Objective: Using a model of natural allergen exposure, we examined the effect of regular treatment with salmeterol on allergen-induced changes in airway responsiveness and exhaled nitric oxide (ENO).
Design: Double-blind, randomized, parallel-group study.
Setting: Specialist allergy unit in a university hospital.
Patients: Asthmatic patients sensitized to pollen allergens were randomly allocated to monotherapy with salmeterol (n = 14) or placebo (n = 13).
Interventions: Salmeterol, 25 μg, and placebo inhalers, two puffs bid, for 6 weeks.
Measurements: Spirometry, the level of a provocative concentration of a substance (methacholine) causing a 20% fall in FEV1 (PC20), the PC20 level for adenosine 5′-monophosphate (AMP), and ENO were measured before the pollen season and were repeated at the height of the pollen season after 6 weeks of treatment with salmeterol or placebo.
Results: The decrease in FEV1 during the pollen season was significantly larger in the placebo group than in the salmeterol group, the mean difference in the change between the groups being 0.20 L (95% confidence interval, 0.03 to 0.35; p = 0.047). Changes in PC20 for methacholine, PC20 for AMP, and ENO levels were not significantly different between treatment groups. However, a mean (± SEM) decrease in the PC20 for methacholine of −1.0 ± 0.4 doubling concentrations was observed within the placebo group (p = 0.03), whereas no significant changes were observed within the salmeterol group. A significant decrease in PC20 for AMP (doubling concentrations) was observed within the placebo group (−2.1 ± 0.6; p = 0.003) and the salmeterol group (−1.5 ± 0.4; p = 0.003). ENO concentrations increased significantly among the placebo and the salmeterol groups during natural pollen exposure.
Conclusion: These observations indicate that natural allergen exposure and the regular use of salmeterol are not associated with a greater increase in ENO and airway responsiveness than allergen exposure alone.