November 1997

Comparison of Dorzolamide and Timolol as Suppressors of Aqueous Humor Flow in Humans

Author Affiliations

From Mayo Medical School, Rochester, Minn (Ms Wayman); Department of Ophthalmology, Uppsala University, Uppsala, Sweden (Drs Larsson and Aim); and Mayo Clinic and Mayo Foundation, Rochester (Drs Maus and Brubaker).

Arch Ophthalmol. 1997;115(11):1368-1371. doi:10.1001/archopht.1997.01100160538002

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, placebocontrolled 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 μL/min (mean±SD) to 2.53±0.60 μL/min, a reduction of 18% (P<.001). Timolol reduced aqueous flow from the same beginning rate to 1.64±0.35 μL/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 μL/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.