Acute and chronic theophylline therapy in exercise-induced bronchospasm.

This study examined the effectiveness of theophylline therapy in modifying exercise-induced bronchospasm (EIB) in children with perennial asthma and evaluated whether tolerance to theophylline developed with prolonged use. Twenty-one children between 7 and 16 years of age were studied by a standardized treadmill exercise test carried out before administration of theophylline, 90 minutes after administration of theophylline, and again after three weeks of round-the-clock theophylline treatment. Changes in forced expiratory volume at one second, forced expiratory flow between 25% and 75% of vital capacity, and peak expiratory flow rate were measured before and after each exercise test. Theophylline inhibited EIB in 20 of 21 subjects. There was considerable intersubject variation in the response to theophylline, however, ranging from complete inhibition in five subjects to no inhibition at all in one subject, even though theophylline controlled perennial asthma in all subjects, and all but one had theophylline levels between 10 and 22 microgram/ml when tested. On repeated testing after three weeks of therapy, no tolerance developed to theophylline. These findings suggest that EIB and perennial asthma may result from different causes and tha theophylline's ability to control asthma will not predict its effect on EIB. Subjects who have severe EIB should be retested after theophylline pretreatment of evaluate the effectiveness of therapy.