Risperdal

[Risperidone]

Risperidone could be subject to two kinds of drug-drug interactions ( see PRECAUTIONS -Drug Interactions) . First, inhibitors of CYP 2D6 interfere with conversion of risperidone to 9-hydroxyrisperidone. This occurs with quinidine, giving essentially all recipients a risperidone pharmacokinetic profile typical of poor metabolizers. The therapeutic benefits and adverse effects of risperidone in patients receiving quinidine have not been evaluated, but observations in a modest number ( n 70) of poor metabolizers given risperidone do not suggest important differences between poor and extensive metabolizers. Second, co-administration of known enzyme inducers ( e. g. , phenytoin, rifampin, and phenobarbital) with risperidone may cause a decrease in the combined plasma concentrations of risperidone and 9-hydroxyrisperidone. It would also be possible for risperidone to nterfere with metabolism of other drugs metabolized by CYP 2D6. Relatively weak binding of risperidone to the enzyme suggests this is unlikely.

Text Continues Below

---

In a drug interaction study in schizophrenic patients, 11 subjects received risperidone titrated to 6 mg/ day for 3 weeks, followed by concurrent administration of carbamazepine for an additional 3 weeks. During co-administration, the plasma concentrations of risperidone and its pharmacologically active metabolite, 9-hydroxyrisperidone, were decreased by about 50% . Plasma concentrations of carbamazepine did not appear to be affected. Co-administration of other known enzyme inducers ( e. g. , phenytoin, rifampin, and phenobarbital) with risperidone may cause similar decreases in the combined plasma concentrations of risperidone and 9-hydroxyrisperidone, which could lead to decreased efficacy of risperidone treatment ( see PRECAUTIONS Drug Interactions and DOSAGE AND ADMINISTRATION Co--Administration of RISPERDAL ® with Certain Other Medications) .

Page:  << Prev | 1 | 2 | 3 | 4 | 5 | Next >>