Effect of treatment duration on plasma levels of clozapine and N-desmethylclozapine in men and women.

Plasma levels of clozapine and its major metabolites, N-desmethylclozapine and clozapine-N-oxide, were measured in 18 schizophrenic patients at different times (4, 6 and 24 weeks) during the course of treatment with multiple doses of the drug, by using high performance liquid chromatography (HPLC) with UV detection. Plasma levels of clozapine and N-desmethylclozapine were significantly higher in females than in males after 4 and 6 weeks, but not after 24 weeks, of treatment. No sex difference was found at any time with respect to plasma levels of clozapine-N-oxide.