cool severe hyperthermia → identify end-organ injury

Benzodiazepine-based sedation is a central early intervention.

Hypertension Management

Many patients improve substantially after:

• Sedation
• Reduced stimulation
• Control of hyperthermia

Persistent severe hypertension with end-organ injury may require a short-acting titratable antihypertensive/vasodilator chosen according to the clinical problem.

The historical reliance on nitroprusside as the default drug is no longer necessary because several titratable agents are available.

β-Blockers – Important Nuance

Older teaching warned against every β-blocker in stimulant toxicity because of theoretical “unopposed α stimulation.”

Modern evidence is more nuanced and does not support treating all β-blockers as universally contraindicated.

However, in acute sympathomimetic poisoning:

• Sedation remains foundational.
• Drug selection should match the cardiovascular complication.
• Pure β-blockade is generally not the first reflexive treatment for an undifferentiated hyperadrenergic patient.

Management of myocardial ischemia, dysrhythmia, or severe hypertension should follow current toxicology/cardiology guidance.

Hypotension

Hypotension in severe poisoning may indicate:

• Volume depletion
• Hyperthermic collapse
• Cardiomyopathy
• Dysrhythmia
• Acidosis
• Multiorgan failure
• Coingestion

Treatment depends on the cause.

Appropriate crystalloid may be given when volume depletion is present, while persistent shock may require vasopressors and assessment of cardiac function.

Routine Trendelenburg positioning is obsolete.

GI Decontamination

Do not induce vomiting.

The historical routine use of gastric lavage is also obsolete.

A single dose of activated charcoal may occasionally be considered after a substantial recent oral ingestion if:

• Presentation is early
• The airway is safe
• The expected benefit outweighs aspiration risk

It should never delay treatment of agitation, seizures, hyperthermia, or cardiovascular instability.

Drug Packets

Suspected internal concealment of stimulant packets is a separate clinical problem.

Distinguish:

• Body packers – planned ingestion of multiple well-wrapped packets
• Body stuffers – hurried concealment of fewer, less securely wrapped packets

Packet rupture can cause abrupt life-threatening sympathomimetic poisoning.

Asymptomatic intact body packers may be candidates for monitored whole-bowel irrigation according to specialist protocols.

Packet rupture or severe toxicity may require urgent surgical and critical-care management.

Imaging for Drug Packets

The historical recommendation for routine abdominal radiographs is incomplete.

CT is generally more sensitive than plain abdominal radiography for detecting body-packing packets.

A negative plain film does not reliably exclude concealed packets.

No Specific Antidote

There is no direct antidote for amphetamine poisoning.

Treatment is based on:

• Sedation
• Cooling
• Seizure control
• Cardiovascular support
• Management of rhabdomyolysis
• Treatment of organ complications

Observation

The historical universal 4–6-hour observation rule is too rigid.

Duration depends on:

• Immediate-release versus extended-release formulation
• Specific drug
• Route
• Amount
• Clinical symptoms
• Coingestants
• Persistent psychiatric symptoms
• Vital signs
• Evidence of end-organ injury

Long-acting or modified-release products may produce prolonged toxicity.

Admission

Hospital admission is appropriate for clinically significant:

• Persistent agitation
• Recurrent seizures
• Hyperthermia
• Persistent severe tachycardia or hypertension
• Dysrhythmia
• Chest pain or ischemia
• Rhabdomyolysis
• Acute kidney injury
• Hepatic injury
• Coagulopathy
• Altered mental status

Severe hyperthermia or multiorgan toxicity generally warrants intensive care.

Chronic Stimulant Use

Long-term or repeated use can be associated with:

• Weight loss
• Sleep deprivation
• Psychiatric symptoms
• Cardiomyopathy
• Hypertension
• Vascular complications
• Dental and nutritional problems depending on circumstances
• Substance-use disorder

Injection additionally creates risks unrelated to the stimulant molecule itself, including:

• Endocarditis
• Abscess
• Blood-borne infections
• Sepsis

Stimulant Withdrawal

After prolonged heavy use, abrupt cessation can produce:

• Fatigue
• Hypersomnia
• Depressed mood
• Increased appetite
• Psychomotor slowing or agitation
• Craving

Severe depression and suicidality require direct assessment.

