A patient started on oral acetazolamide 250 mg four times daily for acute angle-closure glaucoma returns after five days complaining of tingling around the mouth and fingers, loss of appetite, and general malaise. The most likely biochemical explanation is:

• A Hyperkalemic acidosis from potassium-sparing activity
• B Respiratory alkalosis from central hyperventilation
• C Metabolic acidosis from renal bicarbonate loss ✓
• D Hyperchloremic alkalosis from chloride retention

Explanation

Acetazolamide inhibits carbonic anhydrase in the proximal tubule, causing urinary bicarbonate diuresis with sodium and potassium loss. The resulting hyperchloremic metabolic acidosis produces the classic paresthesias, anorexia, malaise and dysgeusia seen with systemic therapy. Potassium depletion rather than retention occurs, and respiratory alkalosis is not produced by this drug. Supplementing potassium and monitoring acid-base status are advised during prolonged systemic use.

Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.

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Written and medically reviewed by the StethoPrep medical team.