Deposition and clinical efficacy of terbutaline sulphate from Turbuhaler, a new multi-dose powder inhaler

Abstract

A radioaerosol technique has been developed in order to assess deposition patterns from a new metered dose powder inhaler (Turbuhaler, Astra Pharmaceuticals). The radionuclide Tc99m dissolved in chloroform was added to a spheronised formulation of micronised terbutaline sulphate and the chloroform was allowed to evaporate. Turbuhaler subsequently delivered 0.5 mg of treated drug per metered dose. In vitro tests with a multistage liquid impinger showed that the fractionation of the drug dose between different particle size bands was similar to the fractionation of radioactivity. In a group of ten asthmatic patients, a mean 14.2% (SEM 2.1) of the drug dose was deposited in the lungs, with 71.6% (3.0) of the dose in the oropharynx. Of the remainder, 13.7% (2.1) was deposited on the mouthpiece, and 0.5% (0.2) recovered from exhaled air. The radiolabel was present in both central and peripheral zones of the lungs. All patients bronchodilated; forced expiratory volume in one second (FEV1) increased from 1.40 (0.24) l to 1.77 (0.24) l (p < 0.01) 20 min after inhalation. These results suggest that both the distribution of drug and the clinical effect of terbutaline sulphate delivered from Turbuhaler are similar to those from a pressurised metered dose inhaler (MDI).