The efficacy and safety of dorzolamide as adjunctive therapy to timolol maleate gellan solution in patients with elevated intraocular pressure. Additivity Study Group.

PURPOSE: Two parallel, randomized, double-masked, placebo-controlled studies were conducted to assess the efficacy and safety of 2% dorzolamide hydrochloride as adjunctive therapy to 0.5% timolol maleate ophthalmic gellan (gel-forming) solution in patients with elevated intraocular pressure (IOP) that was inadequately controlled with 0.5% timolol maleate gellan solution alone. METHODS: Both studies began with an open-label 2-week run-in period on 0.5% timolol maleate gellan solution once a day. The only variation in method between the two studies was the dosage of 2% dorzolamide. In one study, 202 patients received 0.5% timolol maleate gellan solution once daily plus either 2% dorzolamide or placebo three times daily. In the other study, 181 patients received 0.5% timolol maleate gellan solution once daily plus either 2% dorzolamide or placebo twice daily. RESULTS: After 85 days, additional mean percent reductions in IOP from baseline at morning trough for the groups receiving 2% dorzolamide three times daily and placebo three times daily were 12.5% and 8.4%, respectively. Mean percent reductions for the groups receiving 2% dorzolamide twice daily and placebo twice daily were 13.1% and 6.5%, respectively. Burning and/or stinging on instillation were the only adverse experiences that affected significantly more of the patients receiving 2% dorzolamide twice or three times daily than those receiving placebo. CONCLUSION: When administered concomitantly with 0.5% timolol maleate gellan solution, 2% dorzolamide three times daily or twice daily produced a statistically significant reduction in IOP at morning trough and peak and was generally well tolerated.