A patient admitted with acute decompensated heart failure is already receiving full-dose intravenous metoprolol. Inotropic support is required. Which agent retains its effectiveness despite concurrent beta-receptor blockade?
- A Dobutamine
- B Isoproterenol
- C Milrinone ✓
- D Dopamine at low dose
Correct answer: C. Milrinone
Explanation
Milrinone inhibits phosphodiesterase type 3 in cardiac myocytes, raising intracellular cyclic AMP independently of beta-adrenergic receptors. Its inotropic and vasodilating actions therefore persist when beta receptors are occupied by metoprolol. Dobutamine, isoproterenol and dopamine act through beta-adrenergic receptor stimulation and are blunted or abolished by therapeutic beta-blockade. This receptor-independent pathway is the classic reason milrinone is chosen in beta-blocked patients.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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