A 26-year-old woman on topiramate for migraine prophylaxis presents with renal colic and reports new difficulty finding words and tingling of her fingertips. The mechanisms underlying both the kidney stone and the paresthesia share which property?
- A Inhibition of carbonic anhydrase causing alkaline urine and systemic acidosis ✓
- B Inhibition of renal tubular sodium reabsorption causing volume depletion
- C Increased intestinal calcium absorption causing hypercalciuria
- D Direct tubular toxicity causing crystalluria
Correct answer: A. Inhibition of carbonic anhydrase causing alkaline urine and systemic acidosis
Explanation
Topiramate inhibits carbonic anhydrase, producing bicarbonate loss and metabolic acidosis. Alkaline urine promotes precipitation of calcium phosphate stones, and the acidosis plus hypokalemia drives the distal tubular calcium shift that produces perioral and digital paresthesias. Word-finding difficulty is another recognised cognitive effect. Volume depletion and hyperabsorption of calcium are not features of topiramate.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.