Pharmacology · Vasopressors and inotropes
Milrinone !
An intravenous inodilator that blocks phosphodiesterase 3: it strengthens the heartbeat and widens vessels in acute decompensated heart failure.
Updated 2026-11-01
No structure of milrinone bound to PDE3 is available; the figure shows trequinsin, another PDE3 inhibitor, in the catalytic site of human PDE3A.
Mechanism of action
Milrinone, a bipyridine, selectively inhibits phosphodiesterase 3 in heart and vascular muscle. cAMP is broken down more slowly: in myocytes, more calcium enters and contraction strengthens; in vascular smooth muscle, cAMP causes relaxation. Because it bypasses beta receptors, it still works in patients on beta blockers.
- Milrinone inhibits phosphodiesterase 3
- cAMP is broken down more slowly
- Heart: more calcium entry, stronger contraction
- Vessels: relaxation, lower preload and afterload
Pharmacokinetics
- Distribution
- Small volume of distribution
- Elimination
- Mainly by the kidneys as unchanged drug; elimination slows markedly in kidney impairment
- Half-life
- Mean terminal half-life about 2.3 hours in heart failure (label)
Indications
- Short-term intravenous treatment of acute decompensated heart failure Heart failure →
Adverse effects
Common
- Hypotension
- Headache
- Angina and chest pain
- Hypokalaemia
- Tremor
Contraindications
- Hypersensitivity to milrinone
- Severe obstructive aortic or pulmonic valve disease in place of surgical relief (not recommended)
Key interactions
- Furosemide injected into the same line
- Immediate precipitate: not given through the milrinone line
- Diuretics
- Better cardiac output can increase diuresis; potassium and fluid balance need watching
What is monitored
- Continuous ECG
- Blood pressure and heart rate
- Potassium and other electrolytes
- Kidney function and urine output
- Platelet count
Administration and safety
- Intravenous infusion by pump, often after a loading dose; in a monitored setting.
- Do not inject furosemide into the milrinone line: they form a precipitate.
- The rate is reduced in kidney impairment; the prescriber adjusts it to creatinine clearance.
- Check the infusion site; avoid extravasation.
Nursing care
- Before: correct low potassium; check kidney function.
- During: continuous ECG; report new arrhythmias, chest pain or a fall in blood pressure.
- Check potassium, fluid balance and urine output, as diuresis may increase.
- If blood pressure falls too much, the infusion is slowed or stopped as instructed.
Pregnancy and breastfeeding
Human data are limited; it is used when the maternal circulation needs support.
Test yourself
Think of the answer, then tap the question to see it.
How does milrinone raise contractility?
By inhibiting phosphodiesterase 3, cAMP is broken down more slowly, so more calcium enters the myocyte and contraction strengthens.
Why can milrinone work in a patient on a beta blocker when dobutamine does not?
Milrinone acts downstream of the beta receptor, at phosphodiesterase 3, so it does not need beta-receptor activation.
Which common diuretic must not be injected into a milrinone line?
Furosemide, which forms a precipitate with milrinone.
Why is the milrinone infusion adjusted in kidney failure?
It is eliminated mainly unchanged by the kidneys; in kidney impairment its elimination half-life increases markedly.
Related drugs
Related conditions
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - MILRINONE LACTATE IN DEXTROSE injection, solution (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Farmacología básica y clínica (Katzung), cap. 13 (McGraw Hill, 2025).
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Representative model, for educational purposes only.