Relationship of Serum Theophylline Concentration to Inhibition of Exercise-Induced Bronchospasm and Comparison With Cromolyn

Abstract

Exercise-induced bronchospasm was induced by treadmill running in 12 children on two days preceding either inhaled cromolyn sodium (Intal) or oral theophylline (Slo-Phyllin tablets), 7.5 mg/kg, administered in a double-blind manner. A second exercise period identical to the first followed two hours later; the medication administration had been timed so that the second exercise stress followed two hours after theophylline administration and 15 minutes following cromolyn administration. The patients subsequently were exercised twice more at two-hour intervals on both days. Blood was drawn for serum theophylline measurement immediately after each of the exercise periods. There was little demonstrable exercise-induced bronchospasm resulting from the first postmedication exercise period following theophylline administration. The two subsequent exercise periods were associated with some return of postexercise bronchospasm. The degree of inhibition of exercise-induced bronchospasm correlated with serum theophylline levels that averaged 16, 13, and 10 µg/ml at two, four, and six hours after the theophylline dose (mean Spearman rank correlation coefficient = .71, P < .01). The effect of cromolyn in suppressing exercise-induced bronchospasm was generally much less, but two of the 12 patients exhibited suppression of exercise-induced bronchospasm that matched or excelled that seen with theophylline.