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JT Whitson, G Hollo, R Faulkner, M Curtis, B McCue, H Wieland, L DeSantis, J Przydryga, DC Dahlin; Distribution of Betaxolol to the Human Retina, Optic Nerve Head and Choroid Following Multiple Topical Ocular Administration of Betoptic S . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4094.
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Purpose:To measure steady-state concentrations of betaxolol (BTX) in tissues of human eyes following surgery in patients requiring enucleation for glaucoma-related ocular pain and blindness. BTX has potential for enhancement of retinal blood flow and neuroprotection through BTX calcium-channel blocking activity. Therefore, concentrations in the retinal and optic nerve head (ONH) were of interest. Methods:Five Caucasian patients (3 F, 2 M) with ages ranging from 27 to 79 years were enrolled. Patients instilled Betoptic S (betaxolol 0.25% suspension) BID in the eyes to be enucleated for at least 28 days prior to surgery. On the day of surgery, 1 drop of betaxolol was instilled into the eye prior to the procedure. After enucleation the eyes were dissected to provide samples of iris, ciliary body, choroid, retina and ONH. One of the eyes was aphakic. The tissues were analyzed for betaxolol by LC/MS/MS. Results:The mean (SD) betaxolol concentration in retina tissue from the 4 phakic eyes was 64.5 ± 26.1 ng/g (range 46.6 to 94.4 ng/g), the concentration in the ONH was 38.6 ± 11.7 ng/g (range 26.1 to 54.4 ng/g). In the one aphakic eye the retinal and ONH levels were 140 and 32.8 ng/g, respectively. Anterior segment and choroidal tissues contained higher concentrations, where levels were 91.1 ± 101.7, 4.9 ± 3.1 and 1.6 ± 1.3 micrograms/g in iris, ciliary body and choroid, respectively. Conclusion:When applied topically, betaxolol distributed to all ocular tissues studied, including retina and ONH. The concentrations in these tissues were much greater than those shown to exhibit vasodilatory effects in human small retinal arteries and arterioles (threshold = 10-12 M, or <1 pg/ml), indicating that the levels in human retina and ONH are pharmacologically meaningful (Yu, DY, Cringle, SJ, Alder, VA, Yu, PK, Desantis, L., «Effect of Betaxolol, Timolol and Nimodipine on Human and Pig Retinal Arterioles,» Exp. Eye Res., (1998) 67, 73-81).
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