Fetal endoscopic tracheal occlusion reverses the natural history of right-sided congenital diaphragmatic hernia: European multicenter experience.

OBJECTIVE: To evaluate the neonatal outcome of fetuses with isolated right-sided congenital diaphragmatic hernia (iRCDH) based on prenatal severity indicators and antenatal management. METHODS: This was a retrospective review of prospectively collected data on consecutive cases diagnosed with iRCDH before 30 weeks' gestation in four fetal therapy centers, between January 2008 and December 2018. Data on prenatal severity assessment, antenatal management and perinatal outcome were retrieved. Univariate and multivariate logistic regression analysis were used to identify predictors of survival at discharge and early neonatal morbidity. RESULTS: Of 265 patients assessed during the study period, we excluded 40 (15%) who underwent termination of pregnancy, two cases of unexplained fetal death, two that were lost to follow-up, one for which antenatal assessment of lung hypoplasia was not available and six cases which were found to have major associated anomalies or syndromes after birth. Of the 214 fetuses with iRCDH included in the neonatal outcome analysis, 86 were managed expectantly during pregnancy and 128 underwent fetal endoscopic tracheal occlusion (FETO) with a balloon. In the expectant-management group, lung size measured by ultrasound or by magnetic resonance imaging was the only independent predictor of survival (observed-to-expected lung-to-head ratio (o/e-LHR) odds ratio (OR), 1.06 (95% CI, 1.02-1.11); P = 0.003). Until now, stratification for severe lung hypoplasia has been based on an o/e-LHR cut-off of 45%. In cases managed expectantly, the survival rate was 15% (4/27) in those with o/e-LHR ≤ 45% and 61% (36/59) for o/e-LHR > 45% (P = 0.001). However, the best o/e-LHR cut-off for the prediction of survival at discharge was 50%, with a sensitivity of 78% and specificity of 72%. In the expectantly managed group, survivors with severe pulmonary hypoplasia stayed longer in the neonatal intensive care unit than did those with mildly hypoplastic lungs. In fetuses with an o/e-LHR ≤ 45% treated with FETO, survival rate was higher than in those with similar lung size managed expectantly (49/120 (41%) vs 4/27 (15%); P = 0.014), despite higher prematurity rates (gestational age at birth: 34.4 ± 2.7 weeks vs 36.8 ± 3.0 weeks; P < 0.0001). In fetuses treated with FETO, gestational age at birth was the only predictor of survival (OR, 1.25 (95% CI, 1.04-1.50); P = 0.02). CONCLUSIONS: Antenatal measurement of lung size can predict survival in iRCDH. In fetuses with severe lung hypoplasia, FETO was associated with a significant increase in survival without an associated increase in neonatal morbidity. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Surfactant use in late preterm infants: a survey among Belgian neonatologists.

Specific recommendations on surfactant administration in late preterm (LPT) infants with pulmonary disease are lacking. We performed an online-based, nationwide survey amongst all (n = 102) Belgian neonatologists to identify the use of surfactant in LPT infants suffering from several respiratory pathologies. The survey used clearly defined clinical cases and resulted in a 86% response rate. Neonatologists adhere to the 200 mg/kg initial surfactant dosing scheme. Surfactant is widely used in respiratory distress syndrome (70.1%), but there is less unanimity on its use in meconium aspiration syndrome (58.0%), transient tachypnoea of the newborn (30.6%), congenital pneumonia (27.2%) and congenital diaphragmatic hernia (8.6%). Respondents adhere to the European guideline of a timely referral to a newborn intensive care unit (non-invasive ventilation and FiO2 > 0.30 at 12 h of age), in order to minimise the risk of deterioration.Conclusion: We demonstrate a wide variety in the use of surfactant within LPT infants. The majority of Belgian neonatologists therefore urge for an investment in multi-centre trials on surfactant administration in LPT infants, in order to create an evidence-based practice as well as to reduce the strain on health care budgets.Trial registration: https://clinicaltrials.gov What is Known: • Any late preterm (LPT) infant with respiratory distress needs a timely referral to a neonatal intensive care unit in case of non-invasive ventilation and FiO2 > 0.30 at 12 h of life, in order to minimise the risk of acute deterioration as well as chronic lung disease. • Any modest increase in morbidity in the sizeable group of LPT infants exerts a significant strain on health care budgets. What is New: • We report the attitudes and opinions of Belgian neonatologists about the use of surfactant in LPT infants suffering from several respiratory diseases. • Our survey demonstrates a significant variability in practice between neonatologists during treatment of respiratory pathologies in LPT infants. This highlights an urgent need for univocal therapeutic lines.

