Toxicology – Black Widow Spider Antivenom

Core Concept

Black widow antivenom neutralizes circulating venom from Latrodectus spiders.

Black widow envenomation, or latrodectism, primarily causes a painful neurotoxic syndrome characterized by:

• Severe local or generalized pain
• Painful muscle spasms
• Abdominal or back rigidity
• Diaphoresis
• Nausea/vomiting
• Restlessness
• Tachycardia
• Hypertension

Antivenom can produce rapid improvement in severe systemic envenomation, but its use depends on the available formulation and the balance between benefit and hypersensitivity risk.

Mechanism of Envenomation

The major black widow venom component, α-latrotoxin, acts at presynaptic nerve terminals and causes excessive neurotransmitter release.

This produces marked autonomic and neuromuscular activity.

The result can include:

Pain → muscle spasm → autonomic hyperactivity

Severe cases may produce substantial hypertension and other systemic manifestations.

How Antivenom Works

Traditional black widow antivenom is produced from antibodies obtained from immunized horses.

These antibodies bind circulating venom components and prevent them from interacting with additional target tissues.

Antivenom therefore provides passive immunity against the venom.

It does not simply provide analgesia—it targets the venom itself.

Cross-Reactivity

Antibodies against one medically important Latrodectus species may cross-react with venom from related widow spiders.

However, actual antivenom products and availability vary considerably by country and region.

Treatment should therefore follow the specific locally available product and poison-center/toxicology guidance.

When Antivenom Is Considered

Most black widow bites do not automatically require antivenom.

Supportive treatment is sufficient for many patients.

Antivenom is generally reserved for clinically important systemic envenomation, particularly when there is:

• Severe or persistent pain despite adequate analgesia
• Severe muscle spasms
• Significant autonomic instability
• Severe hypertension
• Respiratory compromise
• Other serious systemic toxicity

Patient-specific factors and the antivenom formulation influence the decision.

Supportive Treatment

Initial management includes:

• Analgesia
• Treatment of severe muscle spasm when necessary
• Monitoring of vital signs
• Supportive respiratory care when required

The historical practice of routinely relying on calcium for black widow muscle spasms is not supported as a consistently effective treatment.

Clinical Response to Antivenom

When effective, improvement may occur relatively rapidly.

Possible responses include:

• Reduction in severe pain
• Decreased muscle spasm
• Improvement in autonomic manifestations

Persistent symptoms require reassessment of:

• Severity of envenomation
• Alternative diagnoses
• Adequacy of supportive therapy
• Whether additional antivenom is appropriate under the product-specific protocol

Major Risk – Hypersensitivity

Equine-derived antivenoms contain foreign proteins and can cause immediate hypersensitivity reactions.

Possible manifestations include:

• Urticaria
• Pruritus
• Flushing
• Angioedema
• Bronchospasm
• Hypotension
• Anaphylaxis

Administration should therefore occur in a monitored setting with the ability to recognize and treat anaphylaxis immediately.

Anaphylaxis

If anaphylaxis develops:

• Stop or pause the suspected triggering infusion as clinically appropriate.
• Assess airway, breathing, and circulation.
• Give epinephrine as first-line treatment.
• Provide oxygen and airway/ventilatory support when needed.
• Give appropriate IV fluids for hypotension.
• Use adjunctive therapies for persistent bronchospasm or other manifestations.

Antihistamines and corticosteroids are adjuncts, not substitutes for epinephrine in anaphylaxis.

This is an important modernization of the older source.

Skin Testing

Older equine-antivenom protocols commonly recommended horse-serum skin testing before treatment.

This has important limitations:

• A negative test does not reliably exclude a serious reaction.
• Testing itself can cause hypersensitivity.
• It can delay urgently needed antivenom.

Modern practice follows the instructions for the specific antivenom product rather than assuming routine skin testing is universally useful.

Delayed Serum Sickness

Equine antivenom can also produce a delayed immune-complex reaction.

Symptoms usually develop days after treatment and may include:

• Fever
• Malaise
• Rash
• Pruritus
• Arthralgia

Less commonly, more significant systemic manifestations occur.

Patients receiving equine antivenom should be informed that delayed symptoms can occur after discharge.

Pregnancy

Pregnancy does not automatically contraindicate antivenom.

Severe maternal envenomation itself can threaten both mother and fetus.

The obsolete FDA pregnancy letter categories should not be used as the primary basis for decision-making.

Treatment depends on maternal disease severity and the expected benefits and risks of the available antivenom.

Monitoring

During antivenom administration monitor:

• Heart rate
• Blood pressure
• Respiratory status
• Oxygenation
• Skin/mucosal findings
• Pain and muscle spasm
• Evidence of hypersensitivity

Continued monitoring is particularly important during administration of equine-derived products.

Key Points

• Black widow venom produces latrodectism, characterized particularly by severe pain, muscle spasm, and autonomic hyperactivity.
• α-Latrotoxin causes excessive neurotransmitter release from presynaptic terminals.
• Antivenom antibodies bind circulating venom and prevent additional toxic effects.
• Mild envenomation generally does not require antivenom.
• Antivenom is considered for significant systemic toxicity or severe symptoms inadequately controlled with supportive care.
• Equine antivenom can cause immediate hypersensitivity and delayed serum sickness.
• Epinephrine is first-line therapy for antivenom-induced anaphylaxis.
• Antihistamines and corticosteroids are only adjunctive treatments for anaphylaxis.
• Routine horse-serum skin testing is not a universally reliable modern strategy.
• Product availability and formulations vary geographically, so current product-specific guidance is essential.

Toxicology – Atropine

Core Concept

Atropine is a competitive muscarinic acetylcholine receptor antagonist.

In toxicology, its most important role is treatment of the dangerous muscarinic manifestations of cholinergic poisoning, particularly from:

• Organophosphate pesticides
• Carbamate pesticides
• Nerve agents
• Other clinically important cholinesterase inhibitors

Atropine is also used in selected cases of symptomatic bradycardia.

Mechanism of Action

Atropine competitively blocks acetylcholine at muscarinic receptors.

This decreases parasympathetic activity in organs such as the:

• Heart
• Bronchial tree
• Salivary glands
• Gastrointestinal tract
• Urinary tract
• Eyes
• Sweat glands

The clinically important toxicologic effect is:

Muscarinic receptor blockade → reduced bronchial secretions and bronchoconstriction

Muscarinic vs Nicotinic Effects

This distinction is essential in cholinergic poisoning.

Muscarinic manifestations

Atropine is effective against:

• Bronchorrhea
• Bronchospasm
• Excess salivation
• Lacrimation
• Bradycardia
• Some GI hyperactivity

Nicotinic manifestations

Atropine does not directly reverse:

• Fasciculations
• Skeletal muscle weakness
• Paralysis
• Respiratory muscle failure

Therefore, improvement in secretions does not necessarily mean the entire cholinergic syndrome has resolved.

Central Nervous System Effects

Atropine crosses the blood-brain barrier.

At sufficient exposure it can produce central antimuscarinic effects such as:

• Agitation
• Confusion
• Delirium
• Hallucinations

This differs from quaternary antimuscarinic drugs such as glycopyrrolate, which have much less CNS penetration.

Main Toxicologic Indication: Cholinergic Poisoning

Severe cholinesterase inhibitor poisoning may produce:

• Miosis
• Salivation
• Lacrimation
• Bronchorrhea
• Bronchospasm
• Vomiting
• Diarrhea
• Sweating
• Bradycardia or tachycardia
• Fasciculations
• Weakness
• Seizures
• Respiratory failure

The major immediate threat is often respiratory compromise from a combination of:

• Copious airway secretions
• Bronchoconstriction
• Respiratory muscle weakness
• CNS dysfunction

Atropine primarily treats the first two components.

Atropine Treatment Endpoint

In severe cholinergic poisoning, atropine should be titrated according to the clinical response, particularly the respiratory findings.

The important endpoint is:

Improved ventilation with substantial control of bronchial secretions and bronchospasm

Useful signs include:

• Drying of excessive pulmonary secretions
• Improved air movement
• Improved oxygenation
• Improved hemodynamic status when muscarinic effects contributed

Do Not Use Pupil Size as the Endpoint

Miosis may persist despite adequate treatment.

Therefore:

Pupil dilation is not required for successful atropinization.

Attempting to normalize pupil size can lead to unnecessary atropine administration.

Do Not Use Heart Rate Alone as the Endpoint

Tachycardia is common during atropine therapy, but it does not necessarily mean treatment should stop.

A patient may still have life-threatening bronchorrhea despite being tachycardic.

Therefore:

Pulmonary secretion control and ventilation are more important endpoints than heart rate alone.

Organophosphate Poisoning

Organophosphates inhibit acetylcholinesterase, producing accumulation of acetylcholine at:

• Muscarinic synapses
• Nicotinic synapses
• CNS cholinergic pathways

Atropine competitively blocks the muscarinic consequences of this acetylcholine excess.

It does not reactivate acetylcholinesterase.

Role of Pralidoxime

In significant organophosphate poisoning, pralidoxime may be used in addition to atropine.

The two drugs have different roles:

Atropine

Controls muscarinic manifestations, especially:

• Bronchorrhea
• Bronchospasm
• Bradycardia

Pralidoxime

Can reactivate inhibited acetylcholinesterase before irreversible enzyme “aging” occurs and may particularly help with:

• Fasciculations
• Muscle weakness
• Respiratory muscle dysfunction

Atropine should not be delayed while waiting for pralidoxime.

Carbamate Poisoning

Carbamates also inhibit acetylcholinesterase but generally bind reversibly.

Atropine remains the primary treatment for clinically important muscarinic toxicity.

The role of pralidoxime is less straightforward than in organophosphate poisoning and depends on the specific exposure and clinical circumstances.

Nerve-Agent Exposure

Nerve agents are potent organophosphorus cholinesterase inhibitors.

Severe exposure may cause rapid:

• Bronchorrhea
• Bronchospasm
• Seizures
• Fasciculations
• Paralysis
• Respiratory failure

Management may require:

• Airway and ventilatory support
• Atropine
• An oxime such as pralidoxime
• Benzodiazepines for seizures

Symptomatic Bradycardia

Atropine can increase heart rate by reducing parasympathetic influence on the:

• Sinoatrial node
• AV node

It may be appropriate for selected symptomatic bradycardias associated with poor perfusion.

However, atropine is not equally effective for every toxicologic bradycardia.

Toxicologic Bradycardias

Important causes include:

• Beta-blockers
• Calcium channel blockers
• Digoxin
• Clonidine/imidazolines
• Cholinergic agents
• Opioids

In many of these poisonings, atropine may provide little or only transient benefit.

The priority is the toxin-specific mechanism and treatment.

Examples include:

• Digoxin toxicity → digoxin immune Fab when indicated
• Severe beta-blocker/CCB toxicity → mechanism-directed cardiovascular support
• Opioid toxicity → naloxone when respiratory depression is present
• Cholinergic poisoning → atropine is directly relevant

Expected Antimuscarinic Effects

Atropine itself can produce:

• Tachycardia
• Mydriasis
• Cycloplegia
• Dry mouth
• Reduced sweating
• Flushed skin
• Reduced bowel motility
• Urinary retention

Larger exposures may cause:

• Hyperthermia
• Agitation
• Hallucinations
• Delirium

These findings represent an anticholinergic syndrome.

Hyperthermia Risk

Atropine decreases sweating.

Because sweating is important for heat dissipation, antimuscarinic therapy can increase susceptibility to hyperthermia, particularly in:

• Hot environments
• Young children
• Patients already hyperthermic
• Patients receiving other anticholinergic medications

Temperature should therefore be monitored during substantial atropine therapy.

Ophthalmic Effects

Topical atropine causes:

Mydriasis

Dilation of the pupil.

Cycloplegia

Paralysis of accommodation.

The ocular effects can persist considerably longer than atropine’s cardiovascular effects.

Possible consequences include:

• Photophobia
• Blurred near vision
• Increased intraocular pressure in susceptible patients

Angle-Closure Glaucoma

Ophthalmic antimuscarinic medications can precipitate or worsen acute angle closure in anatomically susceptible eyes.

This is particularly relevant when atropine is being used specifically as an ophthalmic medication.

In a life-threatening systemic poisoning, however, relative contraindications should not prevent necessary antidotal atropine treatment.

Systemic Absorption from Eye Drops

Atropine administered ophthalmically can be absorbed systemically.

Systemic anticholinergic effects are more concerning in:

• Children
• Older adults
• Patients receiving excessive topical medication

Possible manifestations include:

• Tachycardia
• Dry mouth
• Flushing
• Hyperthermia
• Confusion

Drug Interactions

Atropine’s antimuscarinic effects may be increased by other medications with anticholinergic properties, including certain:

• First-generation antihistamines
• Antipsychotics
• Tricyclic antidepressants
• Antiparkinsonian drugs
• Antispasmodic medications

Combining substantial anticholinergic burdens can increase the risk of:

• Delirium
• Hyperthermia
• Urinary retention
• Ileus
• Tachycardia

The older source’s description of sympathomimetics simply “potentiating atropine” is an oversimplification; rather, their physiologic effects can overlap, particularly tachycardia and hyperthermia.

Atropine Toxicity

Excess atropine produces an antimuscarinic toxidrome.

Typical findings include:

• Mydriasis
• Dry mucous membranes
• Dry skin
• Flushing
• Tachycardia
• Hyperthermia
• Urinary retention
• Reduced bowel sounds
• Agitation
• Delirium
• Hallucinations

Severe poisoning can cause marked CNS and cardiovascular abnormalities.

Physostigmine and Atropine Toxicity

Physostigmine is a centrally active acetylcholinesterase inhibitor that can reverse selected severe pure antimuscarinic delirium.

However, it is not automatically appropriate whenever atropine-like symptoms occur.

Before considering it, clinicians must exclude important contraindications and alternative causes, particularly:

• Sodium-channel-blocking poisoning
• Significant QRS widening
• Certain conduction abnormalities
• Mixed overdose

Supportive care remains fundamental.

Atropine Administration in Severe Cholinergic Poisoning

Severe organophosphate poisoning may require very large cumulative quantities of atropine compared with ordinary bradycardia treatment.

The principle is more important than memorizing a fixed maximum:

Escalate atropine rapidly enough to control life-threatening muscarinic pulmonary toxicity.

Once adequate control is achieved, ongoing therapy may be required because the toxicant can persist much longer than atropine.

Exact dosing should follow current poison-center or critical-care protocols.

Recurrent Cholinergic Toxicity

Atropine’s clinical effect may wear off while the cholinesterase inhibitor remains active.

Therefore, patients can develop recurrent:

• Bronchorrhea
• Bronchospasm
• Bradycardia
• Other muscarinic manifestations

Continued reassessment is essential.

Monitoring

During significant atropine treatment, monitor:

• Airway
• Respiratory effort
• Pulmonary secretions
• Oxygenation
• Heart rate and rhythm
• Blood pressure
• Temperature
• Mental status
• Bowel and urinary function when relevant

In cholinergic poisoning, also monitor for:

• Fasciculations
• Progressive weakness
• Respiratory muscle failure
• Recurrent secretions

Pregnancy

The historical FDA pregnancy categories such as Category C are obsolete.

When atropine is required for a serious maternal indication, including significant cholinergic poisoning, pregnancy should not prevent necessary treatment.

Maternal stabilization remains the priority.

Common Pitfalls

Stopping atropine because tachycardia develops

Tachycardia does not prove that pulmonary muscarinic toxicity has resolved.

Waiting for the pupils to dilate

Pupil size is not the treatment endpoint.

Expecting atropine to reverse muscle weakness

Nicotinic neuromuscular dysfunction is not directly reversed by atropine.

Giving atropine but ignoring ventilation

Patients with severe organophosphate poisoning can still require airway and ventilatory support.

Using a fixed maximum dose in severe poisoning

Massive cholinergic toxicity may require unusually large cumulative atropine exposure.

Assuming every toxicologic bradycardia will respond

Many cardiotoxic poisons require specific therapies beyond atropine.

Important Modernization of the Older Source

Several points from the original material require updating:

• Atropine is best described specifically as an antimuscarinic, rather than broadly as an “anticholinergic antidote.”
• Its most important endpoint in cholinergic poisoning is control of bronchorrhea/bronchospasm and improvement in ventilation, not normalization of pupil size or heart rate.
• Atropine does not treat nicotinic weakness or paralysis.
• Severe organophosphate poisoning may require very large amounts, with treatment guided by clinical response rather than a conventional maximum dose.
• Pralidoxime has a complementary role in significant organophosphate poisoning.
• Atropine is not reliably effective for all poison-induced bradycardias.
• Routine atropine as a premedication for pediatric procedural sedation is not standard modern practice.
• FDA pregnancy letter categories are obsolete.
• Sympathomimetics do not simply “potentiate atropine”; rather, several physiologic effects can overlap.
• Relative contraindications to atropine should not prevent its use when treating life-threatening cholinergic poisoning.

Key Points

• Atropine is a competitive muscarinic acetylcholine receptor antagonist.
• It has little direct effect at nicotinic receptors.
• Its major toxicologic use is treatment of muscarinic cholinergic toxicity.
• It is especially important for bronchorrhea and bronchospasm caused by organophosphates, carbamates, and nerve agents.
• The major treatment endpoint is adequate ventilation with control of excessive pulmonary secretions.
• Do not titrate atropine to pupil size.
• Do not stop treatment merely because tachycardia develops.
• Atropine does not directly reverse fasciculations, skeletal muscle weakness, or paralysis.
• Pralidoxime complements atropine in significant organophosphate poisoning by targeting the inhibited acetylcholinesterase mechanism.
• Severe cholinergic poisoning may require unusually large cumulative atropine exposure.
• Atropine can treat selected symptomatic bradycardias, but many toxicologic bradycardias require toxin-specific treatment.
• Excess atropine causes an antimuscarinic syndrome with tachycardia, mydriasis, dry skin/mucosa, urinary retention, hyperthermia, and delirium.
• Significant cholinergic poisoning requires continued monitoring because toxicity may recur after atropine’s effects diminish.

Toxicology – Adenosine

Core Concept

Adenosine is an extremely short-acting antiarrhythmic medication used primarily to terminate certain regular supraventricular tachycardias (SVTs) that depend on the AV node for maintenance.

Its extremely short duration of action makes both its therapeutic effects and most adverse effects brief.

In toxicology, adenosine may occasionally be useful for a true AV-node-dependent SVT, but it does not treat the underlying poisoning.

