Effect of chronic theophylline treatment on the methacholine dose-response curve in allergic asthmatic subjects.

Theophylline is a bronchodilator and immunomodulator drug which has recently been demonstrated to attenuate the recruitment and activation of inflammatory cells into lungs of asthmatics. This study investigated the effect of chronic treatment with theophylline for its ability to alter airway responsiveness, as indicated by changes in airway sensitivity and reactivity to inhaled methacholine. The subjects studied were mild asthmatics who relied on beta-agonist medication only and who were randomized into two groups, one receiving theophylline (median dose 250 mg twice daily; range 250-375 mg twice daily) and the other placebo. A number of parameters was measured before and after treatment, including baseline forced expiratory volume in one second (FEV1), the provocative concentration of methacholine causing a 20% fall in FEV1 (PC20; sensitivity), dose-response slope (reactivity) and percentage eosinophils, eosinophil cationic protein and T-cell markers in peripheral blood (by flow cytometry). After 2 months of treatment with theophylline there was a significant lowering of airway reactivity (slope) to methacholine and improvement in methacholine sensitivity (PC20). However, such changes were not associated with any significant change in the number or activation status of eosinophils and lymphocytes in peripheral blood. In conclusion, chronic treatment with theophylline reduces the reactivity of the airways to methacholine, which might be beneficial in the treatment of persistent asthma. The cellular mechanisms of this improvement remain to be clarified.