Risperidone-Carbamazepine Interactions: Is Cytochrome P450 3A Involved?

Sir: De Leon and Bork recently highlighted potential pharmacokinetic interactions between risperidone and carbamazepine. They presented a patient in whom carbamazepine coadministration lowered plasma levels of risperidone greater than 2-fold. Earlier, Ereshefsky indicated that carbamazepine can induce the activities of cytochrome P450 3A (CYP3A) and possibly CYP2B. Accordingly, de Leon and Bork1 further suggested that risperidone metabolism, which is known to involve CYP2D6, also involves CYP3A.