Main Clinical Role

Adenosine is most useful for:

• Regular, narrow-complex SVT
• AV nodal reentrant tachycardia (AVNRT)
• AV reentrant tachycardia (AVRT) involving an accessory pathway when the rhythm is appropriate for adenosine
• Selected regular monomorphic wide-complex tachycardias when SVT with aberrancy is being considered and use is clinically appropriate

Vagal maneuvers are generally attempted first in a stable patient with an appropriate regular SVT.

Mechanism of Action

Adenosine acts primarily at A1 adenosine receptors in cardiac nodal tissue.

This produces:

• Increased potassium conductance
• Reduced calcium-dependent activity
• Hyperpolarization of AV nodal cells
• Slowing of AV nodal conduction
• Increased AV nodal refractoriness

The key clinical result is:

Transient AV nodal block

If a tachycardia requires the AV node as part of its reentry circuit, briefly interrupting AV conduction can terminate the rhythm.

Why the Effect Is So Brief

Adenosine is rapidly taken up and metabolized by cells in blood and vascular tissues.

Its plasma half-life is only a few seconds.

Therefore:

• It must reach the circulation rapidly.
• Its therapeutic effect occurs almost immediately.
• Most adverse effects resolve rapidly.
• Recurrent tachycardia can occur if the underlying trigger persists.

Adenosine and Toxicologic Tachycardia

Adenosine should not be viewed as a general treatment for tachycardia caused by poisoning.

Many toxicologic tachycardias are compensatory or driven by persistent mechanisms such as:

• Sympathetic stimulation
• Hyperthermia
• Hypovolemia
• Hypoxia
• Metabolic acidosis
• Anticholinergic effects
• Withdrawal

In these situations, slowing the AV node does not correct the underlying problem.

The priority is to treat the toxicologic mechanism.

Theophylline Toxicity

Theophylline deserves special attention.

Theophylline is a methylxanthine and adenosine-receptor antagonist, so it can reduce the effectiveness of adenosine.

Theophylline poisoning commonly causes:

• Marked sinus tachycardia
• Supraventricular dysrhythmias
• Tremor
• Vomiting
• Hypokalemia
• Hyperglycemia
• Seizures

Therefore, persistent tachycardia in theophylline poisoning should not automatically be treated as an adenosine-responsive SVT.

Caffeine

Caffeine is also a methylxanthine and antagonizes adenosine receptors.

Recent substantial caffeine exposure may therefore reduce responsiveness to adenosine.

This interaction is especially relevant with large caffeine exposures or toxicity.

Dipyridamole

Dipyridamole can potentiate adenosine’s effects by interfering with cellular adenosine uptake.

This can produce a stronger or more prolonged response than expected.

Medication history is therefore important before administration.

Carbamazepine

Carbamazepine can enhance AV nodal conduction suppression and may increase the risk of excessive bradycardia or AV block when combined with adenosine.

Extra caution is appropriate when significant carbamazepine exposure is suspected.

What Adenosine Does NOT Usually Convert

Adenosine generally does not terminate rhythms whose circuit does not depend on the AV node.

Examples include:

• Atrial fibrillation
• Atrial flutter
• Most atrial tachycardias
• Sinus tachycardia
• Ventricular tachycardia

However, transient AV nodal blockade may sometimes expose underlying atrial activity and thereby help clarify the diagnosis.

Atrial Flutter

Adenosine may transiently block conduction through the AV node without eliminating the atrial flutter circuit.

The ECG may briefly reveal flutter waves more clearly.

Thus:

Adenosine may reveal atrial flutter without actually treating the underlying flutter.

Atrial Fibrillation

Adenosine does not terminate atrial fibrillation.

Particular caution is required when atrial fibrillation occurs with an accessory pathway, such as pre-excited atrial fibrillation, because AV nodal blockade can be dangerous.

An irregular wide-complex tachycardia should therefore not be reflexively treated with adenosine.

WPW and Accessory Pathways

The older source broadly lists Wolff-Parkinson-White syndrome as an indication, but this requires important clarification.

Adenosine can terminate orthodromic AVRT, in which the AV node forms part of the reentry circuit.

However:

Pre-excited atrial fibrillation is different and AV nodal blocking agents should be avoided.

Therefore, the rhythm itself—not simply the presence of WPW—determines whether adenosine is appropriate.

Regular vs Irregular Tachycardia

A high-yield distinction is:

Regular narrow-complex tachycardia

Adenosine may be appropriate if AV-node-dependent SVT is suspected.

Regular monomorphic wide-complex tachycardia

Adenosine may sometimes be considered in carefully selected stable cases.

Irregular wide-complex tachycardia

Do not routinely give adenosine; consider atrial fibrillation with pre-excitation, polymorphic VT, and other dangerous rhythms.

Unstable Tachycardia

Adenosine should not delay definitive treatment in a patient with hemodynamic instability.

Important instability findings include:

• Hypotension
• Shock
• Ischemic chest discomfort
• Acute heart failure
• Altered mental status from poor perfusion

An unstable tachyarrhythmia generally requires immediate synchronized cardioversion when appropriate, rather than repeated attempts at pharmacologic conversion.

Diagnostic Value

Because adenosine briefly suppresses AV nodal conduction, it can sometimes help distinguish:

• AV-node-dependent SVT
• Atrial flutter
• Certain atrial tachycardias

Continuous ECG recording during administration is useful because the diagnostic changes may last only seconds.

Expected Transient Effects

Patients should be warned, when circumstances allow, that adenosine can produce a sudden and unpleasant sensation.

Common transient symptoms include:

• Flushing
• Chest pressure or tightness
• Dyspnea
• Lightheadedness
• Nausea
• Sense of impending doom

These symptoms usually resolve rapidly because the drug disappears from the circulation within seconds.

Transient Bradycardia and AV Block

Adenosine intentionally produces transient AV nodal suppression.

The monitor may briefly show:

• Marked bradycardia
• AV block
• A short pause
• Transient asystole

This can look dramatic but usually resolves almost immediately.

Resuscitation equipment should nevertheless be readily available.

Bronchospasm

Adenosine can provoke bronchoconstriction.

Greater caution is warranted in patients with:

• Active bronchospasm
• Significant reactive airway disease
• Severe asthma

Clinically important bronchospasm is uncommon but potentially serious.

Major Contraindications / Situations Requiring Avoidance

Important situations include:

• Second-degree AV block without a functioning pacemaker
• Third-degree AV block without a functioning pacemaker
• Significant sinus-node dysfunction without pacing
• Irregular wide-complex tachycardia
• Pre-excited atrial fibrillation
• Significant active bronchospasm

Clinical context and ECG interpretation remain essential.

Administration Principle

Because adenosine disappears from circulation extremely rapidly, it must be delivered as a rapid IV bolus followed immediately by a flush.

A proximal peripheral IV can be used effectively; a central venous line is not routinely required.

This corrects the older source’s implication that adenosine needs to be administered through a central line.

Monitoring During Administration

Use:

• Continuous ECG monitoring
• Blood pressure monitoring
• Clinical observation
• Appropriate resuscitation equipment

A rhythm strip should ideally capture the period before, during, and after administration.

Pediatric Use

Adenosine is well established in modern pediatric resuscitation practice for appropriate SVT.

This differs from the older source’s statement that adequate pediatric evidence was lacking.

Pediatric administration is weight-based and should follow current pediatric resuscitation protocols.

Pregnancy

The old FDA pregnancy-letter categories such as Category C are obsolete.

Adenosine has an extremely short half-life and is used clinically during pregnancy when treatment of an appropriate SVT is necessary.

Pregnancy does not automatically preclude its use.

Failure of Adenosine

If an apparent SVT does not terminate, reconsider:

• Was the medication delivered rapidly enough?
• Is the rhythm actually AV-node dependent?
• Is this sinus tachycardia?
• Is it atrial flutter?
• Is it atrial tachycardia?
• Could this be ventricular tachycardia?
• Is a methylxanthine such as theophylline antagonizing adenosine?
• Is an ongoing toxicologic stimulus continuously recreating the rhythm?

Repeated treatment should not substitute for reassessing the ECG diagnosis.

Adenosine in Poisoning

In toxicology, always ask:

Is this a primary reentrant SVT, or is the tachycardia an expected physiologic consequence of the poison?

For example:

• Stimulant toxicity → control sympathetic excess and hyperthermia.
• Anticholinergic toxicity → treat the underlying syndrome.
• Theophylline toxicity → treat theophylline poisoning.
• Hypovolemia → restore appropriate circulating volume.
• Hypoxia → correct oxygenation/ventilation.
• Metabolic acidosis → identify and treat the cause.

Suppressing the heart rate without correcting the underlying process may provide little benefit and can sometimes be harmful.

Important Modernization of the Older Source

Several points require updating:

• Adenosine is not a general antidote for toxicologic tachycardia.
• Its principal role is AV-node-dependent reentrant SVT.
• A central IV line is not required; rapid administration through an appropriate peripheral line is standard.
• Pediatric use is now well established.
• FDA pregnancy letter categories are obsolete.
• WPW alone is not an indication; the specific rhythm determines whether adenosine is appropriate.
• Adenosine should be avoided in pre-excited atrial fibrillation.
• It does not normally convert atrial fibrillation or atrial flutter.
• Unstable tachyarrhythmias should receive appropriate immediate electrical management rather than allowing adenosine attempts to delay definitive treatment.

Key Points

• Adenosine is an ultra-short-acting AV nodal blocking antiarrhythmic.
• Its main therapeutic target is AV-node-dependent reentrant SVT, particularly AVNRT and appropriate AVRT.
• Its half-life is only a few seconds.
• It transiently slows or blocks AV nodal conduction.
• It does not treat ordinary sinus tachycardia caused by poisoning.
• Atrial flutter and atrial fibrillation generally do not convert with adenosine.
• Adenosine can sometimes transiently reveal atrial activity and aid rhythm diagnosis.
• Theophylline and caffeine antagonize adenosine.
• Dipyridamole potentiates adenosine.
• Use caution with significant conduction disease and bronchospastic disease.
• Avoid routine adenosine in an irregular wide-complex rhythm, particularly possible pre-excited atrial fibrillation.
• WPW-associated orthodromic AVRT may respond, but pre-excited AF is a fundamentally different situation.
• Administration requires a rapid IV bolus followed immediately by a flush.
• A central line is not routinely necessary.
• Brief flushing, chest discomfort, dyspnea, and a sensation of impending doom are common but usually disappear within seconds.
• Continuous ECG monitoring and resuscitation capability should be available.
• In poisoning, always treat the underlying toxicologic mechanism rather than treating the heart rate alone.

Toxicology – Activated Charcoal

Core Concept

Activated charcoal is a gastrointestinal decontamination agent that adsorbs many drugs and chemicals within the GI tract, reducing the amount available for systemic absorption.

It can be used in two distinct ways:

• Single-dose activated charcoal (SDAC) → attempts to reduce absorption after selected acute ingestions.
• Multiple-dose activated charcoal (MDAC) → enhances elimination of a small group of toxins after absorption.

Activated charcoal is not routinely indicated for every overdose.

Adsorption, Not Absorption

Activated charcoal works by adsorption.

This means toxic molecules attach to the charcoal’s enormous porous surface rather than being absorbed into the charcoal itself.

The resulting:

Charcoal–toxin complex → remains within GI tract → passes through stool

This decreases gastrointestinal availability of the toxin.

Why Activated Charcoal Works

Activated charcoal is specially processed to create:

• Extensive microscopic pores
• Very large surface area
• Numerous binding sites for organic molecules

Binding is strongest for many relatively large, nonpolar or poorly water-soluble organic compounds.

Small, highly ionized substances are generally less effectively adsorbed.

Single-Dose Activated Charcoal

The purpose of SDAC is to:

Bind toxin still present in the GI tract → reduce subsequent systemic absorption

It is most useful when:

• The ingestion is potentially clinically important.
• The substance is well adsorbed by charcoal.
• Administration occurs reasonably soon after ingestion.
• The patient’s airway is safe.

The potential benefit generally decreases as time passes because progressively more toxin has already been absorbed.

Timing

Activated charcoal provides its greatest theoretical benefit when given early after ingestion, particularly within approximately the first hour.

However, time alone should not determine its use.

Later administration may occasionally be considered when absorption is delayed, such as with:

• Extended-release preparations
• Enteric-coated products
• Drugs that slow gastrointestinal motility
• Very large ingestions
• Substances capable of forming pharmacobezoars

Therefore:

Charcoal should be selected according to the toxicant, formulation, timing, clinical condition, and aspiration risk—not simply because an overdose occurred.

Substances Commonly Adsorbed

Activated charcoal adsorbs many clinically important drugs, including various:

• Antidepressants
• Antipsychotics
• Anticonvulsants
• Acetaminophen
• Salicylates
• Theophylline
• Cardiovascular medications
• Sedative medications
• Antihistamines

However, charcoal adsorption varies between substances.

Important Substances Poorly Adsorbed

A useful mnemonic is:

PHAILS

• P – Pesticides? (not a reliable component of the mnemonic because many organic pesticides can actually bind charcoal)
• H – Hydrocarbons
• A – Alcohols
• I – Iron
• L – Lithium
• S – Strong acids/alkalis

A more reliable approach is to remember the major groups directly.

Activated charcoal is generally ineffective or inappropriate for:

• Lithium
• Iron
• Potassium
• Methanol
• Ethylene glycol
• Ethanol
• Isopropanol
• Strong acids
• Strong alkalis
• Many simple inorganic ions

These substances are either poorly adsorbed or present other reasons why charcoal is inappropriate.

Toxic Alcohols

Activated charcoal has essentially no useful role for:

• Methanol
• Ethylene glycol
• Isopropanol
• Ethanol

These small alcohol molecules are poorly adsorbed and are rapidly absorbed.

Management instead depends on the particular alcohol and may involve:

• Supportive care
• Fomepizole for methanol/ethylene glycol
• Correction of metabolic abnormalities
• Hemodialysis in selected severe cases

Iron

Activated charcoal does not effectively adsorb iron.

Therefore, charcoal should not be relied upon after significant iron ingestion.

Selected severe iron ingestions may instead require:

• Supportive management
• Whole-bowel irrigation in appropriate circumstances
• Deferoxamine for significant systemic toxicity

Lithium

Lithium is a small ion and is poorly adsorbed by charcoal.

Activated charcoal therefore has no meaningful role for an isolated lithium ingestion.

However, if a mixed overdose contains lithium plus another charcoal-adsorbable drug, charcoal may potentially benefit the other substance, not the lithium.

Caustic Ingestion

Activated charcoal is generally inappropriate after strong acid or alkali ingestion.

Reasons include:

• Poor therapeutic benefit
• Vomiting/aspiration risk
• Potential interference with endoscopic evaluation
• Failure to prevent direct tissue injury

Management emphasizes airway assessment, supportive care, and appropriate evaluation of caustic injury.

Hydrocarbon Ingestion

Charcoal is generally avoided after isolated hydrocarbon ingestion.

The major danger is often:

Aspiration → chemical pneumonitis

Charcoal adds aspiration risk while offering limited clinical benefit for many hydrocarbons.

Airway Protection

The most important safety consideration is aspiration.

Activated charcoal should generally not be administered to a patient who cannot reliably protect their airway unless the airway has already been secured for independent clinical reasons.

High-risk findings include:

• Significant CNS depression
• Recurrent seizures
• Severe agitation
• Repeated vomiting
• Loss of protective airway reflexes

Charcoal aspiration can produce severe pulmonary injury.

Important Airway Principle

Do not intubate a patient solely to administer activated charcoal unless the overall clinical situation independently justifies airway control.

The potential benefit of charcoal must outweigh the risks of both the procedure and aspiration.

Contraindications and Situations to Avoid Charcoal

Activated charcoal should generally be avoided or used only after specialist consideration when there is:

• Unprotected airway
• High aspiration risk
• Gastrointestinal obstruction
• Ileus
• Suspected GI perforation
• Significant caustic ingestion
• Isolated hydrocarbon ingestion with substantial aspiration potential
• A substance known not to bind meaningfully to charcoal

MDAC particularly requires adequate gastrointestinal motility.

Adverse Effects

The most common problems are gastrointestinal.

Possible adverse effects include:

• Nausea
• Vomiting
• Constipation
• Abdominal distension

Less common but serious complications include:

• Aspiration pneumonitis
• Airway obstruction from aspirated charcoal
• Ileus
• Charcoal bezoar
• Bowel obstruction
• Rare gastrointestinal perforation

Risk increases when repeated doses are used or GI motility is impaired.

Charcoal Aspiration

Pulmonary aspiration is the most clinically important complication.

It may cause:

• Hypoxemia
• Pneumonitis
• Airway obstruction
• Severe respiratory failure

The risk-benefit assessment should therefore occur before charcoal administration, not after the patient becomes sedated or develops seizures.

Cathartics

Older practice commonly combined charcoal with:

• Sorbitol
• Magnesium-containing cathartics
• Other laxatives

Routine cathartic administration is no longer recommended.

They have not demonstrated meaningful improvement in poisoning outcomes and may cause:

• Diarrhea
• Dehydration
• Electrolyte abnormalities

Repeated cathartic administration is particularly inappropriate.

Multiple-Dose Activated Charcoal

MDAC differs fundamentally from a second dose given simply because gastrointestinal absorption is prolonged.

The purpose of true MDAC is to:

Increase systemic elimination of selected toxins

It may work by:

• Interrupting enterohepatic recirculation
• Binding drug secreted into the intestinal lumen
• Maintaining a concentration gradient that promotes movement of drug from blood toward the gastrointestinal tract

This phenomenon is sometimes described as gastrointestinal dialysis.

Classic MDAC Drugs

The major substances for which MDAC has an established toxicokinetic role can be remembered as:

ABCD

• A – not traditionally included
• B – Barbiturates, especially phenobarbital
• C – Carbamazepine
• D – Dapsone

And importantly:

• Quinine
• Theophylline

A practical high-yield list is therefore:

Carbamazepine – Dapsone – Phenobarbital – Quinine – Theophylline

Phenobarbital

MDAC can increase phenobarbital elimination.

It may be considered in significant poisoning when:

• Toxicity is substantial
• GI motility is adequate
• The airway is protected
• The anticipated benefit outweighs aspiration and GI risks

Carbamazepine

Carbamazepine is particularly relevant because large overdoses can cause:

• Delayed absorption
• CNS depression
• Seizures
• Anticholinergic effects
• QRS widening
• Dysrhythmias

MDAC can enhance elimination in significant poisoning.

Severe poisoning may additionally require extracorporeal treatment in selected circumstances.

Dapsone

Dapsone can produce:

• Methemoglobinemia
• Hemolysis
• Recurrent toxicity

Its metabolites undergo enterohepatic circulation.

