The influence of rifampin on quinidine and digoxin.

Serum drug concentration data from the first of the two patients described herein suggest that rifampin may directly increase the metabolism of quinidine and thereby negate the influence of quinidine on the serum digoxin concentration (SDC). Data on the second patient suggest that rifampin may directly increase the metabolism of digoxin producing lower SDC values. In both cases, the discontinuation of rifampin therapy appears to have allowed reversion toward prerifampin metabolism of both quinidine and digoxin.