Which diuretic class does spironolactone belong to?

• A. Thiazide
• B. Loop
• C. Potassium-sparing
• D. Osmotic

Answer: (C)

Spironolactone is a potassium-sparing diuretic. It works by blocking the mineralocorticoid (aldosterone) receptors in the late distal tubule and collecting ducts, which reduces sodium reabsorption and water reabsorption while preserving potassium. That selective action on aldosterone’s effects is what keeps potassium in the body, hence the term potassium-sparing.

Other classes act at different sites and have different effects on potassium. Thiazide diuretics act in the distal tubule to block the Na-Cl transporter and tend to cause potassium loss. Loop diuretics act in the loop of Henle to inhibit the Na-K-2Cl transporter and also promote potassium wasting. Osmotic diuretics increase water excretion by creating an osmotic force in the tubules rather than altering aldosterone’s action.