Racing against time: leveraging preclinical models to understand pulmonary susceptibility to perinatal acetaminophen exposures.

Over the past decade, clinicians have increasingly prescribed acetaminophen (APAP) for patients in the neonatal intensive care unit (NICU). Acetaminophen has been shown to reduce postoperative opiate burden, and may provide similar efficacy for closure of the patent ductus arteriosus (PDA) as nonsteroidal anti-inflammatory drugs (NSAIDs). Despite these potential benefits, APAP exposures have spread to increasingly less mature infants, a highly vulnerable population for whom robust pharmacokinetic and pharmacodynamic data for APAP are lacking. Concerningly, preclinical studies suggest that perinatal APAP exposures may result in unanticipated adverse effects that are unique to the developing lung. In this review, we discuss the clinical observations linking APAP exposures to adverse respiratory outcomes and the preclinical data demonstrating a developmental susceptibility to APAP-induced lung injury. We show how clinical observations linking perinatal APAP exposures to pulmonary injury have been taken to the bench to produce important insights into the potential mechanisms underlying these findings. We argue that the available data support a more cautious approach to APAP use in the NICU until large randomized controlled trials provide appropriate safety and efficacy data.

Comparative safety and efficacy of paracetamol versus non-steroidal anti-inflammatory agents in neonates with patent ductus arteriosus: A systematic review and meta-analysis of randomized controlled trials.

AIM: Ibuprofen and indomethacin are the preferred drug treatment for patent ductus arteriosus (PDA) in preterm neonates. The comparative safety and efficacy of paracetamol as an alternative has not yet been well established. The aim of our study was to define the comparative efficacy and safety of paracetamol versus ibuprofen and indomethacin for PDA. METHODS: We performed a systematic literature search in PubMed, Scopus and Cochrane databases on randomized controlled trials comparing the efficacy and/or the safety of paracetamol versus ibuprofen and/or indomethacin and meta-analysed the available data. RESULTS: There were 1718 neonates from 20 eligible studies. Paracetamol did not differ from ibuprofen or indomethacin regarding the primary (odds ratio [OR]: 0.93; 95% confidence interval [CI]: 0.69-1.26, P-value: 0.650, when compared to ibuprofen, and OR: 0.78; 95% CI: 0.20-3.02, P-value: 0.716, when compared to indomethacin) and overall (OR: 1.17; 95% CI: 0.82-1.66, P-value: 0.394, when compared to ibuprofen, and OR: 1.12; 95% CI: 0.58-2.15, P-value: 0.733, when compared to indomethacin) PDA closure rates. Paracetamol resulted in significantly reduced risk of oliguria and a tendency towards less gastrointestinal bleeding. CONCLUSION: There was no significant difference between paracetamol and ibuprofen or indomethacin in the PDA closure rates. However, paracetamol caused fewer adverse effects.

Negligible risk of prenatal ductus arteriosus closure or fetal renal impairment after third-trimester paracetamol use: evaluation of the German Embryotox cohort.

OBJECTIVE: Risk of fetotoxicity after paracetamol exposure in the third trimester. DESIGN: Observational cohort study and retrospective case assessment. SETTING: Germany, 2008-2017. POPULATION: Pregnant women exposed to paracetamol. METHODS: Prospectively enrolled third-trimester pregnancies that had been exposed to paracetamol (604) were compared with pregnancies exposed to paracetamol in the first and/or second trimester only (1192). Exclusion criteria were exposure to nonsteroidal anti-inflammatory drugs (NSAIDs) in the second or third trimester. Additionally, the Embryotox 'adverse drug reaction in pregnancy' database was screened for cases of fetotoxicity. MAIN OUTCOME MEASURES: The prenatal study end points focused on narrowing or closure of ductus arteriosus Botalli, late fetal death, and oligohydramnios. The postnatal end points included patent ductus arteriosus (PDA), primary pulmonary hypertension (PPHT), and impaired renal function. RESULTS: In both cohorts, no fetus with intrauterine narrowing or closure of the ductus arteriosus Botalli was reported (0/604 versus 0/1192). Oligohydramnios was diagnosed at a similar frequency in both cohorts: 1.3% (8/604) versus 1.6% (19/1192). There was one stillbirth in the study cohort (1/604, 0.2%) and four stillbirths in the comparison cohort (4/1192, 0.3%). The rates of PDA in neonates were similar: 0.7% (4/615) versus 0.7% (9/1212). PPHT as well as serious postnatal renal disorders were reported once in each cohort. In 12 out of 96 retrospective cases, there were indicators for study end points; however, co-exposure to NSAIDs or complex situations weaken the assumption of paracetamol toxicity. CONCLUSIONS: Fetal cardiovascular or renal toxicity of maternal third-trimester paracetamol use appears to be negligible. TWEETABLE ABSTRACT: Paracetamol use in the third trimester does not seem to be associated with a relevant risk of fetotoxicity.

