Hypokalemia and suspected renal tubular acidosis associated with topical carbonic anhydrase inhibitor therapy in a cat

Objective: To describe the occurrence of hypokalemia, metabolic acidosis, and suspected renal tubular acidosis associated with the administration of topical ophthalmic carbonic anhydrase inhibitor (CAI) in a cat. Case Summary: A 2-year-old, 5.3 kg, male, castrated, domestic short-haired cat developed hyporexia 6 weeks after starting topical ophthalmic dorzolamide 2% therapy for treatment of ocular hypertension. Two weeks later, the cat was evaluated for severe weakness, cervical ventroflexion, and anorexia. Plasma electrolyte and acid–base measurement revealed hypokalemia (K⁺ = 2.9 mmol/L; reference interval 3.8–5.4 mmol/L) and metabolic acidosis (plasma HCO₃ ⁻ = 9.8 mmol/L; reference interval 15–23 mmol/L) in the presence of a urine pH of 7.5 (reference interval 6.5–7.5). The pH abnormalities were consistent with a renal tubular acidosis. Clinical and biochemical abnormalities resolved with short-term supportive care, potassium supplementation, and discontinuation of dorzolamide therapy. New or Unique Information Provided: This is the first report of hypokalemia and metabolic acidosis associated with topical CAI therapy in a cat.