Antipsychotic Agent Overdose

Conventional antipsychotics act mainly on CNS dopamine receptors; examples include

• Chlorpromazine

• Haloperidol

• Droperidol

Newer "atypical" antipsychotics also interact with serotonin receptors; examples include

• Risperidone

• Olanzapine

• Ziprasidone

• Quetiapine

• Aripiprazole

Drowsiness, orthostatic hypotension, especially with α-blocking agents

Large overdose

• Miosis

• Severe hypotension

• Tachycardia

• Convulsions

• Obtundation or coma

Prolongation of QRS interval (thioridazine) or QT interval (with possible torsades de pointes)

An acute extrapyramidal dystonic reaction may occur with therapeutic or toxic doses

• Spasmodic contractions of the face and neck muscles, extensor rigidity of the back muscles, carpopedal spasm, and motor restlessness

• More common with butyrophenones, less common with atypical drugs

Severe rigidity, hyperthermia, and metabolic acidosis (neuroleptic malignant syndrome) may occasionally occur and are life-threatening

Atypical antipsychotics have also been associated with weight gain and diabetes mellitus, including diabetic ketoacidosis

Largely based on history of exposure

Most agents are not detected in routine rapid toxicology screens

Serum levels are not helpful

ECG monitoring for QRS, QT prolongation

Activated charcoal

• Give 60–100 g (in aqueous slurry) orally or via gastric tube

• Do not use for comatose or convulsing patients unless they are intubated with a cuffed endotracheal tube

Widened QRS interval

• Seen in thioridazine poisoning

• May respond to intravenous NaHCO₃ as used for tricyclic antidepressants

Hypotension often responds to intravenous saline boluses; cardiac arrhythmias associated with widened QRS intervals on the ECG may respond to intravenous sodium bicarbonate as is given for tricyclic antidepressant overdoses

Prolonged QT interval or torsades de pointes, or both

• Magnesium 1–2 g intravenously

• Consider overdrive pacing

Treat hyperthermia, maintain cardiac monitoring

For extrapyramidal signs

• Diphenhydramine, 0.5–1.0 mg/kg intravenously, or benztropine mesylate, 0.01–0.02 mg/kg intramuscularly

• Continue with oral doses for 1–2 days

Bromocriptine (2.5–7.5 mg daily orally) may be effective for mild or moderate neuroleptic malignant syndrome

Dantrolene (2–5 mg/kg intravenously) has also been used for muscle contractions but is not a true antidote