Comparison of the ocular hypotensive effect of brimonidine, dorzolamide, latanoprost, or artificial tears added to timolol in glaucomatous monkey eyes

Purpose: To investigate the additive ocular hypotensive effect of brimonidine, dorzolamide, latanoprost, or artificial tears to timolol in monkey eyes with laserinduced unilateral glaucoma. Methods: Eight monkeys were used and each animal received all four combinations of drugs in a randomized fashion during the study. The washout period between each combination was at least 2 weeks. Intraocular pressure (IOP) was measured at 8:30 AM, 11:00 AM, 1:00 PM, and 3:30 PM on day i (untreated baseline), day 2 (timolol treatment alone), and days 3 through 5 (combination therapy with two drugs). One drop of 0.5% timolol was topically applied at 3:45 PM on day 1 and at 8:45 AM and 3:45 PM on days 2 through 5. One drop of 0.2% brimonidine or 2% dorzolamide or artificial tears was added on day 2 at 4:00 PM and at 9:00 AM and 4:00 PM on days 3 through 5, or latanoprost was added at 9:00 AM on days 3 through 5. Results: Compared with timolol alone, the maximal additive reduction in IOP which occurred on day 5 was 4.8 ± 0.8 mm Hg (mean ± standard error of the mean) with timolol plus brimonidine, 5.6 ± 1.0 mm Hg with timolol plus dorzolamide, 4.3 ± 1.0 mm Hg with timolol plus latanoprost, and 2.0 ± 0.5 mm Hg with timolol plus artificial tears (P < 0.01). At all measurements, timolol plus brimonidine, timolol plus dorzolamide, and timolol plus latanoprost caused greater (P < 0.05) IOP reductions than did timolol plus artificial tears. The additive IOP-lowering effect was similar (P > 0.60) when comparing timolol plus brimonidine and timolol plus dorzolamide, timolol plus brimonidine and timolol plus latanoprost, timolol plus dorzolamide and timolol plus latanoprost at all measurements, but timolol plus dorzolamide caused a greater (P < 0.05) reduction of IOP than did timolol plus latanoprost at 0 hours on day 5. Conclusions: The addition of brimonidine, dorzolamide, or latanoprost to timolol caused similar additional reductions of IOP in glaucomatous monkey eyes.