Toxicology – Carisoprodol

Core concept

Carisoprodol is a centrally acting sedative muscle relaxant that is metabolized to the longer-acting sedative-hypnotic meprobamate.

The characteristic overdose syndrome is:

CNS depression + ataxia → respiratory depression/coma ± hypotension

However, unlike a simple sedative overdose, carisoprodol can also cause:

• Agitation
• Myoclonus or abnormal movements
• Seizures
• Delirium
• Serotonergic features

Severe poisoning is especially dangerous when combined with:

Opioids + benzodiazepines + alcohol or other CNS depressants

because respiratory-depressant effects are additive. Current labeling documents fatal overdoses both from carisoprodol alone and particularly in multidrug exposures.

The main treatment is:

Airway protection + ventilation + supportive cardiovascular care

There is no established specific antidote.

Current Forms and Uses

Carisoprodol remains available as an oral prescription muscle relaxant.

Current U.S. labeling recommends:

250–350 mg orally three times daily and at bedtime

for the relief of discomfort associated with:

Acute painful musculoskeletal conditions

Treatment should be limited to:

2–3 weeks

because longer-term effectiveness has not been established and dependence/abuse become increasingly important concerns.

Pediatric use

The older text states that the drug is not recommended below age 12.

Current labeling states:

Safety, efficacy, and pharmacokinetics have not been established in patients <16 years.

Controlled Substance / Abuse Potential

In the United States, carisoprodol is a:

Schedule IV controlled substance

and has recognized potential for:

• Abuse
• Misuse
• Dependence
• Diversion
• Withdrawal

This is clinically important because many severe overdoses occur in people also using:

• Opioids
• Benzodiazepines
• Alcohol
• Other sedatives

A 2025 UK government review similarly emphasized increased overdose danger when carisoprodol is combined with opioids or benzodiazepines.

Combination Products

Carisoprodol has historically been marketed in combination preparations containing:

• Aspirin/salicylate
• Aspirin + codeine

Therefore, whenever a commercial combination preparation is involved:

Do not attribute the entire syndrome to carisoprodol.

Specifically consider:

• Salicylate toxicity
• Opioid toxicity

according to the actual ingredients.

Toxic Dose

There is no reliable single toxic dose.

Gram-level ingestion can produce serious toxicity, but severity varies greatly depending on:

• Opioid/sedative tolerance
• Coingestants
• Age
• Renal function
• Hepatic function
• CYP2C19 phenotype
• Chronic carisoprodol exposure

The older concept that “gram quantities intoxicate an adult” remains qualitatively useful, but there is no validated numerical dose that separates mild from severe poisoning.

Therefore:

Clinical findings matter more than the reported dose.

Pathophysiology

Central nervous system effects

The precise therapeutic mechanism is still not completely established.

Current FDA labeling states that carisoprodol:

• Acts centrally
• Does not directly relax skeletal muscle
• Is associated experimentally with altered interneuronal activity in the spinal cord and descending reticular formation.

Modern pharmacologic evidence also supports modulation of:

GABA-A receptor activity

which helps explain its:

• Sedative
• Anxiolytic
• Abuse
• Respiratory-depressant

properties.

Meprobamate – Important Active Metabolite

Carisoprodol undergoes hepatic metabolism through:

CYP2C19

to form:

Meprobamate

Meprobamate has significant:

• Sedative
• Anxiolytic
• CNS-depressant

activity.

This creates a clinically important two-stage toxicology picture:

Carisoprodol exposure → parent-drug effects → conversion to longer-acting meprobamate

Pharmacokinetics

Current labeling gives approximate half-lives of:

Carisoprodol

~2 hours

Meprobamate

~10 hours

Therefore:

Sedation can persist substantially longer than the parent carisoprodol concentration would suggest.

This is especially relevant after:

• Large overdose
• Repeated dosing
• Chronic misuse
• Renal dysfunction

CYP2C19 Pharmacogenetics

CYP2C19 activity varies substantially between individuals.

Poor metabolizers can have approximately:

4-fold greater carisoprodol exposure

with correspondingly reduced conversion to meprobamate.

This may partly explain variation in:

• Clinical effects
• Duration
• Neuroexcitation versus sedation

Drug Interactions

CNS depressants

The most clinically important interaction is:

Carisoprodol + another CNS depressant → additive sedation/respiratory depression

Important agents include:

• Opioids
• Benzodiazepines
• Alcohol
• Tricyclic antidepressants
• Sedating antihistamines
• Other muscle relaxants

CYP2C19 inhibitors

Examples include:

• Omeprazole
• Fluvoxamine

These may:

↑ carisoprodol exposure + ↓ meprobamate formation

CYP2C19 inducers

Examples include:

• Rifampin
• St John’s wort

These may:

↓ carisoprodol exposure + ↑ meprobamate formation

Clinical Features

CNS Depression

The most common overdose manifestation is:

CNS depression

which may progress through:

• Dizziness
• Drowsiness
• Ataxia
• Dysarthria
• Poor coordination
• Stupor
• Coma

Current FDA labeling specifically reports:

• Coma
• Respiratory depression
• Death

after overdose.

Respiratory

Severe toxicity may cause:

Respiratory depression → hypoventilation → hypercapnia/hypoxia → respiratory arrest

Risk increases substantially with:

• Opioids
• Benzodiazepines
• Alcohol

Patients with profound CNS depression may lose airway reflexes and require intubation.

Neuroexcitation / Abnormal Movements

Carisoprodol poisoning is unusual among sedatives because some patients develop marked CNS excitation.

Reported manifestations include:

• Agitation
• Tremor
• Myoclonus
• Rigidity
• Dystonic reactions
• Choreiform or unusual “robot-like” movements
• Hyperreflexia
• Delirium

The clinical pattern can differ from that of pure meprobamate poisoning.

The 2025 UK toxicology review describes parent carisoprodol toxicity as more likely to produce:

• Tachycardia
• Tremor
• Shivering
• Myoclonus/abnormal movements
• Agitation

whereas meprobamate more typically causes:

CNS depression + hypotension + hyporeflexia/flaccidity.

Seizures

Seizures have been reported in overdose.

Current labeling notes that many seizure cases involve:

• Multiple drug overdoses
• Alcohol
• Drugs of abuse

rather than pure isolated therapeutic exposure.

Serotonin Toxicity

Current FDA labeling states that:

Serotonin syndrome has been reported with carisoprodol intoxication.

Possible findings include:

• Agitation
• Tremor
• Hyperreflexia
• Clonus/myoclonus
• Hyperthermia
• Tachycardia

However:

Serotonin toxicity is not the usual presentation of carisoprodol overdose.

It should be particularly considered when there is:

• Marked neuromuscular excitation
• Hyperthermia
• Clonus
• Coexposure to serotonergic drugs

Case-series evidence has described serotonergic features after high-dose intoxication.

Cardiovascular

Possible manifestations include:

• Tachycardia
• Postural hypotension
• Hypotension
• Syncope

Severe poisoning may produce:

• Profound hypotension
• Cardiovascular instability

Current labeling specifically identifies hypotension as a possible serious overdose manifestation.

Gastrointestinal

Possible effects include:

• Nausea
• Vomiting
• Epigastric discomfort

These are generally less clinically important than respiratory/CNS toxicity.

Pupils / Eyes

Reported overdose findings include:

• Nystagmus
• Blurred vision
• Mydriasis

Thus pupil findings are nonspecific and should not be used to distinguish carisoprodol reliably from other sedatives.

Withdrawal

An important feature largely underemphasized in older descriptions is physical dependence.

Abrupt cessation after prolonged/high-dose use may cause:

• Insomnia
• Anxiety
• Vomiting
• Abdominal cramps
• Headache
• Tremor
• Muscle twitching
• Ataxia
• Hallucinations
• Psychosis

The syndrome can resemble withdrawal from other sedative-hypnotics.

Therefore:

Do not abruptly discontinue heavy chronic carisoprodol use without considering withdrawal risk.

Diagnosis

Diagnosis is mainly clinical:

Exposure history + CNS depression or mixed sedative/neuroexcitant toxidrome

There is no rapidly available serum concentration routinely required for treatment.

Differential Diagnosis

Carisoprodol overdose may resemble:

• Ethanol
• Benzodiazepines
• Barbiturates
• Meprobamate
• Other muscle relaxants
• Gabapentinoids
• Opioids
• Sedating antihistamines
• Clonidine

If abnormal movements, hyperreflexia, or agitation predominate, consider:

• Serotonin syndrome
• Stimulant intoxication
• Anticholinergic poisoning
• Withdrawal syndromes

Essential Assessment

Evaluate:

• Airway
• Respiratory rate
• Depth of ventilation
• Mental status
• Blood pressure
• Heart rate
• Temperature
• Bedside glucose

Pulse oximetry should be used, but remember:

Supplemental oxygen can maintain a normal SpO₂ despite significant hypoventilation.

Therefore, in significant CNS depression consider:

• Continuous capnography
• Venous/arterial blood gas

Laboratory Tests

In moderate/severe poisoning consider:

• Electrolytes
• Glucose
• BUN
• Creatinine
• Bicarbonate
• Blood gas
• CK after seizures/prolonged immobilization

Obtain an ECG in:

• Significant overdose
• Syncope
• Hypotension
• Suspected coingestion

For intentional overdose, consider:

• Acetaminophen concentration
• Salicylate concentration

and other testing based on the actual product involved.

Carisoprodol / Meprobamate Levels

Specific quantitative assays exist but are generally:

• Not rapidly available
• Not required for routine clinical management

Management should be guided primarily by:

• Mental status
• Ventilation
• Hemodynamics
• Coingestants

A standard emergency urine drug screen may not reliably identify carisoprodol unless a specific assay is included.

A recent UK review recommended that specialized toxicologic assessment include both carisoprodol and meprobamate because incomplete testing can miss clinically important exposures.

Treatment

1. Airway and Ventilation

The most important treatment is:

Supportive airway management

For significant CNS depression:

• Position airway appropriately
• Provide supplemental oxygen
• Assist ventilation if necessary
• Suction secretions

Intubate for:

• Loss of airway reflexes
• Severe hypoventilation
• Persistent coma
• Recurrent seizures
• Respiratory failure

Current FDA labeling specifically recommends considering tracheal intubation when severe CNS depression compromises airway protection.

Naloxone

Naloxone is not an antidote to carisoprodol.

However, because opioid coingestion is common:

Respiratory depression + possible opioid exposure → give naloxone appropriately

while continuing ventilatory support.

A response to naloxone suggests an opioid contribution but does not exclude simultaneous carisoprodol toxicity.

Gastrointestinal Decontamination

Do Not Induce Vomiting

Do not induce emesis.

CNS and respiratory depression can develop rapidly, creating substantial aspiration risk.

Current FDA labeling explicitly advises against induced vomiting.

Activated Charcoal

Modern labeling recommends considering activated charcoal only in selected patients with:

• Large overdose
• Early presentation
• No significant CNS depression
• Ability to protect the airway

A typical single dose in poisoning practice is approximately:

1 g/kg

when clinically appropriate.

Important

Do not administer charcoal to a somnolent patient with an unprotected airway.

Gastric Lavage

The older chapter recommends gastric lavage routinely after a large ingestion within 1 hour.

Current 2026 FDA labeling instead emphasizes supportive treatment and selected activated charcoal and no longer recommends routine gastric lavage in its overdose management section.

Therefore:

Routine gastric lavage should not be performed.

It would only rarely be considered in an exceptionally large, immediately life-threatening recent ingestion after:

• Airway protection
• Toxicology consultation

Antidote

There is no established specific antidote.

Management is primarily:

• Ventilation
• Hemodynamic support
• Seizure treatment
• Treatment of coingestants

Flumazenil

This is an important modern pitfall.

One older case report described neurologic improvement after flumazenil in a severe carisoprodol/meprobamate intoxication.

However:

Flumazenil is not recommended routinely for carisoprodol poisoning.

Reasons include:

• Carisoprodol does not behave simply like a benzodiazepine
• Evidence consists largely of isolated case experience
• Many overdoses involve mixed drugs
• Chronic sedative users may be dependent
• Flumazenil can precipitate seizures or withdrawal

The 2025 UK expert review specifically notes that flumazenil is not recommended by the UK National Poisons Information Service for acute carisoprodol or meprobamate poisoning.

Therefore:

Do not use flumazenil as routine reversal therapy.

Hypotension

Treat initially with:

• Isotonic crystalloid if clinically fluid responsive

Avoid unnecessary large fluid volumes, particularly if prolonged severe meprobamate toxicity is suspected.

If hypotension persists despite appropriate volume:

Use a vasopressor—norepinephrine is generally an appropriate contemporary first-line choice.

The old routine preference for dopamine and Trendelenburg positioning is outdated.

Seizures

First-line:

Benzodiazepines

Examples:

• Lorazepam
• Midazolam
• Diazepam

Current carisoprodol labeling recommends IV benzodiazepines for seizures and phenobarbital when recurrent seizures persist.

For refractory status epilepticus:

• Phenobarbital
• Propofol in an intubated patient

may be appropriate.

Phenytoin is generally not preferred as routine treatment for diffuse toxin-induced seizures.

Serotonin Syndrome

If a convincing serotonergic syndrome develops:

• Stop serotonergic agents
• Benzodiazepine sedation
• External cooling for significant hyperthermia
• IV fluids as appropriate

Severe hyperthermia requires aggressive control.

Because most suspected cases involve multidrug exposures, actively search for another serotonergic agent.

Enhanced Elimination

Forced Diuresis

The older literature sometimes lists forced diuresis.

Routine forced diuresis should not be used.

It provides uncertain benefit and can cause:

• Volume overload
• Electrolyte disturbances

Hemodialysis

Carisoprodol itself is technically dialyzable, and current FDA labeling acknowledges that both hemodialysis and peritoneal dialysis can remove carisoprodol.

Meprobamate has also historically been removed by hemodialysis in severe poisoning.

However:

Hemodialysis is not routine treatment for ordinary carisoprodol overdose.

Most patients improve with:

• Airway support
• Ventilation
• Hemodynamic care
• Time

Consider extracorporeal therapy only in unusual, severe situations such as:

• Persistent profound coma/respiratory failure
• Severe refractory hypotension
• Progressive deterioration despite intensive supportive treatment
• Marked meprobamate accumulation
• Severe toxicity with impaired renal elimination

This decision should involve:

• Medical toxicology/poison center
• Nephrology

There are no modern standardized EXTRIP-type indications for carisoprodol.

Monitoring

Symptomatic patients require:

• Continuous pulse oximetry
• Frequent respiratory assessment
• Continuous ECG in significant poisoning
• Blood pressure monitoring
• Serial neurologic examinations

Consider:

• Capnography

because hypoventilation may develop before hypoxemia becomes obvious.

Observation

Carisoprodol itself has a relatively short half-life, but the active metabolite:

Meprobamate lasts considerably longer.

Therefore, a rigid historical:

“6 hours = safe discharge”

should not be applied to every exposure.

Observation duration should account for:

• Dose
• Clinical symptoms
• Coingestants
• Chronic use
• Renal/hepatic dysfunction
• Recurrent sedation

Admission

Hospital admission is appropriate for:

• Significant CNS depression
• Ataxia preventing safe ambulation
• Recurrent vomiting with sedation
• Hypotension
• Seizures
• Abnormal movements with substantial toxicity
• Respiratory depression
• Significant intentional overdose
• Major coingestants

ICU care is appropriate for:

• Intubation/mechanical ventilation
• Coma
• Recurrent seizures
• Shock
• Severe mixed overdose

Discharge

Discharge should require:

• Normal or baseline mental status
• Normal ventilation
• Stable vital signs
• Safe ambulation
• No recurrent sedation
• No clinically important coingestant toxicity

Intentional overdose requires appropriate psychiatric/safety assessment.

A patient should not be discharged simply because initial carisoprodol effects improved if significant:

• Opioid
• Benzodiazepine
• Salicylate
• Meprobamate

toxicity remains possible.

Dependence and Withdrawal

Long-term carisoprodol therapy should be avoided.

Current labeling specifically limits therapeutic use to:

2–3 weeks

partly because abuse, dependence, and withdrawal have been documented.

A patient chronically taking large doses may require an individualized taper rather than abrupt discontinuation.

Pregnancy

The historical FDA Pregnancy Category C classification is obsolete.

Current labeling states that decades of available human data have not identified a consistent drug-associated increase in major birth defects, miscarriage, or other adverse pregnancy outcomes from carisoprodol, and available meprobamate data likewise do not show a consistent major-malformation pattern.

This does not make overdose benign.

In maternal poisoning:

Maternal airway, ventilation, and circulation remain the priorities.

Breastfeeding

Carisoprodol and meprobamate can enter breast milk.

A breastfed infant should be monitored for:

Sedation

Current labeling reports at least one infant sedation case.

Prognosis

Most isolated mild-to-moderate overdoses recover completely with good supportive care.

Poor outcomes are usually related to:

• Respiratory arrest
• Aspiration
• Prolonged hypoxia
• Severe hypotension
• Seizures
• Multiple CNS depressants

Fatal poisoning can occur, including with carisoprodol alone, but the risk is markedly greater with:

• Opioids
• Benzodiazepines
• Alcohol

Important Pitfalls

1. Thinking carisoprodol is merely a “muscle relaxant”

Clinically it behaves as a:

Centrally acting sedative drug with an active sedative-hypnotic metabolite.

2. Ignoring meprobamate

Carisoprodol half-life:

~2 h

Meprobamate:

~10 h

Therefore, toxicity may persist after the parent drug has substantially declined.

3. Missing opioid coingestion

Carisoprodol is frequently encountered with other CNS depressants.

Respiratory depression should prompt consideration of:

Opioid coexposure → naloxone when appropriate

while simultaneously supporting ventilation.

4. Assuming all toxicity is simple sedation

High-dose carisoprodol may instead produce:

• Myoclonus
• Tremor
• Agitation
• Abnormal movements
• Delirium
• Serotonergic features

5. Giving flumazenil routinely

Despite an isolated successful case report:

Flumazenil is not an established carisoprodol antidote and is not routinely recommended.

6. Performing routine gastric lavage

Current labeling favors:

Selected activated charcoal in an early large overdose with an intact airway

rather than routine gastric lavage.

7. Giving charcoal to a sedated patient

Carisoprodol can rapidly impair airway reflexes.

Airway protection takes priority over decontamination.

8. Forgetting combination formulations

A preparation may contain:

• Aspirin
• Codeine

An unexplained:

• Acidosis
• Tinnitus
• Tachypnea

should prompt evaluation for salicylate toxicity.

Respiratory depression/miosis should prompt evaluation for opioid toxicity.

9. Missing dependence and withdrawal

Abrupt cessation after prolonged high-dose use can cause:

Tremor + insomnia + hallucinations + psychosis

and should not be mistaken automatically for a new psychiatric disorder.

10. Assuming dialysis is standard treatment

Carisoprodol is technically dialyzable, but:

Most overdoses are managed with supportive care.

Extracorporeal removal is reserved for exceptional severe cases after specialist consultation.

High-Yield Toxicology Pearls

Carisoprodol overdose = sedative toxicity with a long-acting meprobamate metabolite

Think:

Ataxia + drowsiness → coma + respiratory depression ± hypotension

but remember that the parent drug can also produce:

Agitation + tremor/myoclonus + abnormal movements

Key points:

• Carisoprodol is a centrally acting muscle relaxant
• U.S. Schedule IV
• Current adult dose: 250–350 mg TID + bedtime
• Therapeutic use should be limited to 2–3 weeks
• Safety/efficacy are not established below age 16
• Metabolism:
• 
  
• CYP2C19 → meprobamate
• Half-life:
• 
  
• Carisoprodol ~2 h
• Meprobamate ~10 h
• Poor CYP2C19 metabolizers can have substantially increased parent-drug exposure
• Major toxicity:
• 
  
• CNS depression
• Respiratory depression
• Coma
• Hypotension
• Seizures
• Carisoprodol itself may cause:
• 
  
• Agitation
• Myoclonus
• Rigidity/dystonia
• Serotonergic features
• Major overdose danger:
• 
  
• Opioids
• Benzodiazepines
• Alcohol
• Main treatment:
• 
  
• Airway + ventilation + supportive care
• Naloxone treats an opioid coingestion, not carisoprodol itself
• Do not induce vomiting
• Activated charcoal only for selected early, large exposures with an intact/protected airway
• Routine gastric lavage is obsolete
• Seizures → benzodiazepines
• Recurrent seizures → phenobarbital
• No specific antidote
• Do not routinely use flumazenil
• Persistent hypotension → fluids when appropriate + norepinephrine
• Forced diuresis is not recommended
• Carisoprodol/meprobamate are dialyzable, but hemodialysis is not routine
• Chronic use can cause dependence and significant withdrawal
• Withdrawal may cause:
• 
  
• Insomnia
• Tremor
• Muscle twitching
• Hallucinations
• Psychosis
• Most patients recover completely if respiratory failure and hypoxia are prevented

Toxicology – Carbon Monoxide

Core concept

Carbon monoxide (CO) is a colorless, odorless, tasteless gas produced by incomplete combustion of carbon-containing fuels.

