In vitro and in vivo aspects of quantifying intrapulmonary deposition of a dry powder radioaerosol

Pulmonary delivery of pharmaceutical aerosols can be quantified using gamma scintigraphy. Technetium-99m. the most commonly used radionuclide in scintigraphic studies, cannot be incorporated into the drug molecule and, therefore., may be distributed differently from the drug itself, particularly if the drug is presented as a solid in a liquid suspension or as a dry powder formulation. This study demonstrated the importance of using conditions relevant to the in vivo situation in the in vitro characterisation of a dry powder aerosol of Tc-99m-labelled lactose. The influence of inspiratory flow on the distribution of aerosol within the lungs was investigated in eight healthy subjects who inhaled the Tc-99m-labelled lactose at four flows (30, 40, 60 and 80 l/min). No differences in penetration index (PI) or count density distribution of radioactivity were seen, indicating that regional distribution of aerosol in healthy airways was insensitive to differences in the inspiratory effort exerted by the subject while inhaling the experimental dry powder radioaerosol. (C) 2002 Elsevier Science B.V. All rights reserved.