Studies on liposome-encapsulated carboquone II. Effect of liposomal encapsulation of carboquone on distribution and clearance in animals.

The effects of encapsulation of carboquone (CQ) in the liposomes were investigated on the plasma clearance and tissue distribution of CQ in rabbit and rat. CQ-Liposome, the liposomes in which CQ was encapsulated, was prepared by the method described in a previous report. By intravenous administration at the same dose. CQ-liposome showed approximately three times higher plasma concentration than free CQ in rabbit and rat. However, prolonged release from liposomes or stabilization of CQ in plasma was not observed by encapsulation. The distribution to lung and reticuloendothelial-rich organs such as liver and spleen was enhanced, but on the contrary the distribution to the peripheral tissues such as muscle and skin was decreased. In rats pretreated with drug free liposomes, high plasma CQ concentration was obtained after intravenous administration of CQ-liposome. From these results, it is considered that the large parts of CQ-liposome is distributed into reticuloendothelial system (RES) and RES is saturable with liposomes. And it is also presumed that the high plasma concentration obtained after intravenous administration of CQ-liposome, would be caused by altering the tissue distribution of CQ by encapsulation.