TOTAL AND REGIONAL LUNG DEPOSITION OF TERBUTALINE SULFATE INHALED VIA A PRESSURIZED MDI OR VIA TURBUHALER (R)

The deposition patterns of terbutaline sulphate delivered from pressurized metered dose inhaler (MDI) and Turbuhaler(R) have been compared by gamma scintigraphy. The radionuclide Tc-99m 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(R). If the Turbuhaler(R) data were corrected for an observed mismatch in the size distributions of radiolabel and unlabelled drug, then the mean lung deposition from Turbuhaler(R) 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(R) (P < 0.01). It is concluded that pressurized MDI and Turbuhaler(R) produce broadly similar regional deposition in the lungs, but that the inter-subject variability of deposition is less for Turbuhaler(R).