Nano- or submicron-sized liposomes as carriers for drug delivery

Liposomes are tiny spheres ranging in diameters from 50 nm to several microns. The scope of this mini review is to introduce the concept of liposomes and to describe some aspects and mechanisms of stimulating topical and injectable products with liposomes. Two examples discussed in this article are topical delivery across skin and injectable formulations for anticancer drugs. Classic liposomes are of little value as carriers for drug delivery via the skin because they do not penetrate it deeply. Only specially designed liposomes have been shown to be capable of achieving enhanced delivery. The incorporation of additives, such as anionic surfactants and ethanol, can fluidize the phospholipid bilayers, thus increasing the depths to which liposomes can penetrate the intercellular pathways of the skin. Also, liposomes that have been conjugated with PEG or antibodies can increase the residence time of anticancer drugs in the circulation and enhance drug accumulation in tumors.