The effect of systemic acetazolamide administration on intraocular pressure in healthy horses—A preliminary study

Objectives: In equine glaucoma, topical treatment with carbonic anhydrase inhibitors (CAIs) is recommended. Oral acetazolamide, a systemic CAI, is used in horses with hyperkalemic periodic paralysis. Information regarding its effect on equine intraocular pressure (IOP) is scarce. The aim of the study was to determine the effect of oral acetazolamide treatment on IOP in horses, in a case–control study. Animals: Ten healthy horses. Procedures: Horses were treated with oral acetazolamide (4.4 mg/kg) BID for 1 week. Serum acetazolamide concentrations were determined by liquid chromatography/tandem mass spectrometry, and IOP were measured before treatment, daily during treatment, and at 48 and 72 h after treatment. Results: Acetazolamide serum levels reached steady state at 72 h after the first oral dose. In a mixed effect model logistic regression, there was a significant decrease in IOP on the third treatment day, of 2.4 mmHg (p =.012) and 2.7 mmHg (p =.006) in the left (OS) and right eye (OD), respectively. On the seventh day, there was a decrease in 2.5 mmHg (p =.008) and 2.7 mmHg (p =.007) OS and OD, respectively. A significant increase occurred 48 h following treatment discontinuation (3.6 mmHg, p <.001 and 3.5 mmHg, p <.001 OS and OD, respectively). The area under the concentration versus time curve (AUC(0–10h)) was 1.1 ± 0.5 μg/mL*h, mean residence time 6.7 ± 4.3 h, peak plasma concentration (Cmax) 0.4 ± 0.4 μg/mL and time to reach Cmax 1.8 h. There was a significant increase in serum concentrations 1, 2, 48, 72, and 156 h following the first drug administration (p <.05). Conclusions: Further studies are required to determine whether acetazolamide is a potential treatment for equine glaucoma.