Toxicology – Chloral Hydrate

Core concept

Chloral hydrate is an old sedative-hypnotic that is rapidly converted to the active CNS depressant trichloroethanol (TCE).

The characteristic severe overdose syndrome is:

CNS depression → respiratory depression/coma + myocardial depression + catecholamine-sensitive ventricular dysrhythmias

The distinctive toxicologic danger is the combination of:

Coma + refractory ventricular dysrhythmias

Severe poisoning may produce:

• Respiratory failure
• Hypotension
• Ventricular tachycardia
• Torsades de pointes
• Ventricular fibrillation
• Cardiac arrest

Treatment is primarily:

Airway/ventilatory support + continuous ECG monitoring + targeted treatment of dysrhythmias

There is no specific chemical antidote.

Current Status and Uses

Chloral hydrate was historically used for:

• Insomnia
• Sedation
• Pediatric procedural sedation
• Preanesthetic medication
• Alcohol withdrawal

Most of these uses have largely been replaced by medications with better:

• Pharmacokinetics
• Safety margins
• Reversibility

such as benzodiazepines and dexmedetomidine.

The former U.S. product Somnote is listed by FDA as a discontinued chloral hydrate product with no generic equivalent. (FDA Access Data⁠)

Chloral hydrate nevertheless remains in use in some countries and institutions, particularly for pediatric diagnostic/procedural sedation, and may also be encountered through compounded preparations. Contemporary pediatric literature still describes its procedural use internationally. (PubMed Central (PMC)⁠)

In the United States, chloral hydrate remains a:

Schedule IV controlled substance

because of abuse/dependence potential. (PubChem⁠)

Forms

Historically available formulations included:

• Oral solution/syrup
• Capsules/tablets
• Rectal preparations

Current availability varies significantly by country.

The older routine adult insomnia dose of 0.5–1 g is mainly of historical relevance rather than a preferred modern insomnia regimen.

Toxic Dose

There is no reliably safe numerical cutoff after overdose.

Significant toxicity can occur after relatively modest supratherapeutic doses, particularly with:

• Other CNS depressants
• Cardiovascular disease
• Young age
• Delayed airway management

Historical reports describe fatalities after approximately:

4–10 g

but survival has also occurred after much larger doses with aggressive critical care and extracorporeal treatment. (PubMed⁠)

Thus:

Clinical toxicity is more important than the reported dose.

Pathophysiology

Active Metabolite – Trichloroethanol

Chloral hydrate itself has an extremely short presence in the circulation and is rapidly converted, primarily through alcohol dehydrogenase, to:

Trichloroethanol (TCE)

TCE accounts for much of the:

• Sedation
• Hypnosis
• CNS depression

Chloral hydrate and TCE are believed to enhance inhibitory signaling involving:

GABA-A receptors

although their mechanism is less precisely characterized than that of modern benzodiazepines. (PubMed Central (PMC)⁠)

Metabolism

A simplified pathway is:

Chloral hydrate → trichloroethanol → glucuronide metabolites

and:

Chloral hydrate → trichloroacetic acid (TCA)

TCE is the major active metabolite.

At therapeutic exposure its half-life is approximately:

8–12 hours

but in overdose its elimination can be markedly prolonged, with reported half-lives extending toward 24–35 hours or longer. (PubMed Central (PMC)⁠)

Therefore:

Clinical depression may substantially outlast disappearance of the parent chloral hydrate.

Ethanol Interaction

The older description of a simple “disulfiram-like reaction” is incomplete.

The more clinically important interaction is:

Chloral hydrate + ethanol → enhanced and prolonged CNS depression

Human pharmacokinetic studies found that ethanol can increase and prolong plasma TCE concentrations, while TCE can inhibit ethanol metabolism. (ASCPT⁠)

Thus:

Alcohol + chloral hydrate is a particularly dangerous sedative combination.

