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 microL per minute, a reduction of 30% (P < .001), and dorzolamide reduced the flow to 2.65 +/- 0.64 microL 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 microL 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.