Interactions between the cytochrome P450 system and the second-generation antipsychotics.

Awareness of the metabolism of second-generation antipsychotics by the cytochrome P450 (CYP) system can inform the clinician about how to avoid and manage drug-drug interactions involving these enzymes. Clozapine is metabolized primarily by CYP1A2, with additional contributions by CYP2C19, CYP2D6 and CYP3A4. Risperidone is metabolized primarily by CYP2D6 and to a lesser extent by CYP3A4. Olanzapine is metabolized primarily by CYP1A2 and to a lesser extent by CYP2D6. Quetiapine and ziprasidone are metabolized by CYP3A4. At the usual clinical doses, these drugs appear not to significantly affect the metabolism of other medications. There is, however, a lack of in vivo metabolic data, especially for the 3 newest second-generation antipsychotics: olanzapine, quetiapine and ziprasidone.