Systemic levels following PGE1 inhalation in neonatal hypoxemic respiratory failure

Inhaled PGE1 in neonates with hypoxemic respiratory failure: two pilot feasibility randomized clinical trials

Background

Inhaled nitric oxide (INO), a selective pulmonary vasodilator, has revolutionized the treatment of neonatal hypoxemic respiratory failure (NHRF). However, there is lack of sustained improvement in 30 to 46% of infants. Aerosolized prostaglandins I₂ (PGI₂) and E₁ (PGE₁) have been reported to be effective selective pulmonary vasodilators. The objective of this study was to evaluate the feasibility of a randomized controlled trial (RCT) of inhaled PGE₁ (IPGE₁) in NHRF.

Methods

Two pilot multicenter phase II RCTs are included in this report. In the first pilot, late preterm and term neonates with NHRF, who had an oxygenation index (OI) of ≥15 and <25 on two arterial blood gases and had not previously received INO, were randomly assigned to receive two doses of IPGE₁ (300 and 150 ng/kg/min) or placebo. The primary outcome was the enrollment of 50 infants in six to nine months at 10 sites. The first pilot was halted after four months for failure to enroll a single infant. The most common cause for non-enrollment was prior initiation of INO. In a re-designed second pilot, co-administration of IPGE₁ and INO was permitted. Infants with suboptimal response to INO received either aerosolized saline or IPGE₁ at a low (150 ng/kg/min) or high dose (300 ng/kg/min) for a maximum duration of 72 hours. The primary outcome was the recruitment of an adequate number of patients (n = 50) in a nine-month-period, with fewer than 20% protocol violations.

Results

No infants were enrolled in the first pilot. Seven patients were enrolled in the second pilot; three in the control, two in the low-dose IPGE₁, and two in the high-dose IPGE₁ groups. The study was halted for recruitment futility after approximately six months as enrollment targets were not met. No serious adverse events, one minor protocol deviation and one pharmacy protocol violation were reported.

Conclusions

These two pilot RCTs failed to recruit adequate eligible newborns with NHRF. Complex management RCTs of novel therapies for persistent pulmonary hypertension of the newborn (PPHN) may require novel study designs and a longer period of time from study approval to commencement of enrollment.

Trial registration: ClinicalTrials.gov

Pilot one: NCT number: 00598429 registered on 10 January 2008. Last updated: 3 February 2011.

Pilot two: NCT number: 01467076 17 October 2011. Last updated: 13 February 2013.

Electronic supplementary material

The online version of this article (doi:10.1186/1745-6215-15-486) contains supplementary material, which is available to authorized users.

Effect of aerosolized PGE(1) on the ductus arteriosus of neonatal swine

BACKGROUND

Inhaled PGE(1) (IPGE(1)) is a potential pulmonary vasodilator in neonatal respiratory failure. However, its effect on the patency of the ductus arteriosus (DA) has not been described.

OBJECTIVE

To investigate the effect of IPGE(1) on the DA in healthy piglets.

DESIGN/METHODS

IPGE(1) (1200ng/kg/min) [Study] or nebulized saline [Control] was administered using a jet nebulizer. Transthoracic echocardiography (TTE) was performed prior to (T0) and after 24h of aerosol therapy (T24). The DA was also evaluated histomorphologically at autopsy.

RESULTS

Fifteen piglets, 1-9 days old (study=9; control=6), were evaluated for DA patency. Study piglets received IPGE(1) for 12-24h. TTE was performed on 12 piglets at T0. Nine animals showed no ductal flow and 3 (1 study, 2 control) had a small DA. TTE at T24 in 5 animals showed no change in DA. At autopsy, the ductal diameter and histologic maturity stage were comparable in study and control animals.

CONCLUSIONS

High dose IPGE(1) given for 12-24h does not exert significant effect on the DA of healthy term piglets as evaluated by echocardiography and histomorphology. We conclude that ductal patency in neonates is influenced not only by prostaglandins but also by factors like hypoxemia, prematurity, and heart disease.

Toxicity of prolonged high dose inhaled PGE1 in ventilated neonatal pigs

OBJECTIVE

To study the toxicity of inhaled PGE1 (IPGE1) in healthy ventilated piglets.

METHODS

Mechanically ventilated anesthetized piglets received either high dose IPGE1 (IPGE1 group) or nebulized saline (control group) continuously for 24h. Cardio-respiratory parameters, complete blood counts and serum electrolytes were monitored. Lung histology was evaluated by a masked pathologist for the severity (minimal, moderate, and severe) and extent (focal, multifocal, and diffuse) of histologic injury.

RESULTS

Ten neonatal pigs were instrumented. Four received nebulized saline and six received high dose IPGE1. There was no evidence of adverse cardio-respiratory effects, bronchial irritation or hypernatremia related to IPGE1. Diffuse/multifocal alveolar edema and focal polymorphonuclear infiltration was observed in both the control and IPGE1 groups suggesting that alveolar alterations may be secondary to effects of mechanical ventilation. The most distinct histomorphological abnormalities observed in the IPGE1 animals were focal ulceration, flattening of the bronchial epithelium and loss of cilia of moderate to severe degree in the trachea and bronchi.

CONCLUSION

In healthy piglets, inhalation of high dose IPGE1 was not associated with adverse cardiorespiratory effects, bronchial irritation, or hypernatremia and produced minimal signs of pulmonary toxicity even after 24h. Prolonged inhalation of high dose PGE1 therefore appears safe in newborn piglets.

PGE2/TXB2 imbalance in neonatal hypoxemic respiratory failure

BACKGROUND

An imbalance of vaso-constrictor and -dilator mediators has been implicated in the pathogenesis of the pulmonary hypertension accompanying neonatal hypoxemic respiratory failure (NHRF).

AIM

To characterize plasma PGE2, TXB2 and their ratio in normal newborns and in those with NHRF.

METHODS

Twenty newborns with NHRF received inhaled PGE1 (IPGE1) by jet nebulizer in doses of 25, 50, 150 and 300 ng/kg/min followed by weaning. Blood for PGE2 and TXB2 assay using EIA was available in 8 neonates with NHRF prior to IPGE1. Umbilical cord arterial samples were also obtained at delivery from 10 normal newborns to serve as controls.

RESULTS

Compared to normal newborns, those with NHRF had significantly lower PGE2/TXB2 ratios after controlling for preterm gestation (< 37 weeks) and postnatal age (p < 0.05). Notably, all subjects except one in the NHRF group had a value of < 1.0 (range 0.1-1.2) compared to a value of > 1.0 in all subjects in the Control group (range 1.1-5.2).

CONCLUSIONS

Lower PGE2/TXB2 ratio in subjects with NHRF compared with controls reflects a predominance of vaso-constrictor activity in these patients as the basis of pulmonary hypertension. Plasma PGE2/TXB2 ratio may have important implications for the diagnosis and treatment of NHRF.