Distribution of [³H] Prednisolone in Rat Plasma and Tissues after Intramuscular Administration in Liposome-Entrapped Form

Abstract

Positively charged, sonicated liposomes with [³H] prednisolone entrapped in them were administered to the rat hip muscle to examine its distribution in comparison with that after administration of free [³H] prednisolone. Plasma concentration of [³H] prednisolone in liposome-entrapped form was high for a long period of time, the values being 8 times after 30 min and 24 times after 24 hr compared to that in free form. The concentration of [³H] prednisolone in liposome-entrapped form in the liver, kidneys, and spleen was 4-10 times and, in the lung and pancreas, 8-10 times higher than that in free form after 30 min and 24 hr. In the adrenal, the concentration of liposome-entrapped prednisolone was lower than that in free form after 30 min and 1 hr, the former remained in the tissue, and the concentration was maintained at a high level after 24 hr, being about 28 times higher than that in free form. Even in the duodenum and large intestine, the liposome-entrapped form remained in the tissue for a long period of time. These facts suggested the usefulness of a small dose of intramuscular administration allowing the steroid to remain in the plasma and tissues for a long period of time.