Milrinone (Primacor)

• Inodilator: Used for acute decompensated heart failure and low-output states; increases inotropy and lusitropy while reducing afterload and pulmonary vascular resistance
• β-Receptor Independent: Unlike catecholamines (dobutamine), milrinone works independently of β-receptors, so it can be useful in patients on chronic β-blockers or with downregulated β-receptors
• Hemodynamic Profile: ↑ cardiac output, ↓ SVR and PVR, but often with hypotension due to vasodilation. May precipitate or worsen shock in borderline patients
• Typical Adult Infusion: 0.25–0.75 mcg/kg/min IV, often without a loading dose in the ICU to avoid abrupt hypotension. Loading dose 50 mcg/kg over 10 minutes exists on-label but is frequently omitted
• Renal Elimination: Eliminated renally with a relatively long half-life (~2 hours in normal function, longer in CKD) → effects linger after you turn it off, especially in renal failure
• Major Risks: Ventricular arrhythmias, hypotension, and accumulation in renal impairment; avoid or use extreme caution in significant hypotension, severe aortic stenosis, or advanced CKD

• Generic Name: Milrinone lactate
• Brand Names: Primacor, generics

Phosphodiesterase-3 (PDE3) inhibitor; inodilator (inotrope + vasodilator)

Mechanism of Action:

• Selective inhibition of phosphodiesterase-3 (PDE3) in cardiac and vascular smooth muscle
• In cardiac myocytes: PDE3 inhibition ↑ intracellular cAMP → ↑ calcium influx during systole → positive inotropy and improved lusitropy (relaxation)
• In vascular smooth muscle: ↑ cAMP leads to vasodilation of systemic and pulmonary vasculature → ↓ SVR and PVR, ↓ ventricular afterload, ↓ filling pressures
• Independence from β-adrenergic receptors allows effect even in the presence of β-blockade, but also means there is no β-receptor down-titration control of effect
• Chronotropic effect is modest compared to dobutamine, but tachyarrhythmias can still occur due to increased inotropy and intracellular calcium

Pharmacokinetics:

• Onset: Hemodynamic effects begin within 5–15 minutes of starting infusion (faster if a loading dose is given)
• Distribution: Volume of distribution ~0.4–0.7 L/kg; minimally protein bound; distributes well into tissues
• Metabolism: Minimal hepatic metabolism; drug is largely unchanged
• Elimination: Primarily renal (~80–90% excreted unchanged in urine); elimination half-life ~2–2.5 hours with normal renal function, prolonged significantly in renal impairment
• Special Considerations: Because of the relatively long half-life, changes in rate take time to equilibrate, and toxicity (hypotension, arrhythmias) may persist after stopping the infusion—especially in CKD

• Short-term treatment of acute decompensated heart failure with low cardiac output, especially when cardiac index is low despite adequate filling pressures
• Adjunct in cardiogenic shock in selected patients, typically when systemic blood pressure is adequate or supported by vasopressors, and afterload reduction is desired
• Support after cardiac surgery for low-output syndrome or RV dysfunction, often in combination with vasopressors
• Occasionally used in pulmonary hypertension or RV failure (off-label) due to pulmonary vasodilation, with careful attention to systemic blood pressure

Available Forms:

• Vials or ampules: typically 10 mg/10 mL (1 mg/mL) or 20 mg/20 mL
• For infusion, commonly diluted in 0.9% NaCl or D5W to concentrations like 200 mcg/mL or institution-specific standard
• Administered via controlled IV infusion pump; central access preferred for higher concentrations or prolonged infusions

Adult Dosing (IV):

Contraindications:

• Known hypersensitivity to milrinone or formulation components
• Severe obstructive aortic or pulmonic valvular disease where increasing inotropy and decreasing afterload may worsen outflow obstruction
• Severe hypotension or profound shock where additional vasodilation would be dangerous (unless vasopressors are in place and the risk is accepted)

Major Precautions:

• Renal impairment: markedly reduced clearance and prolonged half-life; accumulation greatly increases risk of hypotension and arrhythmias
• History of significant ventricular arrhythmias or severe ischemic cardiomyopathy: milrinone can precipitate or worsen ventricular ectopy and VT/VF
• Electrolyte abnormalities (hypokalemia, hypomagnesemia) increase proarrhythmic risk; correct before and during therapy
• In acute myocardial infarction with hypotension, use very cautiously; inodilators can worsen ischemia by lowering diastolic pressure and increasing demand
• Long-term use in chronic heart failure is associated with increased mortality and is generally avoided outside of palliative or advanced HF (bridge to transplant/LVAD) settings

Common:

• Hypotension (most common)
• Ventricular ectopy (PVCs), non-sustained ventricular tachycardia
• Headache
• Tremor, nervousness
• Thrombocytopenia (less common but reported)

Serious:

• Sustained ventricular tachycardia or ventricular fibrillation
• Severe hypotension with end-organ hypoperfusion requiring vasopressors
• Atrial arrhythmias (e.g., atrial fibrillation with rapid ventricular response)
• Worsening ischemia in patients with severe coronary artery disease

Elderly Patients:

• Often have reduced renal function; adjust dose accordingly
• Start at lower end of dosing range (0.125–0.25 mcg/kg/min)
• Higher risk of arrhythmias

Renal Impairment:

• Dose reduction essential based on CrCl (see dosing table)
• CrCl 30–50: reduce by 25–50%
• CrCl <30: reduce to 0.1–0.25 mcg/kg/min or avoid
• Monitor closely for prolonged effects after dose changes

Hepatic Impairment:

• Minimal hepatic metabolism; no specific dose adjustment for hepatic impairment alone
• However, liver disease often coexists with renal dysfunction—monitor accordingly

Pregnancy:

• Category C: Limited data; use only if benefit justifies potential risk
• Used in peripartum cardiomyopathy in select cases

Lactation:

• Unknown if excreted in breast milk; use caution

Clinical Monitoring:

• Continuous ECG monitoring for ventricular ectopy and tachyarrhythmias
• Blood pressure and heart rate continuously or very frequently during initiation and titration
• Invasive hemodynamic monitoring (A-line +/- PA catheter) in high-risk patients to guide titration based on CI, SVR, and filling pressures
• Renal function (serum creatinine, urine output) at baseline and regularly thereafter to adjust dosing
• Electrolytes (especially potassium and magnesium) before and during therapy

• 1. Lexicomp. (2024). Milrinone: Drug information. Wolters Kluwer.
• 2. Felker, G. M., Benza, R. L., Chandler, A. B., et al. (2003). Heart failure etiology and response to milrinone in decompensated heart failure: Results from the OPTIME-CHF study. Journal of the American College of Cardiology, 41(6), 997–1003. https://doi.org/10.1016/S0735-1097(02)02968-6
• 3. Cuffe, M. S., Califf, R. M., Adams, K. F., et al. (2002). Short-term intravenous milrinone for acute exacerbation of chronic heart failure: A randomized controlled trial. JAMA, 287(12), 1541–1547. https://doi.org/10.1001/jama.287.12.1541
• 4. Tariq, S., & Aronow, W. S. (2015). Use of inotropic agents in treatment of systolic heart failure. International Journal of Molecular Sciences, 16(12), 29060–29068. https://doi.org/10.3390/ijms161226147
• 5. EMCrit Project. (2023). Inotropes & vasopressors in cardiogenic shock. https://emcrit.org/