Effects of topical administration of 0.5% apraclonidine on intraocular pressure, pupil size, and heart rate in clinically normal cats.

OBJECTIVE: To evaluate the effect of a topical alpha 2-agonist, 0.5% apraclonidine, on intraocular pressure (IOP), pupil size, and heart rate in clinically normal cats.
DESIGN: Randomized masked saline-controlled case study. ANIMALS: Nine clinically normal conditioned adult cats of either sex. PROCEDURE: Normal diurnal variation in IOP, pupil size, and resting heart rate was determined from 7 AM to 7 PM (day 1). On day 2, the same measurements were made after the topical application of 30 microliters of 0.5% apraclonidine to 1 randomly chosen eye of each cat. The contralateral eye received saline solution.
RESULTS: Apraclonidine lowered IOP a mean of 4.8 mm of Hg (24.0%) when compared with IOP in the fellow saline-treated eye 6 hours after treatment. Unilateral administration of the drug also may have reduced IOP in both eyes. Pupil size was reduced a mean 46% in only the apraclonidine-treated eye, and miosis persisted for up to 24 hours. Heart rate was significantly lower (11.8%) at 3 hours, and 8 of 9 cats vomited after topical administration of the drug. Mild blanching of the conjunctiva occurred in all apraclonidine-treated eyes.
CONCLUSIONS: Apraclonidine reduced IOP, pupil size, and resting heart rate in clinically normal cats, but also induced undesirable systemic side-effects. In contrast to dogs where the drug induced mydriasis, apraclonidine caused miosis in cats. CLINICAL RELEVANCE: The current commercially available formulation of topical 0.5% apraclonidine is too toxic for clinical use in cats. Reformulation, or identification of a less toxic congener, may result in a clinically useful antiglaucoma preparation for cats.