Rifampin accelerates elimination and thereby may decrease the effectiveness of the following drugs: angiotensin-converting enzyme inhibitors, atovaquone, barbiturates, beta-blockers, calcium channel blockers, chloramphenicol, clarithromycin, oral and systemic hormone contraceptives, corticosteroids, cyclosporine, dapsone, digoxin, doxycycline, fluconazole, haloperidol, itraconazole, ketoconazole, the non-nucleoside reverse transcriptase inhibitors delavirdine and nevirapine, opioid analgesics, phenytoin, protease inhibitors, quinidine, sulfonylureas, tacrolimus, theophylline, thyroxine, tocainide, tricyclic antidepressants, voriconazole, warfarin, and zidovudine.