The retrospective cohort study, led by Stefani M. Doucette and senior author Abhay Lodha, examined the records of 676 extremely preterm infants born at less than 29 weeks’ gestational age. The researchers compared outcomes before and after their units introduced routine prophylactic arginine supplementation during the first 28 days of life. The primary outcome was bronchopulmonary dysplasia, defined as a continuing need for oxygen at 36 weeks’ postmenstrual age, with severity classified according to the evidence-based criteria developed by Jensen and colleagues. What the team found was striking: the incidence of any bronchopulmonary dysplasia fell from 85 percent to 73 percent after routine supplementation began, a drop of twelve percentage points in a population where nearly every infant had previously been expected to develop some degree of the disease.

Because a before-and-after comparison can be confounded by concurrent changes in care, the investigators went beyond raw numbers. Using multivariable regression analysis to adjust for other factors that influence lung outcomes, they calculated an adjusted odds ratio of 0.50 for any bronchopulmonary dysplasia, with a 95 percent confidence interval of 0.27 to 0.90. In practical terms, even after accounting for other variables, infants exposed to prophylactic arginine had roughly half the odds of developing the disease compared with those who did not receive it. The composite outcome of bronchopulmonary dysplasia or death before 36 weeks’ postmenstrual age was similarly reduced, with an adjusted odds ratio of 0.51 and a confidence interval of 0.28 to 0.91, suggesting that the benefit was not simply an artifact of shifting survival patterns.

Yet the story is not one of unqualified triumph. When the researchers looked specifically at severe disease, grades 2 and 3 on the Jensen scale, the protective signal disappeared. The adjusted odds ratio for severe bronchopulmonary dysplasia was 0.94, with a confidence interval spanning 0.41 to 2.14, a range that includes no effect at all. This pattern suggests that arginine supplementation may primarily prevent milder forms of the disease, or that the study, despite its respectable size, lacked the statistical power to detect a benefit against the most serious outcomes. The distinction matters enormously for families and clinicians, because severe disease carries the heaviest burden of long-term respiratory morbidity, neurodevelopmental impairment, and healthcare cost.

To understand why an amino acid might influence lung development at all, one has to look at the biochemistry of nitric oxide. L-arginine is the obligate substrate for nitric oxide synthase, the enzyme family that converts arginine into nitric oxide, a gaseous signaling molecule with profound effects on vascular tone. In the developing lung, nitric oxide promotes vasodilation of the pulmonary vasculature, supports endothelial function, and helps coordinate the intricate angiogenic crosstalk between blood vessels and the forming air sacs. Extremely preterm infants are known to have low circulating arginine levels, partly because arginine is consumed rapidly by the urea cycle and by arginase enzymes, and partly because the pathways that normally synthesize it are immature. When arginine availability falls, nitric oxide production falters, and the pulmonary vessels that should be remodeling and expanding instead constrict and develop abnormally.

This mechanistic framework is supported by decades of animal research. Studies in hyperoxia-exposed newborn rodents, a standard model of bronchopulmonary dysplasia, have shown that impaired nitric oxide signaling contributes to arrested alveolar growth and pulmonary vascular remodeling, and that restoring downstream intermediates such as L-citrulline can attenuate these injuries. Depletion of arginine by overactive arginase has been implicated in impaired relaxation of lung parenchyma in exposed neonatal animals. Clinical observations add further weight: neonates with pulmonary hypertension have been found to have abnormalities in urea-cycle intermediates and reduced nitric oxide production, linking arginine metabolism directly to pulmonary vascular disease in human newborns.

The arginine hypothesis also fits within a broader, and somewhat humbling, therapeutic history. Inhaled nitric oxide, the direct administration of the very molecule that arginine helps produce, has been tested extensively in preterm infants as a potential preventive therapy for bronchopulmonary dysplasia. Multiple randomized trials and an individual-patient-data meta-analysis failed to demonstrate a consistent benefit, and recent masked randomized controlled trials targeting early pulmonary hypertension have continued to yield uncertain results. The apparent failure of inhaled nitric oxide has pushed researchers toward upstream and systemic approaches, including enteral arginine supplementation, which is cheaper, easier to administer, and may support nitric oxide production throughout the body rather than only in the ventilated airways.

Interestingly, this is not the first time arginine has shown promise in neonatology. Earlier clinical work by some of the same Calgary investigators demonstrated that arginine supplementation could reduce the incidence of necrotizing enterocolitis, a devastating intestinal disease of prematurity, and an updated systematic review has supported that association. The common thread is nitric oxide biology: in the gut, nitric oxide maintains mucosal blood flow and barrier integrity, while in the lung it supports vascular and alveolar development. Arginine’s role as a shared substrate for these protective pathways has made it an attractive candidate for multi-target prophylaxis in the smallest infants, and the new findings extend that logic from the intestine to the lung.

