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

Objective: To compare the efficacy of topical 2% dorzolamide hydrochloride (Trusopt) as a suppressor of aqueous humor flow in the human eye with the efficacy of systemically administered acetazolamide (Diamox). Design: A randomized, double-masked, placebo-controlled study of 40 human subjects in 2 academic centers. The effect of dorzolamide on aqueous humor flow was compared with that of acetazolamide as measured by the rate of clearance of topically applied fluorescein. Results: Acetazolamide reduced aqueous flow from 3.18+/-0.70 (mean+/-SD) to 2.23+/-0.48 mu L per minute, a reduction of 30% (P<.001), and dorzolamide reduced the flow to 2.65+/-0.64 mu L per minute, a reduction of 17% (P<.001). The difference between the effect of acetazolamine and dorzolamide was significant (P<.001). When acetazolamide is added to dorzolamide, the aqueous flow was reduced further to 2.21+/-0.47 mu L per minute, an additional reduction of 16% (P<.001). When dorzolamide was added to acetazolamide, no additional reduction was observed (P=.73). Similar effects were observed for intraocular pressure. Acetazolamide reduced pressure from 12.5+/-2.2 (mean+/-SD) to 10.1+/-2.2 mm Hg, a decrease of 19% (P<.001) and dorzolamide reduced it to 10.8+/-2.1 mm Hg, or a decrease of 13% (P<.001). The greater effect of acetazolamide than dorzolamide was significant (P=.03). Conclusions: For reasons that are not known, the topically applied carbonic anhydrase inhibitor 2% dorzolamide hydrochloride is not as effective as systemically administered acetazolamide. Clinicians who prescribe dorzolamide should expect less of an ocular hypotensive effect than that experienced from systemically administered acetazolamide.