Milrinone is an important inodilator drug used mainly in acute and advanced heart failure, especially in ICU and peri-operative cardiac settings. It is a high-yield pharmacology topic, often compared with digoxin and dobutamine in exams.
What Is Milrinone?
Milrinone is a phosphodiesterase-3 (PDE-3) inhibitor that increases cardiac contractility while simultaneously causing vasodilation.
Quick Drug Profile
| Feature | Details |
|---|---|
| Drug class | PDE-3 inhibitor |
| Special name | Inodilator |
| Brand name | Primacor |
| Route | Intravenous |
| Main use | Acute heart failure |
| Setting | ICU / hospital |
Why Milrinone Is Called an “Inodilator”
Milrinone has two simultaneous actions:
1. Inotropic → increases cardiac contractilityThis dual effect improves cardiac output without significantly increasing oxygen demand.
.jpg "Milrinone (Primacor) - Mechanism, Uses in Heart Failure & Side Effects")
Mechanism of Action (Very High-Yield)
Milrinone works by inhibiting phosphodiesterase-3 (PDE-3) in cardiac and vascular smooth muscle.
Step-by-Step Mechanism
1. Milrinone inhibits PDE-3In cardiac muscle
- ↑ Calcium influx
- ↑ Contractility (positive inotropy)
In vascular smooth muscle
- ↓ Calcium
- Vasodilation
One-Line Exam Answer
Milrinone increases cAMP by inhibiting PDE-3, producing inotropy and vasodilation
Hemodynamic Effects of Milrinone
| Parameter | Effect |
|---|---|
| Cardiac output | ↑ |
| Preload | ↓ |
| Afterload | ↓ |
| Pulmonary vascular resistance | ↓ |
| Heart rate | Mild ↑ or neutral |
Very useful in low-output heart failure states.
Clinical Uses of Milrinone
1. Acute Decompensated Heart Failure
- Especially when unresponsive to standard therapy
- Improves cardiac output rapidly
2. Heart Failure with High Afterload
- Reduces systemic vascular resistance
- Improves forward flow
3. Post-Cardiac Surgery (ICU Use)
- Low cardiac output syndrome
- Pulmonary hypertension after surgery
4. Bridge Therapy
Temporary support before transplant or mechanical supportWhen Milrinone Is Preferred
- Patients already on beta-blockers
- Acute heart failure with high pulmonary pressures
- When increased heart rate is undesirable
Exam Pearl:
Milrinone works independently of beta-receptors.
Pharmacokinetics (Simplified)
| Parameter | Details |
|---|---|
| Administration | IV infusion |
| Onset | Rapid |
| Half-life | ~2–3 hours |
| Elimination | Renal |
| Dose adjustment | Required in renal failure |
Adverse Effects (High-Yield)
Cardiovascular
- Hypotension (due to vasodilation)
- Ventricular arrhythmias
- Atrial arrhythmias
Others
- Headache
- Thrombocytopenia (rare)
Long-term use increases mortality → not used chronically.
Contraindications & Cautions
Use cautiously in:
- Severe hypotension
- Renal impairment
- Ventricular arrhythmias
Avoid chronic outpatient use.
Milrinone vs Digoxin (Exam Favorite)
| Feature | Milrinone | Digoxin |
|---|---|---|
| Mechanism | PDE-3 inhibition | Na⁺/K⁺-ATPase inhibition |
| Route | IV | Oral / IV |
| Onset | Rapid | Slow |
| Use | Acute HF | Chronic HF + AF |
| Mortality benefit | No | No |
| Toxicity | Arrhythmias | Narrow therapeutic index |
Milrinone vs Dobutamine
| Feature | Milrinone | Dobutamine |
|---|---|---|
| Receptor dependent | No | Yes (β₁) |
| Use with beta-blockers | Effective | Reduced effect |
| Vasodilation | Yes | Mild |
| Tachycardia | Less | More |
Milrinone preferred in beta-blocked patients.
Important Exam-Oriented Points
- Used only IV
- Short-term therapy
- Improves symptoms, not survival
- Avoid in chronic stable HF
- Monitor BP and rhythm continuously
Easy Memory Tricks
Mechanism
“MIL-rinone → Makes cAMP High”
Drug Class
“PDE-3 blocker = Inodilator”
FAQs
1. What is milrinone mainly used for?
Milrinone is used in acute decompensated heart failure to improve cardiac output.
2. What type of drug is milrinone?
It is a phosphodiesterase-3 (PDE-3) inhibitor.
3. Why is milrinone called an inodilator?
Because it increases contractility and causes vasodilation.
4. Does milrinone work on beta-receptors?
No, it works independently of beta-adrenergic receptors.
5. Can milrinone be used long term?
No, long-term use increases mortality.
6. What is the major side effect of milrinone?
Hypotension and arrhythmias.
7. Is milrinone useful in patients on beta-blockers?
Yes, it remains effective despite beta-blocker therapy.
8. How is milrinone administered?
Only by intravenous infusion.
9. Does milrinone reduce preload?
Yes, due to its vasodilatory action.
10. Is milrinone better than digoxin in acute HF?
Yes, milrinone is preferred in acute ICU settings.
