The inodilator: milrinone strengthens the heart and opens the circulation at once. It shines in the failing, high-afterload ventricle — and disappoints wherever the immature preterm heart or a leaky blood pressure gets in its way.
Milrinone is a niche agent, not a general pressor. It earns its place in post-ligation cardiac syndrome and pulmonary hypertension with ventricular dysfunction, where inotropy plus afterload reduction is exactly what’s needed — but it can drop blood pressure hard, and it does not prevent low blood flow during the preterm transition.
01 The inodilator, mechanistically
Milrinone blocks phosphodiesterase-3, so cyclic AMP is not broken down and accumulates in cardiac and vascular smooth muscle — acting beyond the β-adrenergic receptor.1,7 Three effects follow:
Raised cAMP increases trans-sarcolemmal calcium flux and myocardial contractility — boosting cardiac output.1,7
It speeds diastolic relaxation, helping the stiff ventricle fill — useful in the diastolic failure of post-ligation syndrome.2
It relaxes both the systemic and the pulmonary arterial beds, lowering the load the heart pumps against.1
02 Where it shines — the loaded ventricle
In post-ligation cardiac syndrome, sudden ductal closure exposes the non-compliant preterm left ventricle to a steep rise in afterload, precipitating LV systolic and diastolic dysfunction 6–12 h after surgery, with afterload the primary driver.2 An inodilator is physiologically ideal — supporting contractility while easing afterload. It’s also well suited to pulmonary hypertension with ventricular dysfunction, where its main benefit is lowering pulmonary vascular resistance.3
But because it vasodilates, the choice hinges on the baby’s baseline diastolic pressure (echo-guided consensus):2
When diastolic arterial pressure is normal or high — there is room to vasodilate while supporting the pump.
When the infant is already hypotensive with low diastolic pressure — milrinone risks worsening it; dobutamine is the safer inodilator here.
03 Where it fails — the preterm transition
The hope that milrinone could prevent the low-systemic-flow state of the first day of life did not survive testing. In a landmark randomised placebo-controlled trial, prophylactic milrinone failed to prevent low superior vena cava flow, low right-ventricular output or hypotension in very preterm infants — and it slowed ductal closure.4,5
The likely reason is developmental: milrinone’s inotropy depends on calcium handling through the sarcoplasmic reticulum, which is underdeveloped in the immature myocardium — so it is a weaker inotrope in the very preterm heart, and prophylactic use isn’t supported.3
04 The risks that shape its use
Its vasodilation can cause profound hypotension — the commonest clinical adverse event — and the risk climbs with a rapid loading dose or if the infant is volume-depleted.5
In the largest NICU cohort (1,446 infants), thrombocytopenia was the most common laboratory adverse event during milrinone therapy.5
References
- Joynt C, Cheung PY. Cardiovascular supportive therapies for neonates with asphyxia — a literature review of pre-clinical and clinical studies. Front Pediatr. 2018;6:363. doi.org/10.3389/fped.2018.00363
- Giesinger RE, Bischoff AR, McNamara PJ. Anticipatory perioperative management for patent ductus arteriosus surgery: understanding postligation cardiac syndrome. Congenit Heart Dis. 2019;14(2):311–316. doi.org/10.1111/chd.12738
- Giesinger RE, More K, Odame J, et al. Controversies in the identification and management of acute pulmonary hypertension in preterm neonates. Pediatr Res. 2017;82(6):901–914. doi.org/10.1038/pr.2017.200
- Paradisis M, Evans N, Kluckow M, et al. Randomized trial of milrinone versus placebo for prevention of low systemic blood flow in very preterm infants. J Pediatr. 2009;154(2):189–195. doi.org/10.1016/j.jpeds.2008.07.059
- Samiee-Zafarghandy S, Raman SR, van den Anker JN, et al. Safety of milrinone use in neonatal intensive care units. Early Hum Dev. 2015;91(1):31–35. doi.org/10.1016/j.earlhumdev.2014.10.007
- Paradisis M, Jiang X, McLachlan AJ, et al. Population pharmacokinetics and dosing regimen design of milrinone in preterm infants. Arch Dis Child Fetal Neonatal Ed. 2006;92(3):F204–F209. doi.org/10.1136/adc.2005.092817
- Joynt C, Cheung PY. Treating hypotension in preterm neonates with vasoactive medications. Front Pediatr. 2018;6:86. doi.org/10.3389/fped.2018.00086
Educational summary for clinicians and trainees. Referenced to primary sources; items marked mechanistic, echo-guided consensus or low-certainty evidence reflect reasoning or practice rather than definitive trial evidence. Doses are for orientation only — always follow your unit’s formulary and senior review. This supports, and does not replace, local guidelines and individualised clinical judgement.