Summary The aim of this study was to determine the combination effect of latanoprost and pilocarpine on the intraocular pressure and pupil size in normal rabbits. In this study, 18 rabbits were randomized to three groups of 6 animals each. The right eyes of rabbits in group 1 were treated topically with latanoprost, in group 2 with pilocarpine and in group 3 with latanoprost and pilocarpine. The left eyes received placebo. Drugs were instilled once a day at 8 am over 4 days. IOP and pupil diameter measurements were made at 8 am, 10 am, 12 noon, 2 pm and 4 pm during the 4 days of treatment, the 2 days that preceded treatment, and 3 days following treatment. The occurrence of blepharospasm and conjunctival hyperemia were also evaluated at the same times that the measurements were made. The mean IOPs were significantly lower than the contralateral eyes in 8 of the 20 time intervals (40%) in both latanoprost and pilocarpine-treated and in 18 of 20 time intervals (90%) in latanoprost plus pilocarpine-treated eyes in the treatment period. The mean daily hypotensive effects of latanoprost, pilocarpine and their combination were 4.5 (31%), 2 (14.4%) and 5 mmHg (34.7%), respectively. Although the mean IOPs in group 3 have decreased more than other groups, the differences between the three groups are not significant. Conjunctival hyperemia was observed in the treated eyes of the three groups. It is concluded that topical instillation of the combination of latanoprost and pilocarpine was not as effective in IOP reduction than by drugs alone and that hyperemia is the most frequent side effect observed during the treatment period.

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