This interaction contributed historically to chloral hydrate’s notorious use in drug-facilitated intoxication.

Cardiac Toxicity

Cardiotoxicity is one of the most distinctive features of severe chloral hydrate poisoning.

Effects include:

• Reduced myocardial contractility
• Increased cardiac automaticity
• Shortened refractory periods
• Sensitization of the myocardium to catecholamines

This catecholamine sensitization predisposes to:

Ventricular ectopy → VT → VF

especially when endogenous or administered catecholamines are high. (PubMed Central (PMC)⁠)

Clinical Features

Neurologic

Possible manifestations include:

• Dizziness
• Lightheadedness
• Ataxia
• Dysarthria
• Somnolence
• Confusion
• Depressed reflexes

Severe poisoning:

• Coma
• Respiratory depression
• Rare seizures

The dominant neurologic syndrome is generally:

Sedative-hypnotic CNS depression

Respiratory

Severe poisoning may cause:

Bradypnea → hypoventilation → hypercapnia → apnea

Additional complications include:

• Loss of airway reflexes
• Aspiration
• Hypoxic injury

Early intubation is appropriate for:

• Progressive CNS depression
• Inadequate ventilation
• Loss of airway protection
• Severe cardiovascular toxicity

Current pediatric toxicology guidance specifically emphasizes early intubation when CNS or cardiovascular toxicity is progressing. (Royal Children’s Hospital⁠)

Cardiovascular

Possible effects include:

• Sinus tachycardia
• Hypotension
• Myocardial depression
• Ventricular ectopy
• Bigeminy
• Supraventricular tachyarrhythmias
• Ventricular tachycardia
• Torsades de pointes
• Ventricular fibrillation

A case series reported transient bigeminy after an estimated 219 mg/kg ingestion and torsades/VF after a much larger ingestion. (PubMed⁠)

Cardiovascular toxicity can dominate the presentation even when ventilation is being supported.

Gastrointestinal

Chloral hydrate is directly irritating to the GI tract.

Possible symptoms:

• Nausea
• Vomiting
• Epigastric pain
• Esophageal discomfort
• Abdominal pain

Gastric mucosal irritation can be substantial after large ingestion.

HEENT

Reported findings include:

• Miosis
• Mucosal irritation
• Occasionally a characteristic pungent/pear-like odor on the breath

These findings are neither sensitive nor specific enough to establish the diagnosis.

Hypothermia

Like other sedative-hypnotic poisonings, severe intoxication may result in:

Hypothermia

particularly after prolonged coma or environmental exposure.

Diagnosis

Diagnosis is generally:

Exposure history + sedative toxidrome ± characteristic ventricular dysrhythmias

There is no routine rapidly available serum chloral hydrate concentration that guides emergency management.

Laboratory Investigations

For significant poisoning obtain:

• Bedside glucose
• Electrolytes
• Potassium
• Magnesium
• Calcium
• Bicarbonate
• BUN
• Creatinine

In severe toxicity consider:

• Blood gas
• Lactate
• Liver enzymes
• CK after prolonged coma/seizures

For intentional overdose obtain appropriate coingestant testing, including:

• Acetaminophen concentration
• Salicylate concentration

when relevant.

ECG

Every significant chloral hydrate overdose requires an ECG and continuous cardiac monitoring.

Look for:

• Ventricular ectopy
• Bigeminy
• QT abnormalities
• Ventricular tachycardia
• Torsades
• VF

Serious dysrhythmias may occur abruptly.

Trichloroethanol Levels

Specialized laboratories can measure:

• TCE
• Trichloroacetic acid
• Related metabolites

However:

These levels are generally not rapidly available and should not guide initial emergency treatment.

Treatment remains clinical.

