Update on rifampin and rifabutin drug interactions.

Rifampin is a potent inducer of cytochrome P-450 oxidative enzymes as well as the P-glycoprotein transport system. Several examples of well-documented clinically significant interactions include warfarin, oral contraceptives, cyclosporine, itraconazole, digoxin, verapamil, nifedipine, simvastatin, midazolam, and human immunodeficiency virus-related protease inhibitors. Rifabutin reduces serum concentrations of antiretroviral agents, but less so than rifampin. Examples of clinically relevant interactions demonstrated by recent reports include everolimus, atorvastatin, rosiglitazone/pioglitazone, celecoxib, clarithromycin, caspofungin, and lorazepam. To avoid a decreased therapeutic response, therapeutic failure, or toxic reactions when rifampin is added to or discontinued from medication regimens, clinicians need to be cognizant of these interactions. Studies and cases of rifampin drug interactions continue to increase rapidly. This review is a timely reminder to clinicians to be vigilant.