The classic poisoning syndrome is:

Headache + dizziness + nausea → confusion/syncope → coma/seizures/cardiac ischemia

The organs most vulnerable are the:

Brain + heart

because of their high oxygen requirements.

The key management principle is:

Suspected CO poisoning → immediately give 100% oxygen

Do not wait for the carboxyhemoglobin (COHb) result.

Severe poisoning may warrant hyperbaric oxygen therapy (HBOT), but the evidence for HBOT preventing long-term neurocognitive injury remains mixed. The 2025 ACEP clinical policy concludes that selected symptomatic patients may benefit, with the decision individualized according to severity and practical availability.

Sources of Carbon Monoxide

CO is generated whenever carbon-containing fuel burns incompletely.

Common sources include:

• Portable generators
• Faulty furnaces
• Gas or oil heaters
• Water heaters
• Fireplaces
• Charcoal grills
• Propane stoves
• Gasoline-powered tools
• Cars/trucks
• Internal-combustion engines
• Boats
• Structure fires

Running combustion engines or generators in enclosed or poorly ventilated spaces can rapidly generate lethal concentrations.

Important Noncombustion Source – Methylene Chloride

Methylene chloride (dichloromethane) is metabolized in the liver to carbon monoxide.

It has historically been present in:

• Paint removers
• Industrial solvents
• Degreasers

This exposure is distinctive because:

Methylene chloride → continued hepatic metabolism → continued CO production even after exposure ends

Therefore:

COHb may continue rising or rebound for hours after the patient leaves the exposure.

These patients may require more prolonged oxygen therapy and observation than ordinary combustion-related CO exposures.

Epidemiology

The older estimate of up to 8,000 U.S. deaths annually is not representative of current accidental non-fire CO epidemiology.

Current CDC information reports that each year in the United States:

• >400 people die from unintentional non-fire CO poisoning
• >100,000 ED visits occur
• >14,000 hospitalizations occur

CO remains an important and highly preventable toxicologic emergency.

Pathophysiology

CO poisoning is much more than simply “low blood oxygen.”

1. Carboxyhemoglobin Formation

CO binds hemoglobin with approximately 200-fold greater affinity than oxygen.

This produces:

CO + hemoglobin → carboxyhemoglobin

leading to:

↓ available hemoglobin for O₂ transport

2. Left Shift of the Oxyhemoglobin Dissociation Curve

CO also increases the oxygen affinity of the remaining unoccupied hemoglobin sites.

Therefore:

COHb formation + left shift → impaired O₂ carriage + impaired O₂ unloading

So even the oxygen still bound to hemoglobin is released less effectively to tissue.

3. Myoglobin Binding

CO binds cardiac and skeletal-muscle myoglobin.

This contributes to:

• Myocardial dysfunction
• Reduced cardiac oxygen reserve
• Skeletal muscle injury

4. Mitochondrial Toxicity

CO binds heme-containing mitochondrial proteins, including cytochrome systems.

Therefore:

CO → impaired mitochondrial respiration → cellular oxygen-utilization failure

This partly explains why clinical toxicity may be much worse than predicted by COHb alone.

5. Oxidative and Inflammatory Injury

CO also initiates:

• Nitric oxide–related injury
• Free-radical formation
• Lipid peroxidation
• Endothelial dysfunction
• Apoptosis
• Immune-mediated inflammation

These mechanisms are thought to contribute particularly to delayed neurologic injury. The current ACEP policy emphasizes that CO poisoning produces both hypoxic and inflammatory/immunologic cellular damage.

6. Anaerobic Metabolism

Severe tissue hypoxia causes:

Anaerobic glycolysis → lactate elevation → metabolic acidosis

A high lactate supports severe physiologic stress but does not correlate perfectly with COHb.

Risk Groups

Patients particularly vulnerable to CO include:

• Pregnant patients and fetuses
• Infants
• Young children
• Older adults
• Patients with coronary artery disease
• Patients with anemia
• Patients with significant respiratory disease

Patients with coronary disease may develop ischemia at CO exposures tolerated by otherwise healthy individuals.

Clinical Features

Symptoms depend on:

CO concentration × duration of exposure

plus the patient’s underlying physiology.

Importantly:

COHb concentration does not correlate reliably with symptom severity or outcome.

Mild–Moderate Poisoning

Common symptoms:

• Headache
• Dizziness
• Weakness
• Fatigue
• Nausea
• Vomiting
• Difficulty concentrating
• Lightheadedness
• Dyspnea
• Chest discomfort

A classic clue is:

Several people in the same building developing “flu-like” symptoms without fever.

Pets may also become ill.

Neurologic Toxicity

Progressive toxicity may cause:

• Confusion
• Impaired judgment
• Ataxia
• Syncope
• Altered consciousness
• Seizures
• Coma

Patients may be unable to recognize that they are being poisoned and therefore may fail to escape the environment.

Cardiovascular Toxicity

CO can cause:

• Sinus tachycardia
• Hypotension
• Dysrhythmias
• Myocardial ischemia
• Myocardial infarction
• Transient cardiomyopathy
• Cardiogenic shock
• Cardiac arrest

Cardiac injury may occur even in individuals without obstructive coronary disease.

In one major cohort of moderate/severe poisonings, myocardial injury occurred in approximately 37% and was associated with substantially higher long-term mortality.

Therefore:

Cardiac toxicity is not a secondary curiosity—it is a major prognostic feature.

Respiratory

Possible findings include:

• Tachypnea
• Dyspnea
• Hypoxemia from associated pulmonary disease
• Pulmonary edema

Severe exposures may also be complicated by:

• Aspiration
• Smoke-inhalation injury
• ARDS

CO itself generally causes tissue hypoxia rather than primary airway injury, so prominent airway burns or bronchospasm should prompt consideration of additional smoke toxicants.

Skin Findings

The classic:

“Cherry-red skin”

is not a useful clinical sign.

It is uncommon in living patients and is more often described in severe or postmortem cases.

Do not wait for it.

Musculoskeletal / Renal

Severe poisoning, particularly with prolonged coma, may cause:

• Muscle necrosis
• Elevated CK
• Rhabdomyolysis
• Myoglobinuria
• Acute kidney injury

Pressure injury from prolonged immobilization may coexist.

Diagnosis

Diagnosis is based on:

Compatible exposure + clinical syndrome + blood carboxyhemoglobin measurement

but treatment should begin before laboratory confirmation.

Carboxyhemoglobin Measurement

The preferred confirmatory test is:

Blood COHb measured by multiwavelength co-oximetry

Either:

• Venous blood
• or
• Arterial blood

may be used.

An arterial sample is not required solely to measure COHb.

Interpretation of COHb

CDC guidance states that:

• ≥2% in a nonsmoker
• >9% in a smoker

strongly supports CO exposure.

However:

COHb is an exposure marker—not a severity score.

A critically ill patient may have a relatively low measured COHb if:

• Exposure ended hours earlier
• EMS already administered oxygen
• The patient received oxygen before blood was drawn

Therefore:

Treat the patient, not the COHb number.

Smokers

Smokers may have chronically elevated baseline COHb.

Thus, a mild elevation must be interpreted in context.

The old statement that smokers routinely reach 12% should not be used as a universal “normal smoker value”; current CDC guidance instead considers >9% supportive of CO poisoning when the clinical context fits.

Conventional Pulse Oximetry – Major Pitfall

A normal SpO₂ does not exclude CO poisoning.

Standard two-wavelength pulse oximeters cannot reliably distinguish:

Oxyhemoglobin from carboxyhemoglobin

and may therefore display a falsely reassuring saturation such as:

SpO₂ 99%

in a significantly poisoned patient.

Therefore:

Normal pulse oximetry does not rule out carbon monoxide poisoning.

PaO₂ Can Also Be Normal

Another important pitfall:

Arterial PaO₂ measures dissolved oxygen in plasma.

It does not tell you how much hemoglobin is occupied by CO.

Therefore a patient can have:

Normal PaO₂ + dangerous COHb + severe tissue hypoxia

A standard ABG alone does not diagnose CO poisoning unless co-oximetry is performed.

Pulse CO-Oximetry

Noninvasive devices can estimate COHb as SpCO.

However, ACEP has recommended that:

Pulse CO-oximetry should not be used to definitively diagnose or exclude CO toxicity.

Blood co-oximetry remains the confirmatory method.

Essential Investigations

For clinically significant poisoning obtain:

• Blood COHb by co-oximetry
• Bedside glucose
• Electrolytes
• Bicarbonate
• BUN/creatinine
• ECG

In moderate/severe poisoning also consider:

• Troponin
• Lactate
• Blood gas
• CK
• Urinalysis

Cardiac Testing

For moderate or severe CO poisoning:

ECG + cardiac biomarkers are important.

ACEP specifically recommends ECG and cardiac biomarker testing to identify acute myocardial injury because cardiac injury predicts poorer outcome.

Consider echocardiography for:

• Shock
• Elevated troponin
• Significant ECG abnormalities
• Suspected cardiomyopathy

Lactate

Lactate may rise because of:

• Tissue hypoxia
• Seizures
• Shock
• Catecholamine response

A markedly elevated lactate in a patient with structure-fire smoke exposure should also raise concern for:

Concurrent cyanide poisoning

because fire victims can have both:

CO + cyanide toxicity

simultaneously.

Neuroimaging

CT or MRI is not required for every mild exposure.

Consider neuroimaging for:

• Persistent altered consciousness
• Focal neurologic findings
• Severe poisoning
• Alternative intracranial diagnosis

Possible abnormalities include:

• Globus pallidus injury
• Cerebral edema
• White-matter abnormalities

A normal scan does not exclude significant CO poisoning or future delayed neurologic sequelae.

Differential Diagnosis

Toxicologic

Consider:

• Cyanide
• Hydrogen sulfide
• Simple asphyxiants
• Opioids
• Sedative-hypnotics
• Ethanol
• Toxic alcohols
• Other smoke-inhalation toxins

Medical

Consider:

• Viral illness
• Hypoglycemia
• Stroke
• Intracranial hemorrhage
• Sepsis
• Migraine
• Acute coronary syndrome
• Seizure/postictal state

Treatment

1. Remove From Exposure

Immediately move the patient to uncontaminated air.

Rescuers must not enter a dangerous enclosed atmosphere without appropriate respiratory protection.

Also remember:

Multiple victims may still be in the same environment.

Emergency services should identify and eliminate the source.

2. Give 100% Oxygen Immediately

This is the fundamental treatment.

Administer:

100% oxygen by a tightly fitting non-rebreather mask

using sufficient flow to keep the reservoir inflated.

If intubated:

FiO₂ = 1.0

should initially be used.

CDC recommends 100% oxygen until symptoms resolve, commonly approximately 4–5 hours in uncomplicated cases, while performing serial neurologic examinations.

COHb Elimination

Approximate COHb half-life:

Room air

~5 hours

100% high-flow oxygen

~60–90 minutes

Hyperbaric oxygen

~20–30 minutes

The 2025 ACEP policy cites approximately 5 hours, 85 minutes, and 20 minutes, respectively.

Thus:

High-concentration oxygen dramatically accelerates CO elimination.

Oxygen and COPD

The older suggestion that COPD-associated CO₂ retention is a contraindication to 100% oxygen is misleading.

In clinically important CO poisoning:

Do not withhold high-concentration oxygen because the patient has COPD.

If hypercapnia is a concern:

• Monitor ventilation
• Obtain blood gas when needed
• Provide ventilatory support

The immediate threat from CO-mediated hypoxia outweighs theoretical concern about oxygen-induced hypercapnia.

Treatment Endpoint

Do not treat to a specific COHb concentration alone.

Continue oxygen until:

• Symptoms have resolved or clearly improved
• Neurologic examination is reassuring
• Cardiac/hemodynamic abnormalities are addressed
• Hyperbaric treatment is initiated when selected

A falling COHb does not necessarily mean cellular injury has resolved.

Hyperbaric Oxygen Therapy

HBOT provides oxygen at increased atmospheric pressure, producing:

• Faster COHb dissociation
• Very high dissolved plasma oxygen concentrations
• Improved tissue oxygen delivery
• Potential effects on inflammatory/oxidative pathways

However:

The long-term neurocognitive benefit remains controversial.

The 2025 ACEP clinical policy found no Level A or Level B recommendation supporting routine HBOT for all CO-poisoned adults.

Its Level C recommendation is:

Selected symptomatic patients may benefit from HBOT according to clinical severity and availability, including transport distance/time.

This is an important modernization of the older textbook’s relatively rigid HBO criteria.

When to Strongly Consider HBOT

Current CDC clinical guidance recommends considering HBOT when there is:

• COHb >25–30%
• Transient or prolonged loss of consciousness
• Significant neurologic impairment
• Abnormal neuropsychological testing
• Cardiac involvement
• Severe acidosis

and notes that HBOT may be appropriate at lower COHb concentrations when clinical severity warrants it.

Practical high-risk features

Urgent hyperbaric/toxicology consultation is particularly reasonable with:

• Coma
• Persistent altered consciousness
• Syncope attributable to CO
• Seizures
• Focal neurologic deficits
• Significant myocardial ischemia/injury
• Severe metabolic acidosis
• Hemodynamic instability after stabilization
• Severe exposure with persistent symptoms
• Pregnancy

Do Not Use COHb Alone to Decide HBOT

A patient can be critically poisoned with a modest COHb if:

• Oxygen was already administered
• Presentation was delayed

Conversely, an awake clinically well patient may have had a relatively high measured COHb.

Therefore:

HBOT decisions are primarily clinical—not based on one cutoff.

Timing of HBOT

When HBOT is selected, consultation and transfer should occur early.

Potential benefit is generally considered greatest when treatment is initiated during the early hours after poisoning, but exact protocols vary by hyperbaric center.

Do not delay:

• Airway management
• Hemodynamic stabilization
• High-flow oxygen

while arranging chamber therapy.

HBOT Regimen

There is no single universally mandated regimen.

Treatment centers commonly use oxygen at approximately:

2–3 atmospheres absolute (ATA)

with treatment duration and repeat sessions individualized by:

• Clinical severity
• Neurologic response
• Center protocol

The old fixed protocol of exactly 2.7 ATA for 30 minutes followed by 2.2 ATA for 90 minutes should not be treated as the universal contemporary standard.

HBOT Risks

Potential complications include:

• Middle-ear barotrauma
• Sinus barotrauma
• Claustrophobia
• Oxygen-induced seizure
• Pulmonary barotrauma
• Transport-related deterioration

The 2025 ACEP policy specifically emphasizes that the risks of transfer to a distant chamber and deterioration during transport must be incorporated into the decision.

Untreated pneumothorax

An untreated pneumothorax is a major/absolute contraindication to entering a hyperbaric chamber until treated.

Hemodynamic instability

The older blanket statement that hemodynamic instability is a contraindication is too simplistic.

Severe cardiac injury may itself favor HBOT consideration, but an unstable patient must be adequately stabilized and transported only when the chamber can safely support critical care.

Pregnancy

Pregnancy deserves special treatment because the fetus is at disproportionately high risk.

CO crosses the placenta.

Fetal hemoglobin:

• Has greater affinity for CO
• Accumulates CO more readily
• Eliminates CO more slowly

Fetal COHb may therefore exceed the maternal level, and fetal clearance may be several times slower.

Therefore:

A reassuring maternal COHb does not guarantee fetal safety.

HBOT in Pregnancy

CDC currently states that:

Hyperbaric oxygen is the treatment of choice in pregnant patients with CO poisoning, even when maternal poisoning appears less severe.

Thus pregnancy should prompt:

Early toxicology/hyperbaric consultation at a lower threshold than in a nonpregnant adult.

Consider:

• Obstetric consultation
• Fetal assessment/monitoring when gestationally appropriate

Do not rely on the old single cutoff of:

COHb >15%

as the only indication for HBOT in pregnancy.

Cardiac Toxicity Treatment

Treatment begins with:

• 100% oxygen
• Correction of shock
• Continuous ECG monitoring

Treat true acute coronary syndrome according to standard cardiac principles when appropriate.

However, recognize that CO may cause:

• Myocardial stunning
• Demand ischemia
• Direct myocardial toxicity

even without obstructive coronary disease.

Patients with myocardial injury deserve close follow-up because it is associated with increased long-term mortality.

Hypotension / Shock

Treat according to contemporary shock principles:

• Judicious isotonic crystalloid if fluid responsive
• Vasopressor therapy if hypotension persists

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

The historical preference for:

• Trendelenburg positioning
• Dopamine as the default first vasopressor

is outdated.

Seizures

Treat with:

Benzodiazepines first-line

Examples:

• Lorazepam
• Midazolam
• Diazepam

For refractory seizures, escalate according to standard status-epilepticus/toxicologic seizure management.

Maintain:

• 100% oxygen
• Adequate ventilation
• Glucose
• Temperature control

Rhabdomyolysis

If prolonged coma or seizures occur:

• Check CK
• Check renal function
• Monitor potassium
• Monitor urine output

Treat rhabdomyolysis according to standard principles.

Smoke-Inhalation Patients

A structure-fire victim may have several simultaneous toxicities:

CO + cyanide + airway thermal injury + pulmonary irritants

Do not assume that every abnormality is explained by CO.

Consider cyanide especially with:

• Enclosed-space fire
• Soot
• Severe altered consciousness
• Profound cardiovascular collapse
• Severe lactic acidosis

No Gastrointestinal Decontamination

Ordinary CO poisoning occurs by inhalation.

There is no role for:

• Activated charcoal
• Gastric lavage
• Whole-bowel irrigation

for CO itself.

GI decontamination is relevant only for a separate coingestant.

Antidote

The functional antidotal therapy is:

OXYGEN

at either:

• Normobaric pressure
• Hyperbaric pressure in selected patients

There is no conventional chemical antidote that binds and neutralizes CO in routine clinical use.

Delayed Neurologic Sequelae

This is one of the most important follow-up issues.

After apparent recovery, a patient may experience a lucid interval followed by new neurologic/psychiatric abnormalities.

Current ACEP material describes delayed neurologic findings developing approximately:

2–40 days after the original exposure.

Delayed Symptoms

Possible manifestations include:

• Memory impairment
• Poor concentration
• Personality change
• Depression
• Psychosis
• Apathy
• Cognitive decline
• Gait abnormality
• Tremor
• Parkinsonism
• Urinary incontinence
• Speech disturbance
• Seizures

The syndrome is sometimes termed:

Delayed neurologic sequelae (DNS)

or

Delayed neuropsychiatric syndrome

Who Is at Higher Risk of DNS?

Risk is greater after features such as:

• Older age
• Prolonged exposure
• Loss of consciousness
• Low GCS
• Significant cognitive impairment
• Higher initial COHb
• Abnormal brain imaging

but no available marker reliably predicts DNS in every patient.

Follow-Up

All discharged CO-poisoned patients should be told explicitly that neurologic or psychiatric symptoms can appear after apparent recovery.

CDC recommends:

Repeat medical and neurologic examination in approximately 2 weeks.

Earlier reassessment is warranted for:

• New confusion
• Memory problems
• Personality change
• Gait disturbance
• Tremor
• Urinary incontinence
• New weakness
• Seizure

Observation and Admission

Mild Poisoning

Patients with mild symptoms may be considered for discharge once:

• Exposure has ended
• Symptoms have resolved with oxygen
• Neurologic examination is normal
• Vital signs are stable
• No cardiac injury is identified
• The exposure source has been made safe

A specific COHb concentration alone should not determine discharge.

Hospital Admission

Admission is appropriate for:

• Persistent neurologic symptoms
• Loss of consciousness
• Seizures
• Significant cardiac injury
• Abnormal ECG/troponin
• Severe metabolic acidosis
• Persistent hypotension
• Pulmonary complications
• Significant rhabdomyolysis
• Need for continued oxygen/monitoring

Patients with severe poisoning generally require ICU-level care.

Pregnancy warrants a particularly low threshold for prolonged observation and specialty consultation.

Occupational Exposure Standards

The older occupational-standard section needs correction.

OSHA

Current federal OSHA PEL:

50 ppm as an 8-hour TWA

There is not a general OSHA 200-ppm ceiling in the standard general-industry PEL table.

NIOSH

Current NIOSH recommendations:

REL TWA: 35 ppm

Ceiling: 200 ppm

IDLH: 1,200 ppm

Therefore, the older source incorrectly attributes the 200-ppm ceiling to OSHA; it is the NIOSH ceiling recommendation.

ACGIH

Current occupational information cites:

ACGIH TLV-TWA: 25 ppm

Thus the older ACGIH 25-ppm TWA remains broadly consistent, whereas the OSHA ceiling statement does not.

Prevention

CO poisoning is highly preventable.

Important measures include:

• Install functioning CO detectors near sleeping areas
• Maintain furnaces/heaters
• Never use charcoal grills indoors
• Never operate portable generators indoors or in enclosed spaces
• Avoid running vehicles in attached or poorly ventilated garages
• Ensure combustion appliances are properly vented

CDC recommends battery-powered or battery-backup CO alarms and regular detector replacement according to manufacturer guidance.

A poisoned patient should not return to the exposure site until the CO source has been identified and corrected.

