Which of the following is a potassium-sparing diuretic?

Spironolactone is classified as a potassium-sparing diuretic because it works by antagonizing aldosterone, a hormone that promotes sodium retention and potassium excretion. By blocking aldosterone's action in the distal convoluted tubule, spironolactone allows the body to retain potassium while still promoting the excretion of sodium and water. This makes it particularly useful in conditions where potassium levels need to be conserved, such as in patients with heart failure or those at risk for hypokalemia from other diuretics.

In contrast, furosemide and bumetanide are loop diuretics and primarily promote the excretion of both sodium and potassium. Chlorthalidone, a thiazide diuretic, also leads to potassium loss. Therefore, spironolactone stands out as the potassium-sparing option due to its distinct mechanism of action targeting aldosterone.