Differential Diagnosis

Consider other causes of CNS depression including:

• Ethanol
• Benzodiazepines
• Barbiturates
• Opioids
• Meprobamate
• Carisoprodol
• Baclofen
• Other sedative-hypnotics

If prominent ventricular dysrhythmias are present, also consider:

• Tricyclic antidepressants
• Cocaine
• Sodium-channel blockers
• Chlorinated hydrocarbons
• Electrolyte abnormalities

Treatment

1. Airway and Ventilation

The cornerstone of therapy is:

Aggressive supportive airway management

Provide:

• Oxygen
• Ventilatory assistance as necessary
• Continuous pulse oximetry
• Capnography when available

Intubate early for:

• Progressive coma
• Hypoventilation
• Recurrent vomiting with impaired consciousness
• Cardiovascular deterioration

Do not wait for profound hypoxemia.

2. Continuous ECG Monitoring

Significant poisoning requires:

• Cardiac monitor
• Defibrillator immediately available
• Frequent blood-pressure measurement
• Serial electrolytes

Correct:

• Hypokalemia
• Hypomagnesemia
• Hypocalcemia

because electrolyte abnormalities can amplify ventricular dysrhythmia risk.

3. Ventricular Dysrhythmias – Key Toxicology Point

Chloral-hydrate dysrhythmias may be unusually resistant to routine antiarrhythmics because of:

Myocardial catecholamine sensitization

Historical and modern case literature repeatedly describes successful control with:

β-adrenergic blockade

particularly:

• Esmolol
• Propranolol

(PubMed⁠)

Esmolol

Esmolol is particularly attractive in severe poisoning because:

• Very short half-life
• Rapid titratability
• Can be quickly discontinued if hypotension worsens

Thus:

Refractory catecholamine-sensitive ventricular tachydysrhythmia → consider esmolol with toxicology/cardiology input.

This is not routine therapy for uncomplicated sinus tachycardia.

Torsades de Pointes

Treat according to standard principles:

• Immediate defibrillation if unstable/pulseless
• Correct potassium
• Correct magnesium

Give:

IV magnesium sulfate

for torsades, although case guidance notes that it may not completely suppress chloral-hydrate–driven dysrhythmia. (Royal Children’s Hospital⁠)

β-blockade may still be needed when catecholamine sensitization is driving recurrent ventricular arrhythmia.

Ventricular Tachycardia

For unstable VT:

• Immediate synchronized cardioversion when appropriate

For pulseless VT/VF:

• Defibrillate according to ACLS

Lidocaine has occasionally been successful, but response is inconsistent. (PubMed⁠)

Therefore:

Do not repeatedly cycle through standard antiarrhythmics while ignoring the characteristic catecholamine-sensitive mechanism.

Catecholamines – Important Pitfall

Because chloral hydrate sensitizes the myocardium to catecholamines:

Exogenous β-adrenergic stimulation can precipitate or worsen ventricular dysrhythmias.

Pediatric toxicology guidance therefore advises avoiding catecholamine inotropes when possible in chloral hydrate poisoning. (Royal Children’s Hospital⁠)

One reported severe poisoning switched norepinephrine to the predominantly α-adrenergic agent phenylephrine because of this concern. (PubMed Central (PMC)⁠)

Practical approach

For hypotension:

1. Optimize oxygenation/ventilation
2. Give cautious isotonic fluid if volume responsive
3. Correct dysrhythmias
4. Seek toxicology/critical-care input early

If a vasopressor is necessary, an α-predominant strategy such as phenylephrine may be considered when catecholamine-sensitive ventricular arrhythmias are present.

This is a specialized situation; profound shock requires individualized critical-care management.

4. Hypotension

Possible mechanisms include:

• Myocardial depression
• Dysrhythmia
• Vasodilation
• Sedative toxicity

Give:

• Isotonic crystalloid when clinically fluid responsive

Avoid:

• Unnecessary large fluid loads
• Unnecessary β-adrenergic stimulation

If persistent shock accompanies severe cardiotoxicity, involve:

• Medical toxicology/poison center
• Critical care
• Cardiology

early.

