Ocular drug delivery system: a reference to natural polymers.

INTRODUCTION: Ocular drug delivery is a very challenging endeavor due to the unique anatomical and physiological barriers. The low ocular bioavailability (<10%) obtained from conventional formulations has forced the scientists to develop new formulations to deliver drugs to ocular tissues at a controlled rate to reduce frequent instillations. The natural polymers have represented the potential to deliver drugs topically through the limited precorneal area and release over a prolonged time period. AREAS COVERED: The important points to be considered during the fabrication of ophthalmic formulations for example, properties of drug molecule and polymer which affect the release rate are discussed. Novel polymers, like arabinogalactan, xyloglucan, gum cordia, locust bean gum, carrageenan and Bletilla striata polysaccharide, besides the conventional polymers like chitosan, starch, sodium alginate, sodium hyaluronate, xanthan gum, gelatin, gellan gum, guar gum, collagen and albumin, have demonstrated the potential to safely deliver drugs at a controlled rate in different ophthalmic formulations. EXPERT OPINION: The limitations of topical delivery of genes and chemotherapeutic drugs can be overcome by using natural polymers with characteristic properties. Despite the wide applicability, tremendous efforts are required to establish natural polymers in novel formulations on a commercial scale.