The duration of protection from exercise-induced asthma by inhaled salbutamol, and a comparison with inhaled reproterol.

beta-Adrenergic bronchodilators can prevent the development of exercise-induced asthma (EIA). To investigate the duration of this effect, we determined the time at which the protective effect of salbutamol diminished significantly in six subjects. All had stable asthma known to be triggered by exercise. Following a control exercise test, identical tests were repeated weekly at various times (1-6 hours) after inhalation of 200 micrograms of salbutamol. Significant protection (less than 75%) was lost in two subjects at 2 hours, in two at 4 hours and in two at 6 hours. A further exercise test was performed after inhalation of 1 mg of reproterol, at the time when salbutamol no longer afforded significant protection. There was a significantly smaller fall in peak expiratory flow rate after exercise (P less than 0.01) with reproterol than with salbutamol, at the same time after inhalation. There was no relationship between the degree or duration of protection from EIA and the bronchodilator effect of the drugs, the age and sex of the subjects, the length of asthma history or severity of base-line EIA, except perhaps the requirement for regular treatment with a steroid aerosol or sodium cromoglycate.