A 50–year old man has a history of frequent episodes of renal colic with high calcium renal stones. The most useful diuretic in the treatment of recurrent calcium stones is :
First, I need to recall the different diuretics and their effects on calcium excretion. Thiazide diuretics, like hydrochlorothiazide, are known to reduce calcium excretion by the kidneys. They work by inhibiting the sodium-chloride cotransporter in the distal convoluted tubule. This leads to increased reabsorption of calcium, thereby decreasing the amount of calcium in the urine, which can help prevent stone formation.
On the other hand, loop diuretics like furosemide increase calcium excretion, which is bad for someone with calcium stones. Potassium-sparing diuretics don't really affect calcium much. So the correct answer should be a thiazide diuretic.
Looking at the options, the correct one would be Hydrochlorothiazide. The other options—furosemide, spironolactone, and amiloride—are either loop or potassium-sparing, which don't help with calcium stones.
I should also remember that thiazides are first-line for hypercalciuria-related stones. The key point is that thiazides decrease urinary calcium, reducing stone risk. So the answer is Hydrochlorothiazide.
**Core Concept**
Recurrent calcium kidney stones often result from hypercalciuria. Thiazide diuretics reduce urinary calcium excretion by enhancing tubular reabsorption, decreasing stone formation risk. The sodium-chloride cotransporter (NCC) in the distal convoluted tubule is the target.
**Why the Correct Answer is Right**
Thiazide diuretics (e.g., hydrochlorothiazide) inhibit the NCC, reducing sodium reabsorption. This lowers luminal negative charge, increasing calcium reabsorption via paracellular pathways. Lower urinary calcium reduces supersaturation, preventing calcium oxalate/urate stone formation. They are first-line for idiopathic hypercalciuria.
**Why Each Wrong Option is Incorrect**
**Option A (Loop diuretic, e.g., furosemide):** Increases calcium excretion via inhibition of the Na-K-2Cl cotransporter in the loop of Henle, worsening hypercalciuria.
**Option B (Potassium-sparing diuretic, e.g., spironolactone):** No significant effect on calcium handling; may even increase risk via aldosterone antagonism.
**Option C (Osmotic diuretic, e.g., mannitol):** Not used for stone prevention; promotes diuresis without calcium-specific effects.
**Clinical Pearl / High-Yield Fact**
Thiazides paradoxically reduce stone risk despite causing hypernatremia. Monitor serum calcium and potassium; combine with potassium citrate to address metabolic alkalosis. Avoid loop diuretics in calcium stone formers due to increased calciuria.
**Correct Answer: C. Hydrochlorothiazide**