MDAC can help interrupt this recycling and may be useful in significant poisoning.

Theophylline

MDAC can substantially increase theophylline elimination.

Severe theophylline poisoning may produce:

• Persistent vomiting
• Tachycardia
• Hypokalemia
• Hyperglycemia
• Seizures
• Dysrhythmias

Extracorporeal removal may also be required in severe cases.

Quinine

MDAC can increase quinine elimination.

Quinine toxicity may produce:

• Tinnitus
• Hearing abnormalities
• Visual disturbances
• Hypotension
• Dysrhythmias

Its use must still be balanced against the risks of repeated charcoal administration.

Not Every Extended-Release Ingestion Needs MDAC

This distinction is important.

A later or additional charcoal dose intended to capture drug that is still being absorbed is not necessarily the same as MDAC used for enhanced systemic elimination.

Extended-release formulations may sometimes justify additional GI decontamination strategies, but this depends on:

• Drug involved
• Amount
• Timing
• GI function
• Clinical course

Whole-bowel irrigation may sometimes be considered instead for selected extended-release or poorly charcoal-adsorbed substances.

Drug Interactions

Activated charcoal can adsorb medications administered orally.

This includes:

• Therapeutic drugs
• Oral antidotes
• Other necessary medications

MDAC may also increase elimination of some medications already present systemically.

Therefore, medication timing and route should be considered when charcoal is being used.

Pregnancy

Activated charcoal is not systemically absorbed in meaningful amounts.

Pregnancy itself is therefore not generally considered a contraindication when charcoal is otherwise clinically indicated.

The same fundamental risk-benefit assessment applies, particularly regarding:

• Aspiration
• Maternal stability
• Toxicant severity

Children

Children can receive activated charcoal when genuinely indicated, but particular attention should be given to:

• Aspiration risk
• Ability to cooperate
• Vomiting
• Airway size
• Fluid/electrolyte complications from inappropriate cathartic use

Routine charcoal after every pediatric ingestion is not appropriate.

Older Adults

Older patients may have:

• Reduced GI motility
• Greater aspiration risk
• Multiple medications
• Increased susceptibility to bowel complications

MDAC can also interfere with or increase elimination of necessary therapeutic medications.

Monitoring During Charcoal Therapy

Monitor for:

• Vomiting
• Abdominal distension
• Bowel function
• Respiratory deterioration
• Aspiration
• Mental-status changes

During MDAC, reassess whether:

• GI motility remains adequate
• Toxicity is improving
• Continued charcoal remains beneficial
• Complications are developing

When to Stop MDAC

There is no universal fixed duration appropriate for every poisoning.

Treatment should be individualized according to:

• Clinical improvement
• Toxicant concentrations when useful
• Expected toxicokinetics
• GI function
• Development of complications
• Availability of more effective elimination methods

Activated Charcoal vs Whole-Bowel Irrigation

These techniques work differently.

Activated Charcoal

Adsorbs selected chemicals.

Whole-Bowel Irrigation

Physically moves gastrointestinal contents through the bowel.

Whole-bowel irrigation may be considered for selected situations such as:

• Certain sustained-release preparations
• Iron
• Lithium
• Drug packets

The appropriate method depends on the substance and clinical situation.

Activated Charcoal vs Hemodialysis

Charcoal primarily acts within the gastrointestinal tract.

Hemodialysis removes suitable toxins from the bloodstream.

Some severe poisonings may involve both gastrointestinal decontamination and extracorporeal elimination, depending on the toxicant and timing.

Important Modernization of the Older Source

Several recommendations in the original material reflect older toxicology practice.

Modern management does not support:

• Giving charcoal routinely for nearly every poisoning
• Automatically giving charcoal merely because symptoms are present late after ingestion
• Routine cathartics with the first dose
• Repeated cathartic administration
• Automatic redosing after vomiting
• Routine repeated charcoal for broad categories of overdoses
• Fixed MDAC schedules without individualized reassessment

Current practice uses activated charcoal selectively, based on anticipated benefit versus aspiration and gastrointestinal risk.

Key Points

• Activated charcoal adsorbs many drugs in the GI tract and reduces their availability for absorption.
• It is most useful when given relatively early after a clinically important, charcoal-adsorbable ingestion.
• Benefit generally declines as time from ingestion increases.
• Delayed absorption may occasionally justify later consideration.
• Charcoal does not effectively adsorb lithium, iron, potassium, or toxic alcohols.
• It is generally inappropriate for strong caustics and isolated hydrocarbon exposures.
• The major complication is pulmonary aspiration.
• An unprotected airway with impaired consciousness is a major contraindication.
• Routine cathartics are no longer recommended.
• MDAC is used for enhanced elimination, not simply because an overdose is severe.
• High-yield MDAC substances are carbamazepine, dapsone, phenobarbital, quinine, and theophylline.
• MDAC should not be used when significant ileus or bowel obstruction is present.
• Activated charcoal can adsorb orally administered therapeutic medications and antidotes.
• Whole-bowel irrigation and hemodialysis are fundamentally different techniques and may be preferable for particular toxins.
• Modern toxicology favors selective charcoal use based on toxicant, timing, formulation, airway safety, GI function, and expected clinical benefit rather than routine administration.

Toxicology – Acute Visual Loss and Visual Disturbances

Core Concept

Acute visual disturbance after a toxic exposure can result from injury anywhere along the visual pathway, including:

• Cornea and conjunctiva
• Lens
• Retina
• Optic nerve
• Central visual pathways
• Extraocular muscles and their innervation

Symptoms can range from mild blurring or abnormal color perception to visual-field loss or complete blindness.

Sudden visual loss is an ophthalmologic emergency until a serious ocular, neurologic, vascular, or toxic cause has been excluded.

Major Toxicologic Causes

Methanol

Methanol is one of the most important toxicologic causes of acute visual impairment.

Methanol is metabolized to formic acid, which produces metabolic acidosis and is particularly toxic to the retina and optic nerve.

Visual complaints may include:

• Blurred vision
• Reduced visual acuity
• Central visual defects
• Photophobia
• “Snowfield” or “snowstorm” vision
• Severe visual loss or blindness

Systemic findings may include:

• Headache
• Nausea/vomiting
• Abdominal discomfort
• CNS depression
• High-anion-gap metabolic acidosis
• Tachypnea

Severe poisoning can progress to seizures, coma, cardiovascular instability, and permanent blindness.

Methanol: Important Diagnostic Pattern

A particularly concerning combination is:

Visual disturbance + unexplained high-anion-gap metabolic acidosis

The osmolal gap may be elevated early but can become normal later as methanol is converted to toxic metabolites.

Therefore:

A normal osmolal gap does not exclude late methanol poisoning.

Direct methanol measurement is preferred when available.

Methanol Management

Important treatment principles include:

• Stabilization and supportive care
• Inhibition of toxic alcohol metabolism with fomepizole
• Correction of clinically important acidosis
• Folate-related adjunctive therapy in appropriate cases
• Hemodialysis for selected severe poisoning

Visual symptoms are an important marker of serious methanol toxicity and warrant urgent toxicology involvement.

Quinine and Related Drugs

Quinine toxicity can cause significant ocular toxicity.

Possible manifestations include:

• Blurred vision
• Reduced visual acuity
• Constricted visual fields
• Altered color vision
• Scotomas
• Severe visual impairment

Systemic features of quinine toxicity may include:

• Tinnitus
• Hearing disturbance
• Dizziness
• Nausea/vomiting
• Headache
• Dysrhythmias

The combination of tinnitus and visual abnormalities can be an important clue.

Chloroquine and Hydroxychloroquine

These agents can affect vision through different mechanisms depending on the exposure pattern.

Severe acute chloroquine/hydroxychloroquine poisoning is primarily characterized by:

• Hypotension
• Hypokalemia
• QRS/QT abnormalities
• Ventricular dysrhythmias
• Seizures
• Cardiovascular collapse

Long-term hydroxychloroquine exposure can produce retinal toxicity, potentially causing:

• Paracentral visual defects
• Reduced visual acuity in advanced disease
• Altered color vision
• Progressive retinal damage

Chronic retinal toxicity differs from the cardiovascular emergency of acute overdose.

Digoxin and Cardiac Glycosides

Digoxin toxicity can produce characteristic disturbances in visual perception.

Possible complaints include:

• Blurred vision
• Photophobia
• Halos
• Altered color perception
• Yellow or yellow-green vision

These findings may accompany:

• Nausea/vomiting
• Confusion
• Bradycardia
• AV block
• Other dysrhythmias

Visual symptoms support the diagnosis but are not required for digoxin toxicity.

Anticholinergic Agents

Antimuscarinic drugs may cause blurred vision through:

• Marked mydriasis
• Cycloplegia
• Loss of accommodation

Patients may have difficulty focusing on near objects.

Associated findings include:

• Tachycardia
• Dry mouth
• Dry, flushed skin
• Reduced bowel sounds
• Urinary retention
• Agitation or delirium

Topical ophthalmic anticholinergics can produce particularly prominent ocular findings.

Botulism

Botulism causes presynaptic inhibition of acetylcholine release.

Early neurologic manifestations frequently involve the cranial nerves.

Visual complaints can include:

• Blurred vision
• Diplopia
• Difficulty focusing
• Ptosis

These may be followed by:

• Dysarthria
• Dysphagia
• Facial weakness
• Descending symmetric paralysis
• Respiratory failure

The patient is generally alert unless another process is present.

Ethambutol

Chronic ethambutol exposure can cause optic neuropathy.

Possible manifestations include:

• Reduced visual acuity
• Central visual defects
• Impaired color discrimination
• Bilateral visual symptoms

Early recognition and medication review are important because recovery is more likely when toxicity is recognized promptly.

Deferoxamine

Prolonged or excessive exposure can occasionally produce ocular toxicity, including:

• Reduced visual acuity
• Visual-field abnormalities
• Altered color perception
• Retinal or optic-nerve dysfunction

Visual abnormalities may improve after appropriate modification of therapy.

Mercury

Significant chronic mercury exposure can cause neurologic and visual abnormalities.

Possible manifestations include:

• Visual-field constriction
• Tremor
• Paresthesias
• Ataxia
• Neurobehavioral changes

The exact clinical pattern depends on the chemical form and exposure route.

Thallium

Thallium poisoning primarily produces gastrointestinal and neurologic toxicity but may occasionally affect the visual system.

Other clues include:

• Painful peripheral neuropathy
• Weakness
• Gastrointestinal symptoms
• Delayed alopecia

Vitamin A Toxicity

Excess vitamin A can increase intracranial pressure.

Possible findings include:

• Headache
• Nausea
• Diplopia
• Papilledema
• Visual disturbance

Chronic toxicity may also produce skin and hepatic abnormalities.

Chemical Eye Injury

Direct exposure to corrosive substances can damage:

• Conjunctiva
• Corneal epithelium
• Corneal stroma
• Anterior chamber
• Deeper ocular structures

Important exposures include:

• Strong alkalis
• Strong acids
• Phenolic chemicals
• Other corrosive agents

Symptoms may include:

• Severe pain
• Blepharospasm
• Tearing
• Redness
• Photophobia
• Blurred vision
• Corneal clouding

Alkali Versus Acid Injury

Alkali injuries are often particularly dangerous because they can penetrate deeply and continue damaging ocular tissue.

Severe alkali exposure may cause:

• Corneal opacification
• Limbal ischemia
• Anterior-segment injury
• Scarring
• Permanent visual impairment

Acids often cause more superficial coagulation injury, although concentrated acids can also cause severe ocular damage.

Important Principle: Pain Does Not Equal Severity

A painless eye after chemical exposure is not necessarily reassuring.

Severe chemical injury can damage sensory nerve endings and reduce pain despite extensive tissue injury.

Irritant Eye Exposures

Lacrimators and irritant chemicals may cause:

• Burning
• Tearing
• Conjunctival redness
• Blepharospasm
• Temporary blurred vision

Examples include:

• Pepper spray
• Tear gas
• Chlorine
• Other irritant gases or aerosols

Most uncomplicated irritant exposures improve after effective decontamination, but persistent symptoms require examination for corneal injury.

Immediate Management of Chemical Eye Exposure

The priority is:

Begin irrigation immediately.

Do not delay irrigation while trying to identify the exact chemical.

General principles include:

• Remove contact lenses when possible.
• Irrigate copiously with available clean fluid.
• Ensure the eyelids and conjunctival spaces are adequately exposed.
• Remove retained particulate material when appropriate.
• Check ocular pH in significant acid/alkali exposures.
• Continue irrigation until pH remains near physiologic range.

The clinical endpoint and normalization of ocular pH are more important than an arbitrary fixed irrigation volume.

Eye Examination

Assessment should include:

• Visual acuity in each eye
• Pupil size and reactivity
• Extraocular movements
• Visual fields when possible
• Eyelid and conjunctival examination
• Corneal clarity
• Fluorescein examination
• Slit-lamp examination when available

Intraocular pressure should be measured when glaucoma or other pressure-related pathology is suspected and when doing so is safe.

Fluorescein Examination

Fluorescein helps identify:

• Corneal epithelial defects
• Abrasions
• Ulceration
• Chemical injury

Significant chemical burns generally require ophthalmologic assessment.

Nontoxicologic Differential Diagnosis

Do not attribute acute visual loss automatically to poisoning.

Important alternatives include:

• Central retinal artery occlusion
• Retinal detachment
• Vitreous or retinal hemorrhage
• Acute angle-closure glaucoma
• Optic neuritis
• Ischemic optic neuropathy
• Stroke
• Intracranial hemorrhage
• Migraine
• Orbital disease
• Giant cell arteritis in the appropriate age group
• Raised intracranial pressure

Sudden painless monocular visual loss is particularly concerning for a retinal or vascular emergency.

Key Diagnostic Tests

Depending on the presentation, consider:

• Visual acuity testing
• Slit-lamp/fluorescein examination
• Ocular pH after chemical exposure
• Electrolytes and bicarbonate
• Anion gap
• Blood gas
• Serum osmolality/osmolal gap
• Methanol concentration
• ECG
• Digoxin concentration when indicated

Additional ophthalmologic or neurologic testing depends on the suspected cause.

Disposition

Systemic poisoning with visual abnormalities often requires admission or prolonged monitored treatment.

Chemical eye injuries require ophthalmologic follow-up, with urgent specialist evaluation for:

• Reduced visual acuity
• Significant epithelial injury
• Corneal clouding
• Limbal ischemia
• Persistent abnormal pH
• Severe pain
• Suspected penetrating injury

Key Points

• Visual toxicity may arise from corneal injury, retinal injury, optic neuropathy, neurologic dysfunction, or altered accommodation.
• Methanol + visual symptoms + high-anion-gap metabolic acidosis is a major toxicologic emergency.
• A normal osmolal gap does not exclude late methanol poisoning.
• Fomepizole is preferred for inhibiting methanol metabolism; severe cases may require dialysis.
• Quinine can produce tinnitus together with severe visual disturbance.
• Digoxin may cause halos and altered yellow-green color perception.
• Anticholinergics commonly blur vision through mydriasis and cycloplegia.
• Botulism can begin with diplopia, blurred vision, ptosis, and bulbar weakness.
• Chronic ethambutol exposure can produce optic neuropathy and impaired color vision.
• Chemical eye exposure requires immediate irrigation.
• Severe alkali burns may penetrate deeply and threaten vision.
• Lack of pain does not exclude severe ocular injury.
• Sudden visual loss always requires consideration of nontoxic ophthalmologic and neurologic emergencies.

187. Toxicology – Withdrawal Syndromes

Core Concept

Withdrawal occurs when a person who has developed physiologic adaptation to a substance experiences symptoms after:

• Abrupt cessation
• Rapid dose reduction
• Falling drug concentrations
• Administration of an antagonist
• Administration of certain partial agonists in susceptible opioid-dependent patients

Withdrawal syndromes differ substantially according to the drug class.

The most important distinction is:

Alcohol and sedative-hypnotic withdrawal can be life-threatening.

Typical opioid and stimulant withdrawal are usually not directly life-threatening in otherwise healthy adults, although complications and coexisting illness can still be serious.

General Principle

Withdrawal often produces physiologic effects roughly opposite to those produced during intoxication.

Examples:

CNS depressant intoxication → sedation

CNS depressant withdrawal → CNS hyperactivity

Similarly:

Opioid intoxication → miosis, reduced GI activity, CNS/respiratory depression

Opioid withdrawal → mydriasis, diarrhea, autonomic activation

This is useful conceptually but should not replace clinical assessment.

Alcohol Withdrawal

Chronic alcohol exposure causes neuroadaptation involving:

• Reduced inhibitory GABAergic function
• Increased excitatory glutamatergic activity

When alcohol concentrations fall abruptly, this adapted nervous system becomes excessively excitable.

Clinical severity ranges from mild tremulousness to seizures and delirium.

Early Alcohol Withdrawal

Possible findings include:

• Anxiety
• Tremor
• Insomnia
• Nausea
• Diaphoresis
• Tachycardia
• Hypertension
• Headache
• Agitation

Importantly:

Withdrawal can begin while measurable alcohol remains in the blood.

A rapid decline from a chronically high concentration may be sufficient to trigger symptoms.

Alcohol Withdrawal Seizures

Withdrawal can cause generalized seizures.

They often occur relatively early in the withdrawal course.

Important alternative causes should still be considered, including:

• Hypoglycemia
• Hyponatremia
• Head trauma
• Intracranial hemorrhage
• Infection
• Coingestion
• Primary epilepsy

Repeated or atypical seizures require broader investigation.

Alcohol Withdrawal Delirium

The most severe alcohol withdrawal syndrome is alcohol withdrawal delirium, historically called delirium tremens.

Features include:

• Severe agitation
• Confusion
• Disorientation
• Hallucinations
• Tremor
• Marked autonomic hyperactivity
• Tachycardia
• Hypertension
• Diaphoresis
• Hyperthermia

Complications can include:

• Dehydration
• Electrolyte abnormalities
• Rhabdomyolysis
• Dysrhythmias
• Aspiration
• Cardiovascular collapse

This is a medical emergency.

Sedative-Hypnotic Withdrawal

Withdrawal from GABAergic sedative medications can resemble alcohol withdrawal.

Important substances include:

• Benzodiazepines
• Barbiturates
• Certain older sedative-hypnotics

Possible manifestations include:

• Anxiety
• Tremor
• Insomnia
• Agitation
• Tachycardia
• Hypertension
• Perceptual disturbances
• Delirium
• Seizures

Severe withdrawal can be fatal.

