Comparison of oral and inhaled metaproterenol for prevention of exercise-induced asthma.

The effectiveness of inhaled versus oral metaproterenol in preventing exercise-induced asthma (EIA) was studied. Inhaled metaproterenol given 10 min before the exercise significantly reduced the degree of EIA in a group of twenty-four patients, and in 75% of them completely prevented it. The mean percentage decrease in FEV1 was 6.5% with the inhaler and 30.1% with placebo. When inhaled 1 hr before the exercise, metaproterenol was still better than placebo but its effectiveness was considerably lower. Metaproterenol tablets had a slight protective effect given 1 hr before, and none when administered 2 hr before exercise. There was no correlation between the protective effect against EIA and the bronchodilating effect obtained before exercise. Metaproterenol administered by metered-dose inhaler is a very effective prophylactic medication against clinically troublesome EIA, while metaproterenol tablets should not be recommended for this purpose.