[Importance of determining clozapine plasma level in follow-up of schizophrenic patients]

Measures of plasma clozapine were carried out for 15 subjects, for up to 35 months. A positive quadratic relation (r = 0.528, n = 111, p < 0.01) has been established by using different samples at different times from each patient. From 500 mg/day this relation point to forecast an important growth of clozapine plasma concentrations. The analysis of individual data shows a large variability for the individuals and a relative stability in plasma levels for a subject having one posology. The repetition of the dosages attests the compliance. A case of epilepsy, related to an important clozapine level, is presented. So, in practice, even if neither non linear pharmacokinetics, nor genetic polymorphism have been demonstrated, over a posology of 500 mg/day, it seems interesting to proceed a clozapine dosage before increasing the posology and so reduce the comitial seizure risk.