PHARMACEUTICAL STUDIES ON LIPOSOMES IN TOPICAL DRUG FORMULATION

Abstract

Liposomes are microscopic and submicroscopic vesicles consisting of one or more concentric spheres of lipid bilayers separated by a water or aqueous buffer compartments. Liposomes are predominantly formed by phospholipids of natural, semi-synthetic, and I or synthetic origin. When phospholipids (PL) are hydrated, they spontaneously form lipid spheres enclosing the aqueous medium and the solute.

Liposomes are characterized in terms of their size and the number of lipid bilayers surrounding their central aqueous compartment. Liposomes are broadly classified into: (1) Multilamellar vesicles (MLVs) are distinguished by being larger than 0.1 J.lll1 in diameter and having more than five lamellae enclosing the aqueous core. They have moderate aqueous volume to lipid ratio (1-4 L /mole lipid). (2) Large unilamellar vesicles (LUVs), are distinguished by being larger than 0.1 J.lm in diameter and having one lipid bilayer closing one aqueous compartment. They have high aqueous volume to lipid ratio (7 L/ mole lipid). (3) Large oligolamellar vesicles (LOVs) are distinguished by being larger than 0.1 J.lm in diameter and having two to three lipid bilayers. (4) Small unilamellar vesicles (SUVs) consist of one lipid bilayer compartment and measure around 100 run or Jess. SUVs are thermodynamically unstable and susceptible to fusion. Liposomes of different sizes and characteristics usually require different methods of preparation.