Effect of salbutamol and ipratropium bromide on airway calibre and bronchial reactivity in asthma and chronic bronchitis

Abstract

Bronchial reactivity to agonists such as histamine is seen in both chronic bronchitis and asthma, two conditions with different pathological changes in the airways. Salbutamol, when given acutely, reduces bronchial reactivity in patients with asthma, but the mechanism has not been clarified. To determine whether the effect of salbutamol depends on the pathological changes underlying the increased reactivity, we have compared the effect of salbutamol and ipratropium on bronchial reactivity in nine patients with asthma and ten with chronic bronchitis. Each drug was given on separate days in increasing doses (5, 100, 750, 1,000 μg) according to a double-blind, randomized design. Changes in forced expiratory volume in one second (FEV1) and specific airways conductance (sGaw) were measured after each dose, and the provocative concentration of histamine causing a 20% fall in the FEV1 (PD20) was determined after the last dose. Salbutamol and ipratropium were equipotent in the asthmatic subjects and caused a similar maximal increase in FEV1 (0.58 and 0.57l) and sGaw (0.166 and 0.154 s-1·kPaPa-1). The two drugs also produced similar changes in the patients with chronic bronchitis, although the maximum response to both drugs was smaller (FEV1 0.29 and 0.32 l; sGaw 0.056 and 0.060 s-1·kPa-1; p < 0.05). Despite differences in bronchodilatation the increase in histamine PD20 following salbutamol was similar in the asthmatic and bronchitic subjects (2.26 and 1.90 doubling doses (DD)) and greater in both groups (p < 0.05) than the change in PD20 with ipratropium (0.84 and 0.56 DD). These data show that salbutamol causes a greater reduction in bronchial reactivity than ipratropium in patients with asthma and chronic bronchitis, and that both drugs have a similar effect in the two conditions, despite differences in the underlying pathology and despite the greater bronchodilatation observed in asthmatic patients.