Which statement differentiates loop diuretics from thiazide diuretics?

• A. Loop diuretics are used to treat hyperkalemia.
• B. Loop diuretics act on the ascending limb of the loop of Henle and are used for edema and CHF; thiazides act on the distal tubule and are first-line for hypertension.
• C. Loop diuretics are potassium-sparing; Thiazides cause hypokalemia.
• D. Loop diuretics act on the collecting duct.

Answer: (B)

The key idea is where these diuretics act in the nephron and how that relates to their main clinical uses. Loop diuretics block the Na+-K+-2Cl− cotransporter in the thick ascending limb of the loop of Henle, producing a strong diuresis that is especially helpful for edema from heart failure, pulmonary edema, and other fluid overload states. Thiazide diuretics inhibit the Na+-Cl− cotransporter in the distal convoluted tubule, giving a milder diuretic effect and making them a first-line choice for essential hypertension and for milder edema. The other statements don’t fit because loop diuretics are not used to treat hyperkalemia, they are not potassium-sparing, and they do not act on the collecting duct.