- Use of any drugs known to induce or inhibit hepatic drug metabolism (examples of inducers: barbiturates, carbamazepine, phenytoin, glucocorticoids, rifampin/rifabutin; examples of inhibitors: antidepressants, cimetidine, diltiazem, erythromycin, ketoconazole, MAO inhibitors, neuroleptics, verapamil, quinidine), use of an investigational drug or participation in an investigational study within 30 days prior to administration of the study medication.