What is milrinone and its typical starting infusion rate in cardiogenic shock?

• A. Phosphodiesterase-3 inhibitor; 0.25–0.75 mcg/kg/min
• B. Beta-1 agonist; 2–3 mcg/kg/min
• C. Calcium sensitizer; 0.05–0.2 mcg/kg/min
• D. PDE-5 inhibitor; 1–2 mcg/kg/min

Answer: (A)

Milrinone is a phosphodiesterase-3 inhibitor. By blocking PDE-3, it raises cyclic AMP in cardiac muscle and vascular smooth muscle, producing both stronger heart contractions (inotropy) and vasodilation (reduced afterload). In cardiogenic shock, this combination helps boost cardiac output while easing the burden on the failing ventricle, improving organ perfusion.

For infusion, a typical starting rate is 0.25 to 0.75 mcg/kg/min. The dose is titrated based on hemodynamic response and tolerance, with careful monitoring for hypotension and arrhythmias. In patients with renal impairment, lower starting doses and slower titration are often used because milrinone is renally cleared.

Milrinone is not a beta-1 agonist (that would be dobutamine), nor a calcium sensitizer (that would be levosimendan), nor a PDE-5 inhibitor (like sildenafil). These other drugs have different mechanisms and clinical uses.