Association between Furosemide Exposure and Patent Ductus Arteriosus in Hospitalized Infants of Very Low Birth Weight.

OBJECTIVE: To evaluate the association between furosemide exposure and patent ductus arteriosus (PDA) in a large, contemporary cohort of hospitalized infants with very low birth weight (VLBW). STUDY DESIGN: Using the Pediatrix Medical Group Clinical Data Warehouse, we identified all inborn infants of VLBW <37 weeks of gestation discharged from the neonatal intensive care unit after the first postnatal week from 2011 to 2015. We defined PDA as any medical (ibuprofen or indomethacin) or surgical PDA therapy. We collected data up to the day of PDA treatment or postnatal day 18 for infants not diagnosed with PDA. We performed multivariable logistic regression to evaluate the association between PDA and exposure to furosemide. RESULTS: We included 43 576 infants from 337 neonatal intensive care units, of whom 6675 (15%) underwent PDA treatment. Infants with PDA were more premature and more often exposed to mechanical ventilation and inotropes. Furosemide was prescribed to 4055 (9%) infants. On multivariable regression, exposure to furosemide was associated with decreased odds of PDA treatment (OR 0.72; 95% CI 0.65-0.79). Increasing percentage of days with furosemide exposure was not associated with PDA treatment (OR 1.01; 95% CI 0.97-1.06). CONCLUSIONS: Furosemide exposure was not associated with increased odds of PDA treatment in hospitalized infants of VLBW. Further studies are needed to characterize the efficacy and safety of furosemide in premature infants.

Low-dose maternal warfarin intake resulting in fetal warfarin syndrome: In search for a safe anticoagulant regimen during pregnancy.

BACKGROUND: Fetal exposure to maternal ingestion of warfarin is known to produce certain dysmorphic features in the neonate, known as fetal warfarin syndrome (FWS). There is a general consensus that maternal intake of warfarin at a daily dose of 5 mg or less is safe both for the infant and the mother. METHODS: We report four cases of FWS born to mothers with rheumatic heart disease on warfarin prophylaxis during pregnancy at a dose less than 5 mg/day. RESULTS: Along with typical facial features of FWS and multiple epiphyseal stippling in skeletal x-ray, Case 1 had Dandy-Walker malformation and Case 2 had laryngo-tracheomalacia and patent ductus arteriosus. CONCLUSION: We emphasize the need for optimizing the choice and dosage schedule of anticoagulants during pregnancy, least harmful for the mother and her developing fetus.

Predictors of bronchopulmonary dysplasia or death in premature infants with a patent ductus arteriosus.

BACKGROUND: Preterm infants with a patent ductus arteriosus (PDA) are at risk for death or development of bronchopulmonary dysplasia (BPD). However, PDA treatment remains controversial. We investigated if PDA treatment and other clinical or echocardiographic (ECHO) factors were associated with the development of death or BPD. METHODS: We retrospectively studied clinical and ECHO characteristics of preterm infants with birth weight <1,500 g and ECHO diagnosis of a PDA. Logistic regression and classification and regression tree analyses were performed to assess variables associated with the combined outcome of death or BPD. RESULTS: Of 187 preterm infants with a PDA, 75% were treated with indomethacin or surgical ligation and 25% were managed conservatively. Death or BPD occurred in 80 (43%) infants. The results of logistic regression analyses showed that lower gestational age (odds ratio (OR): 0.5), earlier year of birth during the study period (OR: 0.9), and larger ductal diameter (OR: 4.3) were associated with the decision to treat the PDA, whereas gestational age was the only variable associated with death or BPD (OR: 0.6; 95% confidence interval: 0.5-0.8). CONCLUSION: Only lower gestational age and not PDA treatment or ECHO score was associated with the adverse outcome of death or BPD. Further investigation of PDA management strategies and effects on adverse outcomes of prematurity is needed.

