Speed of onset of bronchodilator response to salbutamol inhaled via different devices in asthmatics: a bioassay based on functional antagonism

Aims To evaluate the speed of onset of bronchodilation following salbutamol administered via a metered‐dose inhaler with a spacer (pMDI + Volumatic) and a dry‐powder inhaler (Diskus), as well as the relative potencies of these devices in asthmatic patients with methacholine‐induced bronchoconstriction. Methods Eighteen patients inhaled methacholine (MCh) until FEV1 decreased by 35% of control. Following administration of placebo, 200 µg salbutamol or 400 µg salbutamol through the pMDI + Volumatic or the Diskus, we calculated the time elapsed from drug administration and the appearance of a 90% increase in post‐MCh forced vital capacity (FVC), FEV1 and volume‐adjusted mid‐expiratory flow (recovery times). The salbutamol doses to be delivered by the two inhalation devices to achieve similar recovery times and the relative potencies of the devices were calculated by using the 2‐by‐2 Finney parallel regression method. Results For all functional variables, recovery times were significantly (P