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M. J. Brubaker, L. Bernal-Perez, A. C. Brooks, G. R. Owen; The Correlation of an Innovative in vivo Dosing Method With Clinical Trial Results of the Ocular Penetration of Dexamethasone Using a New TobraDex Formulation. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5676. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine and correlate the ocular penetration and distribution of dexamethasone using results from a clinical study with cataract patients and a rabbit model that simulates dosing in the human eye, comparing TobraDex® ophthalmic suspension to a new formulation containing half the concentration of dexamethasone in a novel suspension technology.
In the clinical study, 957 patients received one drop of either TobraDex® ophthalmic suspension (tobramycin 0.3%, dexamethasone 0.1%) or TobraDex ST suspension (tobramycin 0.3%, dexamethasone 0.05%) at various time points prior to cataract surgery. Clinical samples of the aqueous humor were collected at the time of surgery. In the rabbit model, anesthetized rabbits were given a single topical dose of either suspension followed by a 60 minute controlled period that simulated the human eye with manual blinking (4 blinks/min) and supplementary tearing (2 µL/min). Tear samples were collected every 5 minutes, and after euthanasia, tissue samples were collected at 60 minutes. Dexamethasone concentrations were quantified using HPLC.
In the clinical study, after 60 minutes, the ratio of dexamethasone levels in the aqueous humor was 1.18 in favor of the new formulation (20.7 versus 17.5 ng/mL). In the rabbit model, the mean concentrations of dexamethasone [µg/mL or µg/g ± SE (n=4)] at 60 minutes were as follows: in the aqueous humor 0.77± 0.08 versus 0.64 ± 0.03 (ratio 1.20); in the conjunctiva 1.2 ± 0.3 versus 0.8 ± 0.2 (ratio 1.5); in the cornea 2.8 ± 0.5 versus 1.6 ± 0.4 (ratio 1.75); in the sclera 0.77 ± 0.08 versus 0.64 ± 0.03 (ratio 1.2); and in the iris-ciliary body 2.1 ± 0.3 versus 1.6 ± 0.3 (ratio 1.3). In the rabbit tears, 10 minutes after dosing, the dexamethasone levels were 37 ± 11 versus 11 ± 6 (ratio 3.4).
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