ABSENCE OF EFFECT OF RUFLOXACIN ON THEOPHYLLINE PHARMACOKINETICS IN STEADY-STATE

Several quinolone antibacterial agents are known to inhibit the metabo lism of theophylline, with the potential to cause adverse events due t o raised theophylline concentrations during coadministration. A random ized crossover study was therefore conducted with 12 healthy male volu nteers (ages, 23 to 34 years; body weight, 64 to 101 kg) to evaluate a possible interaction between rufloxacin and theophylline. Both drugs were administered at steady state. Following the administration of an oral loading dose of 400 mg on day I, rufloxacin was given orally at 2 00 mg once daily on days 2 to 7 during one period only. During both pe riods, 146 mg of theophylline was administered orally twice daily for 3 days (which were days 4 to 6 of the rufloxacin coadministration peri od) and intravenously once the next morning to test for an interaction . Theophylline and rufloxacin concentrations were measured by reversed -phase high-pressure liquid chromatography, the pharmacokinetics of th eophylline at steady state following administration of the last dose w ere calculated by compartment-model-independent methods. To compare th e treatments, analysis of variance-based point estimates and 90% confi dence intervals (given in parentheses) were calculated for the mean ra tios of the pharmacokinetic parameters from the test (rufloxacin coadm inistration) over those from the reference (theophylline without ruflo xacin) period. These were as follows: maximum concentration at steady state, 1.01 (0.96 to 1.07); area under the concentration-time curve fr om 0 to 12 h, 0.98 (0.94 to 1.02); half-life, 0.99 (0.95 to 1.03); tot al clearance at steady state, 1.02 (0.99 to 1.06); and volume of distr ibution in the elimination phase, 1.01 (0.97 to 1.05). In conclusion, rufloxacin did not affect theophylline pharmacokinetics at steady stat e. Therefore, therapeutic coadministration of rufloxacin and theophyll ine is not expected to cause an increased incidence of theophylline-re lated adverse events.