A 45-year-old man with recurrent calcium oxalate kidney stones and idiopathic hypercalciuria is started on long-term drug therapy to reduce stone recurrence. The drug chosen acts by:

• A Inhibiting carbonic anhydrase in the proximal tubule
• B Antagonizing vasopressin V2 receptors in the collecting duct
• C Blocking sodium reabsorption in the distal convoluted tubule
• D Increasing proximal tubular calcium reabsorption secondarily to volume contraction ✓

Explanation

Thiazides are the standard therapy for recurrent calcium stones with hypercalciuria. Mild volume contraction from natriuresis enhances proximal sodium and passive calcium reabsorption, while thiazides directly enhance distal calcium reabsorption, lowering urinary calcium. Option C describes the thiazide target itself but does not answer the mechanism of reduced calciuria, and option A would raise urinary calcium.

Reference: Campbell-Walsh Urology, 12th ed.

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