Effects of 1% brinzolamide eye drops on the intraocular pressure, pupil diameter and heart rate in healthy cats.
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Objective – To evaluate the effects of topical administration of 1% brinzolamide eye drops q8h on the circadian rhythm of the intraocular pressure in healthy domestic cats. Animals – Ten adult, healthy domestic short-haired cats (five castrated males, five spayed females). Procedure – This study was part of a larger study, in which the effects of four different topical medications were investigated. During the pre-treatment phase (day 1-6) no medication was administered. During the next placebo phase (day 7-12), artificial tears were administered to the eye selected for medication five times daily, at 7.30, 7.45, 15.30, 19.45 and 23.30 hours. On day 14-19, day 22-27, day 30-35 and day 38-43 the cats received topical medication. The protocols, which were rotated according to a Latin square, consisted of 5 days' administration of: A. dorzolamide 2% eye drops (at 7.30, 15.30 and 23.30 hours) and an artificial tear drop (at 7.45 and 19.45 hours); B. brinzolamide 1% eye drops (at 7.30, 15.30 and 23.30 hours) and an artificial tear drop (at 7.45 and 19.45 hours); C. dorzolamide 2% eye drops (at 7.30, 15.30 and 23.30 hours) and timolol 0.5% eye drops (at 7.45 and 19.45 hours); and D. brinzolamide 1% eye drops (at 7.30, 15.30 and 23.30 hours) and timolol 0.5% eye drops (at 7.45 and 19.45 hours). On each medication time point, an artificial tear drop was administered to the contralateral eye. Throughout the study intraocular pressure, pupil diameter, light intensity at eye level of both eyes and heart rate were measured q3h for 42 days. A linear mixed-effect model was fitted to the data. The time point 9.00h was selected as the reference for the purpose of comparisons. Results – Overall mean IOP (± S.E.) in the placebo phase was 13.6 ± 0.2 mmHg and overall mean IOP in the brinzolamide phase was 11.7 ± 0.2 mmHg. The overall mean IOP was reduced by 1.9 mmHg (14 percent) after administration of brinzolamide. The reduction of the IOP during the brinzolamide phase was significant at all time points, except at 00.00h. There were no significant differences in heart rate between the placebo and brinzolamide phase. Conclusion – Topical administration of brinzolamide 1% is effective in reducing the intraocular pressure in healthy, adult, domestic cats. However, more research is needed in cats with glaucoma.