Pharmacokinetic and Pharmacodynamic Analysis of Acetaminophen and Ibuprofen Dual Therapy for Patent Ductus Arteriosus Closure in Preterm Neonates at Less Than 29 Weeks of Gestation.

Patent ductus arteriosus (PDA) is a blood vessel that critically supports fetal circulation. The ductus naturally closes within a few days after birth. However, it can stay open in premature neonates for an extended period of time, which is associated with increased mortality and various co-morbidities. Ibuprofen and indomethacin are currently the only 2 drugs approved for inducing PDA closure, but both have been associated with adverse renal and bleeding events. Clinical evidence suggests that combining acetaminophen (APAP) and ibuprofen treatments can decrease the need for surgical ligation. The objective of this study was to establish a disease-drug-trial model to characterize and predict PDA closure following single and combination drug therapy with ibuprofen and/or APAP in children at less than 29 weeks of gestation. The model was informed by a comprehensive literature review. The results of our analysis suggest that ibuprofen and APAP achieve therapeutic synergy. They further suggest that the younger the preterm neonates, the higher the treatment benefit. A 5-day oral dosing regimen consisting of ibuprofen (20 mg/kg Q24h on day 1, followed by 10 mg/kg Q24h on days 2-5) plus APAP (15 mg/kg Q6h) was deemed appropriate to achieve at least 90% PDA in all preterm neonates evaluated within 1 month of life. The model can now be used to design prospective pediatric trials to evaluate optimal drug combinations for PDA closure in preterm neonates and to refine optimal dosing regimens in cohorts of differing gestational age.

Ibuprofen Reduces 5-Year Overall Survival of Head and Neck Cancer Patients With Immunotherapy - A Retrospective Case-controlled Real-World Data Analysis of 10,000 Patients.

BACKGROUND/AIM: Resistance to immunotherapy can be explained by an abnormal microbiome of the gut. In Europe in particular, the use of ibuprofen, with or without proton-pump inhibitors to protect the gastric mucosa, is widespread. This study aimed to investigate the impact of ibuprofen use on the effectiveness of immunotherapy in patients with head and neck carcinoma. PATIENTS AND METHODS: Data from patients with head and neck carcinoma (ICD-10-Codes: C00-C14) receiving pembrolizumab, from the TriNetX network, were analyzed. Two groups were formed for the analyses: Cohort I received ibuprofen at least once within 6 months before and after immunotherapy, whereas patients in cohort II received ibuprofen with proton-pump inhibitors or no ibuprofen at all. Cohorts I and II were matched 1:1 with respect to age, sex, lymph node metastases, nicotine dependence, alcohol dependence, and body mass index (BMI). The primary outcome was death and a Kaplan-Meier analysis was performed, and the risk ratio (RR), odds ratio (OR), and hazard ratio (HR) were calculated. RESULTS: The analysis showed that 823 patients with ibuprofen and 724 patients without ibuprofen died within 5 years, showing a significant risk difference of 5.3% (p=0.001). The RR was 1.137 [95% confidence interval (CI)=1.053-1.227], OR was 1.245 (95% CI=1.093-1.418), and HR was 1.202 (95%CI=1.088-1.329). CONCLUSION: Ibuprofen significantly decreases the drug effectiveness of immunotherapy and may be related to changes in the human microbiome. However, further prospective, randomized, and double-blind studies are needed to validate our data and to adequately address confounders.

Cimetidine-associated patent ductus arteriosus is mediated via a cytochrome P450 mechanism independent of H2 receptor antagonism.

