Site and duration of bronchodilation in asthmatic patients after oral administration of terbutaline.

We compared pulmonary function in 15 asthmatic subjects before and after ingestion of 5 mg terbutaline and placebo. Measurements of maximal expiratory flow (VEmax), density-dependence of VEmax (delta VEmax50), volume of isoflow (Viso V), residual volume (RV), and closing capacity (CC) were performed before and 15, 135, 255, and 375 minutes after both treatments. After placebo VEmax improved mildly (P < 0.05) but no significant changes occurred in delta VEmax50, VisoV, RV, or CC. After terbutaline, VEmax increased significantly and VisoV, RV, and CC decreased significantly at all time periods studied. In addition delta VEmax50 increased compared to baseline at 15 and 135 minutes (P < 0.05) and compared to placebo at 135 and 255 minutes (P < 0.05). In our study, orally administered terbutaline apparently caused predominant peripheral airways bronchodilatation in the first few hours after ingestion. Afterwards, the predominant small airways effect appeared to wane, and large and small airways were dilated proportionately equally 375 minutes after oral administration of terbutaline.