Target strategies for drug delivery bypassing ocular barriers

Abstract

The eye is a directly accessible sensitive organ, impairment of which causes direct effect on the quality of life. Efficient ocular drug delivery remains a major challenge for the pharmaceutical scientists and researchers worldwide due to the hindrance offered by the complex ophthalmic environment, i.e., static barriers (stratified corneal epithelium, corneal stroma, sclera and other biological membranes), dynamic barriers (choroidal or conjunctival blood flow, lymphatic clearance, tear turnover) and metabolic barriers, (efflux pumps/enzymes). The anatomy and physiology of each barrier is different and so should be the ways to overcome them. Current review provides an insight into the target strategies that can be employed to surpass each barrier of anterior and posterior segment of the eye separately, exploiting its unique nature viz. hydrophilicity or lipophilicity, total net charge, permeability towards molecules, presence of enzymes etc. This approach can aid in the improvement of transport of therapeutic agents across the barriers, achieve optimum drug levels in the targeted tissues and provide sustained/prolong release of drugs with minimal/no side effects. Modern research describing the utility of novel nanotechnology-based drug delivery approaches for treating the ocular diseases associated with each of the barriers has also been addressed. Clinical trials pertaining to ocular nano-centric technologies have also been discussed which is a crucial step in success of any ophthalmic drug development. Regardless of the significant research and large market potential, the number of novel ocular products entering the market is very small owing to no official regulatory guidance for ophthalmic drug development. This bench to bed gap can be therefore filled by robust product development plan like using safer inactive ingredients in the formulation design. This review additionally presents the regulatory perspectives for the development of a safe and patient complaint ocular drug delivery system.