Persistent patency of the ductus arteriosus (PDA) is a common problem in preterm infants. The antacid cimetidine is a potent antagonist of the H2 histamine receptor but it also inhibits certain cytochrome P450 enzymes (CYPs), which may affect DA patency. We examined whether cimetidine contributes to PDA and is mediated by CYP inhibition rather than H2 blockade. Analysis of a clinical trial to prevent lung injury in premature infants revealed a significant association between cimetidine treatment and PDA. Cimetidine and ranitidine, both CYP inhibitors as well as H2 blockers, caused relaxation of the term and preterm mouse DA. CYP enzymes that are inhibited by cimetidine were expressed in DA subendothelial smooth muscle. The selective CYP3A inhibitor ketoconazole induced greater DA relaxation than cimetidine, whereas famotidine and other H2 antagonists with less CYP inhibitory effects caused less dilation. Histamine receptors were developmentally regulated and localized in DA smooth muscle. However, cimetidine caused DA relaxation in histamine-deficient mice, consistent with CYP inhibition, not H2 antagonism, as the mechanism for PDA. Oxygen-induced DA constriction was inhibited by both cimetidine and famotidine. These studies show that antacids and other compounds with CYP inhibitory properties pose a significant and previously unrecognized risk for PDA in critically ill newborn infants.

Pregnancy outcome in women exposed to leflunomide before or during pregnancy.

OBJECTIVE: Findings from animal studies have suggested that leflunomide may be a human teratogen. In the only human cohort study published to date, an increase in adverse outcomes in pregnancies after exposure to leflunomide was not detected. The aim of the present analysis was to expand on the previously published data with a description of birth outcomes among women who did not meet the previous cohort study criteria but who were exposed to leflunomide either during pregnancy or prior to conception. METHODS: Data on pregnancy exposures and outcomes were collected from 45 pregnant women who had contacted counseling services of the Organization of Teratology Information Specialists in the US or Canada between 1999 and 2009. Sixteen women were exposed to leflunomide during the first trimester of pregnancy and 29 women were exposed preconception. RESULTS: All 16 of the pregnancies with leflunomide exposure during pregnancy and 27 (93%) of the pregnancies with exposure prior to conception resulted in liveborn infants. There were 2 infants with major malformations from mothers who were exposed during pregnancy, and no malformations reported in the preconception group. There was a potential known alternative etiology for at least some of the defects observed. CONCLUSION: These data provide additional reassurance to women who inadvertently become pregnant while taking leflunomide and who undergo the washout procedure, as well as women who discontinue the medication prior to conception but have no prepregnancy documentation of drug clearance. However, until more conclusive data become available, women receiving leflunomide should be advised to use contraceptive methods and avoid pregnancy.

Effectiveness and safety of rectal dexibuprofen versus oral ibuprofen for closure of patent ductus arteriosus in preterm infants with gestational age<34 weeks: A pilot study.

This pilot study aimed to explore the effectiveness and safety of dexibuprofen suppository in the treatment of PDA in preterm infants. Preterm infants with gestational age <34 weeks and color Doppler echocardiographic evidence of hemodynamically significant PDA (hs PDA) with systemic hypoperfusion was intended to be included into this study since January 2020. As of January 1, 2021, this trial had recruited 87 preterm infants who met the inclusion criteria. Neonates were admitted into hospital within 1 hour after birth and were randomly assigned into two groups. Group one included 44 preterm newborns administered with oral ibuprofen. Group two included 43 preterm newborns administered with dexibuprofen suppository. This preliminary study showed that rectal dexibuprofen and oral ibuprofen were both effective for the closure of PDA, and the closure rate of dexibuprofen suppository was comparable to that of oral ibuprofen after the 1st and 2nd courses of treatment. In addition, rectal dexibuprofen did not increase the incidence of adverse outcomes, including bronchopulmonary dysplasia, intraventricular hemorrhage, sepsis, and necrotising enterocolitis. This pilot study showed dexibuprofen suppository is as effective and safe as oral ibuprofen; yet, better designed, muticenter controlled studies are still needed.

