1 Chapter 1 Current Trends in Liposome Research Tamer A. ElBayoumi and Vladimir P. Torchilin Abstract Among the several drug delivery systems, liposomes – phospholipid nanosized vesicles with a bilayered membrane structure – have drawn a lot of interest as advanced and versatile pharmaceutical carriers for both low and high molecular weight pharmaceuticals. At present, liposomal formulations span multiple areas, from clinical application of the liposomal drugs to the development of various multifunctional liposomal systems to be used in therapy and diagnostics. This chapter provides a brief overview of various liposomal products currently under development at experimental and preclinical level. Key words: Liposomes, Drug delivery, Drug targeting, Protein and peptide drugs, Gene delivery The clinical utility of most conventional therapies is limited either by the inability to deliver therapeutic drug concentrations to the target tissues or by severe and harmful toxic effects on normal organs and tissues. Different approaches have been attempted to overcome these problems by providing “selective” delivery of drugs to the affected area using various pharmaceutical carriers. Among the different types of particulate carriers, liposomes have received the most attention. For more than three decades, liposomes – artificial phospholipid vesicles – obtained by various methods from lipid dispersions in water and capable of encapsulating the active drug, have been recognized as the pharmaceutical carrier of choice for numerous practical applications (1–3). From the biomedical point of view, liposomes are biocompatible, cause very little or no antigenic, pyrogenic, allergic and toxic reactions; they easily undergo biodegradation; they protect the host from any undesirable effects of the encapsulated drug, at the same time protecting the entrapped drugs from the inactivating action of 1. Introduction V. Weissig (ed.), Liposomes, Methods in Molecular Biology, vol. 605, DOI 10.1007/978-1-60327-360-2_1, © Humana Press, a part of Springer Science+Business Media, LLC 2010