The effect of 10, 50 and 200 micrograms inhaled fenoterol on exercise induced asthma

In a randomized, double-blind cross-over study we investigated the protective effect of low doses of fenoterol on the airway response to exercise during cold air breathing. In 12 mild to moderate asthmatics with exercise induced asthma (mean age: 26 [range 19-25] years), mean FEV1 87% of predicted, exercise challenges were performed under control conditions and 30 min after the inhalation from a metered dose inhaler of either placebo, or 10, 50, and 200 micrograms fenoterol within a 4 week period. Airway response was determined by measuring specific airway resistance, sRaw. Standardization of exercise challenges was achieved by individually maintaining a constant respiratory heat exchange, with an average (range) of 1.24 (0.98-1.61) kcal/min. Fenoterol aerosol was an effective bronchodilator at all doses administered (P < 0.05), with 200 micrograms significantly more effective than 10 micrograms. Mean sRaw (s.e.m.) pre vs maximal post exercise after control conditions, placebo and 10, 50, and 200 micrograms fenoterol aerosol was 12.9 (1.4) vs 41.8 (6.3), 13.1 (1.6) vs 41.3 (6.3), 9.6 (1.5) vs 26.6 (6.2), 7.9 (0.9) vs 16.4 (3.6) and 5.5 (0.5) vs 7.4 (0.9) cmH2O.s. The protective effect of fenoterol against exercise induced bronchoconstriction was dose-dependent and was significantly different from placebo at 50 and 200 micrograms (P < 0.05). From these observations we suggest that in mild to moderate asthmatics 50 micrograms of fenoterol in a dose which is sufficient to protect against this naturally occurring stimulus.