Chlorpromazine Antidote
There is no specific antidote for chlorpromazine overdose. Management is entirely supportive, focusing on maintaining airway, breathing, and circulation while treating specific complications as they arise 1.
Management Approach
Primary Supportive Care
The cornerstone of chlorpromazine overdose management is aggressive supportive care:
Airway protection and ventilation: CNS depression is the most common effect, with approximately 27% of patients presenting with Glasgow Coma Scale <9 2. Endotracheal intubation may be required, particularly with larger ingestions (median reported dose of 2,000 mg in intubated patients vs. 1,200 mg in non-intubated patients) 2.
Cardiovascular monitoring: Watch for hypotension (occurs in ~8% of cases), which results from alpha-adrenergic blockade 2. Treat with IV fluids and vasopressors if needed. Unlike thioridazine, chlorpromazine does not show a dose-response relationship for QTc prolongation, though it does cause dose-dependent tachycardia and hypotension 3.
Specific Complications to Anticipate
Extrapyramidal symptoms and dystonic reactions can occur, including potentially life-threatening laryngeal-pharyngeal dystonia causing upper airway compromise 4. These are dose-dependent and should be treated with:
- Diphenhydramine (25-50 mg IV/IM in adults)
- Benztropine (1-2 mg IV/IM in adults)
Neuroleptic malignant syndrome (NMS) is a rare but serious complication that can develop 24-48 hours post-ingestion, even after initial sedation resolves 5. Monitor for:
- Progressive confusion and rigidity
- Hyperthermia and tachycardia
- Elevated creatine kinase
Treatment includes benzodiazepines (midazolam), bromocriptine, external cooling, and mechanical ventilation if needed 5.
Seizures occur in approximately 1-2% of cases 2. Treat with benzodiazepines as first-line agents.
Critical Pitfalls to Avoid
Do NOT use flumazenil if benzodiazepines were co-ingested (common in 62% of chlorpromazine overdoses) 2. Flumazenil is contraindicated in patients with co-ingestion of medications like phenothiazines that lower seizure threshold, as it may precipitate seizures or arrhythmias 6, 7.
Avoid abrupt withdrawal in chronic users, as this can cause gastritis, nausea, vomiting, dizziness, and tremulousness 1.
Monitor for delayed effects: The antiemetic properties may mask signs of other drug toxicity or conditions 1.
Observation and Disposition
- Patients with reported ingestions >2,000 mg, particularly isolated chlorpromazine ingestions, have significantly higher risk of requiring ICU admission and intubation 2.
- All symptomatic patients require hospital admission with continuous monitoring.
- Even after initial improvement, watch for delayed development of NMS over 24-48 hours 5.
The absence of a specific antidote underscores the importance of meticulous supportive care and anticipatory management of complications in chlorpromazine overdose.