A 48-year-old man with gout is a marked urate overproducer with recurrent calcium oxalate kidney stones. Which urate-lowering strategy is contraindicated in him?
- A Allopurinol titrated to target urate below 6 mg/dL
- B Probenecid monotherapy ✓
- C Febuxostat with flare prophylaxis
- D Colchicine prophylaxis during initiation
Correct answer: B. Probenecid monotherapy
Explanation
Probenecid lowers serum urate by inhibiting URAT1 and OAT reabsorption in the proximal tubule, increasing urinary urate excretion. In overproducers this floods the urine with uric acid, promoting urate and calcium stone formation, so it is contraindicated with nephrolithiasis history and ineffective when creatinine clearance falls below about 50 mL/min. Xanthine oxidase inhibitors such as allopurinol and febuxostat reduce urate production and are safe in stone formers; colchicine is only flare prophylaxis and does not alter urate handling.
Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.
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