Sai HS. Boddu1,2, Abeer M. Al-Ghananeem1,2, and Vibhuti Agrahari 3
1Department of Pharmaceutical Sciences, College of Pharmacy and Health Sciences, Ajman University, Ajman, UAE
2Center of Medical and Bio-Allied Health Sciences Research, Ajman University, Ajman, UAE
3Department of Pharmaceutical Sciences, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
Ocular drug delivery can have four target sites: the preocular structures (e.g., conjunctiva, eyelids); the cornea; the anterior and posterior chambers along with allied tissues; and the posterior segment (e.g., retina, choroid, and vitreous humor) (1). The most common routes of drug administration for treating anterior segment diseases are topical administration and sub-conjunctival injection, whereas posterior segment diseases are treated by administering drugs via topical, systemic, periocular, and intravitreal routes (2). Even though eye drops are utilized for delivering ~90% of medications to the eyes, they exhibit < 5-10% bioavailability due to the removal of applied medication by tear turnover (0.5-2.2 μL/min) and rapid eyelid blinking (6-15 times/min) (3). The protective mechanisms of the eye can efficiently remove the administered drug at a rate that is 500 to 700 times greater than the rate of drug absorption into the anterior segment tissues (4-7). Drug lipophilicity and tight junctions of the corneal epithelium also play a major role in limiting corneal absorption (8-10). Putting together the anatomical, physiological, and biochemical barriers leads to the failure of conventional dosage forms such as eye drops, ointments, and suspensions.