Benzodiazepine Withdrawal

Withdrawal risk depends on:

• Duration of use
• Dose
• Degree of physiologic dependence
• Drug half-life
• Speed of discontinuation

Shorter-acting agents may produce earlier symptoms, while withdrawal from long-acting agents may be delayed.

Abrupt discontinuation after substantial chronic exposure can cause seizures or severe autonomic instability.

GHB Withdrawal

Chronic heavy gamma-hydroxybutyrate use can produce a particularly severe withdrawal syndrome.

Possible findings include:

• Severe agitation
• Insomnia
• Tremor
• Tachycardia
• Hypertension
• Hallucinations
• Delirium

The syndrome can progress rapidly and may require intensive management.

Alcohol/Sedative Withdrawal Differential Diagnosis

Conditions that can resemble severe withdrawal include:

• Sympathomimetic poisoning
• Anticholinergic toxicity
• Serotonin syndrome
• Neuroleptic malignant syndrome
• MAOI toxicity
• Hyperthyroidism
• Sepsis
• Heat stroke
• Intracranial hemorrhage
• CNS infection
• Primary psychiatric disease

Do not automatically attribute agitation and tachycardia to withdrawal simply because a patient has a history of substance use.

Treatment of Alcohol Withdrawal

Benzodiazepines are first-line therapy.

Treatment aims to control:

• Agitation
• Tremor
• Autonomic hyperactivity
• Seizures
• Progression to severe withdrawal

Medication should be titrated according to clinical severity and monitoring.

Phenobarbital is also used in selected patients and protocols, particularly for severe or difficult-to-control withdrawal.

Thiamine and Supportive Care

Patients with chronic heavy alcohol use may have thiamine deficiency.

Thiamine should be provided when clinically indicated, particularly when malnutrition or Wernicke encephalopathy is a concern.

Also assess and correct:

• Hypoglycemia
• Dehydration
• Potassium abnormalities
• Magnesium abnormalities
• Other nutritional deficiencies

Urgent glucose treatment should not be delayed in a hypoglycemic patient while waiting to administer thiamine.

Withdrawal Seizure Treatment

Benzodiazepines are central to treatment of alcohol or sedative-hypnotic withdrawal seizures.

Phenytoin is generally ineffective for preventing recurrent seizures caused purely by alcohol withdrawal because it does not correct the underlying withdrawal physiology.

It may still be appropriate when the patient has a separate seizure disorder requiring it.

Opioid Withdrawal

Opioid withdrawal results from loss of opioid receptor stimulation after physiologic dependence has developed.

It may follow:

• Abrupt opioid discontinuation
• Major dose reduction
• Naloxone administration
• Inappropriately timed partial-agonist therapy

Clinical Features of Opioid Withdrawal

Typical findings include:

• Anxiety
• Restlessness
• Yawning
• Lacrimation
• Rhinorrhea
• Mydriasis
• Piloerection
• Diaphoresis
• Myalgias
• Abdominal cramping
• Nausea/vomiting
• Diarrhea
• Increased bowel sounds
• Tachycardia

Patients may feel extremely unwell despite the syndrome usually not being directly fatal in otherwise healthy adults.

Complications of Opioid Withdrawal

Severe vomiting and diarrhea may cause:

• Dehydration
• Electrolyte disturbances
• Acute kidney injury

Risk can be greater in:

• Frail patients
• Pregnant patients
• Patients with major comorbidities
• Neonates

Return to opioid use after loss of tolerance also increases subsequent overdose risk.

Opioid Withdrawal Treatment

Modern treatment generally favors opioid agonist therapy when appropriate.

Important options include:

• Buprenorphine
• Methadone

These can relieve withdrawal and support ongoing treatment of opioid use disorder.

Non-opioid medications such as:

• Clonidine
• Lofexidine

may reduce autonomic symptoms but generally do not treat opioid use disorder itself.

Additional symptomatic treatment may address:

• Nausea
• Diarrhea
• Pain
• Dehydration

Precipitated Opioid Withdrawal

An opioid antagonist can rapidly displace opioid agonists and produce abrupt withdrawal.

Similarly, initiating buprenorphine at an inappropriate point after certain opioid exposures can precipitate withdrawal because of its high receptor affinity and partial agonist activity.

This syndrome can be much more abrupt than spontaneous withdrawal.

Stimulant Withdrawal

Withdrawal can occur after cessation of chronic use of:

• Cocaine
• Amphetamines
• Methamphetamine
• Other stimulants

The syndrome differs substantially from alcohol withdrawal.

Stimulant Withdrawal Features

Typical symptoms include:

• Fatigue
• Increased sleep
• Dysphoria
• Depressed mood
• Irritability
• Reduced motivation
• Poor concentration
• Increased appetite
• Drug craving

Some patients experience marked psychomotor slowing.

Unlike severe alcohol or sedative withdrawal, stimulant withdrawal generally does not cause the same autonomic hyperexcitable seizure syndrome.

Mental Health Risk in Stimulant Withdrawal

Although the physical withdrawal syndrome is usually not directly life-threatening, severe depression may occur.

Assessment should include:

• Suicidal thoughts
• Severe depression
• Psychosis
• Ability to care for oneself
• Coexisting substance use

Psychiatric risk may therefore be more important than physiologic instability.

Nicotine and Caffeine Withdrawal

These generally produce milder syndromes.

Nicotine withdrawal

May cause:

• Irritability
• Anxiety
• Difficulty concentrating
• Increased appetite
• Restlessness
• Craving

Caffeine withdrawal

May cause:

• Headache
• Fatigue
• Sleepiness
• Reduced concentration
• Irritability

These syndromes are generally self-limited.

Neonatal Withdrawal

Neonates exposed chronically to certain substances before birth may develop withdrawal after delivery.

Modern terminology for opioid-related neonatal withdrawal includes neonatal opioid withdrawal syndrome (NOWS).

Manifestations may include:

• Irritability
• Tremor
• Abnormal sleep
• Feeding difficulty
• Gastrointestinal symptoms
• Autonomic abnormalities

Management is specialized and differs from adult withdrawal care.

The older source’s recommendation of paregoric as the drug of choice is obsolete and should not be carried into modern study notes.

Diagnostic Evaluation

Withdrawal is primarily a clinical diagnosis supported by exposure history.

Important questions include:

• Substance used
• Duration of use
• Typical amount
• Last use
• Recent dose reduction
• Formulation/half-life
• Other substances
• Previous severe withdrawal
• Previous withdrawal seizures
• Medical comorbidities

Laboratory Evaluation

Testing should be guided by severity.

Potential studies include:

• Bedside glucose
• Electrolytes
• Magnesium
• Renal function
• Liver tests
• CBC
• CK when severe agitation, seizures, or hyperthermia occur

Additional testing may be necessary when altered mental status or seizures have an uncertain cause.

When to Consider Brain Imaging or Other Workup

Withdrawal should not be assumed to explain every neurologic abnormality.

Consider further investigation when there is:

• Head trauma
• Focal neurologic deficit
• Unusual seizure pattern
• Persistent altered mental status
• Fever or meningismus
• Concern for intracranial hemorrhage
• Clinical suspicion of infection

Decontamination

Gastrointestinal decontamination has no routine role in withdrawal because withdrawal results from declining drug exposure rather than an ongoing ingestion.

An exception would be a separate acute ingestion occurring at the same time.

Monitoring

Patients with severe alcohol or sedative-hypnotic withdrawal require monitoring for:

• Mental status
• Agitation
• Seizures
• Respiratory status during sedative therapy
• Heart rate
• Blood pressure
• Temperature
• Hydration
• Electrolytes

Severe withdrawal may require ICU-level management.

Timing of Withdrawal

The onset and duration depend heavily on the substance’s pharmacokinetics.

General principle:

Shorter-acting drug → earlier withdrawal

Longer-acting drug → potentially delayed withdrawal

Therefore, fixed timelines should not be applied rigidly.

Important Pitfalls

• Withdrawal does not require complete abstinence; a substantial fall in drug concentration may trigger it.
• Alcohol withdrawal can begin despite a measurable blood alcohol concentration.
• Long-acting sedative withdrawal may be delayed.
• Do not mistake stimulant intoxication for alcohol withdrawal.
• Do not mistake opioid intoxication for stimulant withdrawal-related sleepiness.
• Phenytoin does not correct the underlying mechanism of uncomplicated alcohol-withdrawal seizures.
• Beta-blockers, clonidine, and antipsychotics may sometimes be adjuncts but do not replace adequate GABAergic treatment for severe alcohol withdrawal.
• Severe agitation should not automatically be attributed to withdrawal; infection, intracranial disease, metabolic disorders, and poisoning must remain in the differential.
• Avoid dismissing reported withdrawal as drug-seeking behavior; assess the syndrome objectively and treat clinically significant findings.

Key Points

• Withdrawal follows cessation, dose reduction, or antagonism after physiologic adaptation.
• Alcohol and sedative-hypnotic withdrawal can cause seizures, delirium, hyperthermia, and death.
• Benzodiazepines are first-line treatment for clinically significant alcohol withdrawal.
• Phenobarbital has an important role in selected severe alcohol/sedative withdrawal protocols.
• Phenytoin is generally ineffective for uncomplicated alcohol-withdrawal seizures.
• Withdrawal can begin while blood alcohol remains measurable.
• Opioid withdrawal typically causes mydriasis, yawning, lacrimation, rhinorrhea, piloerection, myalgias, vomiting, and diarrhea.
• Typical adult opioid withdrawal is usually not directly life-threatening, but dehydration and other complications can occur.
• Buprenorphine or methadone are important modern treatments for opioid withdrawal and opioid use disorder.
• Clonidine or lofexidine can reduce autonomic opioid-withdrawal symptoms.
• Stimulant withdrawal mainly causes fatigue, hypersomnia, dysphoria, depression, and craving.
• Suicide risk and severe depression should be assessed during stimulant withdrawal.
• Long-acting drugs may produce delayed withdrawal, so onset cannot be predicted from a single universal timeline.
• Treatment should address the specific withdrawal syndrome and its complications, while continuing to consider alternative diagnoses.

Toxicology – Ventricular Dysrhythmias

Core Concept

Toxicologic ventricular dysrhythmias are abnormal rhythms or conduction disturbances involving the ventricles that result from exposure to a drug, chemical, or toxin.

They range from:

• Premature ventricular complexes
• Wide-complex tachycardia
• Monomorphic or polymorphic ventricular tachycardia
• Torsades de pointes
• Ventricular fibrillation
• Severe intraventricular conduction delay

In poisoning, treatment should address both the rhythm and the toxicologic mechanism producing it.

Major Mechanisms

Toxins can provoke ventricular dysrhythmias through several pathways.

1. Sodium-Channel Blockade

Fast sodium-channel inhibition slows ventricular depolarization.

This produces:

Slowed conduction → QRS widening → ventricular dysrhythmia

Important causes include:

• Tricyclic antidepressants
• Certain first-generation antihistamines
• Class I antiarrhythmics
• Carbamazepine in severe poisoning
• Some antipsychotics
• Other membrane-stabilizing drugs

Severe sodium-channel blockade may also cause:

• Hypotension
• Seizures
• Coma

2. Potassium-Channel Effects and QT Prolongation

Delayed ventricular repolarization can prolong the QT interval.

Excessive QT prolongation increases susceptibility to torsades de pointes, a polymorphic ventricular tachycardia.

Risk is increased by:

• Hypokalemia
• Hypomagnesemia
• Bradycardia
• Multiple QT-prolonging drugs
• Congenital long-QT syndromes

3. Myocardial Ischemia

Toxicant-associated myocardial ischemia may result from:

• Coronary vasospasm
• Severe hypertension
• Hypotension
• Increased myocardial oxygen demand
• Reduced oxygen delivery

Cocaine and other sympathomimetics are important examples.

Ischemic myocardium is electrically unstable and may develop ventricular dysrhythmias.

4. Hypoxia and Impaired Oxygen Delivery

Ventricular dysrhythmias may occur secondary to:

• Severe hypoventilation
• Pulmonary injury
• Carbon monoxide poisoning
• Methemoglobinemia
• Cyanide toxicity
• Profound shock

Correcting oxygenation and ventilation is therefore part of dysrhythmia management.

5. Electrolyte Disturbances

Important abnormalities include:

• Hyperkalemia
• Hypokalemia
• Hypomagnesemia
• Hypocalcemia

These may directly alter cardiac conduction or increase susceptibility to drug-induced dysrhythmias.

6. Direct Cardiac Toxicity

Certain poisons directly disturb:

• Automaticity
• AV conduction
• Myocardial contractility
• Intracellular calcium handling
• Ion-channel function

Examples include:

• Digoxin
• Beta-blockers
• Calcium channel blockers
• Chloroquine/hydroxychloroquine
• Certain antiarrhythmics

Risk Factors

Severe ventricular dysrhythmias are more likely in patients with:

• Pre-existing structural heart disease
• Coronary artery disease
• Baseline conduction abnormalities
• Congenital long-QT syndrome
• Electrolyte disturbances
• Hypoxia
• Severe acidemia
• Large or mixed overdose
• Multiple QT-prolonging medications

Important Toxicologic Causes

Tricyclic Antidepressants

TCAs produce cardiotoxicity primarily through fast sodium-channel blockade, with additional autonomic and myocardial effects.

Typical findings include:

• Sinus tachycardia
• QRS widening
• Hypotension
• Altered mental status
• Seizures
• Ventricular dysrhythmias

A terminal R wave in lead aVR may support sodium-channel blockade, but it is not specific for TCA poisoning.

Increasing QRS duration generally indicates increasing sodium-channel toxicity.

Sodium bicarbonate is the key treatment for clinically significant TCA-associated sodium-channel blockade.

First-Generation Antihistamines

Certain antihistamines, particularly in severe overdose, can produce both:

• Anticholinergic toxicity
• Sodium-channel blockade

Possible findings include:

• Tachycardia
• Mydriasis
• Dry skin and mucosa
• Delirium
• Seizures
• QRS widening
• QT prolongation
• Ventricular dysrhythmias

Diphenhydramine is an important example.

Class I Antiarrhythmics

These medications can paradoxically produce serious dysrhythmias in overdose.

Depending on the specific agent, effects may include:

• QRS widening
• QT prolongation
• Hypotension
• Ventricular tachycardia
• Torsades de pointes

Adding another sodium-channel-blocking antiarrhythmic may worsen toxicity.

Cocaine and Other Sympathomimetics

Stimulants can produce ventricular dysrhythmias through:

• Catecholamine excess
• Increased myocardial oxygen demand
• Coronary vasoconstriction
• Hyperthermia
• Ischemia
• Acidosis

Cocaine additionally has sodium-channel-blocking properties.

Associated findings include:

• Agitation
• Tachycardia
• Hypertension
• Diaphoresis
• Mydriasis
• Hyperthermia
• Seizures
• Rhabdomyolysis

Theophylline

Theophylline toxicity can cause:

• Marked sinus tachycardia
• Supraventricular dysrhythmias
• Ventricular ectopy
• Ventricular dysrhythmias in severe poisoning

Associated clues include:

• Tremor
• Recurrent vomiting
• Hypokalemia
• Hyperglycemia
• Seizures

Severe theophylline poisoning may require extracorporeal removal.

Digoxin

Digoxin toxicity can produce an unusually broad range of dysrhythmias because it affects both:

• Automaticity
• AV nodal conduction

Possible rhythms include:

• Premature ventricular complexes
• AV block
• Junctional rhythms
• Atrial tachycardia with AV block
• Bidirectional ventricular tachycardia
• Ventricular tachycardia/fibrillation

Associated findings may include:

• Nausea/vomiting
• Confusion
• Visual abnormalities
• Bradycardia
• Hyperkalemia in significant acute poisoning

Bidirectional ventricular tachycardia is an important clue to digoxin toxicity, although it is not completely specific.

Clinically important digoxin toxicity is treated with digoxin immune Fab.

Chloroquine and Hydroxychloroquine

Severe poisoning can rapidly produce:

• Hypotension
• Hypokalemia
• QRS widening
• QT prolongation
• Ventricular dysrhythmias
• Cardiovascular collapse

The combination of profound hypotension, conduction abnormalities, and hypokalemia after a compatible exposure is particularly concerning.

Carbamazepine

Large overdoses may produce:

• CNS depression
• Ataxia
• Nystagmus
• Seizures
• QRS widening
• Ventricular dysrhythmias

Severe cardiotoxicity can resemble other sodium-channel-blocking poisonings.

Organophosphates and Carbamates

Cholinergic poisoning can produce variable cardiac effects.

Possible rhythms include:

• Sinus tachycardia
• Bradycardia
• AV conduction abnormalities
• Ventricular dysrhythmias

Associated findings include:

• Miosis
• Salivation
• Bronchorrhea
• Vomiting
• Diarrhea
• Sweating
• Fasciculations
• Weakness

Heart rate alone cannot reliably identify or exclude a cholinergic syndrome.

Thyroid Hormone

Excess thyroid hormone usually produces:

• Sinus tachycardia
• Supraventricular tachyarrhythmias
• Atrial fibrillation

Ventricular dysrhythmias are less common but may occur in severe thyrotoxicosis, particularly when underlying cardiac disease is present.

Nontoxicologic Differential Diagnosis

Always consider causes unrelated to poisoning, including:

• Acute coronary syndrome
• Myocarditis
• Structural heart disease
• Congenital arrhythmia syndromes
• Intracranial catastrophe
• Hypoglycemia
• Severe hypoxia
• Electrolyte abnormalities
• Acid-base disturbances

A toxic exposure and a primary cardiac disorder may coexist.

Clinical Presentation

Patients may report:

• Palpitations
• Chest discomfort
• Dyspnea
• Weakness
• Dizziness
• Lightheadedness
• Presyncope

Severe ventricular dysrhythmias can cause:

• Syncope
• Hypotension
• Seizure-like activity from cerebral hypoperfusion
• Cardiogenic shock
• Cardiac arrest

In a poisoning patient, sudden syncope should raise concern for a significant dysrhythmia.

Clinical Clues to the Cause

Wide QRS + Seizures + Hypotension

Strongly consider:

• TCA poisoning
• Other sodium-channel blockers

Wide QRS + Anticholinergic Findings

Consider:

• TCA
• Diphenhydramine or another cardiotoxic antihistamine
• Other antimuscarinic drugs with sodium-channel effects

Ventricular Dysrhythmia + Severe Agitation/Hyperthermia

Consider:

• Cocaine
• Amphetamines
• Other sympathomimetics

Dysrhythmia + Vomiting + Tremor + Hypokalemia

Consider:

Theophylline toxicity

Dysrhythmia + AV Block

Consider:

• Digoxin
• Beta-blockers
• Calcium channel blockers
• Other conduction-suppressing drugs

Dysrhythmia + Hyperkalemia

Consider:

• Significant acute digoxin toxicity
• Severe renal failure
• Potassium poisoning
• Severe acidosis/tissue injury

Hyperkalemia itself can produce progressive conduction abnormalities and malignant dysrhythmias.