5. Seizures

Treat with:

Benzodiazepines first-line

Examples:

• Lorazepam
• Midazolam
• Diazepam

For refractory seizures consider:

• Phenobarbital
• Propofol in an appropriately intubated patient

Also correct:

• Hypoglycemia
• Hypoxia
• Electrolyte abnormalities

Gastrointestinal Decontamination

Do Not Induce Vomiting

Never induce emesis.

Rapid CNS depression creates substantial aspiration risk.

The old ipecac recommendation is obsolete.

Activated Charcoal

Activated charcoal should not be given routinely.

It may be considered after a substantial recent ingestion only when:

• The potential benefit is meaningful
• The patient is fully alert with intact airway reflexes

or:

• The airway has been protected by intubation

Current chloral-hydrate poisoning guidance specifically considers charcoal unsafe when the airway is not protected. (Royal Children’s Hospital⁠)

Because deterioration may be rapid:

Airway management takes priority over charcoal.

Gastric Lavage

The old routine recommendation:

“Large ingestion + presentation within 1 hour → gastric lavage”

does not reflect contemporary poisoning practice.

Modern toxicology guidance recommends that gastric lavage not be performed systematically after pharmaceutical overdose because outcome benefit is unproven and complications are significant. (PubMed Central (PMC)⁠)

Therefore:

Routine gastric lavage is not recommended.

Only an extraordinary, immediately life-threatening, very recent ingestion with:

• Protected airway
• Appropriate expertise
• Poison-center/medical-toxicology involvement

could justify consideration.

Antidote

There is no established specific antidote.

Management is primarily:

• Airway/ventilation
• Cardiac monitoring
• β-blockade for selected severe dysrhythmias
• Defibrillation/cardioversion when indicated
• Hemodynamic support
• Extracorporeal therapy in exceptional severe cases

Flumazenil

Because chloral hydrate/TCE likely modulate GABA-A signaling, isolated case observations have suggested possible effects from flumazenil.

However:

Flumazenil is not an established antidote for chloral hydrate overdose.

Its efficacy is uncertain, and seizure risk becomes especially problematic when:

• Exposure is mixed
• Chronic sedative dependence exists
• Proconvulsant coingestants are possible

Therefore routine use is not recommended.

Extracorporeal Elimination

Hemodialysis

Chloral hydrate’s active metabolite TCE is dialyzable.

Historical pharmacokinetic cases demonstrate substantial TCE clearance during hemodialysis, including reduction of TCE half-life from approximately:

35 hours → ~6 hours

in one massive overdose. (PubMed⁠)

Another study found high clearance of:

• TCE
• TCE glucuronide
• TCA

with both hemodialysis and hemoperfusion. (PubMed⁠)

When to Consider Hemodialysis

Modern pediatric toxicology guidance suggests considering hemodialysis with:

• Ongoing hemodynamic instability
• Persistent serious dysrhythmias

despite supportive care. (Royal Children’s Hospital⁠)

Additional reasonable considerations include:

• Prolonged profound coma requiring ventilation
• Massive known ingestion with persistent deterioration
• Refractory cardiotoxicity

Important

Evidence is based primarily on:

• Case reports
• Pharmacokinetic studies

There are no validated numerical serum thresholds or modern randomized trials establishing when dialysis must be used.

Thus:

Hemodialysis is a rescue therapy for severe refractory poisoning—not routine treatment.

Hemoperfusion

Charcoal/resin hemoperfusion can also clear TCE.

However:

• Equipment is less widely available
• Hemodialysis is technically simpler in many modern centers
• Hemoperfusion can cause complications including thrombocytopenia

Older comparative pharmacokinetic work found hemodialysis and hemoperfusion similarly efficient, with investigators favoring hemodialysis because of practical safety considerations. (PubMed⁠)

Thus:

If extracorporeal treatment is required, intermittent hemodialysis is generally the more practical modern option.

