Time course of bronchodilating effect of inhaled formoterol, a potent and long acting sympathomimetic

Abstract

Background - Most of the currently available inhaled β2 agonists are short acting bronchodilators. The aim of this study was to compare the rate of onset and duration of the bronchodilating activity of formoterol and salbutamol. Methods - Fourteen patients with reversible airways obstruction received placebo, 200 μg salbutamol, and 12, 24, and 48 μg formoterol from a metered dose inhaler, according to a double blind, randomised crossover design. Forced expiratory volume in one second (FEV1) and specific airways conductance (sGaw) were measured over 12 hours. Results - Salbutamol and all doses of formoterol caused a significant and substantial increase in sGaw one minute after inhalation. The mean maximum increase in FEV1 was 58% (8%) after 200 μg salbutamol compared with 63% (11%), 62% (10%), and 74% (10%) after 12, 24, and 48 μg formoterol, respectively. The mean maximum increase in FEV1 occurred 57 (12) minutes after administration of salbutamol compared with 137 (16), 141 (21), and 161 (33) minutes after 12, 24, and 48 μg formoterol respectively. The bronchodilating effect of salbutamol did not differ from placebo after six hours. In contrast, the mean increase in FEV1 12 hours after 12 μg formoterol (26% (8%) of baseline) significantly exceeded the change after placebo. Tremor was recorded in four patients after 48 μg formoterol. Conclusion - Formoterol is a potent fast acting bronchodilator with a long duration of action.