Increased clearance w/ enzyme inducers eg, phenytoin, barbiturates, primidone, carbamazepine, rifampicin; oxcarbazepine, topiramate, felbamate, griseofulvin, nevirapine, St. John's wort-containing products. Increased plasma levels w/ enzyme inhibitors eg, ketoconazole, itraconazole, fluconazole; voriconazole; verapamil; erythromycin, clarithromycin, diltiazem; grapefruit juice.