A 58-year-old woman started on oral acetazolamide 250 mg four times daily for elevated intraocular pressure returns after two weeks complaining of numbness and tingling around her mouth and fingertips, fatigue, and loss of appetite. Serum electrolytes show a low bicarbonate with low potassium. The constellation of symptoms is best explained by:
- A Inhibition of carbonic anhydrase in the proximal tubule causing bicarbonate diuresis and metabolic acidosis ✓
- B Direct neurotoxicity of sulfonamide drugs on peripheral sensory nerves
- C Type 2 (distal) renal tubular acidosis from impaired hydrogen ion secretion
- D Hyperventilation induced by central stimulation leading to respiratory alkalosis
Correct answer: A. Inhibition of carbonic anhydrase in the proximal tubule causing bicarbonate diuresis and metabolic acidosis
Explanation
Acetazolamide inhibits carbonic anhydrase in the proximal convoluted tubule, blocking bicarbonate reabsorption and producing a bicarbonate-rich diuresis with metabolic acidosis. The resulting acidosis plus potassium loss causes perioral and digital paresthesias, malaise and anorexia. It is a type 2 proximal, not distal, tubular effect, so option C is wrong. Respiratory alkalosis is the opposite disturbance and is caused by hyperventilation, not by acetazolamide. This is a classic examined adverse-effect profile.
Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.