Background: Inhalation of a single dose of the long-acting beta 2-adrenoceptor agonist salmeterol protects against methacholine-induced airway obstruction and other bronchoconstricting stimuli for at least 12 hours. Hypothetically, twice daily dosing of salmeterol may result in continuous protection.
Objective: This study was designed to investigate the protective effect of a single dose of salmeterol and of continuous twice daily treatment on airway responsiveness to methacholine.
Methods: In a double- blind, parallel study, salmeterol 50 micrograms twice daily was compared with salbutamol 200 micrograms twice daily. Thirty children with mild asthma, who had little or no bronchial obstruction and were hyperresponsive to methacholine (PD20 < or = 150 micro g) were allocated to receive either salmeterol or salbutamol. Airway responsiveness was measured before study entry, 12 hours after a single dose of drug was given, and monthly during 4 months of daily treatment. Measurements were always performed at the same time of the day, 12 hours after the last dose of medication was administered.
Results: No significant differences in FEV 1 were found between treatments at any time point. PD20 significantly increased after the first dose of salmeterol was given (geometric mean, 100 micro g). Geometric mean PD20 values were significantly better during salmeterol treatment than during salbutamol treatment, 52 and 25 micro g, respectively (p = 0.005).
Conclusion: The protection provided by salmeterol during maintenance treatment was less than that provided after the first dose (p <0.001). However, protection did not diminish during the 4-month treatment period and remained significant compared with baseline (p = 0.003).