Drug Interactions between Dexamethasone Intensol and ziprasidone

Coadministration with drugs that are inducers of the CYP450 3A4 isoenzyme may only modestly decrease the plasma concentrations of ziprasidone, as less than 1/3 of ziprasidone metabolic clearance occurs via oxidation mediated by CYP450 3A4. In nine healthy subjects, pretreatment with the potent CYP450 3A4 inducer carbamazepine (100 mg/day titrated to 400 mg/day over 5 days) for 25 days decreased the mean peak plasma concentration (Cmax) and 12-hour area under the concentration-time curve (AUC) of ziprasidone (20 mg orally twice a day for 3 days) by 27% and 36%, respectively, compared to when ziprasidone was administered alone. The half-life was decreased by 1 hour. These changes, although statistically significant, were not considered clinically important. There were also no serious adverse events or clinically significant alterations in ECG or vital signs throughout the study. These findings suggest that ziprasidone dose modifications are unlikely to be necessary in patients receiving potent CYP450 3A4 inducers.