EFFECTS OF TOPICAL ADMINISTRATION OF 0.5-PERCENT 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% a praclonidine, on intraocular pressure (IOP), pupil size, and heart rat e in clinically normal cats. Design-Randomized masked saline-controlle d case study. Animals-Nine clinically normal conditioned adult cats of either sex. Procedure-Normal diurnal variation in IOP, pupil size, an d 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 mu l of 0.5% apraclonidine to 1 randomly chosen eye of each cat. The contralateral eye received saline solution. Results-Apraclonidine lowe red IOP a mean of 4.8 mm of Hg (24.0%) when compared with IOP in the f ellow saline-treated eye 6 hours after treatment. Unilateral administr ation of the drug also may have reduced IOP in both eyes. Pupil size w as reduced a mean 46% in only the apraclonidine-treated eye, and miosi s 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 apraclo nidine-treated eyes. Conclusions-Apraclonidine reduced IOP, pupil size , and resting heart rate in clinically normal cats, but also induced u ndesirable systemic side-effects. In contrast to dogs where the drug i nduced mydriasis, apraclonidine caused miosis in cats. Clinical Releva nce-The current commercially available formulation of topical 0.5% apr aclonidine is too toxic for clinical use in cats. Reformulation, or id entification of a less toxic congener, may result in a clinically usef ul antiglaucoma preparation for cats.