The protective effect of low-dose inhaled fenoterol against methacholine and exercise-induced bronchoconstriction in asthma: a dose-response study.

Abstract

We compared in a randomized, double-blind study the protective effect of low doses of fenoterol on the airway response to exercise during cold air breathing and an inhalation challenge with methacholine. In six asymptomatic asthmatic persons (mean age, 20.3 years) exercise and methacholine challenges were performed under control conditions and 15 minutes after the inhalation from a metered-dose inhaler of either placebo or 30, 50, 100, and 200 micrograms fenoterol, resulting in 12 separate study sessions within a 3-week period. Airway response was determined by measuring specific airway resistance (sRaw). Exercise tests were standardized by maintaining a constant respiratory heat exchange, with an average (range) of 1.28 (1.15 to 1.45) kcal/min. Methacholine was inhaled at increasing doses until sRaw had doubled (PD100sRaw). Mean postexertional increase of sRaw (SD) after control conditions, placebo, and 30, 50, 100, and 200 micrograms fenoterol aerosol was 27.8 (6.9), 28.9 (10.0), 7.20 (2.7), 9.33 (3.8), 5.57 (2.3), and 5.28 (1.6) cm H2O.s. Fenoterol aerosol was equally effective at all doses administered, whereas methacholine-induced bronchoconstriction was attenuated in a dose-dependent manner. From these observations we suggest that low-dose fenoterol protects against bronchoconstriction induced by exercise, a naturally occurring stimulus reflecting airway hyperresponsiveness.