Evaluation of Health-Related Values and Preferences of Adults Who Were Preterm Infants and Parents of Preterm Infants Concerning Use of Prophylactic Cyclooxygenase Inhibitor Drugs.

Importance: There is wide variability in the use of prophylactic cyclooxygenase inhibitor (COX-I) drugs to prevent morbidity and mortality in preterm infants. Parents of preterm infants are rarely involved in this decision-making process. Objective: To explore the health-related values and preferences of adults who were preterm infants and families of preterm infants concerning the prophylactic use of indomethacin, ibuprofen, and acetaminophen initiated within the first 24 hours after birth. Design, Setting, and Participants: This cross-sectional study used direct choice experiments conducted in 2 phases of virtual video-conferenced interviews between March 3, 2021, and February 10, 2022: (1) a pilot feasibility study and (2) a formal study of values and preferences, using a predefined convenience sample. Participants included adults born very preterm (gestational age <32 weeks) or parents of very preterm infants currently in the neonatal intensive care unit (NICU) or having graduated from the NICU in the last 5 years. Main Outcomes and Measures: Relative importance of clinical outcomes, willingness to use each of the COX-Is when presented as the only option, preference for using prophylactic hydrocortisone vs indomethacin, willingness to use any of the COX-Is when all 3 options are available, and relative importance of having family values and preferences included in decision-making. Results: Of 44 participants enrolled, 40 were included in the formal study (31 parents and 9 adults born preterm). The median gestational age of the participant or the participant's child at birth was 26.0 (IQR, 25.0-28.8) weeks. Death (median score, 100 [IQR, 100-100]) and severe intraventricular hemorrhage (IVH) (median score, 90.0 [IQR, 80.0-100]) were rated as the 2 most critical outcomes. Based on direct choice experiments, most participants were willing to consider prophylactic indomethacin (36 [90.0%]) or ibuprofen (34 [85.0%]), but not acetaminophen (4 [10.0%]) when offered as the only option. Among participants who initially chose indomethacin (n = 36), if prophylactic hydrocortisone was offered as a potential therapy with the caveat that both cannot be used simultaneously, only 12 of 36 (33.3%) preferred to remain with indomethacin. Variability in preference was noted when all 3 COX-I options were available, indomethacin (19 [47.5%]) being the most preferred option followed by ibuprofen (16 [40.0%]), while the remainder opted for no prophylaxis (5 [12.5%]). Conclusions and Relevance: The findings of this cross-sectional study of former preterm infants and parents of preterm infants suggest that there was minimal variability in how participants valued the main outcomes, with death and severe IVH being rated as the 2 most important undesirable outcomes. While indomethacin was the most preferred form of prophylaxis, variability was noted in the choice of COX-I interventions when participants were presented with the benefits and harms of each drug.

Cost-Effectiveness Analysis of Ibuprofen Versus Indomethacin or Paracetamol for the Treatment of Patent Ductus Arteriosus in Preterm Neonates.

This was a first-time evaluation that sought to analyze the cost-effectiveness of oral paracetamol and intravenous (IV) indomethacin as alternatives to ibuprofen for PDA in neonates. Decision-analytic, literature-based, economic simulation models were constructed, to follow up the use and consequences of oral/IV ibuprofen versus IV indomethacin, and oral/IV ibuprofen versus oral paracetamol, as first-line therapies for PDA closure. Model outcomes of interest were "success", defined as PDA closure with/without adverse events, or "failure" due to no response to the first course of treatment, death or premature discontinuation of therapy due to adverse events. Oral ibuprofen is dominant/cost-effective over IV indomethacin in 97.9% of simulated cases, but oral paracetamol was 75.2% dominant/cost-effective over oral ibuprofen. Against IV ibuprofen, IV indomethacin was 55.3% dominant/cost-effective, whereas oral paracetamol was dominant/cost-effective in 98.5% of the cases. Sensitivity analyses confirmed the robustness of the study results. For PDA closure, while IV indomethacin was cost-effective against IV ibuprofen, oral paracetamol was cost-effective against both oral and IV ibuprofen.

Factors associated with the response to postnatal dexamethasone use in very low birthweight infants: a nationwide cohort study.

