Comparison of dorzolamide and acetazolamide as suppressors of aqueous humor flow in humans
T. L. Maus, L. I. Larsson, J. W. McLaren and R. F. Brubaker
Department of Ophthalmology, Mayo Clinic, Rochester, Minn., USA.
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.
