A 62-year-old woman with HFrEF on furosemide and ramipril is hypotensive with cold clammy peripheries and urine output 20 mL/hour. An inotrope is required. Which agent acts independently of beta receptors by inhibiting phosphodiesterase-3?

• A Dobutamine
• B Dopamine at low dose
• C Levosimendan
• D Milrinone ✓

Explanation

Milrinone inhibits cardiac and vascular phosphodiesterase-3, raising intracellular cAMP independent of beta-adrenergic receptors. This gives positive inotropy plus vasodilation, useful in patients already receiving chronic beta-blockade whose receptors are occupied or downregulated. Dobutamine and dopamine act through beta receptors, so their effect blunts when a patient is on full-dose beta-blocker therapy. Levosimendan works mainly as a calcium sensitizer with some PDE-3 inhibition, but its defining mechanism differs.

Reference: Katzung Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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