Ophthalmic inserts bioavailability

MF Saettone, B Giannaccini, P Chetoni, G Galli, E Chiellini. (1984). Vehicle effects in ophthalmic bioavailability An evaluation of polymeric inserts containing pilocarpine. J Pharm Pharmacol 36 229-234. 

Frequent instillation of solution or higher drug concentration is needed to achieve the desired therapeutic response. But this attempt is potentially dangerous if drug solution drained from the eye is systemically absorbed from the nasolacrimal duct. To increase precorneal residence time and ocular bioavailability, different ophthalmic delivery systems such as viscous solutions, ointments, gels, suspensions, or polymeric inserts are used. But because of blurred vision (e.g., ointments) or lack of patient compliance (e.g., inserts), these formulations have not been widely accepted. 

It is now common knowledge that the topical controlled delivery of ophthalmic drugs improves their ocular bioavailability with respect to traditional eye drops, by decreasing the rate of drug elimination from the precorneal area. When the controlled delivery is realized via an erodible insert, the drug residence time in the precorneal area, and thereby, the bioavailability will be maximized if the drug release is controlled exclusively by insert erosion, since any parallel release mechanism increases the release rate, and thereby, the dose fraction cleared from the precorneal area by tear fluid draining. 

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