The effect of inhaled salmeterol on methacholine responsiveness in subjects with asthma up to 12 hours.

The duration of the protective effect of 50 and 100 micrograms of inhaled salmeterol against methacholine-induced bronchoconstriction was compared with that of 200 micrograms of inhaled salbutamol in 12 patients with asthma with a baseline FEV1 of at least 70% and a provocative concentration of inhaled methacholine causing a 20% fall in FEV1 (PC20) greater than or equal to 8 mg/ml. The study was placebo controlled, double blind, randomized, and crossover. The bronchodilating effect was no longer significant 4 hours after inhalation of salbutamol, whereas the effect was still present 12 hours after administration of 50 and 100 micrograms of salmeterol. All active treatments caused PC20 to increase at 1 hour (p less than 0.05). PC20 (milligrams per milliliter) thus reached 3.7 +/- 0.8 after placebo, 13.8 +/- 3.0 after 50 micrograms of salmeterol, 23.2 +/- 4.7 after 100 micrograms of salmeterol, and 13.9 +/- 3.4 after 200 micrograms of salbutamol. The protective effect of 200 micrograms of salbutamol was no longer significant at 4 hours, whereas both doses of salmeterol protected against methacholine challenge up to 12 hours after inhalation (p less than 0.01). An increased incidence of tremor (2/12) and palpitations (2/12) was recorded after inhalation of 100 micrograms of salmeterol. We conclude that inhalation of 50 or 100 micrograms of salmeterol causes a long-lasting bronchodilatation and protects against methacholine-induced bronchoconstriction for at least 12 hours.