Diuretics — loop, thiazide, K-sparing

◆Loop diuretics (furosemide, bumetanide, torsemide, ethacrynic acid)

• •Site: thick ascending limb (NKCC2 blocker)
• •Effects: ↑↑ Na, K, Cl, Ca, Mg, H+ excretion; massive diuresis
• •Indications: HF, pulmonary edema, severe HTN, hypercalcemia, refractory edema
• •Side effects: hypokalemia, hypomagnesemia, hypocalcemia, metabolic alkalosis, hyperuricemia (→ gout), ototoxicity (esp. with aminoglycosides)
• •Ethacrynic acid: only loop usable in true sulfa allergy

◆Thiazides (HCTZ, chlorthalidone, indapamide)

• •Site: distal convoluted tubule (NCC blocker)
• •Effects: moderate diuresis; HOLDS calcium (treats hypercalciuria, stones)
• •Indications: essential HTN (first-line), CHF (less effective than loop), calcium-stone prophylaxis, nephrogenic DI
• •Side effects: 'hyperGLUC' = HYPERglycemia, HYPERlipidemia, HYPERuricemia (gout), HYPERcalcemia; HYPOnatremia, HYPOkalemia, HYPOmagnesemia
• •Chlorthalidone preferred over HCTZ (longer half-life, better BP control)

◆K-sparing (spironolactone, eplerenone, amiloride, triamterene)

• •Spironolactone, eplerenone: aldosterone receptor antagonists
• •Amiloride, triamterene: ENaC blockers (collecting duct)
• •Indications: HFrEF mortality benefit (spironolactone, eplerenone), hyperaldosteronism, cirrhosis with ascites, refractory HTN, acne in women, PCOS
• •Side effects: HYPERkalemia, gynecomastia (spironolactone, NOT eplerenone), metabolic acidosis
• •Monitor K every 1–2 weeks initially, then every 3 months

◆Other

• •Mannitol (osmotic): ↑ ICP, glaucoma; CAN cause pulmonary edema
• •Acetazolamide (CA inhibitor): altitude sickness prophylaxis, glaucoma, idiopathic intracranial HTN; causes metabolic acidosis

Diuretic electrolyte effects at a glance