Persistence of beta agonist efficacy over time

Mean FEV1 as a percentage of the predicted value on the first and last days of treatment in patients with asthma. Therapy consisted of salmeterol (40 µg twice daily), albuterol (180 µg four times a day), or placebo. Both beta agonists increased the FEV1, but the effect of a single dose lasted longer with salmeterol. The beneficial effect of both agents persisted at twelve weeks.