Determination of clozapine and its major metabolites in serum samples of adolescent schizophrenic patients by high-performance liquid chromatography. Data from a prospective clinical trial.

This report describes a method for determination of clozapine and its major metabolites N-desmethylclozapine and clozapine N-oxide in serum samples of adolescent schizophrenic patients during maintenance therapy. The method includes deproteinization and subsequent high-performance liquid chromatography with electrochemical detection. The method shows sufficient sensitivity to quantitate clozapine, clozapine N-oxide and N-desmethylclozapine accurately at 0.5, 5, and 0.5 ng/ml, respectively. We were able to demonstrate for 16 patients receiving fixed doses of clozapine that the individual mean values calculated from six consecutive measurements revealed a strong linear dosage and serum level relationship (Pearson's coefficient of correlation): clozapine (r = 0.82, p = 0.0001); N-desmethylclozapine (r = 0.81, p = 0.0001); clozapine N-oxide (r = 0.91; p = 0.0001). Preliminary pharmacokinetic data are presented and dose-response relationship are discussed.