[Euphyllin retard and "exercise-induced" asthma].

In a double blind crossover experiment the protective effect of theophylline slow-releasing coated tablets (Euphyllin retard) on exercise-induced asthma has been compared with that of a placebo. Sixteen patients with bronchial asthma (mean age 23 years, range 16-49 years) who were selected in a preliminary test exhibited an FEV1 decrease greater than 15% 10 minutes after an exhausting 6 minute run on the treadmill. Euphyllin retard and placebo were given 6 hours before the exercise test. Venous blood was sampled 6 hours prior to and immediately before exercise in order to determine the plasma concentrations of theophylline by a tritium radioimmunoassay method. FEV1 was measured prior to and immediately after exercise, 10 and 20 minutes later and after a final orciprenaline inhalation. A group of 9 patients (group 1) has plasma concentrations of theophylline lower than 6.2 microgram/ml (4.8 +/- 0.9 microgram/ml), and a group of 7 patients (group 2) had concentrations higher than 10.0 microgram/ml (13.8 +/- 3.3 microgram/ml). Compared with placebo, a protective effect of Euphyllin retard could be observed in group 2 only (p < 0.025). In group 1 the asthma protection was indistinguishable form that of placebo. Hence, plasma concentrations higher than 10 microgram/ml appear to be required to protect asthmatics from exercise-induced asthma. Although in some patients an effective concentration can be achieved by the recommended dose of one tablet of Euphyllin retard (350 mg aminophylline) every 12 hours, the importance of measuring plasma concentrations must be emphasized in view of the variable absorption and elimination of theophylline. Side effects may occur at concentrations higher than 15 microgram/ml.