Abstract: A number of novel drug delivery systems have emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Encapsulation of the drug in vesicular structures such as liposomes is such a system, which can be predicted to prolong the existence of the drug in systemic circulation, and reduce the toxicity, if selective uptake can be achieved. Advances have since been made in the area of liposomal drug delivery, leading to the development of systems that allow drug targeting, and the sustained or controlled release of conventional medicines. The focus of this review is to bring out the advantages, methods, applications and characterization of liposomal systems.
Introduction
Liposomes are microscopic or submicroscopic structures of 10nm to 20mm in diameter. They are made up of one or many concentrically arranged lipid bilayers constituting an envelope. Liposomes posses unique properties owing to the amphiphilic character of the lipids, which make them suitable for drug delivery. Liposomes were first produced in England in 1961 by Alec D. Bangham, who was studying phospholipids and blood clotting. All methods of preparation of liposomes involve dissolution of cholesterol, lecithin, and charge in organic solvent, followed by drying it to a thin film, and then dispersion of film in an aqueous medium to obtain liposome suspension at a critical hydrating temperature. The hydrating temperature used to prepare liposomes should be above the phase transition temperature of phospholipid used i.e. temperature at which there is transition from gel to liquid phase. It can be altered by using phospholipid mixtures, or by adding sterols e.g. cholesterol. Gel state vesicular delivery system can be improved by adding cholesterol to the lipid in liposomes. This temperature can give good clues to vesicular delivery, system stability, and permeability.1, 2 |
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