Single-dose study of the effect of terfenadine on theophylline absorption and disposition.

Terfenadine, a nonsedating antihistamine, and theophylline, a methylxanthine used extensively in the treatment of asthma, have potential for frequent concomitant administration. A single-dose pharmacokinetic study was performed to investigate the potential for a drug-drug interaction affecting serum theophylline concentrations. No statistically significant effect on theophylline absorption or elimination was found when 60 mg of terfenadine was concomitantly administered with 4 mg/kg of theophylline in 17 normal healthy male volunteers. The results of this single-dose study suggest there is no significant acute pharmacokinetic interaction affecting serum theophylline concentrations when terfenadine and theophylline are administered concomitantly as single isolated doses. Further investigation is needed to determine if repeated administration of terfenadine is equally without effect on theophylline absorption or disposition.