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G. A. Baklayan, E. C. Collins, T. Thetford, A. Soriano, C. K. Song, J. Han; Evaluation of Aqueous Humor Concentrations of Istalol® and Betimol® Following Ocular Instillation Into the Eyes of New Zealand White Rabbits. Invest. Ophthalmol. Vis. Sci. 2008;49(13):350.
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To evaluate the absorption profiles of Istalol® (timolol maleate ophthalmic solution) and Betimol® (timolol maleate ophthalmic solution) formulations following a single instillation into each eye of New Zealand White Rabbits.
Istalol and Betimol were instilled once into each eye of 15 rabbits (3 rabbits per time point per drug product, 30 rabbits total) at a dose volume of 50 µL (equivalent to 0.25 mg timolol). Animals were euthanized following Istalol or Betimol administration at defined intervals (15 minutes, 30 minutes, 60 minutes, 120 minutes, and 180 minutes). The aqueous humor from both eyes of each animal was removed and pooled. Samples were placed into microfuge tubes and analyzed in-house for timolol content. The absorption profiles of Istalol and Betimol were analyzed for timolol content via an HPLC method.
The Istalol formulation showed a peak concentration of 3.705 µg/mL around 15 minutes, tapering off to 0.539 µg/mL by 180 minutes. The Betimol formulation displayed a smaller peak at 15 minutes of 2.239 µg/mL, tapering off to 0.148 µg/mL by 180 minutes.
Istalol exhibited faster absorption and longer residences time compared to Betimol between 15 and 180 minutes. The Cmax of Istalol in the aqueous humor was 1.7 fold greater than the maximum concentration of Betimol at 15 minutes.
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