Which adverse effect is associated with acetazolamide use?

• A. Hyperchloremic metabolic acidosis
• B. Hypokalemia
• C. Ototoxicity
• D. Hypoglycemia

Answer: (A)

Acetazolamide blocks carbonic anhydrase in the proximal tubule, which prevents reabsorption of filtered bicarbonate. This bicarbonate stays in the tubular fluid and is excreted, leading to a bicarbonate diuresis. As bicarbonate is lost, serum bicarbonate falls, causing a non-anion gap (hyperchloremic) metabolic acidosis. The body shifts chloride to maintain electroneutrality, so serum chloride rises, and urine often becomes more alkaline due to the bicarbonate presence. While potassium loss at the distal tubule can accompany carbonic anhydrase inhibition, the characteristic and most expected adverse effect is this hyperchloremic metabolic acidosis. Ototoxicity and hypoglycemia are not typical adverse effects of acetazolamide.