Dysrhythmia + Hypokalemia

Consider:

• Theophylline
• β₂-agonists
• Chloroquine/hydroxychloroquine

Hypokalemia also increases susceptibility to QT-related dysrhythmias.

ECG Evaluation

Obtain a 12-lead ECG and institute continuous cardiac monitoring in clinically important toxicologic dysrhythmias.

Evaluate:

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

Serial ECGs are useful because conduction abnormalities can evolve as absorption and toxicity progress.

QRS Widening

A widened QRS in poisoning should prompt consideration of sodium-channel blockade.

Potential causes include:

• TCAs
• Certain antihistamines
• Class I antiarrhythmics
• Carbamazepine
• Cocaine
• Other sodium-channel blockers

Treatment should be based on the overall evidence of clinically important sodium-channel toxicity, rather than relying on one rigid QRS threshold.

QT Prolongation

QT prolongation indicates delayed ventricular repolarization and may predispose to torsades de pointes.

Assess for:

• QT-prolonging drugs
• Hypokalemia
• Hypomagnesemia
• Hypocalcemia
• Bradycardia

Serial ECG monitoring is important when QT prolongation is substantial or evolving.

Laboratory Evaluation

Useful investigations may include:

• Bedside glucose
• Sodium
• Potassium
• Calcium
• Magnesium
• Bicarbonate
• BUN/creatinine
• Blood gas when clinically indicated
• Lactate

Targeted toxicant concentrations may include:

• Digoxin
• Theophylline
• Salicylate
• Other measurable drugs when clinically relevant

Acetaminophen testing should be considered in significant intentional or unknown ingestions because early toxicity may be clinically silent.

Broad urine drug screening has limited ability to establish the cause of a dysrhythmia.

Initial Management

The first priorities are:

Airway → breathing → circulation → rhythm assessment → identify and reverse the toxicologic mechanism

Immediately address:

• Hypoxemia
• Inadequate ventilation
• Severe acid-base disturbance
• Electrolyte abnormalities
• Hyperthermia
• Hypoglycemia
• Shock

Unstable ventricular rhythms should be managed using appropriate resuscitation principles while toxin-specific treatment is initiated.

Sodium-Channel Blocker Cardiotoxicity

Sodium bicarbonate is the major therapy for significant poisoning characterized by sodium-channel blockade.

Clinical indications can include:

• Significant QRS widening
• Ventricular dysrhythmia attributable to sodium-channel blockade
• Hypotension associated with this mechanism

Therapy requires monitoring of:

• ECG response
• Blood pH
• Sodium
• Potassium

Excessive alkalemia and electrolyte abnormalities should be avoided.

Ventricular Tachycardia

Management depends on:

• Hemodynamic stability
• QRS morphology
• QT interval
• Suspected toxicant
• Underlying mechanism

An unstable patient with ventricular tachycardia requires immediate resuscitative rhythm management.

In toxicology, conventional antiarrhythmic selection must be made carefully because some drugs can worsen the underlying channel disturbance.

For example, adding another sodium-channel blocker to severe sodium-channel-blocker poisoning can aggravate conduction delay.

Torsades de Pointes

Torsades is a polymorphic ventricular tachycardia associated with prolonged ventricular repolarization.

Management includes:

• Stop QT-prolonging agents.
• Correct hypokalemia.
• Correct hypomagnesemia.
• Treat other contributing electrolyte abnormalities.
• Give IV magnesium when torsades occurs.
• Use electrical therapy if the patient is unstable or pulseless.

For recurrent pause-dependent torsades, increasing the heart rate with overdrive pacing may be considered in selected cases.

Additional QT-prolonging antiarrhythmics should generally be avoided.

Digoxin-Associated Dysrhythmias

The most important treatment for severe digoxin-associated cardiac toxicity is:

Digoxin immune Fab

This should be considered particularly when significant poisoning produces:

• Life-threatening ventricular dysrhythmias
• Severe bradydysrhythmias
• Clinically important hyperkalemia in acute toxicity
• Other evidence of severe digoxin poisoning

After Fab administration, routine total serum digoxin measurements can become misleading because assays detect both bound and unbound digoxin.

Electrolyte Correction

Correct clinically important abnormalities promptly.

Potassium

Both high and low potassium can cause or worsen dysrhythmias.

Magnesium

Deficiency increases susceptibility to torsades and other ventricular dysrhythmias.

Calcium

Marked abnormalities can alter cardiac conduction and repolarization.

The goal is to correct the physiologic abnormality while simultaneously treating its toxicologic cause.

Hypotension and Shock

Ventricular dysrhythmia may both cause and result from shock.

Assess for:

• Hypovolemia
• Vasodilation
• Myocardial depression
• Severe bradycardia/conduction block
• Persistent ventricular dysrhythmia

Management may require:

• Careful fluid resuscitation
• Vasopressors
• Poison-specific cardiovascular therapy
• Electrical therapy
• Advanced circulatory support in selected refractory poisonings

Routine large fluid volumes should not be given without considering myocardial function and the mechanism of shock.

Bradyarrhythmias in Poisoning

Although this topic focuses on ventricular dysrhythmias, severe poisoning may produce bradycardia or conduction block.

Important causes include:

• Beta-blockers
• Calcium channel blockers
• Digoxin
• Cholinergic agents
• Clonidine/imidazolines

Standard ACLS measures may be insufficient because the underlying toxic mechanism persists.

Management therefore emphasizes toxin-specific cardiovascular therapy, with pacing used when appropriate.

Decontamination

Do not induce vomiting.

Routine gastric lavage is generally not recommended.

Activated charcoal may be considered for a selected recent, serious, adsorbable ingestion when:

• The airway is adequately protected.
• Aspiration risk is acceptable.
• No major contraindication exists.
• Administration will not delay cardiovascular stabilization.

A patient with ventricular dysrhythmia, seizures, or altered consciousness should be stabilized before gastrointestinal decontamination is considered.

Monitoring and Disposition

A new clinically significant ventricular dysrhythmia associated with poisoning generally requires a high-acuity monitored setting.

Monitor:

• Continuous ECG
• Blood pressure
• Oxygenation
• Ventilation
• Mental status
• Temperature
• Electrolytes
• Acid-base status

Serial ECGs and toxicant-specific laboratory testing may be necessary.

Patients with severe cardiotoxic poisoning may require intensive care.

Important Modernization of the Older Source

Several elements of the source reflect older toxicology practice.

Current management generally avoids:

• Routine gastric lavage
• Routine treatment based solely on one fixed QRS cutoff
• Automatic use of lidocaine for every ventricular ectopic rhythm
• Routine phenytoin/fosphenytoin as therapy for toxicologic ventricular dysrhythmias
• Bretylium, which has essentially disappeared from modern routine practice
• Routine Trendelenburg positioning for hypotension
• Large empiric fluid administration without assessment of the shock mechanism

Modern treatment emphasizes mechanism-directed therapy, ECG interpretation, electrolyte correction, appropriate electrical therapy, and toxin-specific antidotes.

Key Points

• Toxicologic ventricular dysrhythmias can result from ion-channel blockade, myocardial ischemia, hypoxia, electrolyte abnormalities, or direct myocardial toxicity.
• Sodium-channel blockade typically causes progressive QRS widening and may lead to hypotension, seizures, and ventricular dysrhythmias.
• Important sodium-channel-blocking poisons include TCAs, certain antihistamines, class I antiarrhythmics, carbamazepine, and cocaine.
• Sodium bicarbonate is central to treatment of clinically important toxicologic sodium-channel blockade.
• QT prolongation increases susceptibility to torsades de pointes, particularly with hypokalemia or hypomagnesemia.
• Torsades is treated with IV magnesium and correction of contributing factors, with electrical therapy for instability.
• Digoxin can produce almost any dysrhythmia; bidirectional ventricular tachycardia is an important clue.
• Severe digoxin-associated dysrhythmias are treated with digoxin immune Fab.
• Chloroquine/hydroxychloroquine poisoning can cause rapid cardiovascular collapse, QRS/QT abnormalities, ventricular dysrhythmias, and marked hypokalemia.
• Stimulants may cause dysrhythmias through catecholamine excess, ischemia, hyperthermia, and acidosis.
• Correct hypoxia, acid-base abnormalities, potassium, magnesium, and calcium disturbances when clinically important.
• Do not assume that a standard antiarrhythmic is safe merely because the rhythm resembles a conventional cardiac dysrhythmia; the toxicologic mechanism matters.
• Unstable ventricular tachycardia or ventricular fibrillation requires immediate resuscitative electrical management while the underlying poisoning is treated.
• Significant poison-induced ventricular dysrhythmias generally require continuous cardiac monitoring and high-acuity care.

Toxicology – Abnormal Urine Color

Core Concept

Urine can change color because of:

• Normal variation in concentration
• Drugs or their metabolites
• Foods and dyes
• Blood or muscle pigments
• Bile pigments
• Infection
• Metabolic disorders
• Renal or hepatic disease
• Certain toxic exposures

Normal yellow urine is largely related to urochrome pigments. Concentrated urine is generally darker, whereas dilute urine appears paler.

An unusual urine color is therefore a diagnostic clue rather than a diagnosis.

First Diagnostic Question: Is It Really Blood?

Red, reddish-brown, or dark urine should first be evaluated for:

• Hematuria – intact RBCs in urine
• Hemoglobinuria – free hemoglobin from intravascular hemolysis
• Myoglobinuria – myoglobin released from injured skeletal muscle
• Non-heme pigments from medications, foods, or metabolites

Modern urine dipsticks detect the peroxidase activity of heme, so both hemoglobin and myoglobin can produce a positive “blood” result.

A useful approach is:

Urine dipstick positive for blood + many RBCs on microscopy → hematuria

Urine dipstick positive for blood + few/no RBCs → consider hemoglobinuria or myoglobinuria

This corrects the older source description suggesting that myoglobin should produce a negative blood dipstick.

Bright or Fluorescent Yellow Urine

Important causes include:

• Riboflavin (vitamin B₂) – often produces striking fluorescent yellow urine
• Fluorescein dye
• Concentrated urine
• Some vitamin preparations

Yellow-to-amber urine may also occur with bile pigments, although bilirubinuria generally produces darker yellow-brown or tea-colored urine rather than simply bright yellow urine.

Orange Urine

Common causes include:

• Phenazopyridine
• Rifampin
• Dehydration/concentrated urine
• Certain vitamin supplements
• Carotenoid-rich foods
• Bilirubin

Phenazopyridine commonly produces vivid orange or reddish-orange urine.

Rifampin can discolor several body fluids, including:

• Urine
• Tears
• Sweat
• Saliva

This drug-related discoloration is usually expected rather than evidence of renal injury.

Red or Pink Urine

Red urine does not automatically mean hematuria.

Important categories include:

Blood-Related

• Hematuria
• Hemoglobinuria
• Myoglobinuria

Foods

• Beets
• Blackberries
• Certain food dyes

Medications

• Rifampin
• Phenazopyridine
• Doxorubicin
• Some phenothiazines
• Certain other drugs or metabolites

Metabolic Pigments

• Porphyrins

The urinalysis and clinical context usually distinguish these possibilities.

Hematuria

Hematuria means RBCs are present in the urine.

Possible causes include:

• Urinary tract disease
• Stones
• Trauma
• Infection
• Renal disease
• Anticoagulation-associated bleeding
• Coagulopathy

The urine dipstick is typically positive for blood, with RBCs visible on microscopy.

Hemoglobinuria

Hemoglobinuria occurs when intravascular hemolysis releases hemoglobin into plasma and ultimately urine.

Potential toxicologic causes include oxidant-induced hemolysis from selected chemicals or medications.

Typical pattern:

• Dark/red-brown urine
• Positive urine heme test
• Few or no RBCs on microscopy
• Evidence of hemolysis

Additional investigations may include:

• CBC
• Bilirubin
• LDH
• Haptoglobin
• Peripheral blood smear

Myoglobinuria

Myoglobinuria usually results from rhabdomyolysis.

Potential toxicologic triggers include:

• Stimulant poisoning
• Severe hyperthermia
• Prolonged seizures
• Serotonin syndrome
• Neuroleptic malignant syndrome
• Prolonged coma/immobility
• Severe muscle injury

Urine may appear:

• Red-brown
• Tea-colored
• Cola-colored

Typical laboratory pattern:

Positive urine dipstick for blood + few/no RBCs on microscopy + elevated CK → strongly suggests myoglobinuria from muscle injury

Myoglobinuria is clinically important because severe rhabdomyolysis can contribute to acute kidney injury and electrolyte disturbances.

Porphyrins

Porphyrin disorders can produce:

• Red urine
• Reddish-brown urine
• Purple-appearing urine

Some porphyrin-containing urine becomes darker after exposure to light or prolonged standing.

Acute porphyrias may also produce:

• Severe episodic abdominal pain
• Autonomic abnormalities
• Neurologic symptoms
• Psychiatric manifestations
• Hyponatremia

Urine color alone is insufficient to diagnose porphyria.

Purple Urine

Purple discoloration is unusual.

An important modern clinical entity is purple urine bag syndrome, usually occurring in catheterized patients when bacterial metabolism of tryptophan derivatives produces colored pigments that interact with the catheter tubing or collection bag.

Risk factors include:

• Long-term urinary catheterization
• Bacteriuria
• Constipation
• Alkaline urine
• Frailty or chronic illness

The dramatic color itself does not necessarily indicate severe systemic poisoning.

Certain medications, metabolites, or dyes can also produce purple-red discoloration.

Blue or Green Urine

Important medication- or dye-related causes include:

• Methylene blue
• Propofol
• Amitriptyline
• Indomethacin
• Certain diagnostic dyes
• Some drug metabolites

Methylene blue may cause blue-green urine after therapeutic use.

Propofol infusion can occasionally cause green urine through phenolic metabolites; this discoloration is generally benign by itself.

Green Urine and Infection

Greenish urine may occasionally occur with Pseudomonas urinary infection, although urine color alone is neither sensitive nor specific enough to diagnose it.

When infection is suspected, assess:

• Urinalysis
• Microscopy
• Urine culture when indicated
• Clinical signs of urinary or systemic infection

Bile Pigments and Green Urine

Biliverdin and related bile pigments can occasionally produce greenish discoloration.

Associated findings may suggest hepatobiliary disease:

• Jaundice
• Elevated bilirubin
• Abnormal liver tests
• Evidence of biliary obstruction

Brown or Tea-Colored Urine

Important causes include:

• Myoglobin
• Hemoglobin
• Bilirubin
• Metronidazole
• Nitrofurantoin
• Certain antimalarials
• Some laxative metabolites
• Levodopa-related metabolites
• Phenolic compounds
• Porphyrins

Dark urine should therefore trigger consideration of both benign medication discoloration and serious systemic disease.

Bilirubinuria

Conjugated bilirubin is water-soluble and can enter the urine.

Dark yellow-brown or tea-colored urine may therefore occur with:

• Cholestasis
• Biliary obstruction
• Hepatocellular disease causing conjugated hyperbilirubinemia

A key correction to the older source is:

Unconjugated bilirubin is not normally excreted into urine because it is albumin-bound and not water-soluble.

Therefore, bilirubinuria specifically suggests conjugated bilirubin.

Associated jaundice strengthens suspicion for hepatobiliary disease.

Urine That Darkens on Standing

Some pigments become darker after exposure to air or light.

Examples include:

• Porphyrin-related pigments
• Homogentisic acid in alkaptonuria
• Melanin-related pigments
• Certain medication metabolites

The timing of the color change can therefore provide a useful clue.

Black or Very Dark Urine

Potential causes include:

• Severe myoglobinuria
• Hemoglobinuria
• Homogentisic acid
• Melanin-related pigments
• Certain drugs or metabolites

Very dark urine accompanied by muscle pain, weakness, hyperthermia, seizures, or prolonged immobilization should prompt urgent evaluation for rhabdomyolysis.

White, Milky, or Cloudy Urine

Potential causes include:

• Pyuria
• Crystalluria
• Phosphaturia
• Lipiduria
• Chyluria
• Contrast material

Cloudy urine is not synonymous with infection.

Pyuria

Large numbers of leukocytes can produce cloudy urine.

Possible associated findings include:

• Dysuria
• Urinary frequency
• Urgency
• Fever
• Flank pain

Urinalysis and culture are more informative than appearance alone.

Chyluria and Lipiduria

Chyluria

Lymphatic fluid entering the urinary tract may produce a milky appearance.

Lipiduria

May occur with significant renal disease such as nephrotic syndrome.

These are primarily medical rather than toxicologic causes.

Medication-Associated Color Changes

Some particularly useful associations are:

• Riboflavin → fluorescent yellow
• Phenazopyridine → orange/red-orange
• Rifampin → orange-red
• Methylene blue → blue-green
• Propofol → green
• Metronidazole → dark brown
• Nitrofurantoin → brown
• Doxorubicin → reddish
• Levodopa-related metabolites → darkening urine

Medication-related discoloration may be harmless, but the clinical context must still be considered.

Toxicologic Associations

Abnormal urine color becomes particularly important when accompanied by systemic toxicity.

Dark Urine + Muscle Injury

Consider rhabdomyolysis when there is:

• Severe agitation
• Hyperthermia
• Seizures
• Muscle pain
• Muscle weakness
• Prolonged immobilization

Check CK, potassium, renal function, and urinalysis.

Dark Urine + Hemolysis

Consider hemoglobinuria when accompanied by:

• Anemia
• Jaundice
• Weakness
• Elevated LDH
• Reduced haptoglobin

Certain oxidizing drugs and chemicals can precipitate hemolysis, particularly in susceptible individuals.

Cyanosis + Abnormal Dark Urine

Consider methemoglobinemia or associated oxidant exposure, particularly when cyanosis appears disproportionate to pulmonary findings.

Co-oximetry is used to confirm methemoglobinemia.

Dark Urine + Jaundice

Consider:

• Bilirubinuria
• Hepatocellular injury
• Cholestasis
• Hemolysis

Urinalysis and serum bilirubin fractionation help distinguish these possibilities.

Red/Purple Urine + Episodic Abdominal/Neurologic Symptoms

Consider porphyria, particularly when accompanied by:

• Severe abdominal pain
• Autonomic abnormalities
• Neuropsychiatric symptoms
• Peripheral neuropathy
• Hyponatremia

Confirmatory biochemical testing is required.

