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.

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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

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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.

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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

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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.

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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.

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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

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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.