- Use of drugs that induce or inhibit the hepatic metabolizing cytochrome 3A4 enzyme within 2 weeks prior to randomization (e.g. inducers: phenytoin, carbamazepine, phenobarbital, rifampicin, rifabutin, glucocorticoids, thioridazine and St. Johns´wort (=Johanniskraut) and inhibitors: ketaconazole (except for topical use), itraconazole, fluconazole, erythromycin, clarithromycin, fluvoxamine, nefazodone, troleandomycin, indinavir, nelfinavir and saquinavir).