Which agent is an example of a potassium-sparing diuretic?

• A. Spironolactone
• B. Furosemide
• C. Hydrochlorothiazide
• D. Bumetanide

Answer: (A)

Potassium-sparing diuretics work by preventing potassium loss in the distal nephron. Spironolactone does this by acting as an aldosterone receptor antagonist in the collecting duct. By blocking aldosterone’s effects, it decreases Na+ reabsorption (and water following it) while reducing K+ secretion into the lumen, so potassium is retained. The other diuretics listed increase potassium loss: loop diuretics (furosemide, bumetanide) and a thiazide (hydrochlorothiazide) promote Na+ and water excretion and tend to cause potassium excretion. Therefore, spironolactone is the potassium-sparing option.