Dermal drug delivery by liposome encapsulation: clinical and electron microscopic studies.

The fate of liposomes and the encapsulated drug was studied after topical application on the skin. Lidocaine applied on the forearm of human volunteers produced greater local anaesthetic effect in the liposomal form than in the cream form (p less than or equal to 0.001 after 1 h application). Autoradiography demonstrated higher concentration (p less than or equal to 0.01) of 14C-lidocaine in the epidermis and dermis of guinea pigs treated with liposome-encapsulated lidocaine as opposed to lidocaine in Dermabase cream. Electron microscopic observations, using colloidal iron as an electrodense marker, indicated that intact liposomes penetrated into the skin and deposited in the dermis where they acted as a slow release depot system. On the basis of results in the human volunteers and animals, a hypothetical model for liposome-skin interaction is proposed.