Which of the following diuretics causes hyperkalemia by blocking aldosterone-mediated sodium reabsorption in the collecting duct?

Explanation

## Potassium-Sparing Diuretics **Key Point:** Spironolactone is an aldosterone antagonist that blocks mineralocorticoid receptors in the collecting duct, preventing sodium reabsorption and potassium excretion. ### Mechanism of Hyperkalemia 1. Aldosterone normally promotes Na⁺ reabsorption and K⁺ secretion in the collecting duct 2. Spironolactone blocks this effect → reduced K⁺ excretion → hyperkalemia 3. This is a **potassium-sparing** diuretic property ### Comparison of Diuretic Classes | Diuretic Class | Site of Action | K⁺ Effect | Mechanism | | --- | --- | --- | --- | | Loop diuretics (Furosemide) | Thick ascending limb | Hypokalemia | Block Na-K-2Cl cotransporter | | Thiazides (HCTZ) | Distal convoluted tubule | Hypokalemia | Block Na-Cl cotransporter | | Potassium-sparing (Spironolactone) | Collecting duct | Hyperkalemia | Aldosterone antagonism | | Osmotic (Mannitol) | Proximal tubule, loop | Hypokalemia | Osmotic gradient | **High-Yield:** Spironolactone is the ONLY diuretic that causes **hyperkalemia** rather than hypokalemia. This is a frequently tested distinction. **Clinical Pearl:** Spironolactone is often combined with loop or thiazide diuretics to prevent hypokalemia in heart failure and cirrhosis management.