[Factors of elimination of liposome-encapsulated drug model substances after intravenous administration].

Carboxyfluorescein (CF) and fluorescein dilaurate (FDL) have been encapsulated in either small or large multilamellar liposomes of various lipid composition. Cholesterol (CH)-free liposomes showed relatively rapid CF release when dispersed in buffer, plasma or whole blood. The same behaviour was seen with liposomes which contained a lipid whose phase transition temperature was less than 37 degrees C. The CH-free preparations also showed marked aggregation in plasma. After i.v. application to rabbits the elimination of liposomal CF was found to depend upon the typ of phospholipid present, the CH content, the surface charge and vesicle size. The lipophilic substance FDL was lost from circulation more rapidly than the hydrophilic CF. All of the measured plasma levels indicated an open two-compartment model, i.e. with two exits. The calculated microconstants provide information about the distribution kinetics.