Which of the following diuretic causes maximum loss of potassium in urine: March 2010
**Core Concept**
The question is testing the understanding of the mechanism of action of different diuretics and their effects on potassium excretion. The correct answer requires knowledge of how various diuretics affect the renal handling of potassium ions.
**Why the Correct Answer is Right**
Loop diuretics, such as furosemide, work by inhibiting the Na-K-2Cl cotransporter in the ascending limb of the loop of Henle. This leads to an increase in sodium and chloride delivery to the distal nephron, where potassium secretion occurs. As a result, loop diuretics cause a significant increase in potassium excretion in the urine. The increased sodium delivery to the collecting duct also enhances the activity of the Na-K-ATPase pump, which contributes to potassium secretion.
**Why Each Wrong Option is Incorrect**
* **Option A:** Thiazide diuretics, such as hydrochlorothiazide, act on the distal convoluted tubule and inhibit sodium reabsorption. While they do cause some potassium loss, it is not as pronounced as with loop diuretics.
* **Option B:** Osmotic diuretics, such as mannitol, work by increasing osmotic pressure in the glomerular filtrate, which inhibits water reabsorption. They do not directly affect potassium excretion.
* **Option C:** Potassium-sparing diuretics, such as spironolactone, act on the collecting duct to inhibit sodium reabsorption and potassium secretion. They are actually used to prevent potassium loss.
**Clinical Pearl / High-Yield Fact**
Remember that loop diuretics can cause significant hypokalemia due to their potent effect on potassium excretion. This is an important consideration when prescribing these medications, especially in patients with pre-existing potassium imbalances.
**Correct Answer:** C. Furosemide