Diagnostic Approach

Rather than trying to identify a poison from color alone, evaluate the urine systematically.

1. Confirm the color

Determine whether the urine is genuinely:

• Red
• Orange
• Brown
• Green
• Blue
• Purple
• White/cloudy

2. Review exposures

Ask about:

• Prescription drugs
• OTC medications
• Vitamins
• Foods
• Dyes
• Chemicals
• Recent procedures or diagnostic dyes

3. Perform urinalysis

Evaluate:

• Blood/heme
• Bilirubin
• Protein
• Glucose
• Ketones
• Leukocyte esterase
• Nitrite
• Specific gravity
• pH

4. Examine urine microscopically when indicated

Look for:

• RBCs
• WBCs
• Casts
• Crystals
• Organisms

5. Order targeted blood tests

Based on the suspected mechanism.

Important Interpretation of the Urine Blood Dipstick

The older o-tolidine methodology described in the source is obsolete for routine clinical interpretation.

Modern dipsticks react to heme activity.

Therefore:

Dipstick positive + RBCs present

→ Hematuria likely

Dipstick positive + few/no RBCs

→ Consider myoglobinuria or hemoglobinuria

Then use the clinical context:

• Marked CK elevation/muscle injury → myoglobin
• Laboratory evidence of hemolysis → hemoglobin

Useful Laboratory Tests

Depending on the presentation, consider:

• Urinalysis
• Urine microscopy
• CBC
• Electrolytes
• BUN/creatinine
• CK
• AST/ALT
• Total and direct bilirubin
• LDH
• Haptoglobin
• Peripheral smear

Specialized testing should be guided by the suspected disease or toxic exposure.

Management

Urine discoloration itself generally does not require treatment.

Management should target the underlying cause.

Examples:

• Dehydration → appropriate fluid replacement
• Rhabdomyolysis → supportive management and prevention/treatment of complications
• Hemolysis → identify and remove the cause; treat complications
• Hepatobiliary disease → cause-specific management
• UTI → appropriate antimicrobial treatment when indicated
• Methemoglobinemia → specific treatment when clinically significant
• Poisoning → toxin-specific supportive or antidotal therapy

Benign medication-related discoloration generally resolves after the responsible compound and its metabolites are eliminated.

Red Flags

Abnormal urine color warrants greater concern when accompanied by:

• Reduced urine output
• Acute kidney injury
• Severe muscle pain or weakness
• Hyperthermia
• Repeated seizures
• Jaundice
• Significant anemia
• Hypotension
• Cyanosis
• Altered mental status
• Severe abdominal pain
• Significant toxic exposure

These findings suggest that the discoloration may represent a systemic process rather than a harmless pigment.

Key Points

• Urine color is influenced by concentration, endogenous pigments, foods, medications, and disease.
• Abnormal urine color is a clue rather than a diagnosis.
• Red urine does not necessarily indicate bleeding.
• Hematuria = urine heme positive with RBCs on microscopy.
• Myoglobinuria or hemoglobinuria = urine heme positive with few/no RBCs.
• Myoglobinuria should prompt evaluation for rhabdomyolysis, including CK and renal function.
• Hemoglobinuria suggests intravascular hemolysis when supported by other laboratory findings.
• Unconjugated bilirubin is not normally present in urine; bilirubinuria reflects conjugated bilirubin.
• Riboflavin commonly causes bright fluorescent yellow urine.
• Phenazopyridine commonly causes orange urine.
• Rifampin can produce orange-red discoloration of urine and other body fluids.
• Methylene blue may produce blue-green urine.
• Propofol can occasionally produce green urine.
• Metronidazole and nitrofurantoin may cause brown or dark urine.
• Some pigments, including porphyrin-related compounds, may darken after the urine stands.
• White or cloudy urine may reflect WBCs, crystals, lipids, or chyle and is not automatically a UTI.
• Medication-related urine discoloration is often benign, but associated systemic findings determine whether further investigation is necessary.

Toxicology – Approach to an Unknown Ingestion

Core Concept

An unknown ingestion should be approached as a potentially serious poisoning when there is evidence or reasonable suspicion that a drug, chemical, or other toxic substance was taken but the exact agent, amount, or both are uncertain.

The exposure may ultimately prove to be:

• Essentially nontoxic
• A toxic substance taken below a clinically important amount
• A potentially dangerous or life-threatening poisoning
• A mixed ingestion involving several substances

A normal initial examination does not reliably exclude significant poisoning because some toxic effects are delayed.

Immediate Priorities

Management should begin before the exact substance is identified.

A useful initial approach is:

Stabilize → recognize toxidromes → obtain focused history → ECG/glucose/basic investigations → identify high-risk occult poisons → give specific treatment when indicated → reassess repeatedly

The first priorities are:

• Airway protection
• Adequate ventilation
• Oxygenation
• Circulation and tissue perfusion
• Mental status
• Temperature
• Rapid bedside glucose
• Recognition and treatment of seizures or dangerous dysrhythmias

History: Reconstruct the Exposure

The history should be gathered from multiple sources, especially when the patient is confused, unconscious, very young, or unwilling to provide details.

Useful information includes:

• Medications prescribed to the patient
• Medications belonging to household members
• Over-the-counter products
• Herbal or complementary products
• Alcohol and recreational substances
• Household chemicals
• Automotive products
• Pesticides
• Occupational chemicals
• Time the patient was last known well
• Time the exposure may have occurred
• Whether extended-release products are available
• Possibility of multiple substances

Information from family, caregivers, emergency personnel, medication lists, pharmacy records, containers, and scene findings can be valuable.

Empty containers alone do not establish the amount actually ingested.

Do Not Assume Poisoning

Even when an overdose is suspected, consider important alternative diagnoses.

These include:

• Hypoglycemia
• Sepsis
• Meningitis or encephalitis
• Stroke
• Intracranial hemorrhage
• Head trauma
• Seizure/postictal state
• Electrolyte disturbances
• Diabetic ketoacidosis
• Hepatic or uremic encephalopathy
• Hypoxia
• Endocrine emergencies

Poisoning should likewise remain in the differential diagnosis of otherwise unexplained altered mental status or abnormal vital signs.

Toxidrome-Based Assessment

A toxidrome is a recognizable combination of clinical findings suggesting a particular pharmacologic effect.

Toxidromes can narrow the differential, but:

Absence of a classic toxidrome does not exclude poisoning.

Mixed ingestions can also produce overlapping or contradictory findings.

Opioid Pattern

Typical findings include:

• CNS depression
• Bradypnea or apnea
• Miosis

Additional findings may include:

• Hypotension
• Bradycardia
• Hypothermia

The most important manifestation is inadequate ventilation.

Naloxone is indicated when clinically important opioid-induced respiratory depression is suspected.

The therapeutic goal is restoration of adequate ventilation rather than necessarily complete awakening.

Sedative-Hypnotic Pattern

Possible findings include:

• Somnolence
• Slurred speech
• Ataxia
• Nystagmus
• Respiratory depression
• Hypothermia

Potential causes include:

• Benzodiazepines
• Barbiturates
• Ethanol
• Other sedative agents

Profound coma should prompt consideration of coingestants and nontoxic neurologic or metabolic causes.

Anticholinergic Pattern

Characteristic findings include:

• Agitation or delirium
• Mydriasis
• Tachycardia
• Dry mucous membranes
• Dry, flushed skin
• Reduced bowel sounds
• Urinary retention
• Hyperthermia

Potential causes include:

• First-generation antihistamines
• Antimuscarinic medications
• TCAs
• Certain antipsychotics
• Toxic plants

Some agents, particularly TCAs and certain antihistamines, can additionally cause sodium-channel blockade and QRS widening.

Sympathomimetic Pattern

Typical findings include:

• Agitation
• Mydriasis
• Tachycardia
• Hypertension
• Diaphoresis
• Hyperthermia

Severe poisoning can cause:

• Seizures
• Dysrhythmias
• Rhabdomyolysis
• Metabolic acidosis
• Cardiovascular collapse

Examples include cocaine and amphetamine-type stimulants.

A useful distinction is:

Sympathomimetic → sweaty

Anticholinergic → dry

Cholinergic Pattern

Typical muscarinic findings include:

• Miosis
• Salivation
• Lacrimation
• Bronchorrhea
• Bronchospasm
• Vomiting
• Diarrhea
• Sweating

Nicotinic manifestations include:

• Fasciculations
• Weakness
• Paralysis

Severe poisoning can result in respiratory failure from a combination of:

Secretions + bronchospasm + respiratory muscle weakness + CNS toxicity

Organophosphate and carbamate pesticides are important causes.

Vital Signs as Diagnostic Clues

Respiratory Depression

Consider:

• Opioids
• Sedative-hypnotics
• Severe CNS-depressant poisoning

Evaluate ventilation, not simply oxygen saturation.

Rapid or Deep Breathing

Consider:

• Salicylates
• Methanol
• Ethylene glycol
• Carbon monoxide
• Severe metabolic acidosis
• Stimulants
• Theophylline
• Pulmonary injury

Deep, rapid breathing may represent essential compensation for metabolic acidosis.

Tachycardia

Potential causes include:

• Sympathomimetics
• Anticholinergics
• Theophylline
• β₂-agonists
• Withdrawal
• Hypovolemia
• Hyperthermia
• Hypoxia

Bradycardia

Consider:

• Beta-blockers
• Calcium channel blockers
• Digoxin
• Clonidine/imidazolines
• Cholinergic poisoning

The associated blood pressure, ECG, glucose, pupils, respiratory status, and mental state help differentiate them.

Hyperthermia

Important toxicologic causes include:

• Sympathomimetic toxicity
• Anticholinergic toxicity
• Serotonin syndrome
• Neuroleptic malignant syndrome
• MAOI toxicity
• Severe withdrawal

Marked hyperthermia can rapidly produce rhabdomyolysis and multiorgan injury.

Hypothermia

Consider:

• Sedative-hypnotics
• Opioids
• Ethanol
• Antipsychotics
• Prolonged immobilization or environmental exposure

Pupils and Eye Findings

Miosis

Consider:

• Opioids
• Organophosphates/carbamates
• Clonidine or related imidazolines

Pupil size alone is not diagnostic.

Mydriasis

Consider:

• Sympathomimetics
• Anticholinergics
• Hypoxia
• Certain hallucinogens

Nystagmus

May occur with:

• PCP
• Carbamazepine
• Phenytoin
• Sedative/intoxicating agents

Visual Disturbance

Important possibilities include:

• Methanol
• Digoxin
• Carbon monoxide
• Certain other neurologic toxicants

Visual symptoms combined with otherwise unexplained high-anion-gap acidosis are particularly concerning for methanol poisoning.

Skin Findings

Dry, Flushed Skin

Supports anticholinergic toxicity.

Diaphoresis

Consider:

• Sympathomimetics
• Cholinergic poisoning
• Withdrawal
• Salicylates
• Hypoglycemia

Cyanosis

Consider:

• Hypoxemia
• Methemoglobinemia

Persistent cyanosis with unexpectedly preserved PaO₂ should raise concern for a dyshemoglobinemia.

Bullae After Prolonged Unconsciousness

Pressure-related bullous lesions may occur after prolonged coma from several intoxicants and should not be regarded as specific for one poison.

Cardiovascular Clues

An ECG is one of the highest-yield tests in an unknown ingestion.

Assess:

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

QRS Widening

QRS widening should raise concern for sodium-channel blockade.

Important toxicologic causes include:

• TCAs
• Certain antihistamines
• Class I antiarrhythmics
• Some other membrane-stabilizing drugs

Severe sodium-channel toxicity may cause:

• Hypotension
• Seizures
• Ventricular dysrhythmias

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

QT Prolongation

QT prolongation can occur with many medications and electrolyte abnormalities.

Important contributing factors include:

• QT-prolonging antidepressants or antipsychotics
• Certain antiarrhythmics
• Methadone
• Hypokalemia
• Hypomagnesemia
• Hypocalcemia

Marked QT prolongation increases the risk of torsades de pointes.

AV Block

Consider:

• Digoxin
• Beta-blockers
• Calcium channel blockers
• Other conduction-suppressing drugs

The overall clinical syndrome helps distinguish these causes.

Respiratory Findings

Bronchorrhea

Prominent airway secretions suggest:

• Organophosphate poisoning
• Carbamate poisoning
• Severe nicotine toxicity in an appropriate exposure

Bronchospasm

Possible causes include:

• Irritant gases
• Cholinergic poisoning
• Caustic inhalation
• Certain medication reactions

Pulmonary Infiltrates

Consider:

• Aspiration
• Hydrocarbon pneumonitis
• Irritant-gas injury
• Noncardiogenic pulmonary edema
• Infection

A normal initial chest radiograph does not exclude evolving toxic lung injury.

Gastrointestinal Clues

Repeated Vomiting

Consider:

• Iron
• Theophylline
• Digoxin
• Salicylates
• Cholinergic poisoning
• Caustic exposure
• Heavy metals

Reduced Bowel Sounds

Suggest:

• Anticholinergic toxicity
• Opioid effects

Diarrhea and Hyperactive GI Function

Consider:

• Cholinergic poisoning
• Nicotine
• Withdrawal
• Certain toxic mushrooms

Hepatic Injury

Severe hepatocellular injury after an unknown ingestion should immediately raise concern for acetaminophen toxicity, even when the history is unclear.

Other drugs and chemicals can also cause hepatic injury, but acetaminophen is especially important because:

• Early symptoms may be mild or absent.
• Severe hepatic injury is delayed.
• Effective antidotal treatment is available.

A serum acetaminophen concentration is therefore commonly obtained in potentially significant intentional or unexplained ingestions.

Renal Findings

Acute kidney injury may result from:

• Shock
• Rhabdomyolysis
• Ethylene glycol
• Heavy metals
• Direct nephrotoxic drugs
• Prolonged severe poisoning

Dark urine may reflect myoglobinuria after seizures, hyperthermia, prolonged immobilization, or severe agitation.

Electrolyte Clues

Hyperkalemia

Potential toxicologic causes include:

• Digoxin
• Potassium-containing products
• Potassium-sparing medications
• Severe tissue injury
• Severe acidosis

Hyperkalemia should be interpreted together with renal function and ECG findings.

Hypokalemia

Consider:

• β₂-agonists
• Theophylline
• Caffeine
• Barium
• Potassium-wasting diuretics

Marked hypokalemia increases the risk of dysrhythmias.

Hyponatremia

Possible mechanisms include:

• Excess free-water intake
• Drug-induced SIADH
• Certain anticonvulsants or psychotropic medications

Severe acute hyponatremia may cause:

• Confusion
• Seizures
• Coma

High-Anion-Gap Metabolic Acidosis

An unexplained high-anion-gap metabolic acidosis is a major clue in an unknown poisoning.

Consider:

• Methanol
• Ethylene glycol
• Salicylates
• Lactic acidosis
• Severe iron poisoning
• Ketoacidosis
• Renal failure

Other toxicants can produce acidosis through shock, seizures, or mitochondrial dysfunction.

The pattern should be interpreted with:

• Blood gas
• Lactate
• Glucose
• Renal function
• Osmolal gap when appropriate
• Exposure history
• Targeted toxicant concentrations

Neurologic Clues

Ataxia

Consider:

• Ethanol
• Benzodiazepines
• Phenytoin
• Carbamazepine
• Lithium
• Other sedative-hypnotics

Agitated Delirium

Consider:

• Anticholinergic agents
• Stimulants
• Hallucinogens
• Withdrawal
• Hyperthermic syndromes

Coma

Important toxicologic causes include:

• Opioids
• Sedative-hypnotics
• Clonidine
• Anticonvulsants
• Toxic alcohols
• Carbon monoxide
• Severe cardiotoxic poisoning

Always evaluate for nontoxicologic causes as well.

Seizures

Important possibilities include:

• Bupropion
• TCAs
• Isoniazid
• Theophylline
• Stimulants
• Antihistamines
• Camphor
• Withdrawal
• Hypoglycemia

Refractory seizures should prompt consideration of isoniazid toxicity in the appropriate setting.

Rhabdomyolysis

Rhabdomyolysis can follow:

• Severe agitation
• Hyperthermia
• Repeated seizures
• Prolonged immobilization
• Stimulant poisoning
• Serotonin syndrome
• NMS

Evaluation may include:

• CK
• Potassium
• Renal function
• Urinalysis
• ECG

Glucose: Check Early

Bedside glucose should be obtained early in any patient with:

• Altered mental status
• Seizures
• Unexplained autonomic abnormalities
• Suspected overdose

Hypoglycemia may result from:

• Insulin
• Sulfonylureas and related insulin secretagogues
• Ethanol, particularly in young children or susceptible patients
• Severe systemic illness
• Certain other medications

Neuroglycopenia may mimic intoxication.

Initial Diagnostic Workup

Testing should be individualized, but an important baseline evaluation for a significant unknown ingestion often includes:

• Bedside glucose
• Electrolytes
• Bicarbonate
• BUN/creatinine
• ECG
• Continuous cardiac monitoring when appropriate

Additional tests depend on clinical findings.

Acetaminophen and Salicylate Testing

These deserve particular attention because clinically important poisoning can initially be subtle.

In intentional or significant unknown ingestions, clinicians commonly consider measuring:

• Serum acetaminophen concentration
• Serum salicylate concentration

Serial salicylate concentrations may be required when poisoning is suspected because absorption can be delayed and concentrations may continue to rise.

Additional Targeted Testing

Depending on the presentation, consider:

• Calcium and magnesium
• Blood gas
• Lactate
• CK
• Liver tests
• Serum osmolality
• Ethanol concentration
• Lithium concentration
• Digoxin concentration
• Theophylline concentration
• Carbon monoxide testing
• Methemoglobin measurement
• Methanol/ethylene glycol testing

Testing should be driven by the clinical syndrome and plausible exposure.

Urine Drug Screens

Routine urine immunoassay screening has important limitations.

A positive result may indicate previous exposure without proving:

• Current intoxication
• Dose
• Timing
• Causation

A negative screen also does not exclude poisoning, because many important drugs are poorly detected or not included.

Therefore:

Clinical assessment + ECG + targeted laboratory testing are usually more useful than relying on a broad drug screen.

Imaging

Imaging should answer a specific clinical question.

Head CT

Consider when there is:

• Trauma
• Focal neurologic deficit
• Intracranial hemorrhage concern
• Unexplained persistent coma
• Another suspected structural CNS disorder

Chest Imaging

Consider for:

• Respiratory distress
• Aspiration
• Pulmonary edema
• Hydrocarbon exposure
• Inhalational injury

Abdominal Imaging

May occasionally identify certain radiopaque substances or foreign bodies, but:

A normal abdominal radiograph does not exclude ingestion.

