LIPOSOME OCULAR DELIVERY SYSTEMS

Liposomes are microscopic vesicles composed of membrane-like lipid bil ayers surrounding aqueous compartments. This unique feature imparts th e ability of liposomes to encapsulate both lipophilic and hydrophilic compounds. Consequently liposomes have been investigated extensively a s a drug carrier system by various routes of administration. One of th e more recent applications is the concept of employing liposomes as dr ug carriers in ophthalmology. Traditional drug therapy in the eye cons ists of the administration of solutions and suspensions. These dosage forms are compromised in their effectiveness by several limitations in cluding rapid nasolacrimal drainage, poor corneal penetration, nonprod uctive conjunctival losses and unwanted systemic exposure. The need fo r an ocular drug delivery system which has the convenience of a drop, but will localize and maintain drug activity at its site of action, is apparent. Liposomes offer a promising avenue to achieve this goal. Th e simplicity of preparation and the versatility in physical characteri stics confer a unique and useful property to liposomes for use as an o cular drug deliverer. In this review, a historical account of the stud ies is presented to illustrate the potential of liposomes in ophthalmo logy. Consideration is given to methods of preparation, advantages of liposomes as drug carriers as well as some of the general issues surro unding liposomes as a pharmaceutically acceptable dosage form. Various routes of administration such as topical instillation, intravitreal, subconjunctival and systemic injection are also discussed. Significant progress has been made in these areas and a complete understanding of the liposome interaction with ocular tissues should enable the design of liposomal products suitable for ocular drug delivery.