Cardiac Medicine Certification (CMC) Practice Exam

Which diuretic is classified as a potassium-sparing agent?

1. Furosemide

2. Hydrochlorothiazide

3. Spironolactone

4. Chlorthalidone

The correct answer is: Spironolactone

Spironolactone is classified as a potassium-sparing diuretic, which means it helps to prevent the loss of potassium while promoting the excretion of sodium and water. This is particularly important in patients who may be at risk for hypokalemia (low potassium levels) from other diuretics that could lead to significant potassium loss. Potassium-sparing diuretics like spironolactone work by antagonizing the effects of aldosterone, a hormone that normally promotes sodium retention and potassium excretion. By blocking aldosterone's action in the distal nephron of the kidney, spironolactone reduces sodium reabsorption and increases potassium retention, helping to maintain a more balanced electrolyte level in the body. In contrast, furosemide, hydrochlorothiazide, and chlorthalidone are all classified as thiazide or loop diuretics, which are effective in promoting diuresis but often lead to increased excretion of potassium, making them unsuitable for patients who need to retain potassium. Thus, spironolactone is uniquely effective in cases where preserving potassium is essential, such as in certain heart failure or hypertension treatments.