The deposition patterns of terbutaline sulphate delivered from pressurized metered dose inhaler (MDI) and Turbuhaler®have been compared by gamma scintigraphy. The radionuclide99mTc 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®. © 1993.
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