Ocular drug delivery conjunctiva

K. Hosoya, V. H. Lee, and K. J. Kim. Roles of the conjunctiva in ocular drug delivery a review of conjunctival transport mechanisms and their regulation. Eur J Pharm Biopharm 60 227-240 (2005)... 

Typically topical ocular drug administration is accomplished by eye drops. - These are liquid preparations that contain drug substances that are used in ocular drug delivery. The drug substance must be active on the surface of the eye or the internal region of the eye after passage through the cornea or conjunctiva. ... 

Most ocular diseases like dryness, conjunctiva, and eye flu are treated by topical drug application in the form of solutions, suspensions, and ointment. In the earlier period, drug delivery to the eye has been limited to topical application, redistribution into the eye following systemic administration, or direct intraocular/periocular injections. However, one of the major barriers of ocular medication is to obtain and maintain a therapeutic level at the site of action for a prolonged period of time. 

The conventional concentration of benzalkonium chloride in eyedrops is 0.01%, with a range of 0.004-0.02% [111]. While uptake of benzalkonium chloride itself into ocular tissues is limited [113], even lower concentrations of benzalkonium chloride have been reported to enhance corneal penetration of other compounds including therapeutic agents [93,112,114]. The differential effect of this preservative on the cornea compared to the conjunctiva can be exploited to target a drug for corneal absorption and delivery to the posterior segment of the eye [115]. Its use has been proposed as a means of delivering systemic doses by an ocular route of administration [116]. 

The main challenge in ocular delivery is to increase the bioavailability of the drug and its residence time in the cornea, conjunctiva, and epithelia. Nanoscale polymers such as dendrimers can contribute to sustained release of encapsulated drugs at these sites. PAMAM dendrimers have been employed as ophthalmic vehicles in ocular delivery systems with pilocarpine nitrate and tropicamide (Vandamme and Brobeck 2005). 

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