Abstract Objective To assess changes in intraocular pressure (IOP) and pupil diameter (PD) induced by daily application of an unfixed combination of latanoprost and pilocarpine in normal dogs. Animals studied Fifteen mixed breed clinically normal dogs of both sexes. Procedures Three groups of five dogs each were administered in the right eye, one drop of 0.005% latanoprost (group L), 2% pilocarpine (group P), and 0.005% latanoprost with 2% pilocarpine (group LP), respectively. The left eyes received placebo. Drugs were administered once a day at 8 a.m. over a period of 5 days. IOP and PD measurements were conducted daily at 8 a.m., 10 a.m., 12 noon, 2 p.m., and 4 p.m. from 1 day preceding treatment to 7 days following treatment, and the presence of blepharospasm and/or conjunctival hyperemia was noted. Results Compared to baseline values, mean diurnal IOPs significantly decreased during the treatment period, by 4.4 (24.4%), 5.8 (31.4%), and 6.1 mmHg (35%) in the L, P, and LP groups, respectively. Compared to placebo-treated eyes, reductions of 2.1(14.1%), 3.2 (20.1%), and 4.1 mmHg (26.6%) were observed for the L, P, and LP groups, respectively. Although mean IOPs in the LP group decreased slightly more than the other two groups, these differences were not statistically significant. Miosis and conjunctival hyperemia were observed in the treated eyes of all three groups of animals during the treatment period. Conclusions Although both 0.005% latanoprost and 2% pilocarpine individually produced significant decrease in IOP, the topical administration of a combination of latanoprost (0.005%) and pilocarpine (2%) was not associated with a statistically significant synergistic reduction in IOP in dogs; and miosis was the most frequent side effect observed during treatment.

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