Beta-
adrenoceptor agonists such as
albuterol are very effective in preventing
exercise-induced asthma (EIA) when they are given as an
aerosol immediately before exercise. However, their duration of protection against EIA is usually less than 2 h. This may be due partly to their rapid clearance from the airways.
Salmeterol is a highly lipophylic compound that is thought to bind to an exoreceptor near the beta-receptor. The objective of this study was to compare the protective effect of
salmeterol with
albuterol against EIA. Exercise was performed 0.5, 2.5, 4.5, and 6.5 hours after administration of the active drugs. Subjects attended the laboratory on four days within six weeks and cycled for 8 min breathing dry
compressed air. We studied 17 asthmatic subjects (aged 19 to 49 years) with moderate to severe EIA.
Salmeterol (50 micrograms) or
albuterol (200 micrograms) was given from a
metered dose inhaler via a spacer (Volumatic). On the control day, the mean work load +/- 1 SD was 174 +/- 47 W, ventilation (VE) was 77.9 percent +/- 11.2 percent of the target ventilation (60 percent maximum voluntary ventilation [MVV]), and heart rate was 170 +/- 14 beats per minute. This intensity was maintained for all tests. FEV1 was measured before and after exercise and was expressed as percent predicted and as percentage of the preexercise value (percentage of fall). Thirty minutes
after treatment, both drugs were effective in inhibiting EIA--percentage of fall in FEV1, 17 +/- 12 after
salmeterol; percentage of fall in FEV1, 15 +/- 15 after
albuterol. At 2.5, 4.5, and 6.5 hours, the reduction in FEV1 was significantly less (p less than 0.01) after
salmeterol compared with
albuterol. At 6.5 hours, the percentage of fall in FEV1 was 20 +/- 10 after
salmeterol and 36 +/- 12 after
albuterol.
Salmeterol also had a more prolonged action as a
bronchodilator and values for FEV1 were significantly higher compared with those on
albuterol at 4.5 and 6.5 hours. At 6.5 hours, the FEV1 percent predicted was 96 +/- 10 after
salmeterol and 84 +/- 12 after
albuterol (p less than 0.01). We conclude that the extent of protection against EIA and the bronchodilation induced by both drugs was similar, but that
salmeterol has a longer duration of action compared with
albuterol. The reason for its superior duration of action may be due to a slower clearance of the
drug from the airways.