Withdrawal is generally not characterized by the autonomic instability seen with alcohol or sedative-hypnotic withdrawal.

Pregnancy

The historical FDA pregnancy letter categories are obsolete.

Amphetamine exposure during pregnancy should be assessed according to:

• Therapeutic versus nonmedical exposure
• Dose and frequency
• Maternal cardiovascular effects
• Nutrition
• Other substances
• Obstetric status

Severe maternal hyperthermia, hypertension, hypoxemia, or seizures require prompt treatment because maternal instability threatens fetal perfusion and oxygenation.

Safeguarding

Rigid age-based assumptions about neglect, abuse, or intentional poisoning are outdated.

Pediatric exposure should instead be evaluated according to:

• Developmental ability
• Accessibility
• Exposure circumstances
• Consistency of the history
• Recurrent unexplained exposures
• Overall safeguarding concerns

Important Modernization of the Older Source

• Amphetamines primarily increase catecholamine and dopamine signaling rather than simply acting as direct α/β agonists.
• The classic presentation is a sympathomimetic toxidrome.
• Severe hyperthermia is a medical emergency and can rapidly cause rhabdomyolysis, liver failure, coagulopathy, AKI, and brain injury.
• Benzodiazepines are foundational treatment for agitation and seizures.
• Antipyretics do not treat stimulant-induced hyperthermia.
• Phenytoin is generally not preferred for toxicologic seizures.
• Paralysis does not treat cerebral seizure activity and must never substitute for sedation.
• Hypertension often improves after adequate sedation.
• Modern evidence does not support an absolute blanket prohibition on every β-blocker in all stimulant-associated cardiovascular presentations.
• Trendelenburg positioning and routine dopamine-first shock treatment are outdated.
• Routine urinary alkalinization is not recommended for rhabdomyolysis.
• Urine amphetamine screens can be misleading and do not measure severity.
• Routine gastric lavage is obsolete.
• Activated charcoal has only a selective role after recent oral exposure with a safe airway.
• CT is generally more sensitive than plain radiography for body-packet detection.
• There is no specific antidote.
• Observation should be formulation- and symptom-based rather than a universal 4–6-hour rule.

Key Points

• Amphetamines → catecholamine excess → sympathomimetic toxidrome.
• Think agitation + tachycardia + hypertension + mydriasis + diaphoresis + hyperthermia.
• Benzodiazepines are first-line for significant agitation and seizures.
• Severe hyperthermia requires rapid sedation and active cooling.
• Major complications include seizures, stroke, myocardial ischemia, dysrhythmias, rhabdomyolysis, AKI, hepatic injury, and coagulopathy.
• Urine drug screens confirm neither current intoxication nor severity.
• Treat hypertension initially by controlling the hyperadrenergic state; persistent end-organ-threatening hypertension may require titratable cardiovascular therapy.
• Do not induce vomiting or routinely perform gastric lavage.
• No specific antidote exists.

Toxicology – Amoxapine and Loxapine

Core Concept

Amoxapine and loxapine are structurally related dibenzoxazepine drugs with important neurologic and cardiovascular toxicity in overdose.

• Amoxapine – tetracyclic antidepressant with pharmacologic similarities to tricyclic antidepressants (TCAs)
• Loxapine – antipsychotic, not an antidepressant

The most important manifestations of serious overdose are:

• CNS depression
• Seizures
• Tachycardia
• Hypotension
• Cardiac conduction abnormalities
• QRS widening or ventricular dysrhythmias in severe cases

A particularly important feature of amoxapine poisoning is its strong association with seizures, which can be recurrent or prolonged.

There is no specific antidote.

⸻

Pharmacology

Amoxapine and loxapine have complex receptor effects.

