Asian patients from Singapore (n=20) have a lower dosage requirement for clinical efficacy compared to Caucasian patients (from Australia) (n=20) with chronic schizophrenia who were on stable maintenance treatment. Asian patients needed a significantly lower mean clozapine dose (176 mg/day) than the Caucasian group (433 mg/day, P<0.001) to acquire similar plasma clozapine levels between the groups. Asian patients from Singapore had more than twice the effective clozapine concentration to dose ratio (P<0.001) and remained significant after controlling for gender, body mass index, cigarette, alcohol and caffeine use. Conversely, the plasma metabolites (desmethylclozapine and clozapine N-oxide) to clozapine ratios were higher in the Caucasian patients (P<0.01). (Ng et al, 2005)

Consider: appropriate dose adjustment in Asian patients receiving maintenance clozapine therapy.