Management Before the Poison Is Identified

Supportive care is the foundation of treatment.

Treat immediately reversible threats as they appear:

• Hypoxia → respiratory support
• Hypoglycemia → glucose correction
• Seizures → benzodiazepines
• Opioid respiratory depression → naloxone
• Hyperthermia → active cooling
• Sodium-channel blockade → sodium bicarbonate
• Shock → mechanism-directed circulatory support
• Dangerous electrolyte abnormalities → appropriate correction

Treatment should not be delayed while waiting for a definitive toxicologic diagnosis.

Empiric Antidotes

There is no universal antidote cocktail for every unknown ingestion.

Antidotes should be used when the clinical syndrome or available evidence supports a particular poisoning.

Examples include:

• Naloxone for suspected opioid-induced respiratory depression
• Sodium bicarbonate for significant sodium-channel blockade
• Pyridoxine for suspected isoniazid-associated refractory seizures
• Fomepizole when toxic alcohol poisoning is sufficiently suspected
• Digoxin immune Fab for clinically important digoxin toxicity
• Atropine ± pralidoxime for significant organophosphate poisoning

The risk-benefit profile of each antidote should guide empiric use.

Decontamination

Induced Vomiting

Do not induce vomiting.

Gastric Lavage

Routine gastric lavage is not recommended for unknown ingestion.

It carries risks including:

• Aspiration
• Airway injury
• Gastrointestinal injury

Its role is exceptionally limited and should not be treated as routine management of serious overdose.

Activated Charcoal

Activated charcoal may be considered for a selected recent ingestion of a clinically important, charcoal-adsorbable substance.

It should generally be avoided when:

• The airway is unprotected.
• Aspiration risk is substantial.
• Ileus or obstruction is present.
• The substance is poorly adsorbed.
• Its use would delay resuscitation or antidotal treatment.

An unknown ingestion by itself does not automatically justify charcoal.

Observation

The traditional idea that every asymptomatic unknown ingestion can automatically be discharged after a fixed 6-hour observation period is too simplistic.

Observation must account for:

• Suspected substance
• Immediate- versus extended-release formulation
• Time of exposure
• Reliability of the history
• ECG findings
• Laboratory abnormalities
• Development of symptoms
• Possibility of delayed metabolites
• Coingestants

Some dangerous poisonings can remain asymptomatic for longer periods.

Examples include:

• Extended-release medications
• Certain calcium channel blockers
• Bupropion XL
• Methanol
• Ethylene glycol
• Acetaminophen
• Sulfonylureas
• Long-acting opioids
• Delayed organ-toxic exposures

Disposition

Discharge should be based on a sufficiently reassuring overall risk assessment, not simply disappearance of symptoms.

Before discharge, clinicians should establish that:

• The patient is clinically stable.
• Appropriate observation has been completed.
• ECG abnormalities are absent or appropriately resolved.
• Important laboratory abnormalities have been addressed.
• Delayed toxicity is not reasonably expected.
• Appropriate psychiatric assessment has occurred when intentional self-harm is involved.
• A safe disposition and follow-up plan are available.

Patients with significant toxicity, uncertain high-risk exposure, persistent abnormalities, or expected delayed effects require continued observation or admission.

Important Pitfalls

• Do not assume that an asymptomatic patient had a harmless ingestion.
• Do not diagnose poisoning solely from one pupil, skin, or vital-sign abnormality.
• Mixed overdoses may distort classic toxidromes.
• A negative urine drug screen does not exclude important poisoning.
• Do not overlook acetaminophen or salicylates in an intentional unknown ingestion.
• A normal initial ECG does not eliminate every delayed cardiotoxic exposure.
• Normal early laboratory results may precede delayed organ toxicity.
• Do not attribute altered mental status to intoxication until important neurologic, metabolic, infectious, and traumatic causes have been considered.
• Do not use a universal observation period for every unknown ingestion.
• Do not let decontamination delay resuscitation.

Key Points

• An unknown ingestion should initially be treated as potentially toxic until adequate assessment establishes otherwise.
• Stabilization takes priority over identifying the exact poison.
• Obtain information from the patient, witnesses, medication history, available containers, and scene information.
• Use toxidromes as diagnostic clues, not absolute diagnostic rules.
• Early bedside glucose and ECG are particularly valuable.
• Intentional or clinically significant unknown ingestions often warrant consideration of acetaminophen and salicylate concentrations.
• QRS widening should raise concern for sodium-channel blockade.
• High-anion-gap metabolic acidosis should prompt consideration of toxic alcohols, salicylates, lactate-producing poisonings, and important nontoxic causes.
• Naloxone should be used when suspected opioid toxicity causes inadequate ventilation.
• Broad urine toxicology screens have substantial limitations.
• Routine induced vomiting and gastric lavage are not recommended.
• Activated charcoal is reserved for selected appropriate ingestions, not automatically given whenever the substance is unknown.
• A normal initial examination does not exclude delayed toxicity.
• Observation and disposition must be based on the suspected exposure and toxicokinetics rather than a universal fixed time.
• Always keep nontoxicologic disease in the differential diagnosis of an apparently poisoned patient.

Toxicology – Tachycardia

Definition

Tachycardia is an abnormally elevated heart rate relative to age and physiologic state.

In adults, resting heart rate >100 beats/min is generally considered tachycardia.

In children, normal heart rate varies substantially with age, activity, fever, distress, and clinical condition. Therefore, pediatric tachycardia should be interpreted using age-appropriate reference ranges rather than a single rigid cutoff.

Tachycardia is a clinical sign rather than a diagnosis. In toxicology, identifying the mechanism and underlying poison is more important than simply reducing the heart rate.

Pathophysiology

Toxicant-associated tachycardia can develop through several mechanisms:

• Excess sympathetic stimulation
• β-adrenergic receptor stimulation
• Muscarinic receptor blockade
• Peripheral vasodilation with reflex tachycardia
• Myocardial irritability
• Drug-induced dysrhythmia
• Hyperthermia
• Hypoxia
• Hypotension
• Hypovolemia
• Metabolic acidosis
• Withdrawal syndromes

A rapid heart rate may therefore represent an appropriate compensatory response rather than primary cardiac toxicity.

Major Toxicologic Mechanisms

Sympathomimetic Stimulation

Sympathomimetics increase catecholaminergic activity.

Important causes include:

• Cocaine
• Amphetamines
• Methamphetamine
• Ephedrine
• Other stimulants
• β₂-adrenergic agonists

Typical findings include:

• Tachycardia
• Hypertension
• Mydriasis
• Diaphoresis
• Agitation
• Tremor
• Hyperthermia

Severe toxicity can produce:

• Seizures
• Rhabdomyolysis
• Dysrhythmias
• Myocardial ischemia
• Metabolic acidosis

Anticholinergic Toxicity

Antimuscarinic drugs commonly produce sinus tachycardia.

Potential causes include:

• Diphenhydramine
• Other first-generation antihistamines
• Atropine
• Scopolamine
• Antipsychotics with antimuscarinic activity
• Jimsonweed and related plants

Clinical findings include:

• Tachycardia
• Mydriasis
• Dry mucous membranes
• Dry, flushed skin
• Hyperthermia
• Urinary retention
• Reduced bowel sounds
• Agitation
• Hallucinations
• Delirium

A useful distinction from sympathomimetic toxicity is:

Anticholinergic → hot and dry

Sympathomimetic → hot and sweaty

Tricyclic Antidepressants

TCA poisoning commonly causes tachycardia through:

• Antimuscarinic activity
• Norepinephrine reuptake inhibition
• Cardiovascular toxicity

More concerning findings include:

• Altered mental status
• Seizures
• Hypotension
• QRS widening
• Ventricular dysrhythmias

Tachycardia accompanied by QRS widening and hypotension should raise concern for significant sodium-channel blockade.

Sodium bicarbonate is the major treatment for clinically important TCA-related sodium-channel cardiotoxicity.

Other Sodium-Channel-Blocking Drugs

Several drugs can produce:

Tachycardia + QRS widening + hypotension ± ventricular dysrhythmias

Examples include:

• TCAs
• Certain first-generation antihistamines
• Class IA antiarrhythmics
• Some other membrane-stabilizing drugs

ECG evaluation is therefore essential in toxicologic tachycardia.

Theophylline

Theophylline toxicity commonly produces marked tachycardia.

Associated findings include:

• Nausea and vomiting
• Tremor
• Agitation
• Hypokalemia
• Hyperglycemia
• Seizures
• Supraventricular or ventricular dysrhythmias

Severe theophylline poisoning can deteriorate rapidly.

β₂-Adrenergic Agonists

Excessive β₂-agonist exposure can produce:

• Tachycardia
• Tremor
• Hypokalemia
• Hyperglycemia
• Lactic acidosis

The heart-rate elevation may result from both direct β-receptor effects and physiologic responses to metabolic changes.

Digoxin

Digoxin toxicity does not have one characteristic heart rate.

It can cause numerous rhythm disturbances, including combinations of:

• Bradycardia
• AV block
• Atrial tachyarrhythmias
• Ventricular ectopy
• Ventricular tachycardia

Associated findings may include:

• Nausea/vomiting
• Confusion
• Visual disturbances
• Hyperkalemia in significant acute poisoning

The combination of a tachyarrhythmia with AV conduction abnormalities can suggest digoxin toxicity.

Monoamine Oxidase Inhibitors

MAOI toxicity may produce:

• Tachycardia
• Hypertension
• Hyperthermia
• Agitation
• Altered mental status
• Neuromuscular abnormalities

Severe poisoning can progress to:

• Seizures
• Rigidity
• Cardiovascular instability
• Coma

Serotonergic Drugs

Serotonergic toxicity may cause tachycardia as part of autonomic hyperactivity.

Serotonin syndrome typically includes:

• Agitation
• Diaphoresis
• Tachycardia
• Hyperthermia
• Hyperreflexia
• Tremor
• Clonus

Clonus and hyperreflexia are particularly useful diagnostic findings.

Isolated SSRI overdose is often less severe than serotonin syndrome caused by significant serotonergic interactions or more toxic serotonergic agents.

Carbamazepine

Carbamazepine toxicity may produce:

• Tachycardia
• Nystagmus
• Ataxia
• CNS depression
• Coma
• Seizures

Severe poisoning can also produce cardiac conduction abnormalities.

Cholinergic Poisoning

Organophosphate and carbamate poisoning are commonly associated with bradycardia, but tachycardia can also occur.

Clinical findings include:

• Miosis
• Salivation
• Lacrimation
• Sweating
• Bronchorrhea
• Vomiting
• Diarrhea
• Fasciculations
• Weakness

Heart rate alone should therefore not be used to exclude a cholinergic syndrome.

Methemoglobinemia

Methemoglobinemia reduces effective oxygen delivery.

Compensatory findings may include:

• Tachycardia
• Tachypnea
• Cyanosis
• Headache
• Dizziness
• Dyspnea

A characteristic clue is cyanosis with an oxygen saturation that does not improve as expected with supplemental oxygen.

Diagnosis is confirmed using co-oximetry.

Thyroid Hormone Toxicity

Excess thyroid hormone can cause:

• Persistent tachycardia
• Tremor
• Anxiety
• Diaphoresis
• Hyperthermia
• Hypertension

Severe thyrotoxicosis may produce:

• Atrial fibrillation
• Heart failure
• Delirium
• Cardiovascular instability

Symptoms after an acute thyroid hormone ingestion may be delayed because hormonal effects develop over time.

Vasodilators

Vasodilator medications may produce reflex tachycardia secondary to reduced systemic vascular resistance.

Examples include:

• Dihydropyridine calcium channel blockers
• Hydralazine
• Nitrates

The key mechanism is:

Vasodilation → decreased blood pressure → baroreceptor activation → sympathetic response → tachycardia

Withdrawal Syndromes

Withdrawal from certain substances may produce autonomic hyperactivity.

Important causes include:

• Alcohol
• Benzodiazepines
• Barbiturates
• Opioids

Possible findings include:

• Tachycardia
• Hypertension
• Diaphoresis
• Tremor
• Anxiety
• Agitation

Alcohol or sedative-hypnotic withdrawal may additionally cause:

• Hallucinations
• Hyperthermia
• Seizures

Nontoxicologic Causes

Not every tachycardia in a poisoned patient is directly caused by the toxicant.

Important alternative causes include:

• Pain
• Anxiety
• Fever
• Dehydration
• Hemorrhage
• Anemia
• Hypoxia
• Pulmonary embolism
• Sepsis
• Metabolic acidosis
• Hyperthyroidism
• Cardiac dysrhythmia

Persistent unexplained tachycardia should prompt investigation for these conditions.

Clinical Assessment

The first important question is whether the rhythm represents:

Sinus tachycardia or a primary tachydysrhythmia?

Sinus tachycardia is usually a physiologic response to an underlying problem.

A primary tachydysrhythmia may require rhythm-specific management.

Vital-Sign Patterns

Tachycardia + Hypertension

Consider:

• Sympathomimetics
• Anticholinergic poisoning
• MAOI toxicity
• Serotonin syndrome
• Alcohol or sedative withdrawal
• Hyperthermia

Tachycardia + Hypotension

Consider:

• TCA poisoning
• Theophylline toxicity
• Severe vasodilator poisoning
• Chloroquine/hydroxychloroquine toxicity
• Shock
• Volume depletion

This combination is particularly concerning for cardiovascular toxicity or hemodynamic compromise.

Tachycardia + Hyperthermia

Consider:

• Sympathomimetic toxicity
• Anticholinergic toxicity
• Serotonin syndrome
• MAOI toxicity
• Severe withdrawal
• Thyrotoxicosis

Hyperthermia substantially increases the risk of:

• Rhabdomyolysis
• Metabolic acidosis
• Acute kidney injury
• Dysrhythmias
• Multiorgan failure

Pupil and Skin Findings

Mydriasis + Diaphoresis

Suggests:

Sympathomimetic syndrome

Mydriasis + Dry Skin

Suggests:

Anticholinergic syndrome

Miosis + Secretions

Suggests:

Cholinergic syndrome

Cyanosis

Consider:

• Severe hypoxemia
• Methemoglobinemia

Gastrointestinal Findings

Vomiting

May occur with:

• Theophylline
• Salicylates
• Iron
• Digoxin
• Cholinergic poisoning

Reduced Bowel Sounds

Supports an anticholinergic syndrome.

Diarrhea + Excessive Secretions

Supports a cholinergic syndrome.

Neurologic Findings

Agitation and Delirium

Consider:

• Stimulants
• Anticholinergic agents
• Hallucinogens
• Withdrawal

Tremor

Consider:

• Theophylline
• β₂-agonists
• Stimulants
• Thyroid hormone
• Withdrawal

Seizures

Tachycardia accompanied by seizures should raise concern for:

• TCAs
• Bupropion
• Theophylline
• Stimulants
• Antihistamines
• MAOIs
• Severe withdrawal

ECG Evaluation

An ECG should be obtained in persistent or clinically significant toxicologic tachycardia.

Assess:

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

Continuous cardiac monitoring is appropriate when significant poisoning or dysrhythmia is suspected.

QRS Widening

Tachycardia with QRS widening should raise concern for sodium-channel blockade.

Important causes include:

• TCAs
• Class IA antiarrhythmics
• Certain antihistamines
• Other sodium-channel-blocking medications

A prominent terminal R wave in lead aVR can support sodium-channel blockade, but it is not specific enough to diagnose TCA poisoning by itself.

QT Prolongation

Certain toxicants can prolong ventricular repolarization and increase the risk of torsades de pointes.

Potential causes include:

• Some antiarrhythmics
• Antipsychotics
• Certain antidepressants
• Methadone
• Other QT-prolonging medications

Evaluate and correct contributing abnormalities such as:

• Hypokalemia
• Hypomagnesemia
• Bradycardia when clinically relevant

Laboratory Evaluation

Testing should be guided by the clinical presentation.

Possible studies include:

• Bedside glucose
• CBC
• Electrolytes
• Bicarbonate
• Potassium
• Magnesium
• Renal function
• Blood gas
• Lactate
• CK when rhabdomyolysis is suspected

Targeted toxicologic tests may include:

• Salicylate concentration
• Acetaminophen concentration when overdose is possible
• Digoxin concentration
• Theophylline concentration
• Other drug-specific concentrations

Broad urine toxicology screening has limited sensitivity and specificity and should not replace clinical assessment.

Tachycardia With Metabolic Acidosis

Unexplained tachycardia accompanied by metabolic acidosis requires careful investigation.

Potential causes include:

• Salicylates
• Toxic alcohols
• Carbon monoxide
• Cyanide
• Severe stimulant toxicity
• Seizures
• Shock
• Sepsis
• Diabetic ketoacidosis

The anion gap, lactate, blood gas, exposure history, and targeted toxicology testing can help determine the cause.

Management Principles

The major principle is:

Treat the cause of the tachycardia rather than the heart rate alone.

Examples:

• Hypoxia → improve oxygenation/ventilation
• Hypovolemia → appropriate fluid replacement
• Hyperthermia → rapid cooling
• Hypoglycemia → correct glucose
• Electrolyte abnormality → correct the disturbance
• Agitation → appropriate sedation
• Sodium-channel blockade → sodium bicarbonate
• Withdrawal → syndrome-specific treatment

Agitation-Related Tachycardia

Agitation itself can substantially increase sympathetic activity.

When agitation results from stimulant toxicity or withdrawal, benzodiazepines are often first-line therapy.

Appropriate sedation can improve:

• Tachycardia
• Hypertension
• Agitation
• Muscle activity
• Hyperthermia risk

Airway and respiratory status should be monitored during sedative treatment.

Beta-Blockers

Beta-blockade should not be used routinely simply to normalize toxicologic sinus tachycardia.

The appropriateness of a beta-blocker depends on:

• Toxicant involved
• Blood pressure
• Rhythm
• Presence of myocardial ischemia
• Degree of sympathetic stimulation

In stimulant-associated cardiovascular toxicity, treatment generally emphasizes sedation and appropriate vasodilator therapy when needed, rather than reflexively treating the heart rate with isolated beta-blockade.

Hypotension

When tachycardia accompanies hypotension, determine whether the cause is:

• Hypovolemia
• Vasodilation
• Myocardial depression
• Dysrhythmia
• Severe metabolic toxicity

Fluids should be administered according to the patient’s volume status and response.

Persistent shock may require:

• Vasopressors
• Toxin-specific cardiovascular therapy
• Advanced circulatory support in selected severe poisonings

Routine large-volume fluid administration should be avoided when cardiogenic toxicity is possible.

Hypertension

When tachycardia and hypertension result from severe sympathetic activation:

Control agitation and sympathetic excess first.