Amoxapine primarily inhibits neuronal reuptake of:

• Norepinephrine
• To a lesser extent, serotonin

It and its metabolites also have dopamine-receptor antagonist activity.

Loxapine acts primarily as an antipsychotic through:

• Dopamine D₂ antagonism
• Serotonin-receptor antagonism
• Additional adrenergic, histaminergic, and muscarinic effects

The older description that both drugs simply block reuptake of norepinephrine, serotonin, and dopamine is therefore an oversimplification.

⸻

Mechanisms of Toxicity

Several mechanisms may contribute:

CNS toxicity

Produces:

• Sedation
• Altered mental status
• Seizures
• Coma

Cardiac sodium-channel blockade

In substantial poisoning this can impair myocardial depolarization and produce:

• QRS widening
• Conduction delay
• Ventricular dysrhythmias
• Hypotension

α-Adrenergic blockade

Contributes to:

• Peripheral vasodilation
• Hypotension

Antimuscarinic effects

May contribute to:

• Tachycardia
• Altered mental status
• Reduced bowel motility
• Other antimuscarinic findings

⸻

Toxic Dose

There is no sufficiently reliable dose threshold to predict severity in an individual patient.

Historical fatal-dose reports should not be used as bedside treatment cutoffs.

Severity depends on:

• Drug
• Amount
• Patient size
• Coingestants
• Cardiovascular disease
• Seizure susceptibility
• Time to treatment

Clinical findings and ECG abnormalities are more important than the reported dose alone.

⸻

Neurologic Toxicity

Neurologic manifestations may develop abruptly.

Possible findings include:

• Drowsiness
• Confusion
• Agitation
• Lethargy
• Dysarthria
• Seizures
• Coma

Amoxapine is particularly notable because seizures may dominate the overdose syndrome even when severe cardiotoxicity is absent.

⸻

Seizures

Seizures can be:

• Recurrent
• Prolonged
• Difficult to control

Complications include:

• Hypoxemia
• Aspiration
• Hyperthermia
• Lactic acidosis
• Rhabdomyolysis
• Hyperkalemia
• Acute kidney injury
• Secondary brain injury

Therefore, rapid seizure control is one of the highest priorities.

⸻

Cardiovascular Toxicity

Possible manifestations include:

• Sinus tachycardia
• Hypotension
• QRS prolongation
• QT prolongation
• Conduction disturbances
• Ventricular ectopy
• Ventricular dysrhythmias

Serious cardiac toxicity is less consistently prominent than in classic severe TCA poisoning, particularly with amoxapine, but it remains possible.

⸻

ECG Importance

Obtain an ECG after a clinically important overdose.

Assess particularly for:

• QRS duration
• QT/QTc
• Heart rate and rhythm
• AV conduction
• Ventricular ectopy
• Other evidence of sodium-channel blockade

Continuous cardiac monitoring is appropriate for symptomatic or significant poisoning.

⸻

Sodium-Channel Blockade

If myocardial sodium channels are substantially inhibited:

Phase-0 depolarization slows → ventricular conduction slows → QRS widens

Increasing toxicity may then produce:

• Hypotension
• Ventricular dysrhythmias
• Cardiovascular collapse

This resembles the cardiotoxic mechanism of TCA poisoning.

⸻

Sodium Bicarbonate

Clinically important sodium-channel blockade is treated with sodium bicarbonate, particularly when there is:

• Significant QRS widening
• Ventricular dysrhythmia attributable to sodium-channel blockade
• Hypotension associated with conduction toxicity

Its beneficial mechanisms include:

• Sodium loading
• Serum alkalinization
• Reduction in drug binding to sodium channels

Therapy is guided by ECG and physiologic response rather than blindly pursuing an arbitrary bicarbonate dose.

⸻

QT Prolongation

QT prolongation may also occur.

Management includes:

• Continuous ECG monitoring
• Correction of potassium abnormalities
• Correction of magnesium abnormalities
• Removal of additional QT-prolonging drugs

If torsades de pointes develops, treatment follows standard toxicologic torsades management, including magnesium and electrical therapy when clinically required.