The authors and independent observers alike caution that a retrospective, single-center before-and-after design cannot establish causation. Secular trends in neonatal care, including evolving ventilation strategies, caffeine use, surfactant protocols, and nutrition practices, could have contributed to the observed decline in disease rates, even with statistical adjustment. The study was approved by the Conjoint Health Research Ethics Board at the University of Calgary with a waiver of informed consent, and the authors declare no competing interests, but the inherent limitations of observational methodology mean that a randomized controlled trial remains the essential next step. Such a trial would need to be powered to detect effects on severe disease and long-term respiratory outcomes, not merely the milder spectrum of the condition.

Nevertheless, the implications of the study are considerable. Bronchopulmonary dysplasia remains one of the most common and consequential morbidities of extreme prematurity, imposing enormous healthcare burdens through prolonged hospitalization, home oxygen therapy, readmissions, and increased mortality in outpatient populations. If a randomized trial confirms the association reported here, neonatal intensive care units would gain a remarkably low-cost, orally administered preventive therapy that could be folded into existing feeding protocols for infants under 29 weeks. For now, the Calgary findings offer something rarer than a cure: a biologically plausible, mechanistically grounded lead in a field where genuine therapeutic advances have been scarce, and a reminder that sometimes the most powerful medicines are the humblest molecules already present in the body’s own chemistry.

Subject of Research: Prophylactic arginine supplementation to prevent bronchopulmonary dysplasia in extremely preterm infants

Article Title: The role of prophylactic arginine supplementation for prevention of bronchopulmonary dysplasia in extremely preterm infants

Article References: Doucette, S. M., Jain, S. K., Amin, H., Benlamri, A., Hussain, M., Tang, S., Bhandari, V., & Lodha, A. (2026). The role of prophylactic arginine supplementation for prevention of bronchopulmonary dysplasia in extremely preterm infants. Journal of Perinatology. https://doi.org/10.1038/s41372-026-02922-4

Image Credits: AI Generated

DOI: 10.1038/s41372-026-02922-4

Keywords: arginine supplementation, bronchopulmonary dysplasia, extremely preterm infants, nitric oxide, neonatology, retrospective cohort study, pulmonary vascular development, chronic lung disease, prematurity, Journal of Perinatology, role, prophylactic

To understand why sildenafil is used at all in these fragile patients, it helps to grasp what bronchopulmonary dysplasia-associated pulmonary hypertension actually is. The review frames it not as a simple problem of excessive blood vessel constriction, but as a developmental disorder of the pulmonary circulation. In infants born extremely preterm, the lung’s vascular tree fails to grow in parallel with the airspaces. The result is impaired angiogenesis, a reduced pulmonary vascular surface area, and simplified alveolar architecture, the tiny sacs where gas exchange occurs. As the vascular bed underdevelops, pressure in the pulmonary arteries rises, and the right ventricle, the heart chamber that pumps blood into the lungs, gradually becomes uncoupled from the pulmonary artery it feeds. This progressive uncoupling is what ultimately threatens these infants’ lives.

Sildenafil acts on a well-defined molecular pathway. By inhibiting phosphodiesterase type 5, the enzyme that degrades cyclic guanosine monophosphate, the drug amplifies signaling downstream of nitric oxide, the endogenous vasodilator that keeps pulmonary vessels relaxed. Higher cyclic guanosine monophosphate levels activate protein kinase G, which reduces vascular tone and, at least in theory, lowers pulmonary arterial pressure. The logic is elegant, and it is supported by decades of work in adult pulmonary arterial hypertension, where sildenafil and related agents are established therapies. But the review’s authors emphasize that preterm infants are not small adults. Their pulmonary vasculature is still under construction, and the disease process they face is fundamentally different from the adult condition the drug was designed to treat.

Experimental studies offer a mixed but intriguing picture. Animal models of persistent pulmonary hypertension of the newborn have shown that sildenafil can improve pulmonary vascular remodeling, and research in lambs has demonstrated that decreased cyclic guanosine monophosphate-protein kinase G signaling itself impairs angiogenesis, suggesting the pathway sildenafil targets is genuinely central to the disease. Beyond vasodilation, experimental work points to effects on endothelial cell survival, smooth muscle proliferation, angiogenic signaling, and oxidative stress. Some studies have even explored intra-amniotic sildenafil to improve lung blood flow in models of congenital diaphragmatic hernia. Yet the authors caution that the relevance of these findings to human preterm infants remains incompletely validated, a gap that separates promising bench science from bedside certainty.

The clinical evidence tells a more sobering story. Current data support short-term improvements in echocardiographic hemodynamics and oxygenation in selected infants, meaning that on ultrasound-based measures of heart and lung function, treated babies often look better. What the data do not demonstrate is durable reversal of vascular remodeling or improved survival. Meta-analyses of sildenafil in this population have not established clear long-term benefit, and trials of prophylactic sildenafil to prevent bronchopulmonary dysplasia in the first place have yielded unconvincing results. A 2026 study of extremely premature infants found variable clinical and hemodynamic responses to the drug, underscoring that not every infant benefits equally. Meanwhile, pharmacoepidemiological surveys show that pulmonary vasodilators, sildenafil chief among them, are used extensively in United States children’s hospitals and across Europe, often without the trial evidence that would normally underpin such practice.

