Aqueous humor flow in normal human eyes treated with brimonidine and dorzolamide, alone and in combination

To measure the effectiveness of topical 0.2% brimonidine tartrate as a suppressor of aqueous humor flow in the human eye compared with the effectiveness of 2% dorzolamide hydrochloride, and to measure the additivity of the effects of the 2 drugs.

A randomized, double-masked, placebo-controlled study was performed in 20 healthy human subjects. The topical drugs were instilled twice daily the day before and again in the morning on the day of the measurements. The rate of aqueous humor flow was measured from 8 AM to 4 PM by clearance of topically applied fluorescein using a fluorophotometer, after administration of doses of each drug singly and both drugs together. Intraocular pressure (IOP) was measured with applanation tonometry.

Compared with placebo, brimonidine reduced the aqueous humor flow by a mean +/- SD of 28.2% +/- 18.0% (P<.001), dorzolamide by 19.3% +/- 22.0% (P =.007), and the combination of brimonidine and dorzolamide by 37.2% +/- 20.6% (P<.001). The combination of both drugs statistically significantly suppressed aqueous humor flow compared with dorzolamide alone (P<.001) and brimonidine alone (P =.04). The IOP was reduced by a mean +/- SD of 11.6% +/- 10.1% (P<.001) by brimonidine, 8.5% +/- 14.1% (P =.02) by dorzolamide, and 17.9% +/- 16.5% (P<.001) by the combination. The combination of drugs reduced IOP better than dorzolamide (P<.001), but not more than brimonidine (P =.06).

The combination of brimonidine and dorzolamide caused a further reduction of aqueous humor flow compared with each drug applied alone. The IOP was further reduced by the combination compared with dorzolamide alone, but not compared with brimonidine alone.