Biopharmaceutical Study on Certain Solid Ocular Drug Delivery Systems

Abstract

The eyes are among the most readily accessible organs in terms of their location in the body and yet drug delivery to the tissues of the eye is particularly problematic. Limited absorption of

•the drug through the lipophilic corneal barrier is mainly due to short

. precomeal residence time related to the tear tum-over, rapid nasolacrimal ' : drainage of instilled drugs from the tear fluid and non-productive

absorption through the conjunctiva. Only a small proportion (1-3%) of the applied drug penetrates the cornea and reaches intraocular tissues. For these reasons, new ocular delivery systems are urgently needed to be developed.

Drugs administered in traditional topical ophthalmic formulations such as aqueous eye drops suffer from poor bioavailability due to rapid • precomeal elimination. To reach therapeutic levels frequent instillations of the drug is required, leading to low patient compliance. Furthermore, the drug level in the tear film is pulsed, with an initial period of overdosing, followed by a longer period of underdosing.

Acyclovir is a highly specific inhibitor of herpes virus replication. The topical application of Acyclovir is widely used for the treatment of various herpes simplex infections. Corneal epithelial and stromal keratitis caused by herpes simplex virus is a common opportunistic ocular ., infection and a leading cause of blindness.

Acyclovir formulations do not allow suitable drug levels at target sites following oral, local or parenteral administration, due to the low water solubility and low lipid bilayer solubility of the drug. Because of its poor water solubility, Acyclovir has to be formulated as an ophthalmic