⸻

Hypotension

Hypotension may result from:

• α-Adrenergic blockade
• Myocardial sodium-channel blockade
• Dysrhythmia
• Acidemia
• Prolonged seizures
• Sedative coingestants

Treatment should therefore address the underlying mechanism rather than assuming simple volume depletion.

⸻

Management of Hypotension

Initial treatment may include appropriate isotonic crystalloid when volume support is indicated.

Persistent shock may require vasopressor therapy.

Norepinephrine is generally favored for persistent vasodilatory hypotension in modern critical-care practice.

If sodium-channel blockade is contributing, sodium bicarbonate is also important.

The older routine sequence of Trendelenburg positioning followed by dopamine is outdated.

⸻

Pulmonary Complications

Severe poisoning can cause:

• Respiratory depression
• Loss of airway protective reflexes
• Aspiration pneumonitis
• Hypoxemia
• Acute lung injury

Airway management is particularly important when recurrent seizures or coma develop.

⸻

Hyperthermia

Hyperthermia may result from:

• Recurrent muscular activity during seizures
• Agitation
• Severe systemic toxicity

Marked hyperthermia increases the risk of:

• Rhabdomyolysis
• Renal injury
• Coagulopathy
• Multiorgan dysfunction

Temperature should therefore be monitored in severe poisoning.

⸻

Metabolic Acidosis

Prolonged seizures commonly produce lactic acidosis.

Acidemia is particularly concerning when sodium-channel-blocking drugs are involved because lower pH can worsen cardiotoxicity.

Management focuses on:

• Rapid seizure control
• Adequate ventilation and oxygenation
• Restoration of perfusion
• Sodium bicarbonate when sodium-channel cardiotoxicity is present

⸻

Rhabdomyolysis

Repeated seizures can cause substantial skeletal-muscle breakdown.

Possible consequences include:

• Elevated CK
• Hyperkalemia
• Myoglobinuria
• Acute kidney injury

Monitor:

• CK
• Potassium
• Creatinine
• Urine output

when prolonged or repeated seizures occur.

⸻

Renal Injury

Acute kidney injury is usually secondary rather than a direct defining effect.

Potential mechanisms include:

• Rhabdomyolysis
• Hypotension
• Dehydration
• Multiorgan toxicity

⸻

Serotonin Toxicity

Amoxapine has serotonergic activity, so serotonin toxicity is possible particularly with serotonergic coexposures.

However, not every overdose should be labeled serotonin syndrome.

Look for the characteristic syndrome of:

• Agitation
• Hyperreflexia
• Clonus
• Tremor
• Autonomic activation
• Hyperthermia in severe cases

Clonus and hyperreflexia help distinguish serotonin toxicity from nonspecific overdose-related agitation or seizures.

⸻

Loxapine and Extrapyramidal Effects

Because loxapine is a dopamine antagonist, therapeutic use or poisoning can potentially produce:

• Acute dystonia
• Akathisia
• Parkinsonian findings

These should be distinguished from seizure activity.

Severe hyperthermia and rigidity should also raise consideration of neuroleptic malignant syndrome, although acute overdose alone does not automatically imply NMS.

⸻

Diagnosis

Diagnosis is primarily clinical.

Important information includes:

• Exact drug
• Formulation
• Amount
• Time of ingestion
• Coingestants
• Seizure history
• Cardiovascular history

Serum amoxapine and loxapine concentrations are generally not useful for acute bedside management.

⸻

Essential Evaluation

Important early assessment includes:

• Airway and breathing
• Mental status
• Bedside glucose
• ECG
• Continuous cardiac monitoring in significant poisoning

Symptomatic patients may also require:

• Electrolytes
• Bicarbonate
• Creatinine
• Blood gas
• CK
• Urinalysis
• Lactate

⸻

Occult Coingestion

Intentional overdose frequently involves more than one substance.

