Chemically modified hyaluronic acid derivatives as ocular drug carriers: A review

Ocular delivery of therapeutic agents has always been challenging due to the sensitive nature of the eye, restricted permeability through the ocular barrier, and easy wash out of dosage form from ocular surface. These issues have limited the choice of polysaccharides for ocular delivery. In recent times hyaluronic acid (HA) has gained considerable attention as a pharmaceutical excipient in drug delivery. The excellent biocompatible and biodegradable profile of this naturally occurring glycosaminoglycan (GAG) has made it a promising polysaccharide for drug delivery. Being found in ocular regions, HA became a preferred biomaterial for the ocular delivery of medicaments. Alongside its favorable biocompatible nature, the bioadhesive behaviour of HA aids in retaining the dosage form to the ocular surface which enhances the ocular bioavailability of drugs. The flexible and easily modifiable structure of HA has encouraged pharmaceutical researchers to synthesise chemically modified HA derivatives with improved physicochemical properties. Derivatives of HA can improve the mechanical as well as bioadhesive behaviour that can increase ocular retention. This review describes important ocular barriers, the suitability of HA in ocular drug delivery system, the synthesis of several HA derivatives, and their applications in ocular delivery of therapeutic agents.