Distribution of [3H]prednisolone entrapped in lipid layer of liposome after intramuscular administration in rats.

Positivery charged, sonicated liposome entrapping [3H]prednisolone was administered into the rats hip muscle to examine its absorption and distribution in comparison with that of the administration of free [3H]prednisolone. Plasma concentration of prednisolone in liposome-entrapped form showed high concentration for a long period of time, the values being 8 times after 30 min and 24 times after 24 hr compared to the free form. The concentration of liposome-entrapped form in liver, kidney and spleen was 4-10 times, and in lung and pancreas was 8-10 times higher than that of free form after 30 min and 24 hr. But, in adrenal, after 30 min and 1 hr, liposome-entrapped form were lower than that of free form, the former remained longer in the tissue, and the concentration maintained the high level after 24 hr, being about 28 times higher than that of free form. Even in the duodenum and large intestine, absorption of the liposome-entrapped form was very active and remained in the tissue for a long period of time. These facts suggested the possibility of using a small dose in intramuscular administration but allowing the steroid to remain in the tissues for a long period of time.