Topical Drug Delivery to the Posterior Segment of the Eye: Addressing the Challenge of Preclinical to Clinical Translation

Abstract

Topical delivery of therapeutics to the posterior segment of the eye remains the "holy grail" of ocular drug delivery. As an example, anti-vascular endothelial growth factor biologics, such as ranibizumab, aflibercept, and bevacizumab, are delivered by intravitreal injection to treat neovascular age-related macular degeneration and, although these drugs have revolutionized treatment of the disease, less invasive alternatives to intravitreal injection are desired. Multiple reports in the literature have demonstrated topical delivery of both small and large molecules to the back of the eye in small animal models. Despite this progress, successful translation to larger species, and ultimately humans, has yet to be demonstrated. Selection of animal models with relevant ocular anatomy and physiology, along with appropriate experimental design, is critical to enable more relevant feasibility assessments and increased probability of successful translation.

Keywords: formulation; in vivo evaluation; posterior segment; topical delivery; translation.

Fig. 1

Drug distribution pathways through the corneal and conjunctival/scleral routes following topical administration. Reprinted from Advanced Drug Delivery Review, Vol 57, Hughes PM, Olejnik O, Chang-Lin JE, Wilson CG, Topical and systemic drug delivery to the posterior segments, Pages 2010–32, Copyright 2005, with permission from Elsevier.