Important Pitfalls

1. Trusting the pulse oximeter

A patient with severe CO poisoning may show:

SpO₂ = 99%

because conventional pulse oximetry misidentifies COHb.

Use blood co-oximetry.

2. Trusting a normal PaO₂

PaO₂ measures dissolved plasma oxygen.

Normal PaO₂ does not exclude severe CO poisoning.

3. Treating the COHb number instead of the patient

COHb may already have fallen substantially before presentation.

Clinical features and exposure history matter more than a single level.

4. Waiting for a COHb result before giving oxygen

Start 100% oxygen immediately.

There is no benefit to delaying treatment for diagnostic confirmation.

5. Assuming smokers can “normally” have any high COHb

Smoking increases baseline COHb, but current CDC guidance regards:

>9% in a smoker

as strongly supportive of CO poisoning when clinically appropriate.

6. Missing myocardial injury

Obtain:

ECG + troponin

in moderate/severe poisoning.

Cardiac injury predicts important short- and long-term risk.

7. Using a rigid HBOT cutoff

Current practice does not support:

COHb ≥X% = HBO, <X% = no HBO

as an absolute rule.

The 2025 ACEP policy emphasizes selected symptomatic patients and individualized risk/availability considerations.

8. Claiming HBOT definitely prevents delayed neurologic sequelae

Evidence remains conflicting.

HBOT is an important option for selected severe poisoning, but a universal neuroprotective benefit has not been conclusively established.

9. Under-treating pregnancy

The fetus:

• Accumulates more CO
• Clears CO more slowly

Maternal improvement does not guarantee fetal recovery.

Pregnancy warrants aggressive oxygen therapy and early HBOT consultation.

10. Missing delayed neurologic disease

A patient may appear completely recovered and then deteriorate neurologically days to weeks later.

Warn every significant CO-poisoned patient before discharge.

11. Missing methylene chloride

Paint-stripper/solvent exposure may generate CO metabolically.

COHb can continue to rise after exposure ends.

12. Missing cyanide in fire victims

CO does not explain every case of:

• Profound shock
• Severe lactic acidosis
• Rapid collapse

after enclosed-space fire exposure.

Think:

CO + cyanide

13. Failing to identify the exposure source

Treating the patient without correcting:

• Faulty furnace
• Generator placement
• Vehicle exhaust
• Water heater problem

creates a major risk of repeat poisoning.

High-Yield Toxicology Pearls

Carbon monoxide = normal pulse oximeter does NOT mean normal oxygen delivery

Think:

Headache + nausea + dizziness + multiple people affected → CO until proven otherwise

Severe poisoning:

Syncope/coma + seizure + myocardial injury + acidosis

Key points:

• CO is colorless, odorless, and tasteless
• Produced by incomplete combustion
• Common sources:
• Generators
• Furnaces/heaters
• Vehicle exhaust
• Charcoal
• Structure fires
• Methylene chloride is metabolized to CO
• Main mechanism:
• COHb formation
• Left shift of O₂ dissociation curve
• Myoglobin binding
• Mitochondrial dysfunction
• Oxidative/inflammatory injury
• Brain and heart are the major target organs
• Normal SpO₂ does not exclude CO poisoning
• Normal PaO₂ does not exclude CO poisoning
• Confirm with blood co-oximetry
• Venous blood is acceptable
• COHb:
• ≥2% nonsmoker supports exposure
• >9% smoker supports exposure
• COHb correlates poorly with clinical severity
• First treatment:
• 100% oxygen immediately
• Approximate COHb half-life:
• Room air: ~5 h
• 100% O₂: ~60–90 min
• HBOT: ~20–30 min
• Do not withhold 100% O₂ because of COPD
• Moderate/severe poisoning:
• ECG + troponin
• Myocardial injury predicts poorer long-term outcome
• HBOT should be considered particularly for:
• Loss of consciousness
• Significant neurologic toxicity
• Cardiac injury
• Severe acidosis
• COHb approximately >25–30%
• Pregnancy
• HBOT evidence remains controversial
• 2025 ACEP:
• Selected symptomatic patients may benefit
• Consider severity + availability/transport
• Pregnancy:
• Fetal COHb may exceed maternal COHb
• Fetal elimination is much slower
• Early HBOT consultation is recommended
• Fire victim with severe lactic acidosis/shock → consider cyanide co-poisoning
• Delayed neurologic sequelae may appear approximately 2–40 days later
• Arrange neurologic follow-up; CDC suggests reassessment at about 2 weeks
• NIOSH:
• 35 ppm TWA
• 200 ppm ceiling
• 1,200 ppm IDLH
• OSHA:
• 50 ppm 8-hour TWA
• Prevention and elimination of the exposure source are essential

Toxicology – Carbon Disulfide

Core concept

Carbon disulfide (CS₂) is a highly volatile, extremely flammable industrial solvent that can cause acute CNS/respiratory toxicity and chronic neurovascular disease.

The characteristic syndromes are:

Acute high-dose exposure → headache/dizziness → intoxication → agitation or CNS depression → seizures/coma ± respiratory failure

and:

Chronic occupational exposure → distal sensorimotor polyneuropathy + neurobehavioral/CNS effects + cardiovascular disease ± retinal microvascular injury

The most important intervention is:

Immediate removal from exposure + supportive airway/ventilatory care

There is no proven specific antidote.

Physical Properties

Carbon disulfide is:

• Chemical formula: CS₂
• Colorless to faint-yellow liquid
• Highly volatile
• Poorly water soluble
• Lipophilic
• Extremely flammable

Pure CS₂ may have a sweet, ether-like odor, while technical-grade material can smell unpleasant because of sulfur contaminants.

Important physical properties include:

• Boiling point: approximately 46°C / 116°F
• Flash point: approximately −30°C / −22°F
• Lower explosive limit: approximately 1.3%
• Upper explosive limit: approximately 50%

Major safety point

Fire and explosion risk are major hazards.

Carbon disulfide vapors can ignite extremely easily, potentially even from relatively low-energy ignition sources.

Forms and Uses

Current and historical industrial uses include:

• Viscose rayon manufacture
• Cellophane production
• Rubber processing
• Dyes
• Pesticide-related manufacture
• Industrial solvents
• Chemical synthesis
• Cleaning/degreasing applications

Historically, large occupational cohorts were exposed in the viscose rayon industry, which forms much of the evidence base for chronic carbon disulfide toxicity.

Routes of Exposure

Important routes are:

• Inhalation
• Dermal absorption
• Ingestion
• Eye contact

NIOSH specifically assigns carbon disulfide a skin notation, meaning clinically meaningful systemic absorption can occur through skin exposure.

In occupational settings, inhalation is usually the most important route.

Toxic Dose / Concentration

There is no single reliable toxic concentration because toxicity depends strongly on:

Air concentration × duration of exposure

as well as:

• Ventilation
• Workload
• Dermal absorption
• Individual susceptibility
• Coexposures

Acute inhalation

Historical human data suggest:

• Several hundred ppm can produce obvious acute neurologic symptoms
• Around 420–510 ppm has produced symptoms within 30 minutes
• Approximately 1,100 ppm can cause severe symptoms/unconsciousness
• Around 4,800–5,000 ppm for approximately 30–60 minutes has been associated with coma and death

Thus, the older statement:

“4,800 ppm for 1 hour is fatal”

should be understood as a historical observation, not a fixed threshold.

IDLH

Current NIOSH:

IDLH = 500 ppm

Pathophysiology

Carbon disulfide has several toxic mechanisms rather than one single established pathway.

Acute CNS Toxicity

Because carbon disulfide is:

• Highly volatile
• Lipophilic
• Rapidly absorbed

high concentrations readily affect the CNS.

Acute exposure can produce a solvent-like syndrome:

CNS excitation/intoxication → CNS depression → coma

High-dose exposure can also produce:

• Respiratory compromise
• Seizures
• Paralysis

Chronic Neurotoxicity

The best-supported mechanism for chronic peripheral neuropathy involves:

CS₂ → dithiocarbamate protein adducts → protein cross-linking → neurofilament aggregation → impaired axonal transport → distal axonal degeneration

This produces a neurofilamentous distal axonopathy resembling that caused by n-hexane.

Additional proposed mechanisms include:

• Metal chelation
• Abnormal vitamin B6 metabolism
• Oxidative stress

Dopaminergic Effects

Carbon disulfide metabolites may interfere with catecholamine metabolism, including inhibition of:

Dopamine β-hydroxylase

which converts:

Dopamine → norepinephrine

This may contribute to some CNS and movement abnormalities.

Cardiovascular Toxicity

Chronic carbon disulfide exposure has been associated with:

• Coronary artery disease
• Atherosclerotic cardiovascular disease
• Elevated cardiovascular mortality in heavily exposed historical cohorts
• Possible lipid abnormalities

The 2025 ATSDR systematic review found moderate human evidence of cardiovascular effects from inhalational exposure.

Thus, the older concept that carbon disulfide causes vascular injury remains broadly valid, although the mechanism is more complex than simple direct endothelial toxicity.

Clinical Features

Acute Exposure

Mild–Moderate Exposure

Possible manifestations include:

• Headache
• Dizziness
• Lightheadedness
• Fatigue
• Weakness
• Nausea
• Vomiting
• Eye/nasal irritation
• Cough
• Dyspnea

Patients may appear:

• Euphoric
• Disinhibited
• Confused
• “Intoxicated”

similar to other volatile-solvent exposures.

Severe Acute Neurotoxicity

With increasing exposure:

• Agitation
• Delirium
• Psychosis
• Ataxia
• Tremor
• CNS depression
• Seizures
• Paralysis
• Coma

may occur.

Profound exposure can result in:

• Respiratory depression
• Hypoxia
• Cardiovascular collapse
• Death

Respiratory

Acute inhalation may cause:

• Cough
• Dyspnea
• Bronchospasm
• Wheezing
• Hypoxemia

Transient reductions in:

• Vital capacity
• Arterial oxygenation

have been documented after accidental inhalational exposures.

Severe respiratory compromise may require mechanical ventilation.

HEENT / Ocular

Acute exposure can cause:

• Lacrimation
• Conjunctival irritation
• Nasal irritation
• Throat irritation

Chronic exposure has been associated with retinal microvascular abnormalities and other ophthalmologic effects.

The 2025 ATSDR systematic review found moderate human evidence for ophthalmologic effects from chronic inhalational exposure.

Dermatologic

Liquid carbon disulfide can cause:

• Skin irritation
• Dermatitis
• Chemical injury after prolonged contact

More importantly:

Carbon disulfide can be systemically absorbed through skin.

Therefore, dermal contamination should not be treated as merely a local irritant exposure.

Gastrointestinal

Acute exposure may produce:

• Nausea
• Vomiting
• Abdominal discomfort

Chronic exposure has historically been associated with gastritis, although gastrointestinal findings are much less specific than neurologic and cardiovascular effects.

Cardiovascular

Acute high-level exposure may cause:

• Tachycardia
• Hypotension
• Cardiovascular instability

Chronic exposure is more clinically important and has been associated with:

• Atherosclerotic disease
• Coronary heart disease
• Possible hypertension
• Altered lipid homeostasis

Historical occupational cohorts found increased coronary mortality in heavily exposed workers.

Chronic Neurotoxicity

Peripheral Neuropathy

A major chronic manifestation is:

Distal symmetric sensorimotor polyneuropathy

Symptoms include:

• Paresthesias
• Distal numbness
• Burning sensations
• Muscle weakness
• Leg pain
• Gait difficulty
• Reduced reflexes

Nerve-conduction studies may show:

• Slowed conduction
• Axonal dysfunction
• Mixed axonal/demyelinating features

CNS / Neurobehavioral Effects

Chronic exposure may also produce:

• Irritability
• Mood disturbance
• Poor concentration
• Memory impairment
• Psychomotor slowing
• Tremor
• Encephalopathy
• Cerebellar dysfunction

Severe historical exposure has been associated with:

Parkinsonian or Parkinson-like movement abnormalities

ATSDR’s 2025 systematic review considers neurologic toxicity a known human health effect of carbon disulfide inhalation.

Renal and Hepatic Effects

Kidney and liver injury have been reported after substantial exposure.

Possible abnormalities include:

• Increased creatinine
• Proteinuria
• Abnormal liver enzymes

However, these are less characteristic than:

• CNS toxicity acutely
• Neurovascular toxicity chronically

NIOSH lists both the kidneys and liver among potential target organs.

Reproductive and Developmental Toxicity

The older claim that human surveillance definitively demonstrates increased congenital malformations is too strong.

Current ATSDR assessment is more cautious.

Male reproductive effects

Carbon disulfide is considered a suspected male reproductive toxicant based on:

• Inadequate human evidence
• Moderate animal evidence

Reported occupational effects have included:

• Reduced libido
• Erectile dysfunction
• Inconsistent sperm abnormalities

Female pregnancy outcomes

Human evidence for:

• Miscarriage
• Stillbirth
• Prematurity
• Congenital malformations

is inconsistent or inadequate.

Animal studies provide stronger evidence for developmental toxicity than the available human data.

Therefore:

Avoid unnecessary occupational carbon disulfide exposure during pregnancy, but do not state that congenital malformations are proven human effects.

Carcinogenicity

The older statement:

“Carbon disulfide is not carcinogenic.”

is too definitive.

Current OSHA chemical information lists the ACGIH classification as:

A4 — Not classifiable as a human carcinogen

This means:

Insufficient evidence to classify

—not proof that the substance cannot cause cancer.

An IARC advisory report noted that carbon disulfide had not previously undergone a formal IARC Monographs evaluation.

So the clinically appropriate wording is:

Carbon disulfide is not currently established as a human carcinogen; available evidence is insufficient for a definitive carcinogenic classification.

Diagnosis

Diagnosis depends heavily on the exposure history.

Ask about:

• Occupation
• Viscose/rayon work
• Rubber manufacturing
• Chemical production
• Solvent use
• Confined spaces
• Ventilation
• PPE
• Skin contact
• Duration and estimated concentration
• Whether coworkers are symptomatic

The combination of:

Industrial exposure + intoxication/CNS symptoms

suggests acute poisoning.

The combination of:

Long-term occupational exposure + distal neuropathy/neurobehavioral changes

should raise suspicion for chronic toxicity.

Differential Diagnosis

Acute altered mental status

Consider:

• Carbon monoxide
• Hydrogen sulfide
• Cyanide
• Organic solvent intoxication
• Asphyxiant gases
• Toxic alcohols
• Alcohol/sedative intoxication
• Hypoglycemia
• CNS infection
• Stroke

Chronic neuropathy

Consider:

• n-Hexane
• Lead
• Arsenic
• Thallium
• Mercury
• Diabetes
• Vitamin B12 deficiency
• Alcohol-associated neuropathy
• Hereditary neuropathy

Investigations

Acute Exposure

Testing should be guided by severity.

Consider:

• CBC
• Electrolytes
• Glucose
• BUN/creatinine
• Liver tests
• Blood gas
• Lactate
• Urinalysis

In severe exposure:

• Troponin
• Coagulation studies
• CK when seizures/immobility occur

A recent clinical review recommends organ-directed testing for pulmonary, cardiovascular, renal, and neurologic complications rather than relying on a specific CS₂ blood concentration.

ECG

Obtain an ECG in:

• Significant acute exposure
• Syncope
• Chest pain
• Hypotension
• Severe neurologic toxicity

Continuous monitoring is appropriate for critically ill patients.

Respiratory Assessment

For respiratory symptoms:

• Pulse oximetry
• Serial respiratory examination

Consider:

• Blood gas
• Chest radiograph

for:

• Hypoxemia
• Persistent cough
• Significant dyspnea
• Suspected aspiration/pneumonitis

Chronic Neurologic Evaluation

Depending on symptoms, consider:

• Detailed neurologic examination
• Electromyography
• Nerve conduction studies
• Neuropsychological testing

Nerve-conduction abnormalities can persist long after major exposure.

Biomonitoring

Urinary TTCA

The principal occupational biomarker is:

2-thiothiazolidine-4-carboxylic acid (TTCA)

measured in urine.

TTCA generally reflects recent carbon disulfide exposure and is typically obtained at the end of the work shift.

A 2024 NIOSH occupational report cites the current ACGIH biological exposure index:

Urinary TTCA = 0.5 mg/g creatinine at the end of shift

Important limitations

TTCA:

• Is an exposure biomarker, not a severity marker
• Does not directly diagnose acute poisoning
• Can have background contributions from nonoccupational sources
• Is less useful at very low-level exposure

Therefore:

Do not delay emergency treatment while waiting for TTCA.

Blood Carbon Disulfide

Blood or exhaled carbon disulfide measurement may be possible in specialized settings.

However:

• It is rapidly cleared
• Testing is not widely available
• Concentrations correlate poorly with clinical severity in routine practice

Thus, blood levels are generally not clinically useful for emergency treatment decisions.

Treatment

1. Rescuer Safety

Because carbon disulfide is:

Extremely flammable + volatile

rescuers should avoid:

• Sparks
• Flames
• Smoking
• Unprotected entry into confined or heavily contaminated spaces

Unknown/high-concentration environments require appropriate supplied-air respiratory protection.

NIOSH recommends positive-pressure SCBA or equivalent protection for IDLH conditions.

2. Remove From Exposure

For inhalation:

Move immediately to fresh air.

Terminate further occupational exposure.

Do not permit an unprotected rescuer to enter a contaminated confined space.

3. Airway and Breathing

Provide:

• Oxygen for hypoxemia
• Ventilatory support when needed

Intubate for:

• Severe CNS depression
• Inability to protect airway
• Respiratory failure
• Recurrent seizures

There is no role for a specific antidote in reversing CNS depression.

4. Bronchospasm

Treat bronchospasm with:

Inhaled β₂-agonist bronchodilator

such as:

• Albuterol/salbutamol

Other asthma-directed treatment may be used according to the clinical syndrome.

Routine corticosteroids are not established as a carbon-disulfide-specific antidotal treatment.

5. Dermal Decontamination

For liquid contamination:

• Remove contaminated clothing promptly
• Prevent ignition
• Wash exposed skin thoroughly with soap and water

NIOSH specifically recommends immediate soap washing.

Because CS₂ can be absorbed through skin, prompt removal is important.

6. Eye Exposure

Immediately irrigate exposed eyes with:

• Copious water
• Saline if available

Continue irrigation for at least approximately:

15 minutes

and reassess.

Persistent:

• Pain
• Redness
• Visual disturbance

requires further ocular evaluation.

NIOSH recommends immediate eye irrigation.

7. Ingestion

Do not induce vomiting.

Carbon disulfide is:

• Volatile
• CNS depressant at high doses

so vomiting can increase aspiration risk.

Rinse the mouth.

If the patient is awake and can swallow normally, limited oral dilution may be considered, but airway status takes priority.

Activated Charcoal

Older references recommend routine charcoal.

Modern general toxicology principles are more selective:

Activated charcoal should not be given routinely to every poisoned patient.

It can be considered after a recent potentially dangerous ingestion if:

• The substance is likely still in the GI tract
• The patient has an intact/protected airway
• Aspiration risk is acceptable

Because carbon disulfide itself may produce rapid neurologic deterioration, the risk-benefit balance should be individualized with poison-center/toxicology consultation.

Gastric Lavage

The older recommendation for routine nasogastric aspiration or lavage after ingestion is not contemporary routine practice.

Gastric lavage should only exceptionally be considered after:

• An immediately life-threatening ingestion
• Very early presentation
• Protected airway

and only after specialist toxicology input.

Routine lavage is not justified.

Antidote

There is no proven specific antidote for carbon disulfide poisoning.

Historical suggestions such as intravenous urea have no established clinical efficacy and should not be used routinely.

Seizures

First-line:

Benzodiazepines

Examples:

• Lorazepam
• Midazolam
• Diazepam

If refractory:

• Phenobarbital
• Propofol in an intubated patient

may be considered according to standard toxicologic seizure management.

Also correct:

• Hypoxia
• Hypoglycemia
• Electrolyte abnormalities

Hypotension

Treat according to contemporary shock principles:

• Isotonic crystalloid when fluid responsive
• Vasopressor for persistent shock

Norepinephrine is generally an appropriate first-line vasopressor for persistent hypotension.

The old preference for dopamine and Trendelenburg positioning is outdated.

Enhanced Elimination

There is no established role for:

• Hemodialysis
• Hemoperfusion
• Forced diuresis

as routine toxin-removal therapies.

Carbon disulfide rapidly distributes and is metabolized; management is principally supportive.

Dialysis should be used only if a conventional indication develops from organ failure.

Chronic Toxicity – Management

The most important intervention is:

Stop further exposure

Occupational-health involvement is essential.

Management may include:

• Neurology review
• Nerve conduction testing
• Cardiovascular risk assessment
• Blood pressure monitoring
• Lipid profile
• Ophthalmologic evaluation when indicated
• Renal assessment
• Workplace exposure investigation

Engineering controls and respiratory/skin protection are more important than pharmacologic treatment.

Recovery From Neuropathy

The older text states that neuropathy and encephalopathy do not improve after exposure cessation.

That is too absolute.

Recovery varies according to exposure intensity.

