Liposome: A versatile platform for targeted delivery of drugs

Liposomes are colloidal, vesicular structures composed of one or more lipid bilayers surrounding an equal numbers of aqueous compartments. Since, 1960’s pharmaceutical researchers used liposomes as therapeutic tools in medicinal field.A number of liposomal formulations of such drugs have available in the market such as Doxil (Doxorubicin), Fungizone (Amphotericin-B), Novasome (Smallpox vaccine) and NyotranTM (Nystatin). Liposomes used as potential carriers in field like tumor targeting, gene and antisense therapy, genetic vaccination, immunomodulation and skin care and topical cosmetics products. The present review highlights the composition, method of preparation, characterization, therapeutic applications of liposomes and its marketed products.IntroductionLiposomes were discovered in the early 1960’s and subsequently studied as cell membrane models1. They have since gained recognition in the field of drug delivery. The particle size of liposomes ranges from 20 nm to 10 μm in diameter. Liposomes vary in charge and in size depending on their manufacturing protocol and type of (phospho) lipid bilayer used (the small unilamellar vesicle [SUV] size range is 0.02 -0.05 μm, the large unilamellar vesicles [LUV] size range is greater than 0.06 μm and the multilamellar vesicle [MLV] size range is 0.1 – 0.5 μm)2. The physicochemical characteristics of the liposomes, like particle size, lamellarity, surface charge, sensitivity of pH changes and bilayer rigidity can be manipulated. Liposomes showed promising result in the drug delivery but their applicability is limited primarily to specific use because of short half-life in blood circulation. The circulation time of liposomes in the blood stream is dramatically increased by attaching polyethylene glycol (PEG) – units to the bilayer, known as long circulating (Stealth) liposomes3.