Depending on circumstances, evaluate for important clinically silent coingestants, especially acetaminophen.

Salicylate testing may also be appropriate when the history or acid–base pattern warrants it.

⸻

Neuroimaging and Lumbar Puncture

Head CT, lumbar puncture, EEG, and infectious studies are not routine tests for a known uncomplicated overdose.

They become appropriate when:

• The diagnosis is uncertain
• Focal neurologic findings occur
• Trauma is possible
• CNS infection is suspected
• Seizures remain unexplained
• Mental status fails to improve as expected

⸻

Initial Management

Priorities are:

Airway/ventilation → seizure control → ECG assessment → circulation → temperature/metabolic complications

Patients with severe neurologic or cardiovascular toxicity require intensive monitoring.

⸻

Seizure Treatment

Benzodiazepines are first-line therapy for toxicant-induced seizures.

Persistent or recurrent seizures may require:

• Additional benzodiazepine therapy
• Phenobarbital
• Escalation to appropriate anesthetic/critical-care therapy for refractory status epilepticus

At the same time, clinicians should correct:

• Hypoglycemia
• Hypoxemia
• Major electrolyte abnormalities
• Hyperthermia

⸻

Phenytoin – Modern Correction

The historical source recommends phenytoin as an additional anticonvulsant.

Phenytoin is generally not preferred for toxin-induced seizures, because many toxic seizures do not result from the neuronal mechanisms that phenytoin treats effectively.

It is especially unattractive when the poisoning itself may cause sodium-channel cardiotoxicity.

⸻

Neuromuscular Blockade

Neuromuscular paralysis may occasionally be required for airway management or control of dangerous muscular activity in a critically ill patient.

However:

Paralysis does not terminate electrical seizure activity in the brain.

If a patient is paralyzed during refractory seizures, adequate anticonvulsant/anesthetic treatment must continue and EEG monitoring may be necessary.

⸻

Physostigmine – Avoid

Physostigmine should generally be avoided when significant amoxapine or loxapine poisoning is suspected, particularly when there is:

• QRS widening
• Conduction abnormality
• Seizure risk
• Mixed/unknown ingestion

Increasing cholinergic activity in a patient with significant cardiotoxic or proconvulsant poisoning can be dangerous.

⸻

GI Decontamination

Do not induce vomiting.

Abrupt seizures and CNS depression create substantial aspiration risk.

The historical recommendation for routine gastric lavage is also obsolete.

⸻

Activated Charcoal

A single dose of activated charcoal may be considered after a substantial recent ingestion when:

• Presentation is sufficiently early
• The drug is likely to remain in the GI tract
• The airway is protected or reliably intact

Charcoal should never delay:

• Seizure treatment
• Airway stabilization
• Treatment of shock or dysrhythmia

Routine multiple-dose activated charcoal is not established for amoxapine or loxapine poisoning.

⸻

Extracorporeal Removal

Hemodialysis and hemoperfusion are not expected to provide meaningful toxin removal because these drugs have pharmacokinetic properties unfavorable for extracorporeal clearance.

Management remains primarily supportive.

⸻

Observation

The historical universal “normal ECG at 6 hours = discharge” rule should not be applied mechanically.

Observation depends on:

• Drug and formulation
• Estimated amount
• Symptoms
• Serial ECG findings
• Mental status
• Seizures
• Coingestants
• Clinical trajectory

Because severe neurologic toxicity may develop abruptly, significant intentional or uncertain ingestions require appropriate monitored observation.

⸻

Admission

ICU-level management is appropriate for patients with:

• Recurrent seizures
• Coma or substantial CNS depression
• Respiratory failure
• Significant QRS widening
• Ventricular dysrhythmia
• Persistent hypotension
• Severe hyperthermia
• Significant metabolic complications

⸻

Prognosis

Patients without severe seizures, cardiovascular toxicity, or secondary complications often recover with supportive care.

