Total and regional lung deposition of terbutaline sulphate inhaled via a pressurised MDI or via Turbuhaler ®

Abstract

The deposition patterns of terbutaline sulphate delivered from pressurized metered dose inhaler (MDI) and Turbuhaler ® have been compared by gamma scintigraphy. The radionuclide 99mTc was used to label the formulations, and 1 mg terbutaline sulphate was subsequently inhaled from each device in a randomized cross-over fashion by eight healthy volunteers. Both devices were operated at their respective optimal inhalation flow rates. From the pressurised MDI, a mean 16.7% of the dose was deposited in the lungs (range 6.1–30.0%), compared to a mean 21.4% (range 14.1–30.8%) from Turbuhaler ®. If the Turbuhaler ® data were corrected for an observed mismatch in the size distributions of radiolabel and unlabelled drug, then the mean lung deposition from Turbuhaler ® would be 29.3% of the dose. The distribution of radiolabel within the lungs was similar for each device, but oropharyngeal deposition was significantly reduced for Turbuhaler ® ( P < 0.01). It is concluded that pressurized MDI and Turbuhaler ® produce broadly similar regional deposition in the lungs, but that the inter-subject variability of deposition is less for Turbuhaler ®.