Overview
Clinical Meaning
Diuretic selection requires understanding where each drug class acts along the nephron and how site of action determines efficacy, electrolyte effects, and clinical indications.
Diuretic selection requires understanding where each drug class acts along the nephron and how site-of-action determines efficacy, electrolyte effects, and clinical indications. 1. Loop diuretics (furosemide, bumetanide, torsemide) act on the thick ascending limb of the loop of Henle by inhibiting the Na+/K+/2Cl- cotransporter (NKCC2). This site reabsorbs ~25% of filtered sodium, making loop diuretics the most POTENT diuretics available. They also impair the medullary concentration gradient (countercurrent multiplication), reducing the kidney's ability to concentrate urine. Effect: massive natriuresis and diuresis, calciuria (loop diuretics WASTE calcium — opposite of thiazides), hypokalemia, hypomagnesemia, metabolic alkalosis. Key pharmacokinetics: furosemide has variable oral bioavailability (~50%), short duration (6 hours); torsemide has more predictable absorption (~80%) and longer duration (12-16 hours). 2. Thiazide diuretics (hydrochlorothiazide, chlorthalidone, metolazone) act on the distal convoluted tubule by inhibiting the Na+/Cl- cotransporter (NCC). This site reabsorbs only ~5% of filtered sodium, so thiazides are LESS potent than loops. However, they have superior antihypertensive effect at lower doses due to additional vasodilatory properties. Effect: moderate natriuresis, hypocalciuria (thiazides RETAIN calcium — useful in calcium nephrolithiasis and osteoporosis), hypokalemia, hyperglycemia,...