Delirium during clozapine treatment: incidence and associated risk factors

Incidence and risk factors for delirium during clozapine treatment require further clarification.

We used computerized pharmacy records to identify all adult psychiatric inpatients treated with clozapine (1995-96), reviewed their medical records to score incidence and severity of delirium, and tested associations with potential risk factors.

Subjects (n = 139) were 72 women and 67 men, aged 40.8 +/- 12.1 years, hospitalized for 24.9 +/- 23.3 days, and given clozapine, gradually increased to an average daily dose of 282 +/- 203 mg (3.45 +/- 2.45 mg/kg) for 18.9 +/- 16.4 days. Delirium was diagnosed in 14 (10.1 % incidence, or 1.48 cases/person-years of exposure); 71.4 % of cases were moderate or severe. Associated factors were co-treatment with other centrally antimuscarinic agents, poor clinical outcome, older age, and longer hospitalization (by 17.5 days, increasing cost); sex, diagnosis or medical co-morbidity, and daily clozapine dose, which fell with age, were unrelated.

Delirium was found in 10 % of clozapine-treated inpatients, particularly in older patients exposed to other central anticholinergics. Delirium was inconsistently recognized clinically in milder cases and was associated with increased length-of-stay and higher costs, and inferior clinical outcome.