The Effect of Rifampin on Theophylline Kinetics

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Abstract
The effect of rifampin on the pharmacokinetics of theophylline was studied in ten healthy nonsmoking men (age, 23–42 years). Each subject received 5.9‐6.8 mg/kg of aminophyl‐line intravenously over 20 minutes before and at the end of two weeks of oral rifampin therapy (600 mg/d). Theophylline serum concentrations were measured serially over the 24 hours following each aminophylline infusion. In every subject, rifampin caused an increase in total clearance (from 0.88 ± 0.21 to 1.21 ± 0.29 mL/min/kg) and terminal elimination rate constant (from 0.104 ± 0.023 to 0.148 ± 0.030 hr−1) and a decrease in the area under the theophylline concentration‐time curve (from 104 ± 29 to 76 ± 19 hr‐mg/L) and half‐life of theophylline (from 7.0 ± 1.7 to 4.8 ± 0.9 hr). All of these changes were significant (P < .02, Wilcoxon matched‐pair, signed‐rank, two‐tailed test). The apparent volume of distribution of theophylline did not consistently change following rifampin administration (mean change, −4%; range, −18‐+20%, P > .20). Patients should be monitored for signs of decreased theophylline efficacy when rifampin is added, or of increased theophylline toxicity when rifampin is discontinued from maintanence therapy.

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