Optimal gestational age at delivery in isolated left-sided congenital diaphragmatic hernia.

OBJECTIVE: To evaluate the morbidity and mortality of neonates with left-sided isolated congenital diaphragmatic hernia (CDH) according to gestational age at delivery. METHODS: This was a retrospective study of fetuses diagnosed prenatally with isolated left-sided CDH that were delivered in the University Hospitals of Antoine Béclère-Bicêtre and Leuven between 1 January 2010 and 31 December 2018. The Kaplan-Meier method was used to calculate cumulative survival at 28 days after birth according to gestational age at delivery. The association between gestational age at delivery, as a continuous variable, and survival at 28 days was modeled using a fractional polynomial. Adjustment for position of the liver, management center and mode of delivery was performed. The association was also evaluated according to the severity of CDH, as defined by the observed-to-expected lung-to-head ratio (o/e-LHR), which was classified as severe (o/e-LHR < 25%), moderate (o/e-LHR between 25% and 45%) or mild (o/e-LHR > 45%). RESULTS: We included 213 fetuses with isolated left-sided CDH, with a median gestational age at delivery of 38 + 2 weeks (interquartile range, 37 + 0 to 39 + 1 weeks). The survival rates at 28 days and at 6 months were 66.7% (142/213) and 64.3% (137/213), respectively. Kaplan-Meier analysis showed a higher survival rate at 28 days for babies delivered between 37 + 0 and 38 + 6 weeks than for those delivered at or after 39 + 0 weeks (log-rank test, P < 0.001). In the subgroup of moderate CDH, the 28-day survival rate was significantly higher in newborns delivered between 37 + 0 and 38 + 6 weeks than in those delivered at or after 39 + 0 weeks (81.5% vs 61.5%; P = 0.03), and this was also the case for survival rate at 6 months. In the subgroup with moderate CDH, 28-day survival significantly increased with advancing gestational age at birth up to about 38-39 weeks (P = 0.005), and significantly decreased from 39 weeks onwards. CONCLUSION: Delivery between 37 + 0 and 38 + 6 weeks' gestation is associated with a higher survival rate at 28 days in neonates with isolated left-sided CDH and moderate lung hypoplasia, independently of intrathoracic liver, management center and mode of delivery. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Application of a postnatal prediction model of survival in CDH in the era of fetal therapy.

Background: The disease severity in patients with a congenital diaphragmatic hernia (CDH) is highly variable. To compare patient outcomes, set up clinical trials and come to severity-based treatment guidelines, a performant prediction tool early in neonatal life is needed.Objective: The primary purpose of this study was to validate the CDH study group (SG) prediction model for survival in neonates with CDH, including patients who had fetal therapy. Secondary, we aimed to assess its predictive value for early morbidity.Methods: This is a retrospective single-center study at the University Hospitals Leuven on all infants with a diagnosis of CDH live-born between April 2002 and December 2016. The prediction model of the CDHSG was applied to evaluate its performance in determining mortality risk. Besides, we examined its predictive value for early morbidity parameters, including duration of ventilation, respiratory support on day 30, time to full enteral feeding and length of hospital stay.Results: The CDHSG prediction model predicted survival well, with an area under the curve of 0.796 (CI: 0.720-0.871). It had poor value in predicting infants who needed respiratory support on day 30 (area under the curve (AUC) 0.606; CI: 0.493-0.719), and correlated poorly with duration of ventilation, time to full enteral feeding and length of hospital stay.Conclusion: The CDHSG prediction model was in our hands also a useful tool in predicting mortality in neonates with CDH in the fetal treatment era. Correlation with early morbidity was poor.RationaleObjectives: (1) Validation of the CDHSG prediction model for survival in a cohort of neonates with CDH, in whom fetal endoscopic tracheal occlusion was applied according to the severity of lung hypoplasia. (2) Evaluation of performance of the model in the prediction of early morbidity.Main results: (1) Confirmation of the predictive value of the model for survival in neonates with CDH in the era of fetal therapy. (2) No correlation of the model with early morbidity parameters.

