• K Strohmaier, E Snyder, H DuBiner, and I Adamsons.
• Department of Clinical Research, Merck Research Laboratories, West Point, Pennsylvania 19486, USA.
• Ophthalmology. 1999 Dec 1; 106 (12 Suppl): 1-9.

ObjectiveTo evaluate whether a fixed combination of 2% dorzolamide and 0.5% timolol given twice daily showed equivalent efficacy to the concomitant administration of 2% dorzolamide given three times daily and 0.5% timolol given twice daily in patients whose intraocular pressure (IOP) remained elevated during monotherapy with 0.5% timolol twice daily.DesignMulticenter, parallel, randomized, double-masked clinical trial with an open-label extension.Participants And InterventionIn the masked phase, 242 patients received either the dorzolamide-timolol combination twice daily and placebo three times daily or dorzolamide three times daily and timolol twice daily for up to 3 months. In the open-label extension, 220 patients received the dorzolamide-timolol combination twice daily for up to 9 months.Main Outcome MeasuresThe criterion for establishing treatment equivalency was a 95% or greater confidence that the absolute difference in the mean change in IOP from baseline was less than 1.5 mmHg between treatments.ResultsDuring 3 months of treatment, the dorzolamide-timolol combination reduced IOP relative to the 0.5% timolol baseline by approximately 14% at hour 0 (just before the morning dose), 20% at hour 2, and 15% at hour 8. The IOP-lowering effect of concomitant therapy with dorzolamide and timolol was approximately 16% at hour 0, 20% at hour 2, and 17% at hour 8. At hours 0, 2, and 8, there was greater than 97% confidence that the treatments were equivalent. During the open-label extension, the mean IOP reduction ranged from 14% to 15% at hour 0 and from 20% to 21% at hour 2. The treatment groups were generally comparable in terms of adverse events, symptoms, ocular signs, visual acuity, visual fields, physical examination, and laboratory measures.ConclusionsThe IOP-lowering effect of the dorzolamide-timolol combination is comparable to that of dorzolamide three times daily plus timolol twice daily and is maintained for up to 1 year. The dorzolamide-timolol combination provides clinically important reduction in IOP relative to baseline treatment with timolol alone and is generally well-tolerated for up to 1 year.

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