Which of the following agents is most useful for the management of nephrolithiasis due to idiopathic hypercalciuria?

• A. Ethacrynic acid
• B. Dorzolamide
• C. Hydrochlorothiazide
• D. Triamterene

Answer: (C)

Reducing the amount of calcium that ends up in urine lowers the risk of calcium-containing kidney stones seen with idiopathic hypercalciuria. A thiazide diuretic like hydrochlorothiazide does exactly this: it increases calcium reabsorption in the distal tubule, which lowers urinary calcium excretion and helps prevent stone formation.

The other options don’t have the same effect. Ethacrynic acid is a loop diuretic that typically increases calcium excretion, not decreases it. Dorzolamide is a carbonic anhydrase inhibitor with limited and inconsistent impact on urinary calcium for this condition. Triamterene, a potassium-sparing diuretic, doesn’t reliably reduce urinary calcium and isn’t used for preventing calcium stones.

In practice, thiazides are often used with adequate hydration and a normal calcium intake to help prevent recurrence of stones in idiopathic hypercalciuria.