Milrinone

Primacor

Phosphodiesterase-3 inhibitor (inodilator)

Selective PDE3 inhibitor in cardiac + vascular smooth muscle. Increases intracellular cAMP → ↑contractility (positive inotropy) + ↓SVR + ↓PVR (vasodilation). 'INODILATOR' — distinct from pure inotropes (dobutamine) and pure vasodilators. Particularly effective for RV failure and pulmonary hypertension.

Indications

•Acute decompensated heart failure (low cardiac output)
•RV failure / pulmonary hypertension (lowers PVR more than other inotropes)
•Post-cardiopulmonary bypass low cardiac output syndrome
•Bridge to LVAD or transplant
•Pediatric cardiac surgery

Dosing

Context	Adult	Pediatric
Loading dose (often skipped to avoid hypotension)	50 mcg/kg IV over 10-20 min	—
Maintenance infusion	0.25-0.75 mcg/kg/min IV titrated	—
Pediatric cardiac	(weight-based)	0.25-0.75 mcg/kg/min IV

Pharmacokinetics

Onset 5-15 min IV. Half-life 2-3 h (much longer than dobutamine ~2 min). Renal excretion ~85% — accumulates in renal failure (reduce dose).

Hemodynamic effects

↑Contractility, ↓SVR, ↓PVR, modest ↑HR. Particularly valuable for RV failure: reduces PVR while supporting contractility.

Side effects

!HYPOTENSION (vasodilation often dominates inotropy at low doses) — pre-load fluid, cautious in already hypotensive
!Tachyarrhythmia + ventricular arrhythmia (less than dobutamine)
!Thrombocytopenia (rare, prolonged use)
!Increased mortality in chronic outpatient use (OPTIME-CHF) — restricted to acute settings

Contraindications

×Severe hypotension without pre-treatment
×Severe hypovolemia
×Severe renal impairment (relative)

Clinical pearls

★PRIMARY USE in cardiac anesthesia: post-CPB low cardiac output syndrome with pulmonary HTN.
★Often added to NOREPINEPHRINE: norepi for SVR, milrinone for inotropy/PVR — synergistic.
★SKIP THE LOADING DOSE in unstable patients — go straight to 0.25-0.5 mcg/kg/min infusion.
★Long half-life (2-3 h): wash-out takes hours. Plan accordingly.
★RENAL FAILURE: reduce to 0.1-0.3 mcg/kg/min if CrCl <30.