[Blockade of exercise-induced bronchial asthma by fenoterol]

The bronchoconstrictor response to cold air breathing during exercise shows a wide interindividual variation in asthmatic patients. We investigated whether the protective effect of a single, inhaled dose of 0.2 mg fenoterol powder is dependent on the severity of airways obstruction, following placebo pretreatment of an inhalative thermal burden precisely matched in terms of respiratory heat exchange. In ten asthmatic patients 0.2 mg fenoterol powder or placebo were administered via an inhalator in a single blind and random order fashion on separate days. Lung function was measured before and 30 min after treatment (baseline value) and 3, 10, 15 and 30 min after an inhalative provocation consisting of cold air breathing during exercise. After placebo the maximal increase of airway resistance compared to the baseline value ranged from 682% to 50% (means +/- SD: 344.1 +/- 312.2) whereas fenoterol shifted the corresponding data to 58% and -23.0% (means +/- SD: 13.4 +/- 29.2). The protective effect of fenoterol did not depend on the reactivity of the airways to the stimulus applied. The results indicate that the inhalative pretreatment with 0.2 mg fenoterol powder is sufficient to block exercise-induced asthma even in those patients whose airways are highly sensitive to respiratory heat loss.