Poor prognostic features include:

• Refractory status epilepticus
• Prolonged hypoxemia
• Severe hyperthermia
• Persistent shock
• Serious ventricular dysrhythmia
• Severe rhabdomyolysis or multiorgan dysfunction

Permanent neurologic injury generally results from severe secondary insults such as prolonged seizures or hypoxia rather than from a simple mild exposure.

⸻

Pregnancy

The historical FDA pregnancy letter category is obsolete.

In severe poisoning during pregnancy, maternal stabilization is the priority.

Particularly important threats to both mother and fetus include:

• Seizures
• Hypoxemia
• Hypotension
• Hyperthermia
• Dysrhythmias

Necessary resuscitative and anticonvulsant treatment should not be withheld solely because of pregnancy.

⸻

Safeguarding

The older source’s rigid age cutoffs for abuse or intentional poisoning are outdated.

Pediatric poisoning should instead be assessed according to:

• Developmental ability
• Medication accessibility
• Circumstances
• Consistency of the history
• Recurrent unexplained poisoning
• Overall safeguarding concerns

Intentional self-poisoning requires appropriate safety assessment after medical stabilization.

⸻

Important Modernization of the Older Source

• Amoxapine is a tetracyclic antidepressant; loxapine is an antipsychotic.
• Their pharmacology is more complex than simple norepinephrine/serotonin/dopamine reuptake blockade.
• Amoxapine is particularly associated with recurrent and potentially severe seizures.
• Both can produce TCA-like sodium-channel cardiotoxicity in substantial poisoning.
• ECG evaluation should focus on QRS, QT, rhythm, and conduction.
• Sodium bicarbonate is important when clinically significant sodium-channel blockade develops.
• Benzodiazepines are first-line for seizures.
• Phenytoin is generally not preferred for toxicant-induced seizures.
• Neuromuscular paralysis does not treat cerebral seizure activity.
• Physostigmine should generally be avoided in significant poisoning with seizure or conduction risk.
• Trendelenburg positioning and routine dopamine-first treatment of shock are outdated.
• Ipecac and routine gastric lavage are obsolete.
• Activated charcoal has only a selective early role when the airway is safe.
• Routine multiple-dose charcoal is not established.
• Hemodialysis and hemoperfusion do not meaningfully enhance elimination.
• There is no specific antidote.
• Fixed 6-hour discharge rules should not replace individualized clinical and ECG assessment.

Key Points

• Amoxapine overdose → prominent seizure risk ± TCA-like cardiotoxicity.
• Loxapine overdose → CNS depression, seizures, hypotension, and possible conduction toxicity.
• Recurrent seizures can lead to hyperthermia, lactic acidosis, rhabdomyolysis, AKI, aspiration, and hypoxic injury.
• Obtain an ECG and monitor significant exposures continuously.
• QRS widening/ventricular sodium-channel toxicity → sodium bicarbonate therapy.
• Toxicant-induced seizures → benzodiazepines first-line.
• Avoid physostigmine when seizure or sodium-channel cardiotoxicity is possible.
• Do not induce vomiting or routinely perform gastric lavage.
• Dialysis does not meaningfully remove these drugs.
• No specific antidote exists.

Toxicology – Ammonia

Core Concept

Ammonia (NH₃) is a highly water-soluble, alkaline irritant gas with a strong pungent odor.

Important forms include:

• Anhydrous ammonia – concentrated gas or pressurized/liquefied ammonia used industrially
• Aqueous ammonia – ammonia dissolved in water
• Dilute household cleaning products
• More concentrated industrial/commercial solutions

The major toxic effect is direct chemical injury at the site of contact, especially involving:

• Eyes
• Upper airway
• Lungs
• Skin
• Gastrointestinal tract

There is no specific antidote.

