A patient with acute decompensated HFrEF on chronic metoprolol remains hypotensive with low cardiac output despite escalating catecholamine doses. The inotrope best suited because its action does not depend on beta-adrenergic receptors is:
- A Dobutamine
- B Norepinephrine
- C Milrinone ✓
- D Isoproterenol
Correct answer: C. Milrinone
Explanation
Milrinone inhibits phosphodiesterase type 3 in cardiac and vascular smooth muscle, increasing intracellular cAMP independently of beta receptors, so it retains inotropic and vasodilating effects in beta-blocked patients. Dobutamine, norepinephrine, and isoproterenol all act through adrenergic receptors whose signaling is attenuated by metoprolol, making them less effective here. This receptor-independent pathway is the classic exam distinction between milrinone and catecholamines.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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