Lower-level nerve conduction abnormalities may improve after removal from exposure, while severe poisoning can leave abnormalities for years.

Therefore:

Mild/subclinical neuropathy may be reversible; severe axonal injury may be prolonged or incomplete.

Occupational Exposure Standards

The older ACGIH limit of 10 ppm is outdated.

NIOSH REL

Current NIOSH:

TWA = 1 ppm (3 mg/m³)

STEL = 10 ppm (30 mg/m³)

with a skin notation.

NIOSH IDLH

500 ppm

OSHA

Current federal OSHA general-industry limits remain:

TWA = 20 ppm

Ceiling = 30 ppm

Maximum peak = 100 ppm for 30 minutes

Important

The OSHA limit is substantially less protective than the current NIOSH recommended exposure limit.

Current ACGIH Information

A recent NIOSH occupational-health evaluation cites:

ACGIH TLV-TWA = 1 ppm

with:

Urinary TTCA BEI = 0.5 mg/g creatinine at end of shift

Thus, the historical 10-ppm ACGIH TLV should no longer be used.

Pregnancy

Human reproductive data are limited and inconsistent.

Current evidence does not justify saying that carbon disulfide definitively causes human birth defects.

ATSDR’s current assessment is:

• Human developmental evidence: inadequate
• Animal developmental evidence: moderate
• Developmental toxicity remains a suspected hazard

Pregnant workers should minimize exposure according to occupational-health guidance.

For acute maternal poisoning:

Maternal airway, oxygenation, and circulation take priority.

Monitoring

Acute Exposure

Symptomatic patients may require:

• Continuous pulse oximetry
• Cardiac monitoring
• Serial neurologic examinations
• Blood pressure monitoring

Repeat laboratory testing according to:

• Respiratory compromise
• Renal injury
• Hepatic injury
• Shock
• Seizures

Admission

Hospital admission is appropriate for:

• Persistent CNS depression
• Significant confusion
• Seizure
• Hypoxemia
• Bronchospasm not rapidly resolving
• Respiratory distress
• Hypotension
• Significant ingestion
• Evidence of organ injury

Patients with:

• Coma
• Respiratory failure
• Recurrent seizures
• Hemodynamic instability

require ICU-level care.

Observation / Disposition

The historical fixed:

“4–6 hours then discharge”

should not be applied automatically.

A brief, mild inhalational exposure may permit discharge after an appropriate symptom-free observation period when:

• Neurologic examination is normal
• Oxygenation is normal
• Vital signs are stable
• No significant ingestion occurred
• No important coexposure exists

Higher-concentration, intentional, confined-space, or symptomatic exposures warrant longer observation.

Prognosis

Acute Exposure

Patients with mild acute exposure generally recover after removal from the source.

Severe exposure can lead to:

• Coma
• Respiratory failure
• Hypoxic brain injury
• Death

Long-term outcome depends largely on:

• Exposure magnitude
• Duration
• Severity of neurologic injury
• Hypoxic complications

Chronic Exposure

Persistent sequelae may include:

• Peripheral neuropathy
• Cognitive/neurobehavioral impairment
• Parkinson-like abnormalities
• Retinal vascular changes
• Cardiovascular disease

Neurologic recovery can be:

• Complete
• Partial
• Very prolonged

depending on severity.

Important Pitfalls

1. Calling carbon disulfide a gas

At ordinary room temperature:

CS₂ is a highly volatile liquid that readily generates toxic vapor.

2. Ignoring skin absorption

NIOSH assigns a skin notation.

Dermal contamination can add materially to systemic exposure.

3. Forgetting the fire/explosion hazard

Carbon disulfide has an exceptionally low flash point.

Eliminate ignition sources before decontamination/rescue.

4. Relying on odor

The smell is not a safe exposure monitor.

Industrial grades can smell different, and dangerous exposure should be assessed by environmental monitoring rather than odor perception.

5. Treating TTCA as a diagnostic toxin level

TTCA measures recent exposure, not clinical poisoning severity.

Current ACGIH BEI:

0.5 mg/g creatinine at end of shift

6. Using the old ACGIH 10-ppm limit

Current ACGIH/NIOSH guidance is much lower:

1 ppm TWA

7. Calling carbon disulfide definitively noncarcinogenic

ACGIH currently classifies it:

A4 — not classifiable as a human carcinogen

which is not equivalent to proven absence of carcinogenicity.

8. Missing chronic neuropathy

A patient with:

• Distal paresthesias
• Weakness
• Reduced reflexes
• Gait difficulty

who works in rayon/rubber/chemical production should prompt an occupational-exposure history.

9. Assuming chronic neuropathy never improves

Some lower-level effects are reversible after exposure cessation, while severe axonal injury may persist for years.

10. Overstating pregnancy risk

Older reports suggested congenital anomalies, but current human evidence is insufficient to establish a causal developmental effect.

Animal evidence remains concerning.

High-Yield Toxicology Pearls

Carbon disulfide = acute solvent neurotoxicity + chronic neurovascular toxicity

Think:

Industrial worker + headache/dizziness/intoxication → severe exposure can cause seizure/coma

and:

Long-term rayon/industrial exposure + distal neuropathy ± neurobehavioral/cardiovascular disease

Key points:

• Carbon disulfide is CS₂
• It is a highly volatile liquid, not simply a gas
• Extremely flammable/explosive
• Major route: inhalation
• Significant dermal absorption also occurs
• Acute toxicity:
• Headache
• Dizziness
• Nausea
• Intoxication/confusion
• Bronchospasm
• CNS depression
• Seizures
• Coma
• Chronic hallmark: distal sensorimotor polyneuropathy
• Chronic neurotoxicity involves neurofilament protein cross-linking and axonal degeneration
• Parkinson-like and neurobehavioral effects may occur
• Chronic exposure is associated with cardiovascular disease
• TTCA is the main urinary exposure biomarker
• Current ACGIH TTCA BEI: 0.5 mg/g creatinine at end of shift
• TTCA indicates exposure, not poisoning severity
• No specific antidote
• Main acute treatment:
• Remove from exposure
• Oxygen/ventilation as needed
• Benzodiazepines for seizures
• Supportive hemodynamic care
• Remove contaminated clothing
• Wash skin promptly with soap and water
• Irrigate eyes immediately
• Do not induce vomiting
• Activated charcoal is selective, not routine
• Routine gastric lavage is obsolete
• No established role for hemodialysis to remove CS₂
• NIOSH REL:
• 1 ppm TWA
• 10 ppm STEL
• NIOSH IDLH: 500 ppm
• OSHA PEL remains:
• 20 ppm TWA
• 30 ppm ceiling
• 100 ppm for 30-min maximum peak
• ACGIH classification: A4, not classifiable as a human carcinogen
• Chronic neurologic effects may improve after exposure cessation, but severe neuropathy can persist for years

Toxicology – Carbamazepine

Core concept

Carbamazepine is a sodium-channel–blocking antiseizure medication with anticholinergic properties that can cause prolonged and delayed toxicity after overdose.

The characteristic syndrome is:

Nystagmus + ataxia + CNS depression → coma/seizures ± QRS widening, hypotension, and dysrhythmias

A particularly important feature is:

Delayed or recurrent toxicity despite initial improvement

because carbamazepine can:

• Slow gastrointestinal motility
• Form pharmacobezoars/tablet concretions
• Undergo prolonged absorption
• Undergo enterohepatic/enteroenteric recirculation

Peak concentrations after large overdose may be delayed for up to 72 hours.

Forms and Uses

Carbamazepine is available as:

• Immediate-release tablets
• Chewable tablets
• Oral suspension
• Extended-release tablets/capsules

Common indications include:

• Focal epilepsy
• Generalized tonic-clonic seizures in selected patients
• Trigeminal neuralgia
• Bipolar disorder

Common brands have included:

• Tegretol
• Carbatrol
• Equetro
• Epitol

Extended-release preparations are particularly important in overdose because toxicity can be delayed and prolonged.

Toxic Dose

There is no completely reliable dose threshold.

Large adult ingestions of several grams can cause serious poisoning, while smaller amounts can produce significant effects in children.

Clinical severity depends on:

• Dose
• Formulation
• Chronic carbamazepine use
• Age
• Coingestants
• Hepatic metabolism
• Drug interactions

Therefore:

Serum concentration + clinical condition + ECG are more useful than dose alone.

Pathophysiology

Sodium-Channel Blockade

Carbamazepine stabilizes voltage-gated sodium channels in the inactive state.

At therapeutic concentrations this limits repetitive neuronal firing.

In overdose:

Excess sodium-channel blockade → neuronal dysfunction + myocardial conduction slowing

resulting in:

• Ataxia
• Nystagmus
• CNS depression
• Paradoxical seizures
• QRS widening
• Myocardial depression

Antimuscarinic Effects

Carbamazepine also has clinically relevant anticholinergic effects.

These may cause:

• Tachycardia
• Dilated pupils
• Dry mucosa
• Reduced bowel motility
• Ileus
• Urinary retention
• Delirium

Reduced intestinal motility contributes to delayed absorption and recurrent toxicity.

Active Metabolite

Carbamazepine is metabolized mainly by CYP3A4 to:

Carbamazepine-10,11-epoxide

which is pharmacologically active and can contribute to toxicity.

Valproate can inhibit metabolism of the epoxide metabolite and increase its concentration.

Drug Interactions

Drugs that can increase carbamazepine concentrations include CYP3A4 inhibitors such as:

• Clarithromycin
• Erythromycin
• Azole antifungals
• Verapamil
• Diltiazem
• Some SSRIs
• Protease inhibitors
• Grapefruit juice

Carbamazepine itself is also a potent inducer of several CYP enzymes and may reduce concentrations of many other drugs.

Clinical Features

Neurologic

Neurologic toxicity is usually the dominant presentation.

Common findings:

• Nystagmus
• Diplopia
• Dizziness
• Dysarthria
• Ataxia
• Somnolence
• Confusion

Moderate/severe poisoning can cause:

• Agitation
• Hallucinations
• Abnormal movements
• Chorea
• Myoclonus
• Seizures
• Coma

The patient’s mental status may fluctuate:

Somnolence/coma → apparent improvement → recurrent deterioration

This “cyclical coma” reflects delayed and variable drug absorption.

Cardiovascular

Possible findings include:

• Sinus tachycardia
• Hypotension
• Myocardial depression
• PR prolongation
• QRS widening
• AV block
• Ventricular dysrhythmias

The older emphasis on QT prolongation as the main ECG abnormality is less useful than recognizing:

Sodium-channel blockade → QRS widening

which is the more important toxicologic conduction abnormality.

Respiratory

Severe CNS depression may cause:

• Hypoventilation
• Loss of airway reflexes
• Aspiration
• Respiratory failure
• Apnea

Intubation may be necessary in severe poisoning.

Gastrointestinal

Possible manifestations include:

• Nausea
• Vomiting
• Reduced bowel sounds
• Ileus

Anticholinergic ileus can prolong absorption significantly.

Electrolytes

Hyponatremia

Carbamazepine can cause:

SIADH → water retention → hyponatremia

This is more typical of therapeutic/chronic use than isolated acute overdose, but it should be considered when altered mental status or seizures are disproportionate to the measured carbamazepine concentration.

Current labeling identifies SIADH-related hyponatremia as a recognized adverse effect, with greater risk in older patients and patients taking diuretics.

Musculoskeletal

Seizures, agitation, or prolonged coma may cause:

• CK elevation
• Rhabdomyolysis

Monitor CK and renal function when clinically indicated.

Serum Carbamazepine Concentrations

A major correction to the older source:

The usual therapeutic range is approximately 4–12 μg/mL = 4–12 mg/L

—not 6–12 μg/dL.

Approximate toxicity relationships:

• 11–15 mg/L: nystagmus, ataxia, disorientation
• 15–25 mg/L: agitation, hallucinations, marked CNS toxicity
• >25 mg/L: severe toxicity including seizures/coma increasingly likely
• >40 mg/L: strongly associated with severe poisoning

Individual variation is substantial.

Important

A single level is not enough after a major overdose.

Serial Carbamazepine Levels

Obtain serial concentrations approximately:

Every 4–6 hours

until:

• A clear downward trend is established
• The patient is improving clinically

This is critical because concentrations can continue rising after presentation.

A patient whose level is initially modest may deteriorate many hours later.

Why Levels Can Rise Late

Mechanisms include:

• Delayed gastric emptying
• Anticholinergic ileus
• Extended-release formulation
• Tablet concretions/pharmacobezoars
• Continued intestinal absorption
• Enterohepatic/enteroenteric recycling

Therefore:

Never discharge a clinically concerning patient solely because the first carbamazepine level is low.

Diagnosis

Diagnosis is based on:

Exposure history + neurologic syndrome + ECG + serial carbamazepine concentrations

The classic combination is:

Nystagmus + ataxia + CNS depression + tachycardia

with more severe poisoning causing:

• Seizures
• Coma
• QRS widening
• Hypotension

Essential Investigations

Obtain:

• 12-lead ECG
• Continuous cardiac monitoring
• Serial serum carbamazepine concentrations
• Glucose
• Sodium
• Potassium
• Magnesium
• Bicarbonate
• BUN
• Creatinine

Depending on severity:

• CK
• Blood gas
• Lactate
• Liver tests

For intentional overdose also consider:

• Acetaminophen concentration
• Salicylate concentration
• Other relevant coingestants

Differential Diagnosis

Toxicologic causes of CNS depression/ataxia include:

• Phenytoin
• Valproate
• Phenobarbital
• Benzodiazepines
• Alcohols
• Tricyclic antidepressants
• Other sodium-channel blockers

Non-toxicologic causes include:

• Stroke
• Intracranial hemorrhage
• CNS infection
• Hyponatremia
• Hypoglycemia
• Postictal state

Treatment

1. Airway and Ventilation

Supportive care is the foundation.

Intubate if there is:

• Significant coma
• Loss of airway protection
• Recurrent seizures
• Respiratory failure

Severe CNS depression is a recognized indication for airway control in carbamazepine toxicity.

2. IV Fluids and Hypotension

For hypotension:

• Give isotonic crystalloid if clinically volume responsive
• Avoid unnecessary fluid overload if myocardial dysfunction is suspected

Persistent shock should be treated with a direct-acting vasopressor, with:

Norepinephrine

a reasonable contemporary first choice.

The historical preference for dopamine is outdated.

3. Sodium Bicarbonate

Carbamazepine can behave like other sodium-channel blockers in severe overdose.

Indications include:

• QRS widening
• Ventricular dysrhythmia attributable to sodium-channel blockade
• Hypotension with evidence of conduction toxicity

A commonly used regimen is:

Sodium bicarbonate 1–2 mEq/kg IV bolus

repeated according to:

• QRS response
• Hemodynamics
• Acid–base status

A practical target is a serum pH approximately:

7.45–7.55

while avoiding severe alkalemia.

A QRS around >100–110 ms, especially with hemodynamic instability, is commonly used as a treatment trigger.

Monitor for:

• Hypernatremia
• Hypokalemia
• Volume overload
• Metabolic alkalosis

Ventricular Dysrhythmias

First priorities:

• Sodium bicarbonate
• Correction of oxygenation
• Correction of electrolytes

The older recommendation to move routinely to lidocaine after bicarbonate failure is based on limited evidence.

For refractory ventricular dysrhythmia:

• Follow appropriate resuscitation principles
• Seek medical-toxicology input
• Consider extracorporeal treatment early in life-threatening toxicity

4. Seizures

First-line:

Benzodiazepines

Examples:

• Lorazepam
• Midazolam
• Diazepam

If seizures persist:

• Phenobarbital may be considered
• Propofol is reasonable in an intubated patient with refractory status epilepticus

Avoid Phenytoin

The older source recommends phenytoin as a second anticonvulsant.

Modern guidance generally advises against sodium-channel–blocking antiseizure drugs such as:

Phenytoin/fosphenytoin

because carbamazepine already causes sodium-channel blockade and cardiac conduction slowing.

Thus:

Toxicologic seizures → benzodiazepines first; avoid adding another sodium-channel blocker when possible.

Gastrointestinal Decontamination

Do Not Induce Vomiting

Do not use:

• Ipecac
• Deliberate emesis

because CNS depression and seizures may develop.

Single-Dose Activated Charcoal

Activated charcoal may be appropriate after a significant recent ingestion if:

• The airway is intact or protected
• Aspiration risk is acceptable

A typical dose is approximately:

1 g/kg

with common adult dosing around 50 g.

Because absorption can be delayed, charcoal may remain useful beyond the very early period in selected cases, especially after large or extended-release ingestions.

Multiple-Dose Activated Charcoal

This is an important carbamazepine-specific therapy.

Multiple-dose activated charcoal (MDAC) increases carbamazepine elimination.

Mechanisms include:

• Interrupting enterohepatic/enteroenteric recirculation
• “Gut dialysis” of circulating drug

Toxicology guidelines specifically identify carbamazepine as one of the small number of drugs for which MDAC should be considered after a life-threatening ingestion.

Important caveat

Clinical outcome benefit is less firmly established than the pharmacokinetic benefit.

Do not give MDAC when:

• Airway is unprotected
• Significant vomiting prevents safe administration
• Ileus is present
• Intestinal obstruction is suspected

This is particularly relevant because carbamazepine itself can cause anticholinergic ileus.

Gastric Lavage

The older recommendation for routine gastric lavage after large ingestion does not reflect routine contemporary poisoning practice.

It should only rarely be considered in an exceptional:

• Massive
• Very recent
• Life-threatening ingestion

with:

• Protected airway
• Appropriate monitoring
• Toxicology consultation

Whole-Bowel Irrigation

Whole-bowel irrigation is not routine.

It may occasionally be considered after a very large extended-release ingestion when:

• Significant drug is thought to remain in the GI tract
• The patient is stable enough
• The airway is protected
• There is no ileus or obstruction

Current references caution that routine use is not established and intestinal complications are possible.

Antidote

There is no specific antidote for carbamazepine poisoning.

Treatment relies on:

• Supportive care
• Activated charcoal when appropriate
• Sodium bicarbonate for conduction toxicity
• Extracorporeal removal in severe cases

Extracorporeal Treatment

This is one of the biggest changes from the older text.

Historically:

Charcoal hemoperfusion was preferred.

Current EXTRIP guidance states:

Intermittent hemodialysis is the preferred extracorporeal treatment for severe carbamazepine poisoning.

Although carbamazepine is normally significantly protein bound, in overdose:

• Binding becomes relatively saturated
• The free fraction increases

and modern high-flux dialysis can provide clinically useful clearance.

EXTRIP Indications

Extracorporeal treatment is recommended when there are:

Refractory multiple seizures

or

Life-threatening dysrhythmias

It is also suggested when there is:

• Prolonged coma or respiratory depression requiring mechanical ventilation
• Persistent severe toxicity despite supportive care and MDAC
• Carbamazepine concentrations that remain high or continue rising despite treatment

Preferred Modality

EXTRIP recommends:

1. Intermittent hemodialysis — preferred

If unavailable:

• Intermittent hemoperfusion
• Continuous renal replacement therapy

may be used.

Therefore:

Hemoperfusion is no longer the preferred extracorporeal modality.

When to Stop Dialysis

EXTRIP recommends stopping when:

• Clinical improvement is apparent

and suggests a concentration target:

Carbamazepine <10 mg/L

MDAC should generally be continued during extracorporeal treatment when safe and feasible.

Rebound After Dialysis

Because carbamazepine can:

• Redistribute from tissue
• Continue to be absorbed from the GI tract

serum concentrations may rebound after extracorporeal therapy.

Therefore:

Continue serial carbamazepine levels after dialysis.

Clinical improvement plus a falling concentration trend is more important than one post-dialysis level.

Intravenous Lipid Emulsion

Carbamazepine is lipophilic, and IV lipid emulsion has been reported in severe poisoning.

However:

Evidence is limited largely to case reports.

It is not first-line therapy and should not delay:

• Sodium bicarbonate
• MDAC
• Hemodialysis
• Standard resuscitation

Current reviews describe lipid therapy only as a possible rescue adjunct in refractory cases.

Physostigmine

Although anticholinergic manifestations can occur:

Physostigmine should not be used routinely.

The patient may already have:

• Seizure risk
• Cardiac conduction abnormalities

and reversal of peripheral anticholinergic symptoms is not worth these risks.

Monitoring

Patients with significant toxicity require:

• Continuous ECG
• Continuous respiratory monitoring
• Frequent neurologic examination
• Serial carbamazepine concentrations
• Serial electrolytes

Monitor specifically for:

• Rising drug level
• QRS widening
• Hypotension
• Seizures
• Recurrent coma

Observation

A fixed 6-hour observation period is not reliable for all carbamazepine overdoses.

Immediate-release toxicity may begin within several hours, while sustained-release poisoning may be delayed.

A pediatric toxicology guideline notes:

• Immediate-release symptoms often appear within 1–2 hours
• Sustained-release toxicity may appear around 4–8 hours
• Mild symptomatic patients should generally be observed at least 8 hours, with longer observation for controlled-release exposures

Massive overdoses can peak much later, including up to 72 hours.

Therefore:

Large, extended-release, symptomatic, or rising-level ingestions require prolonged observation.

