THE DEPOSITION AND CLEARANCE OF LIPOSOME-ENTRAPPED TC-99M-DTPA IN THEHUMAN RESPIRATORY-TRACT

The size characteristics of aerosols produced by nebulising liposomes from five jet nebulisers have been investigated. The size and size dis tribution of the aerosols was determined by the design of the nebulise r and the gas flow rate employed to drive the nebuliser, rather than o n the properties of the liposome preparations themselves. The clearanc e of inhaled dipalmitoylphosphatidylcholine/ cholesterol liposomes con taining the aqueous phase marker Tc-99m-DTPA was studied by gamma-scin tigraphy following inhalation by three healthy volunteers. Approx. 45% of originally deposited radioactivity remained in the lungs after 24 h. This represents the fraction of the radiolabel remaining in intact alveolar-deposited vesicles, since free Tc-99m-DTPA was removed from t he airways with a half-life of 75 min.