Forced Diuresis

Forced diuresis is not useful for enhanced elimination.

Do not use it routinely. (PubChem⁠)

Dependence and Withdrawal

Chronic high-dose chloral hydrate use can cause:

• Tolerance
• Psychological dependence
• Physical dependence

Abrupt withdrawal has historically produced a syndrome resembling severe sedative-hypnotic or alcohol withdrawal, including:

• Anxiety
• Tremor
• Agitation
• Delirium
• Hallucinations
• Psychosis
• Seizures

(PubChem⁠)

Therefore:

Chronic heavy users should not automatically have chloral hydrate abruptly discontinued without considering sedative-hypnotic withdrawal.

Modern management would generally use a better-characterized sedative agent and specialist supervision rather than restarting unsupervised chloral hydrate.

Monitoring

Significant poisoning requires:

• Continuous ECG
• Continuous respiratory monitoring
• Frequent blood pressure assessment
• Serial neurologic examination

Monitor for:

• Hypoventilation
• Aspiration
• Ventricular ectopy
• VT/VF
• Hypotension
• Recurrent CNS depression

Electrolytes—especially:

• Potassium
• Magnesium
• Calcium

should be corrected aggressively when arrhythmias are present.

Admission

Hospital admission is appropriate for:

• Significant CNS depression
• Ataxia preventing safe ambulation
• Respiratory depression
• Hypotension
• Ventricular ectopy
• Any significant dysrhythmia
• Seizures
• Large intentional ingestion

ICU care is indicated for:

• Coma
• Mechanical ventilation
• VT/VF
• Recurrent dysrhythmias
• Shock
• Need for extracorporeal treatment

Observation and Disposition

The older blanket:

“4–6 hours asymptomatic → discharge”

should be used cautiously.

Chloral hydrate itself is rapidly converted, but:

TCE has a much longer half-life

and overdose elimination can be prolonged.

A truly small isolated exposure with:

• Normal mental status
• Normal vital signs
• Normal ECG
• No evolving symptoms

may be discharged after an appropriate observation period.

However, significant intentional overdose warrants longer observation because:

• CNS depression can persist
• Cardiotoxicity can be severe
• TCE persists for many hours

Do not discharge until:

• Normal/baseline consciousness
• Normal ventilation
• Stable hemodynamics
• Reassuring ECG
• No recurrent dysrhythmia

Pregnancy

The old FDA Pregnancy Category C system is obsolete.

Published safety data are limited because chloral hydrate is now rarely used therapeutically in many settings.

For acute poisoning:

Maternal stabilization takes priority.

Treat:

• Hypoxia
• Respiratory failure
• Dysrhythmias
• Shock

aggressively.

Historical case literature documents successful maternal and fetal recovery after hemodialysis for severe poisoning during pregnancy. (PubMed⁠)

Breastfeeding

Chloral hydrate and its active metabolite enter breast milk.

Current LactMed guidance states that:

• Occasional/short-term use is unlikely to harm most older infants
• Other sedative-hypnotics are preferred for prolonged use
• Particular caution is warranted in neonates and premature infants

Monitor the infant for:

• Sedation
• Poor feeding
• Poor weight gain

because TCE has a prolonged half-life. (NCBI⁠)

Prognosis

Most uncomplicated exposures recover completely with appropriate supportive care.

Severe poisoning can be rapidly fatal from:

Respiratory failure or malignant ventricular dysrhythmias

Good outcomes are possible even after massive overdose when:

• Airway is secured
• Ventilation is maintained
• Dysrhythmias are recognized promptly
• Extracorporeal treatment is used when necessary

Important Pitfalls

1. Thinking chloral hydrate is simply an old benzodiazepine-like sedative

Its overdose has an unusually important:

Cardiotoxic component

with potentially lethal ventricular dysrhythmias.