Admission

Admit patients with:

• Altered mental status
• Ataxia preventing safe ambulation
• Seizures
• Coma
• QRS widening
• Dysrhythmia
• Hypotension
• Rising carbamazepine concentration
• Significant extended-release overdose

Patients with:

• Severe CNS depression
• Mechanical ventilation
• Significant conduction toxicity
• Refractory seizures
• Shock
• Need for extracorporeal treatment

require ICU care.

Discharge

Discharge should require:

• Normal or baseline mental status
• Safe ambulation
• Normal/stable ECG
• No evolving cardiovascular toxicity
• No recurrent symptoms
• Clearly declining carbamazepine concentrations when levels were elevated or ingestion was significant

Do not discharge solely because the patient briefly “wakes up.”

Pregnancy

The historical FDA Pregnancy Category C system is obsolete.

Current labeling recognizes that carbamazepine can cause fetal harm and has been associated with congenital abnormalities, particularly neural tube defects such as spina bifida.

In an acute maternal overdose:

Maternal stabilization remains the priority.

Do not withhold:

• Airway support
• Sodium bicarbonate
• Seizure treatment
• Hemodialysis when indicated

because maternal hypoxia and shock represent immediate fetal threats.

Prognosis

Most mild/moderate overdoses recover with supportive treatment.

However, severe poisoning may persist for:

• 24–48 hours
• Several days after massive or extended-release ingestion

because of delayed absorption.

Serious morbidity may result from:

• Aspiration
• Prolonged hypoxia
• Refractory seizures
• Severe dysrhythmia
• Shock

Early recognition of delayed toxicity and appropriate use of MDAC and hemodialysis have substantially changed modern management.

Important Pitfalls

1. Using the wrong serum units

Therapeutic carbamazepine:

4–12 μg/mL = 4–12 mg/L

The older value expressed as μg/dL is incorrect.

2. Relying on a single drug level

The concentration may continue to rise for many hours.

Repeat every 4–6 hours until clearly falling.

3. Discharging after transient improvement

Carbamazepine can cause:

Cyclical coma

from delayed absorption and redistribution.

4. Missing sodium-channel blockade

Serious ECG toxicity is best recognized by:

QRS widening

rather than focusing only on QT prolongation.

Treat significant QRS widening with:

IV sodium bicarbonate.

5. Treating seizures with phenytoin

Phenytoin is another sodium-channel blocker and can worsen conduction toxicity.

Prefer:

• Benzodiazepines
• Phenobarbital/propofol when necessary

6. Forgetting multiple-dose activated charcoal

Carbamazepine is one of the classic drugs for which MDAC can meaningfully increase elimination after life-threatening poisoning.

7. Giving charcoal to an unprotected airway

CNS depression and vomiting create substantial aspiration risk.

Secure the airway first when necessary.

8. Using charcoal despite ileus

Carbamazepine itself may significantly decrease intestinal motility.

MDAC is contraindicated when bowel obstruction or significant ileus is present.

9. Thinking hemoperfusion is still preferred

Current EXTRIP guidance:

Intermittent hemodialysis is preferred over hemoperfusion.

10. Waiting for a particular serum concentration before dialysis

EXTRIP indications are primarily clinical:

• Refractory seizures
• Life-threatening dysrhythmia
• Prolonged ventilated coma
• Persistent severe toxicity

not simply a numerical drug concentration.

High-Yield Toxicology Pearls

Carbamazepine overdose = sodium-channel blockade + anticholinergic toxicity

Think:

Nystagmus + ataxia + CNS depression + tachycardia

Severe poisoning:

Coma/seizures + QRS widening + hypotension ± ventricular dysrhythmia

Key points:

• Mechanism: voltage-gated sodium-channel blockade
• Active metabolite: carbamazepine-10,11-epoxide
• Therapeutic serum level: 4–12 mg/L
• >40 mg/L strongly suggests severe toxicity
• Serial levels are essential
• Check approximately every 4–6 h until clearly declining
• Peak levels can be delayed up to 72 h after massive overdose
• Anticholinergic ileus and tablet concretions cause delayed absorption
• “Cyclical coma” is classic
• Important ECG finding: QRS widening
• QRS widening/hypotension → sodium bicarbonate 1–2 mEq/kg IV
• Seizures → benzodiazepines
• Avoid routine phenytoin/fosphenytoin
• No specific antidote
• Single-dose charcoal may be used after selected recent ingestions
• Multiple-dose activated charcoal is particularly important in life-threatening poisoning
• Do not use MDAC with an unprotected airway or ileus
• Modern extracorporeal therapy:
• Intermittent hemodialysis preferred
• Hemoperfusion is an alternative
• Dialysis indications include:
• Refractory seizures
• Life-threatening dysrhythmias
• Prolonged ventilated coma
• Persistent/rising toxicity despite MDAC/support
• EXTRIP suggests stopping ECTR with clinical improvement and carbamazepine <10 mg/L
• Do not discharge until clinical recovery is sustained and significant serum levels are demonstrably falling

Toxicology – Carbamate Insecticides

Core concept

Carbamate insecticides produce an acute cholinergic toxidrome by reversibly inhibiting acetylcholinesterase (AChE).

The classic syndrome is:

Excess acetylcholine → bronchorrhea + bronchospasm + salivation + vomiting/diarrhea + miosis + fasciculations/weakness ± seizures

The immediate life-threatening problem is:

Respiratory failure

from a combination of:

Bronchorrhea/bronchospasm + neuromuscular weakness + CNS respiratory depression

The cornerstone of antidotal treatment is:

Atropine

A major modern distinction from organophosphate poisoning is:

Carbamate-AChE inhibition is reversible and does not “age.”

Therefore, pralidoxime is usually unnecessary in a confirmed isolated carbamate poisoning, although it remains reasonable when the pesticide is unidentified or organophosphate exposure cannot be excluded.

Important Agents

Clinically important carbamate insecticides include:

• Aldicarb
• Carbaryl
• Carbofuran
• Methomyl
• Oxamyl
• Propoxur
• Bendiocarb
• Methiocarb
• Pirimicarb
• Thiodicarb
• Carbosulfan

The older classification into “low-, moderate-, and high-toxicity” groups should not be relied on clinically.

Some carbamates—particularly agents such as aldicarb and carbofuran—can produce severe, rapidly fatal poisoning.

Severity depends on:

• Specific compound
• Concentration
• Formulation
• Dose
• Route
• Coformulants/solvents
• Delay to treatment

Routes of Exposure

Carbamate insecticides can be absorbed by:

• Ingestion
• Skin
• Inhalation
• Eyes/mucous membranes

Occupational poisoning frequently occurs through dermal exposure during:

• Mixing
• Spraying
• Agricultural work
• Contact with recently treated plants

Intentional poisoning is usually oral.

Symptoms can develop rapidly after substantial exposure, sometimes within minutes.

Pathophysiology

Normally:

Acetylcholine → binds receptor → acetylcholinesterase rapidly terminates signaling

Carbamates cause:

Carbamylation of AChE → reversible AChE inhibition → acetylcholine accumulation

Excess acetylcholine stimulates:

1. Muscarinic receptors
2. Nicotinic receptors
3. CNS cholinergic pathways

Carbamates vs Organophosphates

Both cause acute cholinergic poisoning.

But:

Carbamates

Reversible carbamylation of AChE

→ spontaneous hydrolysis/reactivation

→ toxicity often resolves within 24 hours, sometimes 24–48 hours

Organophosphates

Phosphorylation of AChE

→ may undergo aging

→ prolonged toxicity

→ oximes have a stronger mechanistic rationale

This distinction becomes especially important when deciding whether to use pralidoxime.

Clinical Features

The Cholinergic Toxidrome

A traditional mnemonic is:

DUMBELS

• D – Defecation/diarrhea, diaphoresis
• U – Urination
• M – Miosis
• B – Bronchorrhea, bronchospasm, bradycardia
• E – Emesis
• L – Lacrimation
• S – Salivation

However, the most clinically useful way to organize toxicity is by receptor type.

Muscarinic Effects

Pulmonary

The most dangerous muscarinic effects are:

• Bronchorrhea
• Bronchospasm
• Excessive oral secretions

These may produce:

• Wheezing
• Crackles
• Hypoxemia
• Respiratory distress

HEENT

• Miosis
• Blurred vision
• Lacrimation
• Rhinorrhea
• Salivation

Gastrointestinal

• Nausea
• Vomiting
• Abdominal cramping
• Diarrhea
• Increased bowel sounds

Genitourinary

• Urinary urgency
• Urinary incontinence

Dermatologic

• Profuse sweating

Remember that sympathetic sweat glands use acetylcholine.

Cardiovascular

Possible findings include:

• Bradycardia
• Hypotension
• AV conduction abnormalities

Nicotinic Effects

At autonomic ganglia, excess acetylcholine may produce either sympathetic or parasympathetic manifestations.

Therefore, patients may have:

• Tachycardia
• Hypertension
• Mydriasis

despite having a cholinergic pesticide poisoning.

At the neuromuscular junction:

Nicotinic stimulation → fasciculations → weakness → flaccid paralysis

Clinical findings include:

• Muscle twitching
• Fasciculations
• Generalized weakness
• Neck weakness
• Respiratory-muscle weakness
• Paralysis

Mixed autonomic presentations are common, so tachycardia does not exclude carbamate toxicity.

CNS Effects

Possible central manifestations include:

• Anxiety
• Restlessness
• Confusion
• Delirium
• Tremor
• Ataxia
• Seizures
• Depressed consciousness
• Coma

Children may show particularly prominent CNS depression.

Respiratory Failure

This is the major cause of death.

Three mechanisms often coexist:

1. Wet lungs

Bronchorrhea + bronchospasm

2. Weak respiratory muscles

Nicotinic neuromuscular toxicity

3. Impaired respiratory drive

Central cholinergic toxicity

Therefore:

Clearing secretions with atropine does not guarantee that ventilation is adequate.

Atropine does not reverse nicotinic skeletal-muscle paralysis.

Cardiovascular Toxicity

Possible abnormalities include:

• Bradycardia
• Tachycardia
• Hypotension
• Hypertension
• AV block
• Atrial dysrhythmias

Severe poisoning can progress to:

• Cardiovascular collapse
• Asystole

Hypoxia is often an important contributor to cardiac instability.

Pulmonary Edema / Aspiration

Chest abnormalities can arise from:

• Cholinergic bronchorrhea
• Aspiration
• Chemical pneumonitis from pesticide solvents
• Secondary pulmonary edema

Many commercial pesticide formulations contain:

• Hydrocarbons
• Surfactants
• Other solvents

Therefore, the complete product formulation matters.

Toxic Dose

There is no clinically useful single toxic dose for carbamate insecticides.

Toxicity varies greatly between compounds.

A small exposure to a highly potent agent may be more dangerous than a much larger exposure to another carbamate.

Therefore:

Do not use the number of tablets, milliliters, or grams alone to exclude serious toxicity.

Whenever possible identify:

• Active ingredient
• Percentage concentration
• Commercial formulation
• Estimated amount
• Route and time

Diagnosis

Diagnosis is primarily clinical:

Compatible exposure + cholinergic toxidrome

Treatment must not wait for cholinesterase testing.

Cholinesterase Testing

Two commonly measured enzymes are:

RBC acetylcholinesterase

More closely reflects AChE activity at neuronal/neuromuscular sites.

Plasma butyrylcholinesterase

Sometimes called:

• Plasma cholinesterase
• Pseudocholinesterase

It is easier to measure in many laboratories.

Important Carbamate Testing Limitation

The older source presents fixed cholinesterase percentages as though they reliably classify poisoning severity.

That is overly simplistic.

Because carbamate-AChE binding is rapidly reversible:

Cholinesterase activity may recover rapidly after blood is drawn or before testing occurs.

Therefore:

• A normal result does not reliably exclude carbamate poisoning
• Sample handling and processing time matter
• Clinical toxicity is more important than a numerical enzyme level

CDC has specifically noted that cholinesterase testing can be unreliable in carbamate poisoning because the inhibition reverses rapidly.

Practical rule

Draw cholinesterase levels when useful—but do not delay atropine or airway management to obtain them.

Other Laboratory Tests

In moderate/severe poisoning obtain:

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

Consider:

• Blood gas
• Lactate

when:

• Hypoxemia
• Shock
• Respiratory failure
• Significant acidosis

is present.

ECG

Obtain:

• 12-lead ECG
• Continuous cardiac monitoring

in symptomatic patients.

Monitor for:

• Bradycardia
• Tachyarrhythmia
• AV block
• Ischemic changes
• Dysrhythmia secondary to hypoxia/electrolyte abnormalities

Chest Imaging

Chest radiography is appropriate when there is:

• Hypoxemia
• Persistent respiratory distress
• Suspected aspiration
• Pulmonary edema
• Abnormal lung examination not resolving with atropine

Remember that persistent crackles after adequate atropinization may represent aspiration, rather than continued cholinergic bronchorrhea.

Differential Diagnosis

Organophosphate poisoning

The most important differential.

Initially:

Treat severe undifferentiated cholinesterase-inhibitor poisoning similarly until the compound is identified.

Other toxicologic causes

• Nicotine
• Neostigmine
• Pyridostigmine
• Physostigmine
• Donepezil
• Pilocarpine
• Bethanechol
• Muscarine-containing mushrooms

Medical mimics

Depending on presentation:

• Myasthenic crisis
• Severe asthma
• Pulmonary edema
• Sepsis
• Bradyarrhythmia from another cause

Treatment

1. Protect Healthcare Personnel

This is an important part of the initial management.

A contaminated patient can expose:

• Paramedics
• Nurses
• Physicians
• Family members

especially through:

• Wet clothing
• Skin contamination
• Vomitus
• Diarrhea
• Pesticide solvents

Healthcare-associated pesticide poisoning has occurred after inadequately decontaminated patients were brought into emergency departments.

Use appropriate:

• Gloves
• Protective gown
• Eye protection

and respiratory protection when the formulation or exposure environment warrants it.

2. Decontamination

Clothing

Remove contaminated clothing promptly.

Removing clothing alone can eliminate a large fraction of external chemical contamination. Current CDC chemical-emergency guidance recommends rapid clothing removal and washing after significant contamination.

Place contaminated clothing in appropriate sealed containers/bags.

Skin

Wash exposed skin and hair thoroughly with:

• Water
• Soap and water
• Then rinse

Do not aggressively abrade the skin.

Current carbamate guidance recommends thorough skin washing because continued dermal absorption can occur.

Eyes

Immediately irrigate exposed eyes with:

• Water
• Normal saline

Remove contact lenses.

3. Airway and Ventilation

The priorities are:

Suction → oxygenation → ventilation → atropine

Clear excessive secretions aggressively.

Early endotracheal intubation is appropriate for:

• Inability to manage secretions
• Severe hypoxemia
• Coma
• Severe respiratory-muscle weakness
• Inadequate ventilation

Avoid Succinylcholine

This is an important anesthesia/intubation pearl.

Because cholinesterase activity can be inhibited:

Succinylcholine paralysis may be markedly prolonged.

A nondepolarizing neuromuscular blocker such as:

Rocuronium

is generally preferable when paralysis is required for rapid-sequence intubation.

Atropine

Main antidote

Atropine is the essential antidote for clinically important muscarinic toxicity.

It competitively blocks muscarinic acetylcholine receptors.

It improves:

• Bronchorrhea
• Bronchospasm
• Salivation
• Bradycardia
• Hypotension related to muscarinic excess

It does not directly reverse:

• Fasciculations
• Neuromuscular weakness
• Respiratory-muscle paralysis

Initial Atropine Dose

A contemporary carbamate reference recommends:

Adult

1–3 mg IV initially

Pediatric

0.05 mg/kg IV

with a minimum dose of approximately:

0.1 mg

Rapid Dose Escalation

If response is inadequate:

Double the atropine dose approximately every 5 minutes

For example:

2 mg → 4 mg → 8 mg → 16 mg → 32 mg

until adequate cardiorespiratory atropinization is achieved.

The older strategy of repeatedly administering the same small dose every 5–10 minutes can take too long in a critically poisoned patient.

Atropine Endpoint

This is one of the most important modern updates.

Do not titrate atropine primarily to:

• Dilated pupils
• Complete dry mouth
• A specific heart rate

Instead target:

Drying of dangerous bronchial secretions + relief of bronchospasm + adequate perfusion

Specifically:

• Bronchorrhea markedly reduced
• Chest substantially clearer
• Oxygenation/ventilation improving
• Blood pressure adequate
• Heart rate adequate for perfusion

Tachycardia Is Not a Contraindication

A poisoned patient may already be tachycardic because of:

• Hypoxia
• Nicotinic ganglionic stimulation
• Stress
• Severe respiratory distress

Therefore:

Do not withhold needed atropine solely because the heart rate is high if the lungs remain wet and bronchospastic.

Atropine Infusion

If repeated toxicity occurs after loading:

Begin an infusion at approximately:

10–20% of the total effective loading dose per hour

and titrate according to:

• Bronchial secretions
• Respiratory status
• Perfusion

Because carbamate toxicity is usually relatively short-lived, prolonged atropine infusions are less commonly necessary than after major organophosphate poisoning.

Atropine Toxicity

Over-atropinization may cause:

• Delirium
• Agitation
• Hyperthermia
• Ileus
• Urinary retention
• Marked tachycardia

Treatment must continually balance:

• Recurrent cholinergic toxicity
• against
• Excess atropine

Pralidoxime (2-PAM)

Major modern update

The older textbook states:

“Atropine and pralidoxime are antidotes for carbamate poisoning.”

That is too broad.

Carbamates spontaneously dissociate from AChE and do not undergo aging.

Therefore:

Pralidoxime is generally not required for a confirmed isolated carbamate poisoning.

Carbaryl

Experimental data have raised concern that pralidoxime may actually increase AChE inhibition in carbaryl poisoning.

Therefore:

Avoid routine pralidoxime in known isolated carbaryl poisoning.

When Pralidoxime IS Reasonable

Real-world pesticide exposure is often uncertain.

If a patient has severe cholinergic poisoning and:

• The pesticide is unidentified
• Organophosphate exposure cannot be excluded
• Mixed pesticide exposure is possible

then:

Give pralidoxime while treating as possible organophosphate poisoning.

The harm from missing severe organophosphate toxicity generally outweighs the limited concern about oxime use in most unidentified pesticide cases.

Practical rule

Confirmed pure carbamate → atropine; usually no 2-PAM

Unknown OP vs carbamate → atropine + consider 2-PAM

Gastrointestinal Decontamination

Do Not Induce Vomiting

Do not use ipecac or induce emesis.

A cholinergic patient already has:

• Vomiting
• Excess secretions
• Risk of altered consciousness
• Risk of seizures
• High aspiration risk

Activated Charcoal

Routine charcoal is not necessary for all carbamate ingestions.

After a massive, very recent ingestion, single-dose activated charcoal may be considered when:

• Presentation is approximately within 1 hour
• Airway is intact or protected
• Aspiration risk is acceptable

Evidence for adsorption and clinical benefit is limited, so toxicology/poison-center consultation is appropriate.

Gastric Lavage

Routine gastric lavage is not standard modern therapy.

It may be considered only in highly selected circumstances involving:

• Massive life-threatening ingestion
• Very early presentation
• Protected airway
• Specialist toxicology input

Resuscitation and atropinization take priority.

Seizures

First-line treatment:

Benzodiazepines

Examples:

• Lorazepam
• Midazolam
• Diazepam

For refractory toxin-induced seizures consider:

• Phenobarbital
• Propofol in an intubated patient

Also aggressively correct:

• Hypoxia
• Hypoglycemia
• Electrolyte abnormalities

Hypotension

First address:

• Hypoxia
• Bradycardia
• Cholinergic excess

Give appropriate isotonic crystalloid if the patient is fluid responsive.

If shock persists despite atropine and appropriate volume:

Norepinephrine is generally an appropriate vasopressor.

The older preference for:

• Trendelenburg positioning
• Dopamine as first-choice pressor

is not part of contemporary shock management.

Bronchospasm

The most important treatment is:

Adequate atropinization

because the underlying process is cholinergic.

Additional inhaled bronchodilator therapy may be used when clinically helpful, but bronchodilators do not replace atropine.

Mechanical Ventilation

Mechanical ventilation may be needed despite atropine if there is:

• Neuromuscular weakness
• Central respiratory depression
• Aspiration
• Severe hypoxemia

Continue ventilatory assessment after lung secretions improve.

Enhanced Elimination

There is no established role for:

• Hemodialysis
• Hemoperfusion
• Urinary alkalinization

for routine removal of carbamate insecticides.

Treatment relies on:

• Decontamination
• Airway/ventilatory support
• Atropine
• Supportive care

Intermediate and Delayed Syndromes

Carbamate poisoning is generally shorter-lived than organophosphate poisoning.

Because there is no aging of the carbamate-AChE bond:

• Prolonged cholinergic toxicity is uncommon
• Classic delayed organophosphate neuropathy is not expected

An intermediate syndrome with persistent muscle weakness has occasionally been reported, but it is substantially less characteristic than with organophosphate poisoning.

