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.

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.

For all functional variables, recovery times were significantly (P < 0.01) shorter in pMDI + Volumatic than Diskus trials. The salbutamol doses to be delivered by the Diskus to achieve recovery times for FVC, FEV₁ and volume‐adjusted mid‐expiratory flow similar to those obtained with 200 µg salbutamol administered via the pMDI + Volumatic were 558 (95% CI 537, 579) µg, 395 (95% CI 388, 404) µg and 404 (95% CI 393, 415) µg, respectively, and corresponded to relative potencies of 2.79 (95% CI 2.68, 2.90), 1.98 (95% CI 1.94, 2.02), and 2.02 (95% CI 1.96, 2.07).

Administration of salbutamol via the pMDI + Volumatic provides faster reversal of induced bronchoconstriction than via the Diskus. The salbutamol dose targeting the lungs with the pMDI + Volumatic is approximately twice that with the Diskus.