Influence of liposomal drug entrapment on percutaneous absorption

Results of permeation experiments involving finite dose diffusion c :Ils with hairless mouse skin as the membrane indicate that neither intact liposome; nor the phospholipid of which they are comprised diffuses across the skin. Lipoph lit drugs like progesterone and hydrocortisone, which are intercalated within th: bilayer structure of the phospholipid in miltilamellar liposomes. seem to pass thr Dugh the skin with comparable facility to free drug (comparable mass transfer toe Ticients). On the other hand, highly polar glucose entrapped in the aqueous compar: ments of the liposome is poorly available for transport. The results of in vitro release rate studies and theoretical calculations indicate that the very slight flux of lif osomally incorporated glucose seen experimentally is attributable to a slow release rate of glucose out of the liposome followed by relatively rapid skin permeation o!f the free solute. On the other hand, for hydrophobic progesterone and hydrocort isone the experimental results and supportive theoretical analysis suggest direct tr.ansfer of drug from liposome to the skin. Considering this mechanism and owing to increased soluble payloads of lipophilic drugs through liposomal incorporation, n ore total drug may be delivered through skin via liposomes relative to simple aqueous solutions.