Differences in bronchodilating potency of salbutamol in Turbuhaler as compared with a pressurized metered-dose inhaler formulation in patients with reversible airway obstruction

Two studies are presented, with the aim of establishing the dose potency ratio for salbutamol given via Turbuhaler and via a pressurized metered-dose inhaler (pMDI). Both studies were of a double-blind, randomized design. Outpatients with mild-to-moderate chronic reversible airway obstruction were given single doses of salbutamol administered via Turbuhaler and via pMDI. Efficacy and safety variables were measured before and during 6 h after each dose. The first study was a four-way crossover study including 12 patients. The salbutamol doses given were: 50, 100 and 2x100 microg via Turbuhaler and 2x100 microg via pMDI (Ventolin). The study showed that 2x100 microg of salbutamol inhaled via Turbuhaler is more potent than 2x100 microg salbutamol inhaled via a pMDI, and that 100 microg salbutamol via Turbuhaler is at least as potent as 2x100 microg salbutamol inhaled via a pMDI. The second study including 50 patients was a placebo-controlled five-way crossover, study. Two doses of salbutamol via Turbuhaler, 50 and 2x100 microg, and via pMDI, 100 and 2x200 microg, were given. There was a dose-dependent response in forced expiratory volume in one second (FEV1) for both inhalers. Adjusted for differences in baseline FEV1 values, the estimated relative dose potency for Turbuhaler versus pMDI was 1.98:1 (95% confidence interval 12-3.2). These studies showed that the same bronchodilating effect can be achieved when half the dose of salbutamol given via a conventional pressurized metered-dose inhaler is given via Turbuhaler.