Which of the following is NOT a thiazide diuretic?

• A. Chlorothiazide
• B. Hydrochlorothiazide
• C. Metolazone
• D. Spironolactone

Answer: (D)

Thiazide diuretics work by blocking the Na+-Cl- cotransporter in the distal convoluted tubule, which decreases sodium reabsorption and increases excretion of water and potassium. Chlorothiazide and hydrochlorothiazide are classic thiazides, and metolazone is a thiazide-like diuretic that acts in a similar way. Spironolactone is not a thiazide; it’s a potassium-sparing diuretic that blocks aldosterone receptors in the collecting ducts, promoting sodium loss while retaining potassium. Therefore, spironolactone is not a thiazide diuretic.