Milrinone (Primacor)

Inotropy Without Tachycardia - Milrinone increases cardiac contractility and cardiac output without the beta-receptor stimulation that drives tachycardia with dobutamine or epinephrine. Good choice when you want inotropy in a patient where tachycardia is problematic (e.g., tight mitral stenosis, hypertrophic obstructive cardiomyopathy (HOCM)).

Pulmonary Vasodilation - One of the most useful aspects in cardiac anesthesia — milrinone lowers PVR and right ventricular (RV) afterload. A go-to for right ventricular failure (RVF) and pulmonary hypertension (PHT) in the perioperative setting, especially post-bypass.

Hypotension - Vasodilation is significant and often the limiting factor. Frequently requires a vasopressor (norepinephrine or vasopressin) running alongside. Have a plan for blood pressure support before starting.

Loading Dose - A bolus can cause a sudden, rapid, and severe hypotension — often avoided in hemodynamically unstable patients. Many practitioners skip the load and start the infusion alone, accepting a slower onset.

Arrhythmia Risk - PDE-3 inhibition increases intracellular cAMP, which can be pro-arrhythmic. Monitor continuously. More of a concern with loading doses or in patients with underlying arrhythmia substrate.

Cardiac Surgery Use - Widely used in cardiac anesthesia for weaning from cardiopulmonary bypass (CPB), particularly in patients with low ejection fraction (EF) or RV dysfunction. Often started in the pump before coming off bypass.

Dose reduction required in renal impairment — milrinone accumulates and effects are prolonged

Excessive Effect - Severe hypotension: stop or reduce infusion, give IV fluids, start or increase vasopressor. Arrhythmias: Use standard antiarrhythmic management; effects will wane as drug clears.

Drug Interactions - Additive hypotension with other vasodilators, volatile anesthetics, and antihypertensives. Synergistic inotropy with catecholamines — the combination of milrinone + norepinephrine is commonly used in cardiac surgery to balance inotropy and vascular tone.

Pediatric Implications - Widely used in pediatric cardiac surgery and congenital heart disease management. Weight-based dosing (loading dose 50 mcg/kg over 10 min, infusion 0.25-0.75 mcg/kg/min). Same hypotension risk — anticipate and prepare.

Obstetric Implications - Limited data. Crosses the placenta. Not used in routine obstetric anesthesia. Reserved for severe peripartum cardiomyopathy (PPCM) in the ICU setting under specialist guidance.

Absolute:

Known hypersensitivity to milrinone

Severe obstructive aortic or pulmonic valvular disease (worsens outflow obstruction)

Relative:

Hypovolemia (exaggerated hypotension)

Atrial fibrillation or flutter without rate control (may accelerate ventricular response)

Severe renal impairment (drug accumulates — reduce infusion rate)

Caution:

Patients with active ventricular arrhythmias

Recent myocardial infarction (MI)

Loading dose: 50 mcg/kg IV over 10 min (often omitted in hemodynamically unstable patients)

0.125-0.75 mcg/kg/min; titrate to effect; reduce in renal impairment

Selectively inhibits PDE-3 in cardiac and vascular smooth muscle -> increased intracellular cAMP -> enhanced calcium handling -> increased myocardial contractility (inotropy), improved relaxation (lusitropy), and systemic/pulmonary vasodilation.

Minimal hepatic

Renal (primarily unchanged)

Often combined with norepinephrine or vasopressin to offset vasodilation while maintaining inotropy

Available as 1 mg/mL and premixed 200 mcg/mL solutions — verify concentration carefully before programming infusion pump