Common Sources and Uses

Ammonia is used in:

• Fertilizer production
• Refrigeration systems
• Chemical manufacturing
• Plastics and synthetic fibers
• Pharmaceutical and dye production
• Industrial cleaning
• Household cleaning products

Severe exposures are particularly associated with:

• Industrial spills
• Refrigeration accidents
• Agricultural exposure
• Pressurized anhydrous ammonia
• Concentrated cleaning solutions

Routes of Exposure

Toxicity can occur through:

• Inhalation
• Ocular exposure
• Dermal contact
• Ingestion

Severity depends strongly on:

• Concentration
• Duration
• Route
• Amount
• Enclosed-space exposure
• Delay before decontamination

Mechanism of Injury

Ammonia is extremely soluble in water.

On contact with moist tissues, ammonia produces an alkaline environment traditionally represented as:

NH₃ + H₂O ⇌ NH₄⁺ + OH⁻

The resulting hydroxide-rich environment causes direct chemical injury.

Alkaline injury can produce:

• Protein disruption
• Cell membrane damage
• Inflammation
• Tissue penetration
• Liquefactive-type necrosis in substantial exposures

Why the Eyes and Airways Are Vulnerable

The:

• Tear film
• Nasal mucosa
• Oropharynx
• Respiratory epithelium

contain abundant water.

Ammonia therefore dissolves rapidly at these surfaces, explaining its intense immediate irritant effect.

Anhydrous Ammonia

Anhydrous ammonia is particularly hazardous because it may be stored under pressure as a liquefied gas.

Release can cause:

• Very high local vapor concentrations
• Severe inhalational injury
• Chemical burns
• Eye injury

Contact with liquefied ammonia can also produce cold-related tissue injury from rapid evaporation in addition to chemical injury.

Inhalational Toxicity

Because ammonia is highly water soluble, much of the initial injury occurs in the upper respiratory tract.

Symptoms may include:

• Burning of the nose and throat
• Cough
• Hoarseness
• Chest discomfort
• Dyspnea
• Wheezing
• Tachypnea

More severe exposure can produce:

• Laryngeal edema
• Laryngospasm
• Stridor
• Bronchospasm
• Chemical pneumonitis
• Acute lung injury
• Noncardiogenic pulmonary edema
• Respiratory failure

Airway Injury

Upper-airway injury is one of the most important immediate threats.

Warning findings include:

• Stridor
• Progressive hoarseness
• Drooling
• Dysphagia
• Respiratory distress
• Oropharyngeal burns
• Increasing work of breathing
• Altered mental status

Airway edema can progress after exposure.

Therefore:

A threatened airway should be secured before edema makes airway management substantially more difficult.

Pulmonary Injury

Lower-airway injury may produce:

• Cough
• Wheezing
• Bronchospasm
• Crackles
• Hypoxemia
• Chemical pneumonitis
• Acute lung injury

Pulmonary edema may evolve after a substantial exposure.

An initially reassuring examination or chest radiograph does not completely exclude evolving lung injury.

Reactive Airways Dysfunction

After significant irritant exposure, some patients can develop persistent airway hyperreactivity, sometimes described as reactive airways dysfunction syndrome (RADS).

Persistent symptoms may include:

• Cough
• Wheezing
• Chest tightness
• Exercise intolerance

Significant exposures may therefore require pulmonary follow-up.

Eye Exposure

Ammonia can rapidly cause severe ocular injury.

Possible manifestations include:

• Burning pain
• Lacrimation
• Conjunctival injection
• Blepharospasm
• Corneal epithelial injury
• Corneal burns
• Visual impairment

High-concentration exposure can threaten vision.

Immediate Ocular Management

The priority is:

Immediate copious irrigation

Do not delay irrigation to:

• Identify the exact concentration
• Measure ocular pH
• Perform a detailed examination

After initial irrigation, ocular pH can help determine whether additional irrigation is required.

Persistent:

• Pain
• Photophobia
• Visual disturbance
• Corneal abnormalities

requires urgent ophthalmic evaluation.

Skin Exposure

Dermal exposure may produce:

• Pain
• Erythema
• Irritant dermatitis
• Blistering
• Chemical burns
• Deeper tissue injury after concentrated exposure

Liquefied anhydrous ammonia may additionally cause cold injury.

