A 55-year-old man with resistant hypertension is found to have hypokalaemia (K+ 2.9 mEq/L) and metabolic alkalosis while on high-dose chlorthalidone. The physician adds a potassium-sparing diuretic. Which drug among the following blocks the mineralocorticoid receptor AND is additionally a diuretic, rather than acting on the epithelial sodium channel?
- A Eplerenone ✓
- B Amiloride
- C Triamterene
- D Bumetanide
Explanation
Eplerenone is a selective aldosterone antagonist (mineralocorticoid receptor blocker) that prevents aldosterone from upregulating ENaC and the Na-K-ATPase in the collecting duct principal cells, thereby retaining potassium and reducing sodium reabsorption. Unlike spironolactone (which also blocks androgen and progesterone receptors causing gynaecomastia), eplerenone is highly selective for mineralocorticoid receptors. Amiloride and triamterene directly block ENaC channels independently of aldosterone, making them sodium channel blockers, not receptor antagonists. Bumetanide is a loop diuretic that does not spare potassium.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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