Pulmonary localization of intravenously injected liposomes

Clearance from the circulation and tissue distribution of liposomes of differing size, surface charge, and composition injected IV into BALB/c mice have been examined. Large (500-3,400 nm diameter) liposomes are cleared from the circulation more rapidly than small sonicated liposomes (less than 100 nm diameter). Negatively charged liposomes are cleared more rapidly than neutral or positively charged liposomes of the same size. The major site at which liposomes injected IV accumulate, irrespective of their composition, is the liver. Accumulation of liposomes at extrahepatic sites, such as the lung, is influenced by liposome size, charge, and composition. Optimal localization and retention of liposomes in the lung were achieved with large negatively charged multilamellar and reversed evaporation phase liposomes containing phosphatidylserine (PS/PC, 3:7 mol ratio; PS/PC/LL 4.95:4.95:0.1 mol ratio).