A 26-year-old woman on an antiepileptic develops flank pain; imaging confirms a renal calculus. She reports tingling of her fingers, weight loss, and difficulty finding words during conversation. The property of her drug most responsible for stone formation is:

• A Induction of CYP3A4 with hyperoxaluria
• B Hypercalciuria secondary to vitamin D activation
• C Increased urinary uric acid excretion
• D Inhibition of carbonic anhydrase, producing alkaline urine and calcium phosphate precipitation ✓

Explanation

Topiramate inhibits carbonic anhydrase, causing bicarbonate loss, systemic acidosis, and alkaline urine that favors calcium phosphate stone formation. Its other signature effects are paresthesias, anorexia with weight loss, cognitive slowing with word-finding difficulty, and angle-closure glaucoma. Oxalate stones follow ethylene glycol poisoning, and topiramate does not raise urinary calcium or uric acid.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.