Acetazolamide

In veterinary medicine, acetazolamide may be used to treat metabolic alkalosis or glaucoma in dogs and cats and hyperkalemic periodic paralysis (HYPP) in horses. Acetazolamide has been used principally for its diuretic action and its effects on aqueous humor production in the treatment of metabolic alkalosis and glaucoma, respectively. This drug may be useful as an adjunctive treatment for increased CSF pressures associated with syringomyelia in dogs.3

Carbonic anhydrase inhibitors (CAIs) such as acetazolamide act via a noncompetitive, reversible inhibition of the enzyme carbonic anhydrase. Inhibition reduces the formation of hydrogen and bicarbonate ions from carbonic acid, which reduces the availability of these ions for active transport into body secretions.3 Within the eye, the pharmacologic effect of CAIs is decreased formation of aqueous humor, which reduces intraocular pressure (IOP). Within the kidney, the pharmacologic effect of CAIs is increased renal tubular secretion of sodium and potassium and, to a greater extent, bicarbonate, leading to increased urine alkalinity and volume.

Acetazolamide has some anticonvulsant activity, which is independent of its diuretic effects. This mechanism is not fully understood but may be caused by an effect on carbonic anhydrase in the brain or induction of metabolic acidosis. In a study comparing the effects of acetazolamide and methazolamide in anesthetized cats, methazolamide did not reduce the hypoxic ventilatory response, but acetazolamide did.3 The study authors believe this response was not a result of carbonic anhydrase inhibition but instead was caused by acetazolamide’s effects on carotid bodies or type I cells.