BACKGROUND: Dexamethasone is widely used as a systemic corticosteroid to treat and prevent bronchopulmonary dysplasia (BPD) in preterm infants. We evaluated the current epidemiology of dexamethasone use to prevent BPD and analyse the factors associated with the response to dexamethasone in very low birthweight infants using a nationwide database. METHODS: We included very low birthweight infants born between January 2013 and December 2020 with a gestational age of 23-31 weeks using data from the Korean Neonatal Network registry. Patients were grouped based on their dexamethasone use into 'Dex' or 'No Dex' groups. Clinical variables and data were collected, and the annual trends of dexamethasone use and the proportion of patients who received dexamethasone according to gestational age were analysed. Respiratory outcomes were compared between the groups. Univariate and multivariate analyses were performed to analyse factors associated with the response to dexamethasone in BPD. RESULTS: Of 11 261 eligible infants, 2313 (20.5%) received dexamethasone, and 1714 (74.1%) of them were diagnosed with moderate-to-severe BPD. The 8-year annual prevalence of dexamethasone use was 17.7-22.3%. The 'Dex' group had more moderate-to-severe BPD, more frequent invasive ventilation use at a postmenstrual age of 36 weeks and longer ventilator duration. Birth weight, 5-minute APGAR score, pulmonary hypertension within the first 28 days, surgical treatment of patent ductus arteriosus, medical treatment of patent ductus arteriosus, pathological chorioamnionitis, hydrocortisone or budesonide use, surgical management of necrotising enterocolitis and fungal sepsis were associated with BPD after dexamethasone use. CONCLUSIONS: Approximately 20.5% of preterm infants received dexamethasone, and the frequency increased as gestational age decreased. Poor response to dexamethasone was associated with antenatal and postnatal inflammation, low birth weight and early pulmonary hypertension.

Antenatal calcium channel blocker exposure and subsequent patent ductus arteriosus in extremely low-birth-weight infants.

This study aimed to assess whether tocolytic fetal exposure to antenatal calcium channel blockers (aCCB) increases the risk for hemodynamically significant patent ductus arteriosus (hsPDA) in extremely low-birth-weight (ELBW) infants. This case-control study investigated ELBW infants (<1,000 g) without cardiac defects in a level 3 neonatal intensive care unit who had survived at least 7 days. Nifedipine was the only aCCB used for this study population. The measurements included the history of aCCB exposure, selected maternal data, hsPDA diagnosis, gestational age at birth, birth weight, mode of delivery, sex, maternal race, location of birth, Apgar scores, and selected neonatal morbidities. The end point of the study was hsPDA, defined as an echocardiographically confirmed PDA with clinical symptoms. A total of 180 infants met the study criteria. The diagnosis was hsPDA for 56% of these patients, 20% of whom had aCCB exposure. Of the infants without hsPDA, 11% had aCCB exposure (p = 0.09). No statistically significant associations were found between aCCB exposure and hsPDA after adjustment for gestational age (odds ratio [OR], 1.5; 95% confidence interval [CI], 0.6-3.7) or for gestational age and cumulative aCCB exposure of 100 mg or more (OR, 2.0; 95% CI, 0.6-6.5). A history of aCCB exposure does not appear to increase hsPDA risk in ELBW infants. Studies using neonatal serum nifedipine concentrations after antenatal exposure should be performed to confirm this conclusion.

Paracetamol Treatment for Patent Ductus Arteriosus, an Apparent Association with Acute Hemolysis in Three Preterm Infants: Case Series.

We report three preterm infants who were treated with paracetamol for hemodynamically significant patent ductus arteriosus and developed acute hemolysis. No other apparent cause of acute hemolysis was found during Neonatal Intensive Care Unit hospitalization. All three infants were born within 1 year. As this side effect of paracetamol has not been reported previously and many preterm infants receive paracetamol for PDA closure, we advocate awareness. We cannot be sure whether the hemolysis occurred due to an underlying cause that was augmented by paracetamol or whether the drug itself caused acute hemolysis in these preterm infants.

