Ocular drug delivery and pharmacokinetics: influence of drug properties and delivery systems

Abstract

SummaryAlthough the eye is readily accessible for drug dosing, drug delivery to the eye remains a major challenge due to multiple static and dynamic barriers. After topical administration, much <10% of the drug in the dosage form reaches intraocular tissues, primarily those in the anterior segment. No topical dosage form is currently approved for back of the eye drug therapy due to inadequate drug delivery. Topical dosing is currently viable only for small molecule drugs since macromolecules are not delivered adequately by this route of administration to be therapeutically effective. Intravitreal dosing through injections and surgical means, while allowing 100% dose delivery to the back of the eye, poses multiple challenges including rapid clearance of small molecules in solution, necessitating the use of slow release delivery systems. Macromolecules are cleared more slowly from the vitreous humor of the eye, allowing drug dosing once every month or two. Currently efforts are underway to reduce dosing frequencies for macromolecules as well. The purpose of this presentation is to describe mechanisms of topical and intravitreal drug delivery, with a key focus on drug and delivery system properties. Also, emerging routes of administration including suprachoroidal and transscleral routes will be discussed.