[Comparison of the bronchodilator and protective effect of methylxanthines].

UNLABELLED: In study I, carried out on 9 asthmatics to investigate whether the bronchodilator and protective effect of intravenous theophylline, dissolved in ethylene diamine (T.E.) or proxyphylline and diprophylline (T.P.D.), showed different dose-effect relationships, 100 mg theophylline with T.E., T.P.D. or NaCl (placebo) were infused 5 times at 30 minute intervals. This was followed by inhalation of 0.4 mg fenoterol. Results showed that the bronchodilator effect of 500 mg theophylline with a serum concentration greater than 15 mg/l was only about 60% of that for fenoterol alone. In study II, 11 patients with exercise-induceable respiratory obstruction received 200 and 351 mg theophylline with T.E., 200 mg with T.P.D. or placebo prior to exercise and cold air inhalation. Here theophylline had a dose-dependent protective effect. With a theophylline serum concentration of 5 mg/l there was already a reduction in exercise asthma by more than 60% in comparison to placebo. At comparable serum concentrations the effect of T.P.D. was better than T.E. in both studies although the difference was not statistically significant.

CONCLUSION: Since the bronchodilator effect of methylxanthines is less than the protective effect, the prophylactic use of theophylline should be given more attention.