Benzodiazepines are particularly useful for stimulant-related agitation.

Persistent severe hypertension or acute target-organ injury may require a short-acting, titratable antihypertensive agent selected according to the toxicant and clinical situation.

Decontamination

Induced vomiting is not recommended.

Routine gastric lavage is generally not indicated.

Activated charcoal may be considered for selected recent, serious, adsorbable ingestions when:

• The expected benefit is meaningful.
• Aspiration risk is acceptable.
• The airway is adequately protected.

Decontamination should never delay cardiovascular stabilization.

Monitoring

Patients with significant toxicologic tachycardia should be monitored for:

• Heart rate and rhythm
• Blood pressure
• Mental status
• Temperature
• Oxygenation
• QRS and QT abnormalities
• Electrolyte disturbances

Additional monitoring depends on the suspected poison.

Disposition

Disposition depends primarily on the underlying toxicant and associated abnormalities, rather than the heart rate alone.

Hospital observation or admission may be necessary when there is:

• Persistent unexplained tachycardia
• QRS or QT abnormalities
• Hypotension
• Severe hypertension
• Hyperthermia
• Seizures
• Altered mental status
• Significant metabolic abnormalities
• Potential delayed toxicity

Key Points

• Tachycardia is a clinical sign, not a specific diagnosis.
• In adults, resting heart rate >100 beats/min generally meets the definition of tachycardia; pediatric interpretation is age-dependent.
• Common toxicologic mechanisms include sympathetic stimulation, anticholinergic activity, reflex tachycardia, hyperthermia, hypoxia, hypotension, and volume depletion.
• Sympathomimetic toxicity causes tachycardia with diaphoresis, whereas anticholinergic toxicity typically causes tachycardia with dry skin and mucous membranes.
• Important toxicologic causes include stimulants, TCAs, antihistamines, theophylline, β₂-agonists, MAOIs, serotonergic drugs, thyroid hormone, and withdrawal syndromes.
• Tachycardia with QRS widening should raise concern for sodium-channel-blocking toxicity.
• A terminal R wave in aVR may support sodium-channel blockade but is not specific for TCA poisoning.
• Theophylline and β₂-agonist toxicity may produce hypokalemia.
• Tachycardia with cyanosis should raise concern for hypoxemia or methemoglobinemia.
• Obtain an ECG in clinically significant or unexplained toxicologic tachycardia.
• Management should focus on the underlying cause rather than simply lowering the heart rate.
• Benzodiazepines are often useful when tachycardia is driven by stimulant-induced agitation or withdrawal.
• Beta-blockers should not be used reflexively for toxicologic sinus tachycardia.
• Persistent tachycardia accompanied by hypotension, hyperthermia, altered mental status, seizures, QRS widening, or metabolic acidosis suggests potentially severe poisoning.

Toxicology – Toxicant-Induced Seizures

Definition

A seizure is a transient episode of abnormal, excessive neuronal activity that may produce:

• Involuntary motor activity
• Altered or loss of consciousness
• Sensory or behavioral abnormalities
• Autonomic manifestations

In toxicology, seizures are an important manifestation of drug or chemical toxicity and are commonly generalized tonic-clonic.

Prolonged or recurrent seizures can cause severe complications including hypoxia, hyperthermia, metabolic acidosis, rhabdomyolysis, aspiration, brain injury, and death.

Pathophysiology

Toxicants can provoke seizures through several mechanisms, including:

• Reduced inhibitory GABA activity
• Excess excitatory neurotransmission
• Sodium-channel effects
• Excess catecholaminergic activity
• Metabolic abnormalities
• Hypoglycemia
• Hypoxia
• Electrolyte disturbances

Some poisonings produce seizures through a highly specific mechanism.

For example:

Isoniazid → pyridoxine depletion → impaired GABA synthesis → severe seizures

Risk Factors

The likelihood of seizures may be increased by:

• Pre-existing epilepsy
• Previous CNS injury
• Large toxic exposure
• Multiple proconvulsant drugs
• Hypoglycemia
• Hypoxia
• Electrolyte abnormalities
• Withdrawal from alcohol or sedative-hypnotic drugs

A seizure in pregnancy requires urgent evaluation for eclampsia and other obstetric causes, even when toxic exposure is also possible.

Important Toxicologic Causes

Tricyclic Antidepressants

TCA poisoning can produce:

• Seizures
• Altered mental status
• Anticholinergic findings
• Tachycardia
• Hypotension
• QRS widening
• Ventricular dysrhythmias

TCA-associated seizures plus QRS widening strongly suggest clinically important sodium-channel blockade.

Sodium bicarbonate is indicated when significant sodium-channel cardiotoxicity is present.

Bupropion

Bupropion is an important cause of drug-induced seizures.

Features may include:

• Agitation
• Tremor
• Tachycardia
• Seizures
• Altered mental status

Severe poisoning may cause:

• Recurrent seizures
• QRS or QT abnormalities
• Ventricular dysrhythmias
• Cardiogenic shock

Extended-release preparations can produce substantially delayed seizures, so an initially asymptomatic patient may still require prolonged observation after a significant exposure.

Isoniazid

Isoniazid is particularly important because seizures may be:

• Severe
• Recurrent
• Resistant to conventional anticonvulsant therapy

Mechanism:

Isoniazid → functional pyridoxine deficiency → decreased GABA synthesis → seizures

Associated findings may include:

• High-anion-gap metabolic acidosis
• Altered mental status
• Coma

Pyridoxine (vitamin B6) is the specific antidotal therapy.

Theophylline

Theophylline toxicity may produce:

• Nausea/vomiting
• Tremor
• Marked tachycardia
• Hypokalemia
• Hyperglycemia
• Dysrhythmias
• Seizures

Seizures may be severe and difficult to control.

Unlike many poisonings, significant theophylline toxicity may cause seizures without a prolonged warning period.

Stimulants

Examples include:

• Cocaine
• Amphetamines
• Methamphetamine
• Other sympathomimetics

Typical findings include:

• Agitation
• Mydriasis
• Diaphoresis
• Tachycardia
• Hypertension
• Hyperthermia

Severe poisoning may progress to:

• Seizures
• Dysrhythmias
• Rhabdomyolysis
• Metabolic acidosis
• Cardiovascular collapse

Antihistamines and Anticholinergic Drugs

First-generation antihistamines and other antimuscarinic agents can produce:

• Agitated delirium
• Mydriasis
• Dry mucous membranes
• Tachycardia
• Urinary retention
• Reduced bowel sounds
• Hyperthermia
• Seizures

Some antihistamines, particularly in severe overdose, can also produce sodium-channel blockade with QRS widening.

Camphor

Camphor exposure is an important cause of rapid-onset seizures, particularly in young children.

Manifestations may include:

• Nausea/vomiting
• Agitation
• Confusion
• Seizures

Neurologic toxicity can develop rapidly.

Lithium

Severe lithium toxicity may produce:

• Coarse tremor
• Hyperreflexia
• Myoclonus
• Ataxia
• Confusion
• Seizures
• Coma

Neurologic toxicity is particularly important in chronic or acute-on-chronic poisoning.

Severe cases may require hemodialysis.

Chloroquine and Hydroxychloroquine

Severe poisoning may cause rapid:

• Seizures
• Hypotension
• Hypokalemia
• QRS widening
• Ventricular dysrhythmias
• Cardiovascular collapse

Neurologic and cardiovascular deterioration can occur quickly.

Local Anesthetic Systemic Toxicity

Systemic local anesthetic toxicity may initially cause neurologic symptoms such as:

• Perioral numbness
• Metallic taste
• Tinnitus
• Agitation
• Tremor

This can progress to:

• Seizures
• CNS depression
• Dysrhythmias
• Cardiovascular collapse

Intravenous lipid emulsion is an important therapy for severe local anesthetic systemic toxicity, particularly when cardiovascular toxicity develops.

Carbon Monoxide

Severe carbon monoxide poisoning can cause:

• Headache
• Nausea
• Dizziness
• Confusion
• Syncope
• Seizures
• Coma

Multiple people developing similar symptoms in the same environment is an important clue.

A normal conventional pulse oximetry reading does not exclude carbon monoxide poisoning.

Hypoglycemic Agents

Insulin and insulin-secretagogue medications can cause neuroglycopenia.

Clinical findings include:

• Sweating
• Confusion
• Behavioral abnormalities
• Weakness
• Seizures
• Coma

Blood glucose should be checked immediately in any patient with an unexplained seizure.

Organophosphate and Carbamate Poisoning

Severe cholinergic poisoning may cause seizures.

Associated findings include:

• Miosis
• Salivation
• Lacrimation
• Bronchorrhea
• Bronchospasm
• Vomiting
• Diarrhea
• Sweating
• Bradycardia
• Fasciculations
• Weakness

Seizures may accompany severe CNS toxicity.

Treatment of significant organophosphate poisoning includes:

• Airway and ventilatory support
• Atropine
• Pralidoxime
• Benzodiazepines for seizures

Salicylates

Seizures are a late and concerning manifestation of severe salicylate poisoning.

Other findings include:

• Tachypnea
• Tinnitus
• Nausea/vomiting
• Diaphoresis
• Respiratory alkalosis
• High-anion-gap metabolic acidosis
• Hyperthermia
• Altered mental status

Seizures suggest severe toxicity and may accompany worsening CNS dysfunction.

Withdrawal Syndromes

Withdrawal from CNS depressants can provoke seizures.

Important causes include:

• Ethanol withdrawal
• Benzodiazepine withdrawal
• Barbiturate withdrawal

Associated findings may include:

• Tremor
• Agitation
• Tachycardia
• Hypertension
• Diaphoresis
• Hallucinations
• Hyperthermia

Benzodiazepines are central to treatment of severe alcohol or sedative-hypnotic withdrawal.

Strychnine: An Important Seizure Mimic

Strychnine causes severe painful muscular spasms rather than true epileptic seizures.

Typical findings include:

• Stimulus-induced muscle spasms
• Generalized rigidity
• Opisthotonus
• Preserved consciousness between or during early spasms

This distinction can help differentiate strychnine poisoning from generalized tonic-clonic seizures.

Nontoxicologic Differential Diagnosis

Not every seizure in a poisoned or potentially poisoned patient is caused by a toxicant.

Important alternative causes include:

Metabolic

• Hypoglycemia
• Hyponatremia
• Hypocalcemia
• Hypomagnesemia
• Uremia
• Hypoxia

Structural CNS Disease

• Intracranial hemorrhage
• Ischemic stroke
• Traumatic brain injury
• Brain tumor
• Cerebral edema

Infection

• Meningitis
• Encephalitis
• Brain abscess

Other

• Epilepsy
• Eclampsia
• Alcohol/sedative withdrawal

Psychogenic nonepileptic seizures can also mimic epilepsy, but should not be diagnosed merely from one historical or examination feature; video-EEG confirmation is the diagnostic standard when uncertainty persists.

Clinical Clues to the Toxicant

Tachycardia + Hypertension + Hyperthermia

Consider:

• Cocaine
• Amphetamines
• Other sympathomimetics
• MAOI toxicity
• Serotonin syndrome
• Severe withdrawal

Tachycardia + Hypotension

Consider:

• TCA poisoning
• Theophylline
• Chloroquine/hydroxychloroquine
• Other severe cardiotoxic poisoning

Bradycardia + Hypotension

Consider:

• Beta-blockers
• Organophosphates
• Carbamates
• Other cardiodepressant agents

Dry Skin + Mydriasis + Tachycardia

Suggests an anticholinergic toxidrome.

Potential causes include:

• First-generation antihistamines
• Antimuscarinic medications
• TCAs

Miosis + Secretions

Miosis accompanied by:

• Salivation
• Bronchorrhea
• Diarrhea
• Sweating
• Fasciculations

strongly suggests a cholinergic syndrome.

Nystagmus

May occur with:

• PCP
• Carbamazepine
• Certain anticonvulsants
• Sedative/intoxicating agents

Rigidity + Hyperthermia

Consider:

• Serotonin syndrome
• Neuroleptic malignant syndrome
• MAOI-related toxicity
• Malignant hyperthermia in the appropriate peri-anesthetic setting

Clonus and hyperreflexia favor serotonin syndrome.

Severe generalized rigidity with a slower onset favors NMS.

Complications of Prolonged Seizures

Prolonged or recurrent seizures can produce:

• Hypoxemia
• Hypercapnia
• Lactic acidosis
• Hyperthermia
• Rhabdomyolysis
• Hyperkalemia
• Acute kidney injury
• Aspiration
• Brain injury
• Cardiovascular instability

A transient lactate elevation and high-anion-gap metabolic acidosis can occur after a generalized tonic-clonic seizure and often improve as the seizure-related lactate clears.

Persistent severe acidosis should prompt investigation for another cause.

Initial Evaluation

Immediate priorities are:

Airway → breathing → circulation → stop seizure → identify reversible causes

Assess:

• Airway protection
• Ventilation
• Oxygenation
• Heart rate and rhythm
• Blood pressure
• Temperature
• Neurologic status

Obtain a rapid bedside glucose immediately.

Laboratory Evaluation

Important investigations may include:

• Glucose
• Electrolytes
• Calcium
• Magnesium
• Bicarbonate
• BUN and creatinine
• Blood gas
• Lactate
• CK

Depending on the exposure, obtain targeted testing such as:

• Salicylate concentration
• Acetaminophen concentration
• Lithium concentration
• Theophylline concentration
• Carbon monoxide testing
• Anticonvulsant concentrations

Broad urine drug screens have important limitations and should not replace toxidrome-based assessment.

ECG

An ECG is essential when toxicant-induced seizure is suspected.

Look for:

• QRS widening
• QT prolongation
• Bradycardia
• AV block
• Ventricular dysrhythmias

Seizure + QRS widening should particularly raise concern for a sodium-channel-blocking drug such as a TCA or certain antihistamines.

Neuroimaging and Lumbar Puncture

Head CT or other neuroimaging should be considered when there is concern for:

• Trauma
• Intracranial hemorrhage
• Focal neurologic deficit
• Structural CNS disease
• Unexplained persistent altered mental status

Lumbar puncture may be required when CNS infection or another appropriate neurologic diagnosis is suspected.

Management of Toxicant-Induced Seizures

First-Line: Benzodiazepines

Benzodiazepines are the preferred initial treatment for most toxicant-induced seizures.

They enhance GABA-mediated inhibition and are particularly useful because many toxic seizures result from excessive CNS excitation.

Examples include:

• Lorazepam
• Diazepam
• Midazolam

Repeated treatment may be necessary for recurrent seizures.

Persistent or Refractory Seizures

If seizures continue despite adequate benzodiazepine therapy, escalation may include:

• Additional GABAergic antiseizure therapy
• Airway control and mechanical ventilation when necessary
• Continuous EEG monitoring
• Specialist toxicology and critical-care management

Phenobarbital is an important second-line option for many toxin-induced refractory seizures.

Severe refractory status epilepticus may require anesthetic therapy in an ICU.

Role of Phenytoin

Phenytoin is generally less useful for many toxicant-induced seizures because it does not correct the mechanisms responsible for many poison-induced convulsions.

In particular, it should not be considered the preferred treatment for seizures caused by:

• Isoniazid
• Theophylline
• Withdrawal
• Many stimulant poisonings

Treatment should instead emphasize benzodiazepines and toxin-specific therapy.

Isoniazid-Induced Seizures

Isoniazid poisoning is a major exception requiring specific antidotal therapy.

Pyridoxine (vitamin B6) should be administered when isoniazid toxicity is strongly suspected, particularly with refractory seizures.

Benzodiazepines are used concurrently.

Failure to recognize isoniazid toxicity can result in persistent seizures despite conventional anticonvulsant therapy.

Neuromuscular Paralysis

Neuromuscular blocking agents may stop visible muscular activity but do not stop cerebral seizure activity.

Therefore, if paralysis is required for airway management or severe refractory convulsive activity:

Continuous EEG monitoring is important when ongoing seizure activity remains possible.

Paralysis must never be mistaken for successful treatment of the underlying seizure.

Airway Management

Endotracheal intubation may be necessary when there is:

• Persistent status epilepticus
• Severe respiratory depression
• Recurrent seizures with inadequate ventilation
• Severe aspiration risk
• Inability to protect the airway
• Need for deep sedation or anesthetic therapy

Airway management should occur alongside treatment of the seizure rather than delaying anticonvulsant therapy.

Decontamination

Do not induce vomiting.

Routine gastric lavage is generally not recommended.

Activated charcoal may be considered only in selected recent, serious, adsorbable ingestions when the airway is adequately protected.

A patient who is actively seizing or has markedly impaired consciousness has a major aspiration risk, so gastrointestinal decontamination should never take priority over stabilization.

Monitoring

Patients with significant toxicant-induced seizures should be monitored for:

• Recurrent seizures
• Respiratory depression
• Oxygenation and ventilation
• Dysrhythmias
• Hypotension
• Hyperthermia
• Rhabdomyolysis
• Electrolyte abnormalities
• Acute kidney injury

Continuous cardiac monitoring is appropriate in significant poisoning.

Continuous EEG may be required for refractory seizures, persistent unexplained coma, or patients receiving neuromuscular blockade.

Key Points

• Toxicant-induced seizures are commonly generalized tonic-clonic seizures.
• Important mechanisms include reduced GABA activity, excessive excitatory neurotransmission, metabolic abnormalities, hypoglycemia, and hypoxia.
• Common toxicologic causes include bupropion, TCAs, antihistamines, stimulants, isoniazid, theophylline, lithium, camphor, salicylates, and withdrawal syndromes.
• Always check bedside glucose immediately in an unexplained seizure.
• Obtain an ECG, because seizures may accompany life-threatening cardiotoxic poisoning.
• Seizure + QRS widening suggests possible sodium-channel-blocker toxicity.
• Isoniazid should be considered when seizures are unusually refractory, especially with compatible exposure history and metabolic acidosis.
• Pyridoxine is the specific antidotal therapy for isoniazid-induced seizures.
• Benzodiazepines are first-line treatment for most toxicant-induced seizures.
• Phenobarbital or other GABAergic therapy may be required for refractory seizures.
• Phenytoin is generally less effective for many toxin-induced seizures and is not the preferred universal second-line therapy.
• Neuromuscular paralysis eliminates visible convulsions but does not terminate cerebral seizure activity.
• Prolonged seizures can cause hyperthermia, lactic acidosis, rhabdomyolysis, hypoxia, aspiration, and brain injury.
• Always evaluate for nontoxicologic causes, including metabolic abnormalities, CNS infection, structural brain disease, epilepsy, and eclampsia.