LIPOSOME OCULAR DELIVERY SYSTEMS

Liposomes are microscopic vesicles composed of membrane-like lipid bilayers surrounding aqueous compartments. This unique feature imparts the ability of liposomes to encapsulate both lipophilic and hydrophilic compounds. Consequently liposomes have been investigated extensively as a drug carrier system by various routes of administration. One of the more recent applications is the concept of employing liposomes as drug carriers in ophthalmology. Traditional drug therapy in the eye consists of the administration of solutions and suspensions. These dosage forms are compromised in their effectiveness by several limitations including rapid nasolacrimal drainage, poor corneal penetration, nonproductive conjunctival losses and unwanted systemic exposure. The need for 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. The simplicity of preparation and the versatility in physical characteristics confer a unique and useful property to liposomes for use as an ocular drug deliverer. In this review, a historical account of the studies is presented to illustrate the potential of liposomes in ophthalmology. Consideration is given to methods of preparation, advantages of liposomes as drug carriers as well as some of the general issues surrounding 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.