Protection against methacholine-induced bronchospasm: salbutamol pMDI versus Clickhaler DPI

Passive dry-powder inhalers (DPIs) have been developed as an alternative to pressurised metered-dose inhalers (pMDIs) to improve aerosol delivery on inhalation and eliminate the need for propellants. However, new DPI formulations of generic drugs must be rigorously compared with conventional pMDI therapy. This randomised, double-blind, double-dummy, placebo-controlled, seven-way crossover study evaluated bronchoprotection from methacholine challenge in order to compare a novel salbutamol DPI (Clickhaler) with a reference salbutamol pMDI (Ventolin). Adult asthma patients with airway hyperresponsiveness to methacholine (provocative concentration of methacholine causing a 20% fall in the forced expiratory volume in one second (PC20) <4 mg x mL(-1)) were treated on separate days with 0, 100, 200 or 400 microg of salbutamol via the DPI or pMDI. Methacholine challenge was performed before and after salbutamol treatment and the PC20 ratios analysed by Finney's bioassay to test for therapeutic equivalence of the inhalers. Eighteen patients completed the study and showed significant dose-related responses to salbutamol. The relative potency of DPI:pMDI was 1.29 (90% confidence interval 1.04-1.63). There were no treatment differences in safety (cardiac frequency, blood pressure, adverse events). Methacholine-challenge methodology provides a sensitive bioassay and has demonstrated therapeutic equivalence of the salbutamol Clickhaler dry-powder inhaler with the conventional salbutamol pressurised metered-dose inhaler.