Mucoadhesive Polymers for Enhancing Retention in Ocular Drug Delivery: A Critical Review

Ocular drug delivery is a very challenging task faced by pharmaceutical scientists, inspite of the fact that eye is the most sensitive and accessible organ for the delivery of drugs. A major disadvantage associated with conventional dosage form is its low bioavailability, i.e, less than 10%. To improve the bioavailability, viscosity-enhancing agents or mucoadhesive polymers are used for treating severe ocular diseases. These polymers play an important role in increasing the precorneal residence of drug at ocular site. Chitosan was initially endorsed to open up the tight junction of epithelium which increases the viscosity and penetration ability of drug solution. Alginate is an anionic polymer which acts as a good penetration enhancer and has high mucoadhesive strength. This review gives an overview of various mucoadhesive polymers such as chitosan, alginate, gellan gum, guar gum, Carbomer, Eudragit, etc. used to increase the bioavailability, precorneal residence time and controlled release with reduced dosing frequency without causing any visual disturbances. Ocular delivery formulations can be made more acceptable and excellent drug delivery systems by using both natural and synthetic polymers. Polymeric materials have a vast potential for exciting new applications in the foreseeable future and will have a great future in ocular drug delivery research.