MILRINONE 

1. BASIC PHARMACOLOGY

• Class: Phosphodiesterase-3 (PDE-3) inhibitor
• Type: Inodilator (↑ inotropy + vasodilation)

 Mechanism of Action

Milrinone inhibits PDE-3 → prevents breakdown of cAMP

 In cardiac myocytes:

• ↑ cAMP → ↑ intracellular Ca²⁺ → ↑ contractility

 In vascular smooth muscle:

• ↑ cAMP → ↓ Ca²⁺ → vasodilation

2. HEMODYNAMIC EFFECTS

Parameter	Effect
Cardiac output	↑↑
Stroke volume	↑
Heart rate	Mild ↑
SVR	↓↓
PVR	↓
LV filling pressure	↓
BP	↓ (due to vasodilation)

 Key takeaway:
 Strong inotrope + potent vasodilator → risk of hypotension

 3. INDICATIONS 

 A. Acute Decompensated Heart Failure (ADHF)

• Especially:
• Low output states
• On chronic beta-blockers (milrinone works independently of β-receptors)

 B. Cardiogenic Shock (Selected cases)

• When:
• High SVR + low CO
• Poor response to catecholamines

 Usually combined with:

• Norepinephrine to prevent hypotension

 C. Right Ventricular Failure / Pulmonary Hypertension

• ↓ PVR → improves RV function
• Useful in:
• Post cardiac surgery
• Acute PE with RV dysfunction (adjunct)

 D. Post Cardiac Surgery Low Output Syndrome

• Improves cardiac output
• Reduces afterload

E. Bridge Therapy

• Bridge to:
• LVAD
• Cardiac transplant

 4. DOSING 

 Standard Dose

• Loading dose: 50 mcg/kg over 10 min (often avoided in ICU → hypotension risk)
• Infusion:
   0.25 – 0.75 mcg/kg/min

 Renal Adjustment 

• Milrinone is renally cleared

CrCl	Dose adjustment
30–50 ml/min	Reduce infusion
<30 ml/min	Significant reduction
ESRD	Avoid or very cautious

 Exam pearl:
 Accumulation → ↑ arrhythmias + hypotension

 5. COMPARISON WITH DOBUTAMINE 

Feature	Milrinone	Dobutamine
Mechanism	PDE-3 inhibitor	β1 agonist
β-receptor dependence	No	Yes
Effect in β-blocked pts	Better	Reduced
Vasodilation	Strong	Mild
Tachycardia	Less	More
Arrhythmias	Yes	Yes (more tachy)
Half-life	Long (2–4 hr)	Short (2 min)
Renal adjustment	Required	Not required

 Clinical preference:

• On β-blockers → Milrinone preferred
• Hypotensive → Dobutamine preferred

 6. ADVERSE EFFECTS

 Cardiovascular

• Hypotension (most common)
• Ventricular arrhythmias
• Atrial fibrillation

 Others

• Thrombocytopenia (rare)
• Headache
• Electrolyte disturbances

 7. MONITORING 

 Hemodynamic Monitoring

• MAP (risk of hypotension)
• Cardiac output (if advanced monitoring available)
• CVP / PA pressures (if PAC in situ)

 Lab Monitoring

• Renal function (daily)
• Electrolytes (K⁺, Mg²⁺)
• Platelet count

 8. CLINICAL PEARLS 

✔ “Inodilator of choice in β-blocked heart failure patient”
✔ Reduces both preload + afterload
✔ Useful in RV failure (↓ PVR)
✔ Long half-life → not easily titratable
✔ Avoid loading dose in ICU → hypotension
✔ Combine with vasopressor if BP low

 9. PRACTICAL ICU SCENARIOS

 Scenario 1: ADHF + On β-blocker

 Start Milrinone infusion
 Avoid dobutamine (poor response)

 Scenario 2: Cardiogenic shock + high SVR

 Milrinone + Norepinephrine

 Scenario 3: RV failure + pulmonary hypertension

 Milrinone preferred (↓ PVR)

 Scenario 4: Hypotensive cardiogenic shock

 Milrinone plus vasopressor