Terbutaline via pressurised metered dose inhaled (P-MDI) and Turbuhaler® in highly reactive asthmatic patients

Abstract

There is some concern over the environmental consequences of chlorofluorocarbons (CFCs) used in pressurized metered-dose inhalers (p-MDIs). Turbuhaler® was designed to deliver a drug as a dry powder without administering additives directly to the airways. The aim of this study was to evaluate the comparative irritant and bronchodilating effects of the same dose of terbutaline delivered by a pMDI and via Turbuhaler®. Ten symptomatic, asthmatic patients, with highly reactive airways (provocative concentration of methacholine producing a 20% fall in forced expiratory volume in one second (PC20) < 0.2 mg · ml-1), inhaled, on separate days, 0.25 mg terbutaline via p-MDI or Turbuhaler®. Changes in airway calibre were followed as specific airways conductance (sGaw). On a third day, patients inhaled from a placebo p-MDI containing all constituents except terbutaline. The study was conducted in a single-blind fashion and in random order. There were no significant differences in baseline sGaw on any of the study days. Inhalation of terbutaline from the p-MDI produced a transient percentage fall in sGaw at 1 min, reaching a mean maximum ± SD of 17 ± 8% at 10 s and then returning to baseline value after 20 s, followed by a progressive increase in sGaw to a maximum of 39 ± 45% above baseline at 45 min. In contrast, inhalation of terbutaline via Turbuhaler® caused no significant bronchoconstriction (fall in sGaw, 3± 16%) at 10 s and achieved a greater increase in sGaw, reaching 63 ± 51% at 45 min, although just failing to reach statistical significance compared to terbutaline p-MDI inhalation. The placebo p-MDI caused a 16 ± 15% fall in sGaw at 10 s, with values not returning to baseline until after one minute The present study showed that in highly reactive patients, inhalation of terbutaline via Turbuhaler® is an alternative to p-MDI, to avoid paradoxical bronchoconstriction.