Monitoring

Symptomatic patients require:

• Continuous ECG
• Continuous pulse oximetry
• Frequent respiratory assessment
• Frequent neurologic assessment

Specifically reassess:

• Bronchial secretions
• Bronchospasm
• Muscle strength
• Ability to ventilate
• Blood pressure

Capnography or blood gases can be useful in significant respiratory compromise.

Admission

ICU

ICU-level care is appropriate for:

• Respiratory distress/failure
• Significant bronchorrhea
• Severe muscle weakness
• Need for intubation
• Repeated/high-dose atropine requirements
• Atropine infusion
• Seizures
• Coma
• Hemodynamic instability

Monitored Admission

Patients requiring atropine should generally be admitted to a monitored setting for continued respiratory assessment.

Moderate poisoning may warrant approximately 24 hours of observation.

Disposition

The older fixed rule of:

“Asymptomatic = discharge after 6 hours”

should not be applied rigidly to every carbamate exposure.

Disposition should consider:

• Specific agent
• Formulation
• Dose
• Route
• Dermal decontamination
• Symptom-free interval
• Coingestants
• Reliability of observation at home

Because carbamate toxicity usually develops rapidly, an adequately observed patient with:

• No symptoms
• Normal vital signs
• No respiratory abnormalities
• Complete decontamination

can often be discharged after an appropriate observation period.

Patients with mild symptoms who never require atropine may also be discharged once completely asymptomatic after observation.

Occupational Exposure

Carbaryl

Current NIOSH Pocket Guide values are:

NIOSH REL: 5 mg/m³ TWA

OSHA PEL: 5 mg/m³ TWA

NIOSH IDLH: 100 mg/m³

Carbofuran

Current NIOSH listing:

NIOSH REL: 0.1 mg/m³ TWA

and:

No specific OSHA PEL listed

Occupational limits are agent specific; they should not be generalized across the entire carbamate class.

Return to Work

The older recommendation that every exposed worker must reach exactly 75% of a personal RBC cholinesterase baseline before returning to all pesticide handling is too simplistic for acute carbamate poisoning.

Return-to-work decisions should consider:

• Full clinical recovery
• Elimination of ongoing exposure
• Workplace investigation
• PPE and engineering controls
• Occupational-health assessment
• Cholinesterase monitoring protocol when applicable

Because carbamate inhibition reverses quickly, a delayed cholinesterase measurement may no longer accurately reflect the acute exposure.

Pregnancy

The old FDA pregnancy letter categories are obsolete.

Significant maternal carbamate poisoning can threaten both mother and fetus through:

• Hypoxemia
• Respiratory failure
• Hypotension
• Severe cholinergic toxicity

Life-saving therapy should not be withheld because of pregnancy.

In particular:

Atropine remains indicated when clinically required.

Maternal stabilization is the priority, with obstetric/fetal assessment according to gestation and poisoning severity.

Prognosis

Compared with organophosphate poisoning, isolated carbamate poisoning generally has:

• Faster spontaneous enzyme recovery
• Shorter duration
• Lower risk of prolonged neurologic syndromes

Most patients recover within approximately:

24 hours

although severe cases can persist for 24–48 hours and may require mechanical ventilation.

Death usually results from:

• Delayed airway management
• Respiratory failure
• Severe aspiration
• Massive exposure
• Severe CNS depression

Important Pitfalls

1. Calling carbamates “low toxicity”

Some carbamate insecticides can cause:

Rapid respiratory failure and death.

Aldicarb and carbofuran are particularly important examples.

2. Waiting for cholinesterase results

Carbamate inhibition is reversible, so cholinesterase results may normalize rapidly or become misleading.

Treat the patient, not the laboratory value.

3. Using pupils as the atropine endpoint

Persistent miosis is not a reason by itself to continue escalating atropine.

The important endpoint is:

Drying of bronchial secretions + improved bronchospasm + adequate perfusion

4. Stopping atropine because the patient is tachycardic

Tachycardia may reflect:

• Nicotinic stimulation
• Hypoxemia
• Physiologic stress

If the chest remains wet and the patient is bronchospastic:

More atropine may still be needed.

5. Assuming atropine corrects muscle weakness

Atropine treats muscarinic toxicity.

It does not reverse nicotinic:

• Fasciculations
• Weakness
• Respiratory paralysis

Continue to monitor ventilation carefully.

6. Giving pralidoxime automatically to every confirmed carbamate patient

For a known isolated carbamate poisoning, oximes are generally unnecessary.

They are particularly controversial in carbaryl exposure.

7. Withholding pralidoxime when the pesticide is unknown

If severe cholinergic poisoning could represent an organophosphate:

Treat empirically as an organophosphate until the exposure is clarified.

8. Failing to protect healthcare workers

Pesticides remaining on:

• Clothing
• Skin
• Hair
• Vomitus

can cause secondary contamination.

PPE and decontamination should occur early.

9. Using succinylcholine for intubation

Cholinesterase inhibition may prolong its action dramatically.

Rocuronium or another nondepolarizing agent is generally preferable.

10. Treating the heart rate instead of the lungs

The most immediate danger is usually:

Bronchorrhea + bronchospasm + respiratory failure

not the exact pulse rate.

High-Yield Toxicology Pearls

Carbamate insecticides = reversible cholinesterase inhibitors

Think:

Wet + pinpoint + twitching + weak

Classic severe syndrome:

Bronchorrhea + miosis + vomiting/diarrhea + fasciculations → weakness → respiratory failure

Key points:

• Mechanism: reversible acetylcholinesterase inhibition
• Unlike organophosphates, carbamates do not undergo aging
• Clinical effects are usually shorter, often resolving within 24–48 h
• Muscarinic effects:
• 
  
• Bronchorrhea
• Bronchospasm
• Salivation
• Lacrimation
• Vomiting/diarrhea
• Miosis
• Bradycardia
• Nicotinic effects:
• 
  
• Fasciculations
• Muscle weakness
• Respiratory paralysis
• Tachycardia/hypertension may occur
• CNS effects:
• 
  
• Confusion
• Seizures
• Coma
• Main cause of death: respiratory failure
• Diagnosis is primarily clinical
• Cholinesterase levels may be misleading because carbamate inhibition reverses rapidly
• Do not delay treatment for cholinesterase testing
• Remove contaminated clothing and wash skin/hair thoroughly
• Protect healthcare workers from secondary contamination
• Avoid induced vomiting
• GI decontamination has only a limited, selected role
• Main antidote: ATROPINE
• Adult atropine start: approximately 1–3 mg IV
• Pediatric atropine: approximately 0.05 mg/kg IV
• If inadequate response: double the atropine dose every ~5 min
• Atropine endpoint:
• 
  
• Drying bronchial secretions
• Reduced bronchospasm
• Adequate perfusion
• Do not titrate atropine to pupil size
• Tachycardia alone does not contraindicate atropine
• Maintenance atropine infusion: approximately 10–20% of total loading dose per hour
• Atropine does not reverse nicotinic muscle paralysis
• Avoid succinylcholine because paralysis may be prolonged
• Pralidoxime usually not needed in confirmed isolated carbamate poisoning
• Avoid routine pralidoxime especially in known carbaryl poisoning
• If the pesticide is unknown and organophosphate exposure remains possible → give atropine and consider pralidoxime
• Seizures → benzodiazepines
• Severe toxicity → early airway control and ICU care

Toxicology – Capsaicin (Hunan-Hand Syndrome)

Core concept

Hunan-hand syndrome is an intensely painful irritant contact reaction caused by direct skin exposure to capsaicin-containing chili peppers.

The characteristic syndrome is:

Capsaicin contact → intense burning/stinging + erythema + hyperalgesia with little visible tissue injury

Capsaicin also causes marked irritation of:

• Eyes
• Nose
• Mouth
• Airways
• Gastrointestinal tract

It is also the principal active capsaicinoid in oleoresin capsicum (OC/pepper spray).

Most exposures are self-limited, but significant ocular injury, bronchospasm, or respiratory distress can occur after concentrated exposure.

Terminology

Hunan-Hand Syndrome

Classically occurs after prolonged handling of:

• Chili peppers
• Jalapeños
• Hot peppers during food preparation

It is best considered an:

Irritant/neurogenic contact dermatitis

rather than a conventional allergic contact dermatitis.

The pain can be strikingly severe despite relatively little visible skin injury.

Capsaicin

Capsaicin is:

8-methyl-N-vanillyl-6-nonenamide

and is better classified as a capsaicinoid/vanilloid amide, rather than simply an “alkaloid” as described in some older texts.

It is one of several pungent capsaicinoids found in Capsicum peppers.

Forms and Uses

Common sources include:

• Fresh chili peppers
• Dried chili powder
• Pepper oils/extracts
• Hot sauces
• Food-processing exposures
• Oleoresin capsicum pepper spray

Capsaicin is also used therapeutically as a topical analgesic.

Current products include:

• OTC creams around 0.025–0.075%
• OTC low-concentration patches
• Prescription capsaicin 8% topical system (QUTENZA)

QUTENZA is currently indicated for neuropathic pain associated with:

• Postherpetic neuralgia
• Diabetic peripheral neuropathy of the feet

and must be applied by a healthcare professional.

Toxic Dose

There is no single clinically useful toxic dose for topical capsaicin exposure.

Severity depends on:

• Capsaicin concentration
• Duration of contact
• Surface area
• Skin integrity
• Mucosal exposure
• Aerosol concentration
• Underlying respiratory disease

For pepper spray, toxicity also varies with:

• Spray formulation
• Distance
• Duration of spray
• Enclosed-space exposure
• Solvents/propellants

Thus:

Concentration × duration × route of exposure

is more important than a fixed dose.

Pathophysiology

The older explanation focusing primarily on substance P is incomplete.

The principal molecular target is:

TRPV1 — Transient Receptor Potential Vanilloid 1

TRPV1 is a nonselective cation channel expressed predominantly on nociceptive sensory neurons.

Capsaicin binds TRPV1 and causes:

TRPV1 activation → Na⁺/Ca²⁺ influx → sensory-neuron depolarization → pain/burning

It also causes local release of neuropeptides including:

• Substance P
• Calcitonin gene-related peptide (CGRP)

producing:

Vasodilation + neurogenic inflammation + erythema + hyperalgesia

Why Capsaicin Feels “Hot”

TRPV1 also responds to:

• Noxious heat
• Acidic conditions
• Certain inflammatory mediators

Therefore the CNS interprets capsaicin stimulation similarly to a thermal noxious stimulus.

Hence:

Chemical TRPV1 activation → sensation of burning heat without actual thermal injury

Why Capsaicin Can Also Treat Pain

Repeated or high-concentration therapeutic activation of TRPV1 produces subsequent:

Desensitization / defunctionalization of nociceptive fibers

This decreases pain transmission and explains why capsaicin can paradoxically be used for neuropathic pain despite initially causing intense burning.

Clinical Features

Dermatologic – Hunan Hand

Typical findings include:

• Severe burning pain
• Stinging
• Tingling
• Hyperalgesia
• Erythema
• Warm sensation

The hands and fingertips are most commonly involved.

Pain may become markedly worse with:

• Warm water
• Hot showers
• Heat exposure

because heat also activates/sensitizes TRPV1.

Visible abnormalities can be surprisingly mild compared with the severity of pain.

Blistering

Classic limited exposure usually does not cause vesiculation.

However, concentrated, prolonged, or repeated exposure can produce:

• Significant inflammation
• Swelling
• Occasionally blistering

Thus the older statement that capsaicin causes no local tissue injury is too absolute.

Ocular Exposure

Capsaicin exposure to the eye produces almost immediate:

• Severe burning
• Lacrimation
• Blepharospasm
• Conjunctival injection
• Blurred vision
• Periorbital swelling

Patients may initially be unable or unwilling to open their eyes.

Pepper-spray studies have demonstrated:

• Punctate epithelial erosions
• Corneal abrasions in a minority of patients

In one human study, approximately 21% of exposed eyes showed punctate epithelial erosions, although visual acuity generally recovered quickly.

Corneal abrasions have also been reported after OC exposure.

Respiratory Exposure

Pepper spray or aerosolized capsaicin can cause:

• Nasal burning
• Rhinorrhea
• Sneezing
• Throat irritation
• Cough
• Chest tightness
• Subjective dyspnea

More significant exposure may cause:

• Bronchospasm
• Wheezing
• Prolonged coughing

Most healthy individuals recover rapidly after removal from exposure and decontamination.

Higher-Risk Patients

More caution is warranted in:

• Asthma
• COPD
• Significant underlying pulmonary disease
• Heavy/prolonged aerosol exposure
• Enclosed-space exposure

Severe respiratory toxicity is unusual but possible.

Gastrointestinal Exposure

Eating chili peppers normally produces only expected pungency.

Large or concentrated capsaicin exposures may cause:

• Oral burning
• Nausea
• Vomiting
• Abdominal pain
• Diarrhea

Treatment is generally supportive.

Major systemic poisoning from ordinary dietary chili exposure is uncommon.

Diagnosis

Diagnosis is usually clinical:

Typical exposure + severe burning pain/erythema with little structural skin injury

No laboratory test is routinely required.

Differential Diagnosis

For severe hand burning consider:

• Hydrofluoric acid exposure
• Strong acid or alkali burns
• Other chemical burns
• Allergic contact dermatitis
• Irritant dermatitis from another agent
• Marine envenomation
• Peripheral neuropathy
• Erythromelalgia

Important distinction

Hydrofluoric acid can cause:

Severe pain with initially minimal skin findings

similar to capsaicin.

However, HF exposure can cause:

• Hypocalcemia
• Hypomagnesemia
• Hyperkalemia
• Life-threatening dysrhythmias

Therefore, an uncertain industrial chemical exposure should not automatically be attributed to Hunan-hand syndrome.

Laboratory Tests

Uncomplicated Hunan Hand

No laboratory testing is usually necessary.

Respiratory Symptoms

Consider:

• Pulse oximetry
• Peak flow when appropriate

For significant or persistent respiratory distress:

• Chest radiograph
• Blood gas
• Other evaluation according to clinical findings

Eye Injury

Persistent:

• Pain
• Foreign-body sensation
• Photophobia
• Reduced vision

warrants:

• Visual acuity
• Fluorescein examination
• Slit-lamp evaluation when available

Treatment

1. Remove the Exposure

Remove:

• Contaminated gloves
• Clothing
• Jewelry that may retain pepper oils

Avoid touching:

• Eyes
• Face
• Genitals
• Contact lenses

with contaminated hands.

2. Skin Decontamination

The fundamental treatment is:

Prompt physical removal of capsaicin from the skin

Wash exposed skin thoroughly with:

• Copious water
• Mild soap

Repeated washing may be necessary because capsaicin is highly lipophilic and only very slightly soluble in water.

Current pepper-spray reviews emphasize thorough decontamination and supportive care.

Water Is Still Appropriate

Because capsaicin is poorly water soluble, various alternative solutions have been proposed.

These include:

• Milk
• Antacid suspension
• Baby shampoo
• Lidocaine gel
• Detergents

However, randomized human studies have not demonstrated superior pain relief from these agents compared with water decontamination.

In a trial comparing:

• Water
• Milk
• Maalox
• Baby shampoo
• 2% lidocaine gel

there was no significant difference between treatment groups; improvement was primarily related to time after exposure.

A separate randomized trial found that adding baby shampoo was no better than water alone.

Therefore:

Copious water irrigation remains a reasonable first-line decontamination method.

Soap

For dermal chili-pepper exposure, mild soap is useful because it assists physical removal of oily capsaicin-containing material.

Wash gently rather than aggressively scrubbing irritated skin.

Avoid Hot Water

Heat activates TRPV1 and may substantially intensify pain.

Therefore:

Cool or lukewarm water is generally preferable to hot water.

Alcohol Washes

The older recommendation to use alcohol is based on the fact that capsaicin dissolves in alcohol.

However:

Routine alcohol application is not recommended.

It can:

• Irritate already inflamed skin
• Produce severe pain on abrasions
• Potentially increase cutaneous penetration

Physical decontamination with water and mild soap is safer.

Vinegar

Older texts recommended dilute acetic acid/vinegar.

There is no good clinical evidence that vinegar is superior to water, and it may irritate already inflamed skin.

Therefore:

Routine vinegar immersion is not recommended.

Milk / Antacid Suspensions

Milk and antacid preparations are popular home remedies.

Controlled testing of OC exposure has not demonstrated a clinically important advantage over water.

Thus they are not required.

3. Pain Control

Most pain improves progressively after decontamination.

Supportive options include:

• Cool compresses
• Oral acetaminophen
• NSAIDs when appropriate

Topical Lidocaine

Older reports suggested that 2% lidocaine gel could relieve Hunan-hand pain.

However, randomized testing in OC-exposed volunteers showed no significant advantage of lidocaine gel over water.

Therefore:

Topical lidocaine is not established as superior routine therapy.

It may occasionally be considered for persistent severe localized discomfort on intact skin, but should not replace adequate decontamination.

4. Eye Decontamination

Immediately:

• Remove contact lenses
• Irrigate the eyes copiously with clean water or saline

Continue irrigation until:

• Marked burning improves
• The patient can comfortably open the eyes

Current reviews support prompt decontamination with water and symptom-directed evaluation.

Contact lenses

Soft contact lenses contaminated with OC should generally be discarded, because capsaicin can remain within the lens despite attempts at cleaning.

Persistent Ocular Symptoms

Perform further evaluation if there is:

• Continued severe pain
• Photophobia
• Foreign-body sensation
• Reduced visual acuity
• Inability to open the eye after irrigation

Consider:

• Fluorescein staining
• Slit-lamp examination

because corneal epithelial injury or abrasion can occur.

Ophthalmology consultation is appropriate for:

• Significant corneal injury
• Persistent visual abnormality
• Severe pain despite irrigation

5. Respiratory Exposure

Immediately:

Move the patient to fresh air

Remove contaminated clothing where practical.

Most respiratory symptoms improve rapidly.

Provide:

• Oxygen if hypoxemic
• Observation
• Supportive treatment

Bronchospasm

For wheezing/bronchospasm:

Inhaled β₂-agonist bronchodilator

such as:

• Albuterol/salbutamol

is appropriate.

Severe or persistent respiratory distress warrants:

• Continuous oxygen saturation monitoring
• Further pulmonary evaluation
• Escalation of respiratory support as needed

6. Ingestion

For oral exposure:

• Rinse the mouth
• Give small amounts of oral fluid if tolerated
• Treat nausea/vomiting supportively

Routine:

• Activated charcoal
• Gastric lavage
• Induced vomiting

are not indicated for ordinary isolated capsaicin ingestion.

Severe persistent GI symptoms or ingestion of a concentrated chemical formulation warrants poison-center/toxicology assessment.

Antidote

There is no specific antidote for capsaicin toxicity.

TRPV1 antagonists have been investigated experimentally, but they are not established clinical antidotes for accidental capsaicin or pepper-spray exposure.

Pepper Spray / Oleoresin Capsicum

OC spray causes a rapid combination of:

Blepharospasm + tearing + facial burning + cough/chest discomfort

Symptoms usually begin within:

• Seconds

and uncomplicated exposure often improves markedly within:

• 30–60 minutes

after removal from exposure and decontamination.

Secondary Contamination

Healthcare workers can become exposed from:

• Contaminated clothing
• Aerosolized residue
• Patient hair/skin

Therefore:

• Use gloves
• Remove contaminated clothing
• Place clothing in an appropriate bag
• Perform decontamination in a well-ventilated location when possible

Admission

Admission is usually unnecessary for uncomplicated Hunan-hand syndrome.

Consider hospital observation/admission for:

• Persistent hypoxemia
• Severe bronchospasm
• Respiratory distress
• Significant underlying pulmonary disease with persistent symptoms
• Major ocular injury
• Unexpected systemic abnormalities
• Significant exposure to a mixed chemical agent

Discharge

Patients can generally be discharged when:

• Pain is adequately controlled
• Eyes can open comfortably
• Vision is normal or appropriately assessed
• Respiratory symptoms have resolved
• Oxygenation is normal
• No significant secondary injury is identified

Prognosis

Hunan Hand

Symptoms generally resolve completely.

Pain may persist:

• Several hours
• Occasionally 1–2 days or longer after substantial exposure

Long-term injury is unusual.

Pepper Spray

Most effects resolve within approximately:

• 30–60 minutes

although residual skin/eye irritation can persist longer.

Persistent symptoms should prompt assessment for:

• Corneal injury
• Bronchospasm
• Alternative chemical exposure
• Traumatic injury

Prevention

When handling hot peppers:

• Wear nitrile or other appropriate impermeable gloves
• Avoid touching the eyes/face
• Wash hands carefully after preparation
• Do not assume thin gloves provide indefinite protection if heavily contaminated

When handling high-concentration therapeutic capsaicin, specialized precautions are required.

Current QUTENZA labeling specifically instructs healthcare workers to:

• Use nitrile, not latex, gloves
• Work in a well-ventilated area
• Consider facial/eye protection

because aerosolized capsaicin can irritate the eyes and respiratory tract.

Important Pitfalls

1. Using the old substance-P-only mechanism

The principal receptor is:

TRPV1

Substance P and CGRP are downstream mediators of neurogenic inflammation.

