Acute clozapine overdose: Plasma concentration and outcome

Clozapine is a tricyclic dibenzodiazepine derivative that is classified as an "atypical neuroleptic" drug for treatment of psychotic diseases. A 19-year-old schizophrenic female, treated with 400 mg clozapine per day, was admitted to the emergency department after ingestion of 5000 mg (50 x 100 mg tablets) of clozapine. Clozapine plasma level 2.5 hours after ingestion was 3.8 mu g/ml (normal range 0.2-0.7 mu g/ml) and very high in gastric lavage. Contrary to reported cases with such high plasma concentrations the patient suffered only from somnolence with intermittent periods of agitation and a mild anticholinergic syndrome with sinus tachycardia and slight hypotension. After detoxication with gastric ravage and short-term administration of pyridostigmine she remained stable, and 24 hours after ingestion she was transferred to the psychiatric unit without further sequelae. To prevent late-onset complications she was carefully monitored for five days. The clozapine plasma level 24 hours after the first measurement was normal. This case and others reported in the literature confirm that signs and symptoms after clozapine intoxication are variable and that high plasma levels are not lethal in every case.