Dermal Decontamination

Management begins with:

• Removal from the contaminated environment
• Removal of contaminated clothing
• Copious irrigation
• Standard assessment of resulting chemical/cold burns

Significant burns should be managed according to burn-care principles.

Ingestion

Aqueous ammonia ingestion primarily produces corrosive gastrointestinal injury.

Possible symptoms include:

• Oral pain
• Drooling
• Dysphagia
• Odynophagia
• Vomiting
• Chest pain
• Abdominal pain

Severe exposure can injure:

• Oropharynx
• Esophagus
• Stomach

Absence of Oral Burns Does Not Exclude Deeper Injury

A normal-looking mouth does not reliably exclude esophageal or gastric injury after a significant caustic ingestion.

Assessment should therefore consider:

• Product concentration
• Amount
• Intent
• Drooling
• Dysphagia/odynophagia
• Chest or abdominal pain
• Vomiting
• Respiratory findings

GI Complications

Severe corrosive injury may result in:

• Ulceration
• Necrosis
• Perforation
• Mediastinitis or peritonitis
• Later esophageal stricture formation

Long-term swallowing problems may therefore develop after significant injury.

Do Not Induce Vomiting

Vomiting should never be intentionally induced after ammonia ingestion.

Re-exposure of the upper GI tract can worsen injury and increase aspiration risk.

Ipecac has no role.

Do Not Neutralize

Do not attempt to neutralize ammonia with an acid.

Chemical neutralization can:

• Generate heat
• Produce additional tissue damage
• Delay appropriate care

The same general principle applies to caustic ingestions:

Do not attempt home chemical neutralization.

Routine Gastric Lavage Is Contraindicated

Gastric lavage is generally inappropriate after caustic ammonia ingestion because it can:

• Re-expose injured tissue
• Increase perforation risk
• Cause aspiration
• Produce additional mechanical trauma

Activated Charcoal

Activated charcoal is generally not useful for ammonia ingestion.

It does not meaningfully prevent the immediate local corrosive injury and may interfere with subsequent endoscopic evaluation.

Oral Dilution – Modern Perspective

Older references sometimes recommended routine administration of water or milk after caustic ingestion.

Modern management does not rely on routine forced dilution.

Do not give large volumes because this may:

• Trigger vomiting
• Increase gastric distension
• Increase aspiration risk

Immediate advice after ingestion should follow current poison-center or caustic-ingestion guidance.

Ammonia + Bleach

Mixing ammonia-containing cleaners with hypochlorite bleach can generate chloramine gases and related respiratory irritants.

This can cause:

• Eye and throat irritation
• Cough
• Chest tightness
• Bronchospasm
• Dyspnea
• Chemical pneumonitis in substantial exposure

The resulting illness should be managed as an irritant gas inhalation, rather than assuming exposure to ammonia alone.

Reactive Airway Disease

Patients with:

• Asthma
• Other reactive airway disease

may experience more pronounced bronchospasm after ammonia or chloramine exposure.

Diagnosis

Diagnosis is usually based on:

• Exposure history
• Product concentration
• Route
• Duration
• Respiratory examination
• Ocular/skin findings
• GI symptoms after ingestion

There is no clinically useful routine serum “ammonia level” for diagnosing inhalational or caustic ammonia exposure.

A plasma ammonia measurement used in hepatic encephalopathy evaluates an entirely different clinical problem.

Laboratory Evaluation

Minor asymptomatic exposure may require no laboratory testing.

For significant inhalational injury, testing may include:

• Pulse oximetry
• Blood gas when respiratory compromise is present
• Electrolytes and other general tests when clinically indicated

Severe caustic ingestion may require additional laboratory evaluation based on the extent of systemic illness.

Chest Imaging

Chest radiography is appropriate when there are significant respiratory symptoms or suspected pulmonary injury.

Possible findings include:

• Infiltrates
• Pulmonary edema
• Other evidence of acute lung injury

However:

A normal early chest radiograph does not exclude evolving inhalational injury.