Ocular inserts erodible

Ocular Inserts Solid ocular dosage forms such as films, erodible and nonerodible inserts, rods, and shields have been developed to overcome the typical pulse-entry-type drug release associated with conventional ocular dosage forms. This pulse entry... 

A number of ocular inserts using different techniques, namely soluble, erodible, nonerodible, and hydrogel inserts with polymers such as cellulose derivates, acrylates, and poly (ethylene oxide), have been investigated over the last few decades. 

Di Colo, G., and Zambito, Y. (2002), A study of release mechanisms of different ophthalmic drugs from erodible ocular inserts based on poly(ethylene oxide), Eur. J. Pharm. Biopharm., 54(2), 193-199. 

FIGURE 51.6 (a-c) Comparison of drug release and insert erosion kinetics for inserts based on PEO of different molecular weight, medicated with PDS. Key , percent of released dose A, percent of eroded insert. Each data point is the mean SD of at least three values. (Reprinted from Eur. J. Pharm. Biopharm., 54(2), Di Colo, G. and Zambito, Y., A study of release mechanisms of different ophthalmic drugs from erodible ocular inserts based on poly(ethylene oxide), 193-199. Copyright 2002, with permission from Elsevier.)... 

An erodible insert developed as a potential ocular drug-delivery system is marketed as a prescription drug for the lubricant properties of the polymer base. Lacrisert is a sterile ophthalmic insert used in the treatment of moderate to severe dry eye syndrome and is usually recommended for patients unable to obtain symptomatic relief with artificial tear solutions. The insert is composed of 5 mg of hydroxypropylcellulose in a rod-shaped form about 1.27 mm diameter by about 3.5 mm long. No preservative is used, since it is essentially anhydrous. The quite rigid cellulose rod is placed in the lower conjunctival sac and first imbibes water from the tears and after several hours forms a... 

VHL Lee, S Li, MF Saettone, P Chetoni, H Bundgaard. (1991). Systemic and ocular absorption of timolol prodrugs from erodible inserts. Proc Int Symp Controlled Release Bioact Mater 18 291-292. 

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. 

The marketed devices of erodible drug inserts are Lacisert, soluble ocular drug insert (SODI), and Minidisc. 

After permeation through the cornea, active substances reach the anterior chamber and afterwards the posterior chamber and vitreous. With cases of external infections absorption should not happen, because the active substance needs to be present in therapeutic concentrations at the cornea and conjunctiva. An example of a targeted local eye preparation are erodible inserts, the active substances diffuse slowly from the matrix at the ocular surface. 

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