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A. Kato, H. Kimura, K. Okabe, J. Okabe, N. Kunou, M. Nozaki, Y. Ogura; Feasibility of Drug Delivery to the Posterior Pole with an Episcleral Implant . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4455.
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Purpose: To evaluate the feasibility of a non-biodegradable polymeric episcleral implant as a new controlled delivery system of betamethasone (BM) to the posterior pole of the eye. Methods: The episcleral implant which is composed of a drug-releasing component and a suture tag, released BM through an ethylene vinyl acetate membrane. The device was implanted on the sclera so that the drug-releasing surface could attach to the sclera at the posterior pole. BM concentrations in the aqueous humor, vitreous, and retina/choroid (posterior half and anterior half) were determined by high performance liquid chromatography (HPLC) at weeks 1, 2, and 4 after implantation. In addition, the intraocular tissue distribution of the drug was evaluated by fluorescein microscopy after implantation of the device loading 6-carboxyl fluorescein diacetate (6-CFDA) as a drug marker. Retinal toxicity was evaluated by electroretinography and histological examination. Results: The device showed zero-order release profiles both in vitro and in vivo for 4 weeks. BM concentrations in the retina/choroid after implantation were maintained above the concentrations effective for suppressing inflammatory reactions for at least 4 weeks. The BM concentration was greater in the posterior half of the retina/choroid than in the vitreous. It was confirmed that 6-CFDA diffused through the sclera and penetrated into the retina/choroid. Fluorescence from 6-CFDA gradually decreased in intensity with increased distance from the implantation site. Electroretinography and histological study showed no substantial toxic reactions. Conclusions: These findings suggested that the episcleral implant might be a useful drug carrier for intraocular delivery of BM, especially for the posterior pole of the eye.
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