Effects of Theophylline on Sulfur Dioxide-Induced Bronchoconstriction in Asthmatic Subjects

Abstract

The purpose of this study was to determine whether asthmatic subjects on chronic theophylline therapy are protected from the bronchoconstrictor effects of inhaled sulfur dioxide (SO2). Twelve asthmatic subjects from 13–39 years of age were exposed to 1.0 ppm SO2 or clean air during 10 minutes of moderate exercise in the morning (3–4 hours after medication useage) and on a different day in the afternoon (8–10 hours after medication useage) in random fashion. Forced expiratory volume in one second (FEV1), total respiratory resistance (RT), and maximal flow at 75% of expired vital capacity (V̇75) were measured before and after the exposures. All exposures were carried out while the subject breathed on a rubber mouthpiece with noseclips in place. Statistically significant changes in pulmonary function were seen after the SO2 exposures in the afternoon; FEV1 decreased 14%; RT increased 29%, and V̇75 decreased 42%. Serum theophylline levels were determined from blood samples taken within 60 minutes of exposure to the test atmospheres. Serum levels in the afternoon ranged from 5.1 to 15.4 μg/ml, but were not correlated with the percent change in pulmonary function. In conclusion, chronic theophylline therapy did not protect asthmatic individuals completely from the inhaled effects of near-ambient levels of SO2.