Increased optic nerve head blood flow after 1 week of twice daily topical brinzolamide treatment in Dutch-belted rabbits

Objectives: Using a three-way crossover study design, we compared the effec ts of brinzolamide 2%, dorzolamide 2%, and placebo (vehicle) on microvascul ar optic nerve head (ONH) blood flow, intraocular pressure (IOP), blood pre ssure, heart rate, and acid-base balance in nine acepromazine-tranquilized Dutch-belted rabbits. Methods: Baseline measurements were taken before trea tment and after drug-free washout periods of 7-14 days. Microvascular ONH b lood flow was measured with a fundus camera-based laser Doppler flowmeter ( LDF). Intraocular pressure was measured with a Tone-Pen XL. One drop of bri nzolamide, dorzolamide, or vehicle was administered twice daily (9 A.M. and 5 P.M.) in right eyes only for 7 days. Experimental measurements were made 90 minutes after the 9 A.M. topical dose was administered on day 8. Result s: ONH blood flow was significantly increased (P less than or equal to 0.05 ) in carbonic anhydrase inhibitor (CAI)-treated rabbits, as compared with v ehicle-treated controls. The percent increase from baseline was 11.2 +/- 1. 8% in brinzolamide-treated animals and 8.4 +/- 4.3% in dorzolamide-treated animals. Compared with controls, IOP in the brinzolamide- and dorzolamide-t reated groups was significantly decreased (P 0.05). The changes in ONH bloo d now and IOP were not significantly different between the CAI treatment gr oups. Small but significant changes in systemic blood gas tensions and pH w ere present in both CAI treatment groups, as compared with the vehicle grou p. Systemic blood pressure and heart rate were not significantly changed. C onclusions: Topical ocular CAI treatment for 1 week with either brinzolamid e or dorzolamide significantly reduced IOP and significantly increased ONH blood flow in tranquilized Dutch-belted rabbits, while eliciting minimal sy stemic acid-base balance disturbances. (C) 2000 by Elsevier Science Inc. Al l rights reserved.