Liposomes and parameters affecting their skin penetration behaviour

It is known that classical and more recently deformable liposomes have shown their ability to increase dermal and transdermal drug delivery. However their penetration mechanism remains controversial and not understood at this time. Different vesicle compositions, preparation methods and drugs have been used, giving vesicles with diverse characteristics. This fact, in addition to the experimental conditions, probably accounts for the lack of understanding with regards to their mode of action. This review focuses on the penetration behaviour of liposomes as a function of their composition. Parameters influencing the mode of action of liposomes are discussed, such as the preparation method, lipid composition, entrapment efficiency, addition of an edge activator or ethanol, size and lamellarity. It also reviews parameters of the experimental set-up (usually Franz type diffusion cells are used for in vitro skin absorption studies) which could affect results of diffusion, such as the skin used, receptor fluid composition, occlusive or non occlusive mode and washing step. The purpose is to highlight parameters which are beneficial or detrimental to skin penetration with the goal of understanding the penetration mechanism of liposomes.