Pulmonary hypertension and reopening of the ductus arteriosus in an infant treated with diazoxide.

Diazoxide is the main therapeutic agent for persistent hyperinsulinemic hypoglycemia. Generally, it is tolerated well, but rarely it can cause severe life-threatening complications. We report a neonate who was treated with diazoxide for hyperinsulinemic hypoglycemia. On the 6th day of the treatment we observed sepsis-mimicking symptoms, mild pulmonary hypertension, and re-opening of the ductus arteriosus. All these findings resolved dramatically shortly after discontinuation of treatment. To our knowledge, this is the first reported case of re-opening of the ductus arteriosus due to diazoxide toxicity.

In vivo dilatation of the ductus arteriosus induced by furosemide in the rat.

Furosemide increases prostaglandin production and may be associated with patent ductus arteriosus (PDA). We aimed to clarify the in vivo ductus-dilating effects of furosemide in neonatal rats. Near-term rat pups delivered by a cesarean section were housed at 33 degrees C. After a rapid whole-body freezing, the DA diameter was measured using a microscope and a micrometer. Pregnant rats (gestational day 21) were s.c. injected with furosemide 4 h before delivery, and the neonatal DA was examined 0, 15, 30, 60, and 120 min after birth. Furosemide was also s.c. injected into 60-min-old rats and the DA diameter was examined 30, 60, and 120 min later. The control rats showed a rapid postnatal DA constriction (diameter: 0.80 and 0.08 mm at 0 and 60 min after birth, respectively). Prenatally administered furosemide delayed postnatal DA closure (0.36 mm at 60 min after birth). Furosemide injection in 60-min-old rats dilated the constricted DA at 60 min (0.25 versus 0.02 mm in the controls). Indomethacin inhibited furosemide-induced DA dilatation. Furosemide delays DA closure and dilates the constricted DA in neonatal rats. If furosemide has similar effects in human preterm neonates, caution may be warranted in its use in the treatment of infants with PDA.

Vasoactivity of magnesium sulfate in chicken ductus arteriosus.

Prenatal treatment with magnesium sulfate (MgSO4) has neuroprotective effects in very preterm infants but its use has been associated with an increased rate of patent ductus arteriosus (DA). MgSO4 is a vasodilator and thus may exert a direct relaxant effect in the DA. We aimed to investigate the vasoactive effects of MgSO4 in the DA using the chicken embryo as experimental model. DA rings from 15-d (E15), 17-d (E17) and 19-d (E19) chicken embryos (total incubation: 21-d) were mounted in a wire myograph for isometric tension recordings. Exposure of DA rings to 21% O2 induced a tonic contraction which was relaxed by MgSO4 (2.4 - 7.2 mmol L-1) in a concentration-dependent manner (mean maximal relaxation E19: 51.4%, SE 6.3; EC50: 3.5 mmol L-1, SE 0.7). The relaxation evoked by MgSO4 was not significantly different between E15, E17 and E19 DA and was not affected by removal of the endothelium or by the presence of the nitric oxide synthase inhibitor L-NAME, the soluble guanylate cyclase inhibitor ODQ, or the cyclooxygenase inhibitor indomethacin. In contrast, when the DA rings were incubated in Ca2+-free solution, or in the presence of inhibitors of L-type Ca2+ channels (nifedipine), or large-conductance Ca2+-activated K+ (BKCa) channels (iberiotoxin), MgSO4-induced relaxation was impaired. Preincubation of the DA rings with MgSO4 concentrations ranging from 0 to 6.0 mmol L-1 did not significantly affect O2-induced contraction that was only impaired by a concentration of 7.2 mmol L-1. In conclusion, MgSO4 induced endothelium-independent relaxation of chicken DA and this relaxation appeared to be mediated through stimulation of BKCa channels and blockade of transmembrane flux of extracellular Ca2+. However, O2-induced DA contraction was only impaired by suprapharmacological concentrations of MgSO4 (> 6.0 mmol L-1). Therefore, our data suggest that the higher incidence of patent DA in preterm infants exposed to MgSO4 is unlikely to be due to a direct pharmacological effect of the drug on the DA.