Cytochrome P450 3A inhibitor itraconazole affects plasma concentrations of risperidone and 9-hydroxyrisperidone in schizophrenic patients.

Background And Objective: Despite the belief that cytochrome P450 (CYP) 2D6 alone is responsible for the metabolism of risperidone, several studies suggest that CYP3A may be involved. The aim of this study was to evaluate the effect of itraconazole, a CYP3A inhibitor, on the plasma concentrations of risperidone and 9-hydroxyrisperidone in schizophrenic patients in relation to CYP2D6 genotype.

Methods: Nineteen schizophrenic patients treated with 2 to 8 mg/d of risperidone received 200 mg/d of itraconazole for a week.