Selective delivery of drugs encapsulated in liposomes: natural targeting to macrophages involved in various disease states.

In recent years, a considerable effort has been made to promote the use of liposomes as potential carriers for systemically administered chemotherapeutic agents. It is our belief that much of this proselytizing has ignored the normal and unavoidable fate of systemically administered liposomes, which is clearance by the reticuloendothelial system. Rather than attempting to avoid this phenomenon, we suggest that this occurrence could be advantageous for the selective delivery of agents to cells of the monocyte-macrophage series involved in various disease states.