- Simultaneous treatment with glucocorticosteroids (e.g. prednisolone, dexamethasone), diltiazem, verapamil, erythromycin, clarithromycin, telithromycin, rifampicin, fluconazole, itraconazole, ketoconazole, voriconazole, indinavir, nelfinavir, ritonavir, nefazodone, bosentan, carbamazepine, St. John's worth, grapefruit.