Effect of rifampin on theophylline disposition.

The concentrations of theophylline from single 400-mg oral doses were evaluated both before and after 7 days of oral rifampin administration (600 mg/day) in six healthy, nonsmoking adults. The mean oral clearance of theophylline was significantly increased from 54.9 +/- 21.2 to 68.9 +/- 26.5 ml/h/kg. The elimination rate constant was significantly increased in five of the six subjects, with a mean increase of approximately 25%. Although intersubject variability was large, these data indicate the potential need to increase theophylline doses in some patients receiving rifampin.