Part of the problem lies in pharmacokinetics, the science of how the body handles a drug. The review highlights that sildenafil exposure in neonates is highly variable, shaped by the maturation of CYP3A, the liver enzyme family responsible for metabolizing the drug, as well as by weight, postnatal age, route of administration, and drug interactions. Population pharmacokinetic studies in extremely premature infants and physiologically based modeling have characterized these sources of variability, and one notable interaction involves fluconazole, an antifungal commonly given to preterm infants, which inhibits CYP3A and can raise sildenafil concentrations. The practical consequence is that two infants receiving the same weight-based dose may experience very different drug exposures, complicating both efficacy and safety assessments.

Safety concerns extend beyond drug interactions. The SILDI-SAFE study, a multicenter randomized placebo-controlled dose-escalation trial, was designed specifically to evaluate sildenafil’s safety in premature infants with severe bronchopulmonary dysplasia, and a related phase II trial has targeted infants at risk of the disease. Researchers have also examined whether sildenafil influences retinopathy of prematurity, the abnormal retinal vessel growth that threatens vision in preterm infants, given that the drug’s vascular effects could theoretically extend to the eye. Hypotension is a recognized risk of vasodilator therapy in general, and the developing brain, the growing lung, and the immature retina all represent organs where manipulating vascular signaling demands caution. The review also notes experimental work on sildenafil-mediated neuroprotection, illustrating how broadly the drug’s biology reaches even as its neonatal safety profile continues to be mapped.

Diagnosis presents its own challenge, and it shapes how treatment decisions are made. There is no single gold standard for detecting pulmonary hypertension in infants with bronchopulmonary dysplasia; echocardiography remains the workhorse, supplemented by emerging tools such as MRI-based pulmonary artery flow measurements that can detect lung vascular pathology in preterms. Early echocardiographic indicators of pulmonary vascular disease are being refined, and targeted neonatal echocardiography programs offer a framework for screening and management. Because some infants who appear to resolve their pulmonary hypertension on ultrasound later show persistent disease, longitudinal follow-up matters as much as initial detection. These diagnostic uncertainties feed directly into treatment decisions, since identifying which infants truly have significant pulmonary vascular disease is a prerequisite for knowing who might benefit from sildenafil.

The review’s most important conceptual contribution may be its reframing of the disease itself. By treating bronchopulmonary dysplasia-associated pulmonary hypertension as a disorder of impaired vascular development rather than a purely reactive vasoconstrictive complication, the authors argue that simply relaxing vessels is not enough. A developmental disease may require therapies that promote vascular growth and repair, not just dilation of the vessels that exist. This perspective aligns with emerging work on endotypes of bronchopulmonary dysplasia, which aims to define molecularly distinct subgroups of preterm infants so that precision-based therapies can be matched to the right patients. It also explains why multidisciplinary approaches to severe bronchopulmonary dysplasia, which address nutrition, growth, and respiratory support alongside vasodilators, have been associated with resolution of pulmonary hypertension in some cohorts.

Where does this leave sildenafil and the infants who receive it? The authors recommend individualized, phenotype-guided use rather than routine prescription, and they call for future trials that incorporate pharmacokinetic-guided dosing and longitudinal outcomes rather than short-term surrogate measures. Such trials would need to answer whether the drug changes the trajectory of vascular remodeling, right ventricular function, and survival, not merely the numbers on an echocardiogram. For now, sildenafil remains a widely used therapy whose mechanistic rationale is sound, whose short-term effects are real for some patients, and whose long-term value in this uniquely vulnerable population is unproven. The gap between those facts is precisely where the next generation of neonatal vascular research will be fought, and the stakes could not be higher for the smallest patients in intensive care.

Subject of Research: Sildenafil treatment of pulmonary hypertension associated with bronchopulmonary dysplasia in preterm infants

Article Title: Sildenafil in bronchopulmonary dysplasia-associated pulmonary hypertension: developmental and translational insights

Article References: Fuentes-Mendoza, J., Sernaqué-Paz, M., Cruz-Riquelme, D., Zavaleta-Corvera, C., & Samanez-Obeso, A. (2026). Sildenafil in bronchopulmonary dysplasia-associated pulmonary hypertension: developmental and translational insights. Pediatric Research. https://doi.org/10.1038/s41390-026-05480-9

Image Credits: AI Generated

DOI: 10.1038/s41390-026-05480-9

Keywords: sildenafil, bronchopulmonary dysplasia, pulmonary hypertension, preterm infants, neonatology, pulmonary vascular development, phosphodiesterase type 5 inhibitor, nitric oxide signaling, pharmacokinetics, echocardiography, right ventricular function, precision medicine