Noneffect of rifampin on theophylline disposition in rabbits.

The pharmacokinetic disposition of theophylline after a single 10mg/kg intravenous dose of aminophylline was evaluated in six rabbits. Three then received rifampin (50mg/kg) a day for 14 days and the disposition of theophylline was re-evaluated in all six rabbits after another 10mg/kg aminophylline dose. The mean theophylline half life before rifampin treatment of 5.11 +/- 0.71 hrs was not different (p greater than 0.10) from the half life of 4.54 +/- 0.71 hrs after treatment with rifampin. In the non-rifampin treated rabbits, the initial mean theophylline half life of 4.78 +/- 1.05 was not different p greater than 0.80) from the half life of 4.94 +/- 1.92 hrs after fourteen days. No significant alterations in clearance or area under the curve were noted for either group. Power analysis indicated that three rabbits were sufficient to detect at least a 25% change in the parameters as being significant (p less than 0.05).