Intrauterine transfusion for fetal anemia due to red blood cell alloimmunization: 14 years experience in Leuven.

OBJECTIVE: The purpose of this study is to report on the pregnancy and neonatal outcome of intrauterine transfusion (IUT) for red blood cell (RBC-)alloimmunization. MATERIAL AND METHODS: Retrospective cohort study of all IUT for RBC-alloimmunization in the University Hospital of Leuven, between January 2000 and January 2014. The influence of hydrops, gestational age and technique of transfusion on procedure related adverse events were examined. RESULTS: 135 IUTs were performed in 56 fetuses. In none of the cases fetal or neonatal death occurred. Mild adverse events were noted in 10% of IUTs, whereas severe adverse events occurred in 1.5%. Hydrops and transfusion in a free loop were associated with an increased risk of adverse events whereas gestational age (GA) at transfusion after 34 weeks was not. Median GA at birth was 35.6 weeks and 9% was born before 34 weeks. Besides phototherapy 65.4% required additional neonatal treatment for alloimmune anemia. Non-hematologic complications occurred in 23.6% and were mainly related to preterm birth. CONCLUSION: In experienced hands, IUT for RBC-alloimmunization is a safe procedure in this era. Patients should be referred to specialist centers prior to the development of hydrops. IUT in a free loop of cord and unnecessary preterm birth are best avoided.

Quantification of amikacin in bronchial epithelial lining fluid in neonates.

Amikacin efficacy is based on peak concentrations and the possibility of reaching therapeutic levels at the infection site. This study aimed to describe amikacin concentrations in the epithelial lining fluid (ELF) through bronchoalveolar lavage (BAL) in newborns. BAL fluid was collected in ventilated neonates treated with intravenous (i.v.) amikacin. Clinical characteristics, amikacin therapeutic drug monitoring serum concentrations, and the concentrations of urea in plasma were extracted from the individual patient files. Amikacin and urea BAL fluid concentrations were determined using liquid chromatography with pulsed electrochemical detection (LC-PED) and capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C(4)D), respectively. ELF amikacin concentrations were converted from BAL fluid concentrations through quantification of dilution (urea in plasma/urea in BAL fluid) during the BAL procedure. Twenty-two observations in 17 neonates (postmenstrual age, 31.9 [range, 25.1 to 41] weeks; postnatal age, 3.5 [range, 2 to 37] days) were collected. Median trough and peak amikacin serum concentrations were 2.1 (range, 1 to 7.1) mg/liter and 39.1 (range, 24.1 to 73.2) mg/liter; the median urea plasma concentration was 30 (8 to 90) mg/dl. The median amikacin concentration in ELF was 6.5 mg/liter, the minimum measured concentration was 1.5 mg/liter, and the maximum (peak) was 23 mg/liter. The highest measured ELF concentration was reached between 6 and 14.5 h after i.v. amikacin administration, and an estimated terminal elimination half-life was 8 to 10 h. The median and highest (peak) ELF amikacin concentrations observed in our study population were, respectively, 6.5 and 23 mg/liter. Despite the frequent use of amikacin in neonatal (pulmonary) infections, this is the first report of amikacin quantification in ELF in newborns.

The fetal respiratory system as target for antenatal therapy.

