Abstract

Inhalation aerosols have been successfully used to deliver drugs to the lung for local and systemic therapeutic effects. In vivo evaluation of pharmaceutical inhalation products is achieved by gamma scintigraphic imaging of the aerosol deposited in the lungs. Imaging provides direct information on the amount and the location of the drug deposited in the lungs after inhalation (1). This local bioavailability, rather than the systemic bioavailability after absorption, is pertinent to drugs that act directly on the lungs. For drugs that act systemically, the deposition site affects the rate and extent of absorption. As a result, lung deposition using gamma scintigraphy has been proposed for bioequivalence studies of aerosol products (2). The deposition data can further be linked to the clinical response and in vitro particle size distribution, adding a new dimension to the interrelationship between them.