Update on rifampin drug interactions.

Rifampin, a potent inducer of the hepatic microsomal system, has been shown to cause clinically important interactions when combined with other drugs, including oral anticoagulants, oral contraceptives, digitoxin, methadone hydrochloride, sulfonylureas, and barbiturates. Additional literature on previously described interactions has been published recently on quinidine, glucocorticoids, digoxin, and theophylline. New rifampin interactions have been described for cyclosporine, ketoconazole, chloramphenicol, beta-blockers, verapamil, and phenytoin. These interactions seem to be of clinical significance.