Effect of rifampicin administration on theophylline pharmacokinetics in humans.

Theophylline pharmacokinetics were studied before and after rifampicin administration (600 mg daily for 1 wk). Rifampicin reduced the area under the concentration-time curve by 18% after the oral administration of sustained release aminophylline (450 mg) to 7 normal subjects (p less than 0.05) and increased the metabolic clearance and volume of distribution by 45% (p less than 0.05) and 17% (p less than 0.05), respectively, after the intravenous administration of aminophylline (5 mg/kg over 30 min) to 8 normal subjects. These findings are consistent with an inducing and choleretic effect of rifampicin on theophylline disposition. In patients receiving theophylline, blood levels should be monitored closely and dosage adjusted if rifampicin therapy is introduced or withdrawn.