Comparison of dorzolamide and timolol as suppressors of aqueous humor flow in humans

Objectives: To measure the effectiveness of topical 2% dorzolamide hydrochloride (Trusopt, Merck & Co Inc, Whitehouse Station, NJ) as a suppressor of aqueous humor flow in the human eye as compared with the effectiveness of 0.5% timolol maleate (Timoptic, Merck & Co Inc) and to measure the additivity of the 2 drugs. Design: A randomized, double-masked. placebo-controlled study of 40 human subjects was carried out in 2 academic centers (Mayo Clinic, Rochester, Minn, and University of Uppsala, Uppsala, Sweden). The rate of aqueous flow was measured from 8 AM to 4 PM by means of fluorophotometry after administration of doses of each drug singly and both drugs together. Results: Dorzolamide reduced aqueous flow from 3.07+/-0.63 mu L/min (mean+/-SD) to 2.53+/-0.60 mu L/min, a reduction of 18% (P<.001). Timolol reduced aqueous flow from the same beginning rate to 1.64+/-0.35 mu L/min, a reduction of 47% (P<.001). The inhibitory effect of timolol was 2.6 times the inhibitory effect of dorzolamide (P<.001). The 2 drugs were almost completely additive, and together reduced the flow to 1.37+/-0.33 mu L/min, a reduction of 55%. Consistent effects were observed on intraocular pressure. Conclusions: Timolol is more effective than dorzolamide as a suppressor of aqueous humor flow in the normal human eye. Timolol and dorzolamide are additive in their effects, both on aqueous flow and intraocular pressure.