2. Ignoring trichloroethanol

The parent drug disappears rapidly, but:

TCE remains active for 8–12 hours or much longer in overdose. (PubMed Central (PMC)⁠)

3. Giving catecholamines reflexively

Chloral hydrate can:

Sensitize the myocardium to catecholamines

and β-adrenergic stimulation may worsen ventricular dysrhythmias. (PubMed Central (PMC)⁠)

4. Missing the characteristic role for β-blockade

Recurrent ventricular dysrhythmias refractory to routine therapy have repeatedly responded to:

Esmolol/propranolol. (PubMed⁠)

Use this as a specialist-directed therapy, not for routine sinus tachycardia.

5. Calling the ethanol interaction merely “disulfiram-like”

The major toxicologic issue is:

Mutually enhanced/prolonged sedative toxicity with increased TCE exposure and impaired ethanol elimination. (ASCPT⁠)

6. Giving charcoal to a somnolent patient

Rapid progression to coma and aspiration makes this dangerous.

Protect the airway first.

7. Performing routine gastric lavage

Modern poisoning practice does not support systematic lavage after pharmaceutical overdose. (PubMed Central (PMC)⁠)

8. Assuming there is no role for dialysis

Severe refractory poisoning is unusual among sedative-hypnotic overdoses because:

TCE can be efficiently removed by hemodialysis. (PubMed⁠)

9. Using hemoperfusion automatically because older texts prefer it

Both methods clear TCE, but modern intermittent:

Hemodialysis is generally more available and practical

and historical comparative data found similar clearance. (PubMed⁠)

10. Forgetting dependence and withdrawal

Chronic use can produce:

• Tolerance
• Dependence
• Delirium
• Psychosis
• Seizures after withdrawal

High-Yield Toxicology Pearls

Chloral hydrate = sedative-hypnotic poisoning with distinctive ventricular cardiotoxicity

Think:

Coma + respiratory depression + ventricular ectopy/VT after old sedative exposure

Key points:

• Chloral hydrate is rapidly converted to trichloroethanol (TCE)
• TCE produces most of the prolonged CNS effects
• Mechanism probably involves GABA-A enhancement
• TCE half-life:
• Usually ~8–12 h
• May extend toward 24–35 h in overdose
• Parent drug toxicity may therefore outlast its brief plasma presence
• Current U.S. conventional chloral hydrate products such as Somnote are discontinued
• Chloral hydrate remains a U.S. Schedule IV substance
• Main acute toxicity:
• CNS depression
• Respiratory depression
• Hypotension
• Ventricular dysrhythmias
• Characteristic cardiac mechanism:
• Myocardial sensitization to catecholamines
• Dysrhythmias may include:
• Bigeminy
• VT
• Torsades
• VF
• Obtain continuous ECG monitoring after significant ingestion
• Airway/ventilation is the main treatment
• Ventricular dysrhythmias may respond especially well to:
• Esmolol
• Propranolol
• Torsades → magnesium + correction of K/Mg + defibrillation when required
• Avoid unnecessary β-adrenergic catecholamine stimulation
• If severe hypotension coexists with arrhythmias, consider specialist-guided α-predominant vasopressor therapy
• Ethanol greatly increases danger:
• More/prolonged TCE
• Longer ethanol effects
• Greater CNS depression
• Do not induce vomiting
• Activated charcoal only for selected large recent ingestions with an intact/protected airway
• Routine gastric lavage is obsolete
• No specific antidote
• Flumazenil is not established therapy
• Severe refractory toxicity can be treated with hemodialysis
• Consider dialysis for:
• Persistent severe dysrhythmias
• Ongoing hemodynamic instability
• Prolonged severe poisoning despite support
• Hemoperfusion can remove TCE but is no longer the practical default
• Forced diuresis is ineffective
• Chronic use can produce sedative-hypnotic dependence and withdrawal

The next chapter can be modernized in the same toxicology-reference format.