In order to clarify whether repirinast, an inhibitor of chemical mediator release, could influence the pharmacokinetics of theophylline, a loading test using intravenous injection of aminophylline was performed in 10 subjects with bronchial asthma before and after treatment with 300 mg/day of repirinast. There was no significant difference in theophylline half-life before treatment (7.25 +/- 2.43 hr) and after treatment (7.82 +/- 3.35 hr). There was no significant difference in theophylline clearance before treatment (0.047 +/- 0.018 L/kg/hr) and after treatment (0.047 +/- 0.020 L/kg/hr). These results demonstrated that repirinast does not modify theophylline pharmacokinetics significantly.