2. Calling capsaicin pain a thermal burn

The characteristic burning sensation results primarily from:

TRPV1 activation of nociceptive neurons

not actual heat injury.

3. Assuming no physical injury can occur

Most exposures cause neurogenic irritation rather than major tissue damage.

However:

• Prolonged skin exposure can blister
• Pepper spray can produce corneal epithelial injury

4. Using hot water

Heat can strongly exacerbate TRPV1-mediated burning.

Use:

Cool/lukewarm water

instead.

5. Recommending milk, Maalox, baby shampoo, vinegar, or lidocaine as proven superior therapy

Randomized data show that several popular decontamination remedies—including:

• Milk
• Maalox
• Baby shampoo
• Lidocaine gel

are not superior to water for pepper-spray pain.

6. Routinely washing with alcohol

Although capsaicin is alcohol-soluble, alcohol can increase irritation and is not required for routine clinical decontamination.

7. Missing corneal abrasion

Persistent ocular pain or foreign-body sensation after irrigation warrants:

Visual acuity + fluorescein examination

because corneal injury can occur.

8. Underestimating respiratory toxicity

Most cases are mild, but patients with:

• Asthma
• COPD
• Prolonged spray exposure
• Enclosed-space exposure

may develop significant bronchospasm or respiratory distress.

9. Forgetting mixed pepper-spray formulations

An incapacitating spray may contain:

• OC/capsaicinoids
• Solvents
• Propellants
• Other riot-control agents

Unexpected toxicity should prompt identification of the actual formulation.

High-Yield Toxicology Pearls

Hunan-hand syndrome = capsaicin-induced TRPV1 activation

Think:

Chili-pepper handling → intense burning hands + erythema with relatively little visible injury

Key points:

• Capsaicin is the major pungent capsaicinoid in chili peppers
• Main receptor: TRPV1
• TRPV1 activation → Na⁺/Ca²⁺ influx → nociceptor firing
• Substance P and CGRP contribute to neurogenic inflammation
• Typical skin effects:
• 
  
• Burning
• Stinging
• Erythema
• Hyperalgesia
• Heat may markedly worsen symptoms
• Classic limited exposure usually causes little or no blistering
• Main treatment: remove exposure + water/mild soap decontamination
• Use cool/lukewarm rather than hot water
• Water is not chemically ideal because capsaicin is lipophilic, but randomized studies have not shown milk, Maalox, baby shampoo, or lidocaine to be superior
• Routine vinegar or alcohol washes are not recommended
• Eye exposure → immediate copious water/saline irrigation
• Remove and discard contaminated soft contact lenses
• Persistent eye pain → fluorescein/slit-lamp examination
• Inhalation → fresh air + supportive care
• Bronchospasm → inhaled β₂ agonist
• No specific antidote
• Most pepper-spray symptoms improve substantially within 30–60 minutes
• Current prescription high-concentration capsaicin therapy includes QUTENZA 8%
• Prevention: impermeable/nitrile gloves and careful hand hygiene

Toxicology – Cantharidin (Blister Beetle)

Core concept

Cantharidin is a potent vesicant toxin produced by blister beetles of the family Meloidae.

The classic systemic poisoning syndrome is:

Severe mucosal irritation/GI bleeding → urinary tract injury + hematuria → acute kidney injury ± multiorgan toxicity

Important severe manifestations include:

• Hematemesis
• Hematuria
• Acute kidney injury
• Coagulopathy
• Seizures
• Shock
• Cardiac dysrhythmias

There is no specific antidote.

Current FDA labeling specifically warns that oral cantharidin exposure can cause life-threatening or fatal toxicity, including severe GI injury, renal failure, coagulopathy, seizures, and flaccid paralysis.

Sources

Blister Beetles

Cantharidin is produced by multiple species of Meloidae, including historically important species such as:

• Lytta vesicatoria — “Spanish fly”
• Epicauta species
• Mylabris species

Cantharidin may constitute approximately 0.2–5% of beetle dry weight, depending on species and other factors.

“Spanish Fly”

Cantharidin-containing preparations have historically been sold as:

• Aphrodisiacs
• Abortifacients
• Traditional remedies

The so-called aphrodisiac effect results from irritation and inflammation of the urinary/genital tract, not enhancement of normal sexual physiology.

Genitourinary irritation may cause:

Pelvic vascular congestion → painful erection/priapism

This is a toxic effect.

Current Therapeutic Use

The older statement that cantharidin is available only as a 1% wart treatment is outdated.

In the United States, FDA approved YCANTH® in 2023:

Cantharidin topical solution 0.7%

for:

Molluscum contagiosum in adults and children ≥2 years

It is administered by trained healthcare professionals.

Each mL contains:

7 mg cantharidin

and each single-use applicator contains approximately:

0.45 mL

or roughly 3.15 mg cantharidin.

Cantharidin is also used in compounded dermatologic preparations for selected lesions such as warts, but these should not be confused with the current FDA-approved indication.

Toxic Dose

The human dose-response relationship is imprecise.

Published reviews estimate that potentially fatal oral exposure may occur around:

10–60 mg of pure cantharidin

although substantial variation exists between cases.

Historical fatal cases have involved estimated doses of approximately:

26–45 mg

of cantharidin.

Therefore:

Very small quantities of concentrated cantharidin can cause severe or fatal poisoning.

Do not rely on a fixed milligram threshold to determine safety because:

• Concentration may be uncertain
• Traditional preparations are poorly standardized
• Beetle toxin content varies
• Patient susceptibility varies

Pathophysiology

Cantharidin is:

• Lipophilic
• A powerful vesicant
• A strong mucosal irritant

A major molecular mechanism is inhibition of:

Protein phosphatase 1 (PP1)

and

Protein phosphatase 2A (PP2A).

This disrupts cellular phosphorylation signaling and contributes to:

• Cellular injury
• Loss of epithelial adhesion
• Inflammation
• Apoptosis
• Tissue necrosis

Vesicant Effect

Cantharidin causes:

Epithelial injury → acantholysis → vesicle/bulla formation

This accounts for its therapeutic blister-forming action on skin and its dangerous effects after inappropriate exposure.

When ingested:

Mouth/esophagus/stomach → erosions, blistering, hemorrhage

When excreted through the urinary tract:

Kidneys/ureters/bladder/urethra → irritation, hemorrhage, hematuria

Renal Toxicity

Cantharidin is strongly associated with kidney injury.

Pathologic effects described include:

• Glomerular injury
• Tubular epithelial degeneration
• Tubular obstruction
• Hemorrhage involving the renal pelvis and urinary tract

Systemic poisoning may progress:

Hematuria/proteinuria → oliguria → acute kidney injury → renal failure

Clinical Features

Onset

Symptoms commonly begin approximately:

2–4 hours after ingestion

although reported onset ranges from minutes to many hours.

Severe multiorgan injury may become increasingly evident during the subsequent 24–48 hours.

HEENT / Mucosal Injury

Early findings may include:

• Burning mouth
• Burning throat
• Oral erythema
• Vesicles
• Bullae
• Ulceration
• Dysphagia
• Painful swallowing
• Oral bleeding

The severity generally increases with toxin concentration.

Current FDA labeling warns that cantharidin must not be used orally, on mucosa, or around the eyes.

Gastrointestinal

GI toxicity is one of the most characteristic manifestations.

Possible findings include:

• Severe epigastric burning
• Crampy abdominal pain
• Nausea
• Vomiting
• Hematemesis
• Diarrhea
• Hematochezia
• Occult GI bleeding

Severe mucosal damage may resemble corrosive gastrointestinal injury.

Genitourinary

Characteristic findings include:

• Dysuria
• Urinary frequency
• Flank/lumbar pain
• Hematuria
• Proteinuria

Hematuria may be:

• Microscopic
• Gross

and can persist after other symptoms begin to improve.

Priapism

Cantharidin may cause:

• Genital edema
• Genital blistering
• Painful urinary symptoms
• Priapism

The historic reputation as “Spanish fly” derives partly from this pathologic genital vascular congestion.

Renal

Renal manifestations include:

• Hematuria
• Proteinuria
• Granular urinary casts
• Oliguria
• Rising creatinine
• Acute kidney injury

Severe renal failure is one of the principal causes of death in reported systemic poisonings.

Possible secondary electrolyte abnormalities include:

• Hyperkalemia
• Hyponatremia
• Hypocalcemia

Cardiovascular

Possible findings include:

• Sinus tachycardia
• Nonspecific ECG abnormalities
• Hypotension

Severe poisoning can progress to:

• Shock
• Ventricular dysrhythmias
• Ventricular fibrillation
• Circulatory failure

Recent reviews identify acute circulatory failure together with acute renal failure among important causes of death.

Hematologic

Severe poisoning may produce:

• Gastrointestinal hemorrhage
• Urinary bleeding
• Thrombocytopenia
• Coagulation abnormalities
• Disseminated intravascular coagulation

Current FDA labeling specifically lists coagulopathy among serious consequences of oral ingestion.

Hepatic

Systemic poisoning can cause:

• Elevated aminotransferases
• Hepatocellular injury
• Hepatic necrosis in severe cases

Recent mechanistic literature suggests cantharidin can induce:

• Oxidative stress
• Apoptosis
• Autophagic dysfunction
• Endoplasmic-reticulum stress

in hepatic tissue.

Neurologic

Severe toxicity may cause:

• Confusion
• Lethargy
• Altered consciousness
• Seizures
• Coma
• Flaccid paralysis

CNS abnormalities should also prompt evaluation for:

• Shock
• Electrolyte disturbance
• Renal failure
• Hypoxia

Pulmonary

The lungs are not usually the primary target.

Severe systemic poisoning has nevertheless been associated with:

• Pulmonary hemorrhage
• Pulmonary edema
• Respiratory distress
• Aspiration pneumonia

Dermatologic Exposure

Cantharidin is intentionally a vesicant.

Local exposure may cause:

• Erythema
• Pain
• Pruritus
• Vesicles
• Bullae
• Erosion
• Ulceration

In current controlled trials of 0.7% topical cantharidin, local skin reactions occurred in 97% of treated patients, although these were predominantly expected treatment-site reactions.

Accidental exposure to normal skin should be removed promptly.

Ocular Exposure

This is potentially very serious.

Current FDA labeling reports possible:

• Severe ocular injury
• Corneal necrosis
• Deep ocular injury
• Ocular perforation

after eye exposure.

Therefore:

Immediately irrigate eyes with water for at least 15 minutes and obtain urgent medical/ophthalmologic assessment.

Diagnosis

Diagnosis is primarily clinical:

Exposure to blister beetle/cantharidin preparation + GI mucosal injury + hematuria/renal abnormalities

There is no routinely available rapid bedside cantharidin assay.

Specialized analytical techniques such as:

• GC-MS
• LC-MS/MS

may confirm exposure in forensic or specialized settings but do not guide immediate resuscitation.

Essential Investigations

For symptomatic ingestion obtain:

Hematologic

• CBC
• Hemoglobin/hematocrit
• Platelet count

Renal

• Electrolytes
• BUN
• Creatinine
• Urinalysis
• Urine output

Hepatic

• AST
• ALT
• Bilirubin

Acid–base

For severe disease:

• Blood gas
• Lactate

Coagulation Studies

In moderate or severe poisoning obtain:

• PT/INR
• aPTT
• Fibrinogen
• D-dimer when DIC is suspected

Cardiac Monitoring

Obtain:

• 12-lead ECG
• Continuous cardiac monitoring

in significant systemic poisoning because serious ventricular dysrhythmias have been reported.

Gastrointestinal Evaluation

Significant:

• Hematemesis
• Persistent dysphagia
• Severe chest/epigastric pain
• Major GI hemorrhage

may warrant gastroenterology consultation.

Endoscopic evaluation should be individualized because the mucosa may be severely friable or injured.

Differential Diagnosis

Consider other causes of:

GI irritation/bleeding + renal injury

including:

• Arsenic
• Mercuric chloride
• Colchicine
• Podophyllin
• Caustic ingestion
• Severe gastroenteritis
• Other nephrotoxic natural products

For hematuria consider:

• Glomerulonephritis
• Nephrolithiasis
• Hemorrhagic cystitis
• Coagulopathy
• Other nephrotoxins

Treatment

1. Initial Stabilization

Management begins with:

• Airway assessment
• Breathing/oxygenation
• IV access
• Hemodynamic assessment
• Continuous monitoring in significant toxicity

Treatment is primarily:

Supportive care

because there is no proven antidote.

2. Fluid Resuscitation

Patients may lose substantial fluid through:

• Vomiting
• GI bleeding
• Reduced oral intake

Use isotonic crystalloid to correct clinically significant volume depletion.

Monitor:

• Blood pressure
• Urine output
• Creatinine
• Electrolytes

Do Not Use Forced Diuresis

The historical recommendation to force urine output above 4 L/day is not appropriate as routine modern management.

Aggressive forced diuresis may cause:

• Volume overload
• Electrolyte disturbance
• Worsening renal injury

Instead:

Maintain euvolemia and adequate renal perfusion.

3. Gastrointestinal Decontamination

Do Not Induce Vomiting

Do not induce emesis.

Cantharidin is a powerful mucosal vesicant, and repeated passage through the esophagus can increase:

• Mucosal injury
• Bleeding
• Aspiration risk

Gastric Lavage

The older recommendation for routine lavage after a recent large ingestion should not be applied routinely.

Modern poisoning guidance discourages systematic gastric lavage, and cantharidin’s severe mucosal injury makes invasive GI decontamination particularly concerning.

If an extraordinarily large, immediately life-threatening ingestion has occurred, any invasive gastric decontamination decision should involve:

• Medical toxicology
• Airway protection
• Careful consideration of existing mucosal injury

Activated Charcoal

Evidence for activated charcoal specifically in human cantharidin poisoning is limited.

Single-dose charcoal may be considered after a very recent potentially severe ingestion if:

• The patient is alert with an intact airway, or intubated
• Significant vomiting/mucosal injury does not make administration unsafe
• A medical toxicologist/poison center recommends it

Routine administration is not supported by strong human outcome data.

Single-dose charcoal should not be routinely given to poisoned patients generally and should only be used when expected benefit outweighs aspiration risk.

4. GI Mucosal Injury

Supportive treatment may include:

• IV fluids
• Antiemetics
• Analgesia
• Acid suppression in significant upper-GI injury

Proton-pump inhibitors have been used in reported systemic poisoning to support healing of gastric erosions/ulceration, although evidence is based largely on case experience.

5. Hemorrhage

For clinically important blood loss:

• Type and crossmatch
• Packed RBC transfusion as required

For severe coagulopathy or DIC:

• Treat according to the clinical bleeding syndrome
• Replace blood components when indicated

6. Hypotension / Shock

Treat with:

• Isotonic crystalloid when fluid responsive
• Blood products if hemorrhage contributes

If shock persists:

Use contemporary vasopressor therapy, generally norepinephrine according to the patient’s shock physiology.

The older recommendation to preferentially use dopamine is outdated.

7. Seizures

Treat toxin-induced seizures with:

Benzodiazepines first-line

Examples:

• Lorazepam
• Midazolam
• Diazepam

For refractory seizures consider:

• Phenobarbital
• Propofol in an appropriately intubated patient

Also correct:

• Hypoglycemia
• Hypoxia
• Electrolyte disturbances

8. Acute Kidney Injury

Management includes:

• Maintain appropriate circulating volume
• Monitor urine output
• Correct electrolytes
• Avoid nephrotoxic medications

Monitor particularly for:

• Hyperkalemia
• Metabolic acidosis
• Progressive oliguria

Hemodialysis

Hemodialysis does not appear to remove cantharidin effectively.

Cantharidin:

• Is lipophilic
• Circulates extensively bound to albumin

Therefore, conventional dialysis should not be used solely as toxin-removal therapy.

However, dialysis remains appropriate for standard complications of renal failure such as:

• Refractory hyperkalemia
• Severe metabolic acidosis
• Fluid overload
• Uremic complications

Hemoperfusion / Hemofiltration

Hemoperfusion and hemofiltration have been used in severe poisoning, including recent cases of multiorgan dysfunction.

A recent review also discusses blood-purification strategies because standard hemodialysis removes the albumin-bound toxin poorly.

However:

Evidence remains limited predominantly to case reports and observational experience.

These should be considered specialist rescue strategies rather than established routine therapy.

Antidote

There is no specific antidote for cantharidin poisoning.

Current treatment is:

Supportive resuscitation + GI/renal monitoring + treatment of bleeding, seizures, shock, and renal failure

Skin Decontamination

For unintended topical exposure:

• Remove contaminated clothing
• Remove residual product promptly
• Wash thoroughly with soap and water

For the current FDA-approved preparation, inadvertent contact with healthy skin should be immediately wiped away; severe local reactions warrant earlier washing rather than waiting the usual 24 hours.

Do not intentionally neutralize cantharidin with strong acids or alkalis.

Eye Decontamination

Immediately:

• Irrigate continuously with water or saline for at least 15 minutes

Then obtain urgent medical evaluation.

Because severe ocular complications include corneal necrosis and perforation, persistent pain or vision symptoms warrant prompt ophthalmologic assessment.

Monitoring

Symptomatic systemic poisoning warrants serial:

• Vital signs
• Mental status
• CBC
• Hemoglobin
• Platelets
• Electrolytes
• BUN/creatinine
• Urinalysis
• Urine output
• Liver enzymes
• Coagulation parameters

Severe cases require:

• Continuous cardiac monitoring
• Respiratory monitoring
• Serial blood gases/lactate as indicated

Admission

Hospital admission is appropriate for:

• Any significant intentional cantharidin ingestion
• Oral/mucosal blistering
• Persistent vomiting
• Hematemesis
• Hematochezia
• Hematuria
• Proteinuria
• Acute kidney injury
• Significant electrolyte abnormalities
• Coagulopathy
• Seizures
• Dysrhythmia
• Hypotension

Because renal and systemic injury may progress after the initial GI syndrome, significant ingestions warrant ongoing inpatient observation, not simply a fixed 6-hour rule.

Severe multiorgan toxicity requires ICU management.

Disposition

The old recommendation that every asymptomatic patient can be discharged after exactly 6 hours is overly rigid.

Disposition should depend on:

• Reliability of exposure history
• Estimated concentration
• Presence of mucosal injury
• Urinalysis
• Renal function
• Hemodynamic status
• Coingestants

A clinically meaningful ingestion deserves poison-center/medical-toxicology input because renal manifestations may evolve after early gastrointestinal symptoms.

Pregnancy

The historical FDA pregnancy-category system is obsolete.

For current topical YCANTH:

• There are insufficient human pregnancy data
• Systemic exposure after appropriate topical treatment is low
• Significant fetal exposure from correctly used topical therapy is not expected according to current labeling.

This is very different from systemic poisoning.

Historically, oral cantharidin has been misused as an abortifacient and can cause severe maternal toxicity.

In poisoning:

Maternal stabilization is the priority.

Breastfeeding

For appropriately applied topical cantharidin, systemic absorption is low.

Current labeling advises avoiding application where the breastfeeding infant could:

• Ingest the product
• Contact treated skin with the eyes or mouth.

Prognosis

Mild topical exposure generally causes only local blistering and irritation.

Significant ingestion may progress rapidly to:

• GI hemorrhage
• Hematuria
• AKI
• Shock
• Multiorgan failure

Severe cases often declare major systemic involvement during the first 24–48 hours.

Renal and urinary abnormalities may persist considerably longer than the acute GI symptoms.

Mortality is uncommon with modern supportive care but can occur after concentrated systemic exposure.

Important Pitfalls

1. Calling “Spanish fly” a harmless aphrodisiac

Cantharidin does not produce a physiologic aphrodisiac response.

It causes:

Genitourinary inflammation → vascular congestion → painful priapism

and may be fatal.

2. Underestimating tiny concentrated doses

Estimated fatal doses are measured in tens of milligrams, not grams of purified cantharidin.

3. Missing delayed renal injury

The early presentation may be dominated by:

• Oral burning
• Vomiting
• GI bleeding

while:

Hematuria + oliguria + rising creatinine

develop later.

4. Forcing urine output

The old target of >4 L/day is not evidence-based and may cause harm.

Maintain appropriate euvolemia instead.

5. Using routine gastric lavage

Cantharidin causes severe mucosal injury.

Routine lavage is not modern standard management and may worsen complications.

6. Assuming hemodialysis removes cantharidin

It generally does not efficiently clear the albumin-bound toxin.

Use dialysis for renal failure complications, not routine toxin extraction.

7. Missing coagulopathy

Severe systemic poisoning may cause:

• Thrombocytopenia
• Coagulation abnormalities
• DIC

Current FDA labeling specifically warns of coagulopathy after oral exposure.

8. Missing serious eye injury

Ocular exposure can cause:

Corneal necrosis or perforation

and requires immediate irrigation and medical assessment.

9. Using the old therapeutic formulation information

Current U.S. FDA-approved cantharidin therapy is:

YCANTH 0.7% topical solution

for:

Molluscum contagiosum in patients ≥2 years

not simply a 1% wart solution.

