In-situ Ophthalmic Gels for the Treatment of Eye Diseases

Topical administration of a drug in the conjunctival cul-de-sac is the treatment of choice for diseases of the anterior segment of eye. Development of ophthalmic drug delivery systems has always been challenging because of the drawbacks with this route, like non-productive absorption, drainage, induced lacrimation, tear turn over, impermeability of drugs to cornea. New approaches have been investigated for delivery of drugs to the eye by means of polymeric delivery of ophthalmic drugs to the pre-and intra ocular tissues, have been attempted to increase the bioavailability and the duration of therapeutic action of ocular drug. Certain new approaches to increase the ocular bioavailability, duration of the drug action and to reduce the undesirable side effects are by using drug carriers that regulate pre-corneal drug loss and improve the corneal contact time. Many of these systems prolong ocular bioavailability but do not control drug penetration through the cornea. Consequently, the drug concentration at the site of action might remain inadequate. Therefore, it is necessary to develop safer, efficacious and more acceptable ocular therapeutic system. The ocular bioavailability of the drugs can be improved by prolonging their residence time in the cul-de-sac and by increasing their corneal permeability. There are various new dosage forms like in-situ gel, collagen shield, etc. INTRODUCTION: Ophthalmic drug delivery is one of the challenging endeavors facing the pharmaceutical scientist today. The structural and functional aspects of the eye render this organ highly impervious to foreign substances. A significant challenge to the formulator is to overcome the protective barriers of the eye without causing permanent tissue damage . The major problems in conventional liquid ophthalmic formulations are washing out of drug from the precorneal area immediately upon instillation because of constant lachrymal secretion, nasolacrimal drainage and short precorneal residence time of the solution. To increase precorneal residence time and ocular bioavailability, different ophthalmic delivery system such as viscous solutions, ointments, gels, suspensions or polymeric inserts are used. But because of blurred vision (e.g. ointments) or lack of patient compliance (e.g. inserts), these formulations have not been widely accepted. This problem can be overcome by using in situ gel forming ocular drug delivery system, prepared from polymer, exhibit sol-to-gel phase transition due to a change in a specific physio-chemical parameter (pH, temperature, ion-sensitive) . In situ gels are conveniently dropped as a solution into the conjunctival sac, where they undergo a transition into a gel with its favorable residence time. The sol-gel transition occurs as a result of a chemical/physical change induced by physiological environment. This type of gel combines the advantage of a solution being patient convenient with the favorable residence time