High-Yield Toxicology Pearls

Cantharidin = vesicant GI/GU toxin

Think:

Severe GI irritation + hematemesis + hematuria + AKI after “Spanish fly”/blister beetle exposure

Key points:

• Produced by blister beetles (Meloidae)
• Historically known as Spanish fly
• Major molecular targets: PP1 and PP2A inhibition
• Potent vesicant
• Oral toxicity causes severe mucosal blistering and hemorrhage
• Genitourinary irritation causes:
• Dysuria
• Hematuria
• Proteinuria
• Priapism
• Major systemic complication: acute kidney injury
• Severe poisoning can also cause:
• Coagulopathy/DIC
• Seizures
• Shock
• Ventricular dysrhythmias
• Hepatic injury
• Estimated fatal pure-can­tharidin doses are roughly 10–60 mg, but individual variability is large
• No specific antidote
• Do not induce vomiting
• Routine gastric lavage is not recommended
• Activated charcoal has uncertain human benefit and should be individualized
• Maintain euvolemia; do not use forced diuresis
• Conventional hemodialysis does not effectively remove cantharidin
• Dialysis is used for conventional complications of renal failure
• Hemoperfusion/hemofiltration have been reported as rescue therapies, but evidence is limited
• Current FDA-approved product: YCANTH 0.7%
• FDA indication: molluscum contagiosum, age ≥2 years
• Oral YCANTH exposure can be fatal
• Eye exposure can cause corneal necrosis/perforation
• Significant ingestion requires prolonged renal, hematologic, and cardiovascular monitoring

Toxicology – Camphor

Core concept

Camphor is a rapidly absorbed, highly lipophilic terpene found in many topical rubs, vapor products, liniments, and household preparations.

The characteristic poisoning syndrome is:

GI irritation → abrupt CNS excitation → seizures ± coma/respiratory failure

The most important clinical feature is the very rapid onset:

Camphor ingestion → oral/GI burning → agitation/tremor → sudden generalized seizures

Seizures often occur within the first 1–2 hours, and patients can deteriorate with little warning.

Forms and Uses

Camphor is:

• Colorless or white
• Crystalline or waxy
• Highly volatile
• Strongly aromatic

It remains present in many:

• Topical analgesic rubs
• Vaporizing preparations
• Liniments
• Antipruritic products
• Counterirritants
• Moth repellents
• Cosmetic or traditional remedies

Modern U.S. OTC external-analgesic monographs permit camphor in specified topical concentrations; for example, camphor-containing counterirritant preparations are generally limited to approximately 11% or less, depending on formulation and indication.

Important

Camphor-containing products may also contain other potentially toxic ingredients such as:

• Menthol
• Methyl salicylate
• Eucalyptus oil
• Alcohols
• Other topical analgesics

Therefore, always identify the entire product, not just the camphor concentration.

Routes of Exposure

Toxicity can occur after:

Ingestion

The most important and common route in children.

Dermal absorption

Systemic poisoning has occurred after:

• Excessive topical application
• Application over large areas
• Application to damaged skin

Inhalation

Usually causes irritation, although significant systemic exposure is less common.

Intranasal or traditional medicinal use

Unusual administration practices can produce systemic poisoning.

Camphor is sufficiently lipophilic to be absorbed through both the gastrointestinal tract and skin.

Toxic Dose

There is no absolute dose that reliably predicts toxicity.

Historical lethal-dose estimates such as 50–500 mg/kg are extremely broad and should not be used as precise clinical thresholds.

A modern evidence-based poison-center guideline recommends emergency evaluation for:

>30 mg/kg of a camphor-containing product

or for any patient with moderate or severe symptoms, including:

• Seizures
• Lethargy
• Ataxia
• Severe nausea/vomiting

regardless of dose.

Therefore:

30 mg/kg is best viewed as a referral threshold, not a guaranteed toxic dose.

Small children are at particular risk because relatively small volumes of concentrated products can deliver substantial mg/kg doses.

Pathophysiology

The precise mechanism of camphor neurotoxicity is incompletely defined.

Major effects include:

Rapid CNS stimulation → neuronal hyperexcitability → seizures

Camphor also acts as a local irritant to:

• Oral mucosa
• Stomach
• Skin
• Eyes
• Respiratory tract

Its rapid gastrointestinal absorption explains why:

• Symptoms occur quickly
• GI decontamination has little benefit once the patient presents

Clinical Features

Onset

Symptoms usually begin rapidly, often within:

5–90 minutes

with most clinically important seizures occurring within the first 2 hours after ingestion.

This rapid onset is a defining feature.

Gastrointestinal

Early symptoms commonly include:

• Burning in the mouth
• Throat irritation
• Epigastric burning
• Nausea
• Vomiting
• Abdominal discomfort

Vomiting may precede neurologic deterioration.

Neurologic

Mild–Moderate Toxicity

Possible findings include:

• Restlessness
• Irritability
• Dizziness
• Confusion
• Tremor
• Fasciculations
• Agitation
• Delirium

Severe Toxicity

The hallmark is:

Generalized seizures

Seizures may:

• Occur suddenly
• Occur without a prolonged prodrome
• Recur
• Progress to status epilepticus

Severe poisoning may also cause:

• CNS depression
• Coma
• Postictal respiratory depression

Respiratory

Respiratory compromise usually results from:

• Postictal hypoventilation
• Recurrent seizures
• Aspiration
• Severe CNS depression

Possible findings:

• Bradypnea
• Apnea
• Hypoxemia
• Aspiration pneumonitis

Respiratory support is therefore a major component of severe-poisoning management.

Cardiovascular

Possible manifestations include:

• Sinus tachycardia
• Occasional hypertension associated with agitation
• Rare hypotension or circulatory collapse in massive poisoning

Serious primary dysrhythmias are less characteristic than the neurologic syndrome.

HEENT

Characteristic findings may include:

• Strong camphor odor on the breath
• Oral burning
• Throat irritation
• Mydriasis

Occupational vapor exposure may produce:

• Eye irritation
• Nasal irritation
• Sore throat
• Headache

Dermatologic

Topical exposure can cause:

• Irritation
• Erythema
• Contact dermatitis

Significant systemic toxicity after dermal exposure is unusual but becomes more plausible with:

• Large surface-area application
• Occlusion
• Damaged skin
• High-concentration preparations
• Infants or small children

Hepatic

Mild aminotransferase elevation has occasionally been described after substantial exposure.

Clinically important hepatotoxicity is not a defining feature of acute camphor poisoning and alternative causes should be sought if severe hepatic injury develops.

Diagnosis

Diagnosis is primarily:

Exposure history + rapid-onset neuroexcitation/seizures + characteristic camphor odor

There is no routinely available clinically useful serum camphor test.

Treatment should never wait for analytical confirmation.

Essential Assessment

For any symptomatic exposure assess:

• Airway
• Respiratory rate
• Oxygenation
• Mental status
• Temperature
• Heart rate
• Blood pressure
• Blood glucose

A bedside glucose should be obtained in any patient with:

• Seizure
• Altered consciousness

Laboratory Investigations

Mild asymptomatic exposure

Routine laboratory testing is usually unnecessary.

Significant toxicity or seizures

Consider:

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

With repeated/prolonged seizures:

• CK
• Urinalysis
• Renal function

In intentional overdose:

• Acetaminophen concentration
• Salicylate concentration
• Evaluation for other coingestants

A blood gas and lactate may be appropriate after:

• Prolonged seizures
• Respiratory failure
• Hemodynamic instability

ECG

Obtain an ECG in:

• Significant intentional ingestion
• Severe poisoning
• Suspected coingestion
• Hemodynamic instability

Continuous cardiac monitoring is appropriate for severe symptomatic cases.

Differential Diagnosis

Camphor poisoning may resemble other causes of sudden toxicologic seizures, including:

• Caffeine
• Theophylline
• Cocaine
• Amphetamines
• Tricyclic antidepressants
• Isoniazid
• Nicotine
• Organophosphates
• Carbamates
• Strychnine
• Lindane
• Other essential oils or topical preparations

Non-toxicologic causes include:

• Hypoglycemia
• Electrolyte disturbance
• CNS infection
• Intracranial hemorrhage
• Epilepsy
• Structural brain disease

Treatment

1. Airway and Breathing

The initial priority is:

Airway protection + adequate oxygenation/ventilation

Provide:

• Supplemental oxygen when indicated
• Suction
• Bag-mask ventilation if needed

Intubate when there is:

• Refractory/recurrent seizure activity
• Persistent coma
• Inability to protect the airway
• Significant respiratory failure

2. Seizures

First-line

Benzodiazepines are the treatment of choice.

Appropriate agents include:

• Lorazepam
• Midazolam
• Diazepam

The evidence-based camphor guideline specifically recommends benzodiazepines for camphor-induced convulsions.

Repeat dosing may be needed.

Refractory Seizures

If seizures persist despite adequate benzodiazepines, consider:

Phenobarbital

For refractory status epilepticus in an intubated patient:

• Propofol
• Continuous benzodiazepine infusion

may be required.

Phenytoin

Older references list phenytoin as an option.

However:

Phenytoin is generally not preferred for toxin-induced seizures.

Toxicologic seizures arise from diffuse chemical neuronal excitation rather than the focal sodium-channel mechanisms for which phenytoin is most effective. Reviews favor barbiturates over phenytoin when benzodiazepines fail.

Gastrointestinal Decontamination

Do Not Induce Vomiting

Never induce emesis.

Camphor can cause sudden seizures and loss of airway reflexes.

Ipecac is specifically contraindicated in modern camphor-poisoning guidance.

Activated Charcoal

The older source recommends activated charcoal.

Current evidence-based guidance does not recommend routine activated charcoal for isolated camphor ingestion because:

• Camphor is absorbed rapidly
• Clinical benefit has not been demonstrated
• Seizure/aspiration risk is significant

Charcoal may occasionally be considered if the product contains other clinically important substances that bind well to charcoal, provided the airway is adequately protected.

Gastric Lavage

Routine gastric lavage is not recommended.

Because camphor is absorbed rapidly and seizures may develop abruptly, the potential benefit is small while aspiration risk is substantial.

The historical recommendation for lavage within 1 hour should therefore not be used routinely.

Skin Exposure

Remove contaminated clothing.

Wash exposed skin thoroughly with:

• Soap
• Water

For extensive topical exposure, particularly in infants or over damaged skin:

• Remove all residual product
• Observe for systemic neurologic symptoms

Eye Exposure

Irrigate promptly and copiously with:

• Water
• Normal saline

Persistent:

• Pain
• Redness
• Visual disturbance

requires ocular assessment.

Inhalation Exposure

Move the patient to:

• Fresh air

Provide:

• Oxygen if clinically indicated
• Supportive treatment for airway irritation

Significant neurologic symptoms after inhalation should be managed the same way as systemic poisoning.

Antidote

There is no specific antidote for camphor poisoning.

Treatment is:

Supportive care + aggressive seizure control + airway management

Hemodialysis

Conventional hemodialysis is not a useful routine enhanced-elimination technique for camphor.

Camphor is:

• Highly lipophilic
• Rapidly distributed

so extracorporeal removal is unlikely to provide meaningful benefit in most cases.

Historical reports of:

• Lipid dialysis
• Resin hemoperfusion

do not establish a modern routine role.

Treatment should focus on supportive critical care.

Rhabdomyolysis

Repeated or prolonged seizures may cause:

• Elevated CK
• Myoglobinuria
• Acute kidney injury

Monitor:

• CK
• Potassium
• Creatinine
• Urine output

and treat according to standard rhabdomyolysis principles.

Observation

A useful feature of camphor poisoning is the rapid onset of symptoms.

An evidence-based poison-center guideline concluded that patients who remain completely asymptomatic for 4 hours after exposure can generally continue observation at home, depending on the reliability of the exposure history and product.

For emergency-department observation, a practical period of approximately:

4–6 hours

is commonly sufficient for an asymptomatic patient after an isolated immediate exposure when:

• History is reliable
• No delayed-acting coingestants are present
• Vital signs remain normal
• Neurologic examination remains normal

The historical routine 6–8-hour observation period is therefore conservative but reasonable in uncertain exposures.

Admission

Hospital admission is appropriate for:

• Any seizure
• Recurrent vomiting with toxicity
• Persistent agitation
• Ataxia
• Altered mental status
• Respiratory depression
• Hypoxemia
• Significant intentional ingestion
• Significant metabolic complications

Patients with:

• Recurrent seizures
• Status epilepticus
• Respiratory failure
• Coma

require ICU-level care.

Prognosis

Camphor poisoning generally has a rapid course.

If severe toxicity does not develop during the early period, delayed deterioration is uncommon.

Most survivors of isolated poisoning recover fully within approximately:

24–48 hours

provided that:

• Seizures are controlled
• Hypoxic injury is prevented

Long-term neurologic injury primarily results from complications such as:

• Prolonged seizures
• Hypoxia
• Aspiration

rather than persistent camphor neurotoxicity.

Pregnancy

The old FDA Pregnancy Category C system is obsolete.

Camphor is capable of crossing the placenta, and severe maternal poisoning poses risk through:

• Maternal seizure
• Hypoxia
• Hemodynamic instability

Management should prioritize:

Maternal resuscitation and seizure control

with obstetric assessment when poisoning is significant.

Occupational Exposure

Current U.S. limits for synthetic camphor are:

OSHA PEL: 2 mg/m³ as an 8-hour TWA

NIOSH REL: 2 mg/m³ TWA

NIOSH IDLH: 200 mg/m³

The older ACGIH value of 2 ppm ≈12 mg/m³ should not be confused with the substantially lower current OSHA/NIOSH TWA of 2 mg/m³.

Important Pitfalls

1. Underestimating how fast toxicity develops

Camphor is absorbed rapidly.

Seizures can develop within minutes and usually occur within the first 1–2 hours.

2. Waiting for laboratory confirmation

There is no clinically useful rapidly available camphor concentration.

Treatment is based on the clinical syndrome.

3. Inducing vomiting

Do not give ipecac or otherwise induce emesis.

The patient may seize abruptly.

4. Giving routine activated charcoal

Modern evidence-based camphor guidance specifically advises against routine charcoal after isolated ingestion.

5. Performing routine gastric lavage

Rapid absorption and seizure risk make lavage an unfavorable routine intervention.

6. Using phenytoin as the preferred second-line anticonvulsant

For toxin-induced seizures:

Benzodiazepines → phenobarbital/appropriate anesthetic therapy

is generally preferable to routine phenytoin.

7. Missing product coingredients

A “camphor rub” may also contain:

• Methyl salicylate
• Menthol
• Eucalyptus oil
• Other active substances

The complete product formulation matters.

8. Forgetting dermal toxicity

Extensive application, especially to:

• Infants
• Damaged skin
• Large body surfaces

can produce systemic absorption.

9. Treating every asymptomatic ingestion as prolonged-risk poisoning

Unlike sustained-release drugs, camphor toxicity generally declares itself rapidly.

A completely asymptomatic patient after an adequate early observation period is unlikely to develop late isolated camphor toxicity.

High-Yield Toxicology Pearls

Camphor = rapid-onset seizures after household-product exposure

Think:

Camphor ingestion → burning/vomiting → agitation → sudden seizure

Key points:

• Camphor is a volatile, rapidly absorbed CNS stimulant
• Main serious toxicity: seizures
• Small children are particularly vulnerable
• >30 mg/kg is a modern poison-center referral threshold, not an absolute toxicity cutoff
• Symptoms generally begin within minutes to a few hours
• Most seizures occur within the first 2 hours
• Strong camphor odor may provide an important diagnostic clue
• Check glucose in any patient with seizure or altered mental status
• Main treatment: airway support + benzodiazepines
• Refractory toxicologic seizures → phenobarbital, with propofol/continuous sedation for refractory status as appropriate
• Phenytoin is not preferred for toxin-induced seizures
• Do not induce vomiting
• Routine activated charcoal is not recommended
• Routine gastric lavage is not recommended
• No specific antidote
• Conventional hemodialysis has no routine role
• Monitor CK/renal function after prolonged or repeated seizures
• Completely asymptomatic patients after approximately 4–6 hours are unlikely to develop delayed isolated camphor toxicity
• OSHA PEL and NIOSH REL: 2 mg/m³ TWA
• NIOSH IDLH: 200 mg/m³
• With prompt seizure control and prevention of hypoxia, recovery is usually complete

Toxicology – Calcium Channel-Blocking Drugs (CCBs)

Core concept

Calcium channel blocker overdose is a potentially lethal cardiovascular poisoning characterized by vasodilation, myocardial depression, conduction disturbance, and impaired insulin secretion.

The classic severe syndrome is:

Hypotension + bradycardia/conduction block + hyperglycemia → shock

A useful mechanistic sequence is:

L-type Ca²⁺ channel blockade → ↓ cardiac contractility + ↓ SA/AV conduction + arterial vasodilation + ↓ pancreatic insulin release → cardiogenic/vasodilatory shock

Current resuscitation guidance emphasizes early high-dose insulin, vasopressors, and IV calcium rather than the older sequence of progressively trying atropine, dopamine, glucagon, and calcium.

Important CCB Classes

Non-dihydropyridines

Verapamil

Most prominent effects:

• Negative inotropy
• Bradycardia
• AV block
• Hypotension

Diltiazem

Similar to verapamil:

• Bradycardia
• AV nodal blockade
• Reduced contractility
• Hypotension

Dihydropyridines

Examples:

• Amlodipine
• Nifedipine
• Nicardipine
• Felodipine
• Isradipine
• Nimodipine
• Nisoldipine

At therapeutic concentrations these predominantly affect vascular smooth muscle, producing:

Peripheral vasodilation → hypotension → reflex tachycardia

However:

In massive overdose, receptor selectivity is lost.

Thus even amlodipine or nifedipine poisoning can eventually produce:

• Bradycardia
• AV block
• Severe myocardial depression
• Cardiogenic shock

Formulations

CCBs may be:

• Immediate release
• Extended release
• Sustained release

Extended-release products are particularly dangerous because they may cause:

Delayed onset + prolonged absorption + prolonged cardiovascular collapse

Occasionally, tablet concretions or pharmacobezoars contribute to prolonged toxicity.

Toxic Dose

There is no single reliable toxic dose applicable to all CCBs.

Severity depends on:

• Specific agent
• Dose
• Immediate- vs extended-release formulation
• Patient age/size
• Cardiac disease
• Hepatic function
• Coingestants

Historical teaching that approximately 1 g of verapamil, diltiazem, or nifedipine may cause severe adult toxicity is useful only as a rough warning, not a safe threshold.

Even relatively small exposures may be dangerous in young children.

Therefore:

Manage according to formulation, clinical findings, ECG, glucose, and hemodynamics—not dose alone.

Pathophysiology

CCBs inhibit L-type voltage-gated calcium channels.

Myocardium

Reduced intracellular calcium causes:

↓ Contractility → ↓ stroke volume → ↓ cardiac output

leading to:

• Hypotension
• Cardiogenic shock

SA and AV Nodes

Calcium current is particularly important for nodal depolarization.

Blockade therefore causes:

• Sinus bradycardia
• PR prolongation
• AV block
• Junctional rhythms
• Escape rhythms

This is most prominent with:

• Verapamil
• Diltiazem

Vascular Smooth Muscle

Reduced calcium entry produces:

Arteriolar vasodilation → ↓ systemic vascular resistance → hypotension

This is particularly prominent in:

• Amlodipine
• Nifedipine
• Other dihydropyridines

Pancreatic β Cells

Insulin secretion is calcium dependent.

Therefore:

CCB blockade → ↓ insulin secretion + insulin resistance → hyperglycemia

At the same time, shocked myocardium increasingly depends on glucose as an energy substrate.

Thus:

CCB poisoning → hypoinsulinemia + impaired myocardial glucose utilization → worsening myocardial dysfunction

This is a major rationale for high-dose insulin therapy.

Hyperglycemia – Important Diagnostic Clue

Hyperglycemia is characteristic of significant CCB toxicity.

It may correlate with severity because pancreatic β-cell calcium channels are inhibited.

A useful toxicologic contrast is:

CCB poisoning → hyperglycemia common

β-blocker poisoning → hypoglycemia may occur

This distinction is helpful but not absolute.

Clinical Features

Cardiovascular

The major findings are:

• Hypotension
• Bradycardia
• Sinus-node suppression
• PR prolongation
• AV block
• Junctional rhythms
• Intraventricular conduction abnormalities
• Reduced cardiac output
• Cardiogenic shock
• Ventricular dysrhythmias
• Cardiac arrest

Dihydropyridine poisoning

Early:

• Severe hypotension
• Reflex tachycardia

Massive overdose:

• Bradycardia
• Myocardial depression

Verapamil/diltiazem poisoning

More likely to produce:

• Severe bradycardia
• AV block
• Negative inotropy
• Cardiogenic shock

Shock Phenotypes

Severe poisoning can produce different forms of shock.

Vasodilatory shock

Especially common with dihydropyridines:

Low SVR + relatively preserved cardiac function

Cardiogenic shock

Especially common with verapamil/diltiazem:

Severely impaired contractility + low cardiac output

Mixed shock

Many severe patients develop:

Vasodilation + myocardial depression