The widespread use of prenatal ultrasound has made the fetus a patient. A number of conditions diagnosed as such may require therapy prior to birth. Herein we describe past, current and potential future procedures designed to treat pulmonary conditions in the antenatal period. When congenital cystic adenomatoid malformation (CCAM) is -associated with fetal hydrops, treatment is required. Prior to viability this may be in utero resection of the pathologic lung lobe or shunting of cystic lesions. More recently, fetuses with isolated congenital diaphragmatic hernia (CDH) with lethal lung hypoplasia have been offered percutaneous fetal tracheal occlusion to provoke lung growth. A very rare condition is laryngeal atresia, which requires peripartum re-establishment of the airways. As we get more -experience with access to the fetal airways, this may open the doors for novel therapies. One of these is gene delivery to treat fetuses with serious monogenic disorders or to induce transient overexpression of certain proteins. We review the individual hurdles that are being met by researchers when designing fetal gene therapeutic strategies, in particular for the fetal lung. Also the use of stem cells for pulmonary disorders is currently explored.

Antenatal fetal VEGF therapy to promote pulmonary maturation in a preterm rabbit model.

AIM: To assess the effects of fetal tracheal administration of VEGF on pulmonary maturation in a preterm rabbit model. METHODS: On day 26 (term=31days), fetal rabbits received recombinant rat VEGF (30microg in 70microL normal saline) or placebo (normal saline 70microL) intratracheally, with or without subsequent tracheal occlusion. Non-operated littermates served as internal controls. Fetuses were harvested on day 28 for morphometric study of the lungs or for mechanical ventilation and measurement of lung mechanics. In total, 96 fetuses from 42 does were used, 47 for ventilation and 49 for morphometry. RESULTS: In fetuses receiving intratracheal VEGF, an increase in immunoreactivity for Flk-1 was observed throughout the lung parenchyma. Tracheal occlusion (TO) adversely affected pulmonary mechanics as compared to un-occluded controls. That effect is partly reversed by intratracheal VEGF. Intratracheal injection of VEGF without tracheal occlusion improves lung mechanics but no more than what was observed in placebo injected controls. CONCLUSION: Antenatal intratracheal VEGF administration was associated with an increase in Flk-1 immunoreactivity. It also improves lung mechanics, however more so when the trachea is occluded. Without TO, the effects were comparable to placebo controls.

Maternal bariatric surgery: adverse outcomes in neonates.

BACKGROUND: The obesity epidemic in developed countries has led to an increased prevalence of obese women of reproductive age. As maternal obesity has far-reaching consequences for both mother and child, the consensus is that weight loss before pregnancy will reduce obesity-related morbidity and mortality. Therefore, an increasing number of women become pregnant after undergoing obesity surgery. RESULTS AND DISCUSSION: From the literature, data shows that perinatal outcome after bariatric surgery is generally considered as favourable for both mother and child. Only a few case reports highlight the possibility of side effects on the foetus and neonate. We report on five cases with severe intracranial bleeding, all possibly related to vitamin K deficiency following maternal bariatric surgery. CONCLUSION: These reports indicate that careful nutritional follow-up during pregnancy after obesity surgery is mandatory, because nutritional deficiencies such as vitamin K deficiency can lead to life-threatening bleeding.

Therapy for foetal pericardial tumours: survival following in utero shunting, and literature review.

We report the first case of foetal pericardial teratoma, treated successfully in utero by pericardio-amniotic shunting, and review the relevant literature. Foetal treatment improves survival in case of hydrops. Foetal pericardio-amniotic shunting could possibly be an alternative to serial pericardiocentesis.

Developmental pharmacology: neonates are not just small adults...

Neonatal drug dosing needs to be based on the physiological characteristics of the newborn and the pharmacokinetic parameters of the drug. Size-related changes can in part be modelled based on allometry and relates to the observation that metabolic rate relates to weight by a kg 0.75 trend. Until adult metabolic activity has been reached, ontogeny, i.e. isoenzyme-specific maturation and maturation of renal clearance also contributes to drug metabolism, making isoenzyme-specific documentation of maturation necessary. Changes in body composition and ontogeny are most prominent in neonates. The body fat content (/kg) is markedly lower and the body water content (/kg) is markedly higher in neonates. These findings have an impact on the distribution volume of both lipophilic and hydrophilic drugs. Drugs are cleared either by metabolism or elimination. While the first is mainly hepatic, the second route is mainly renal. Both hepatic metabolism and renal clearance display maturation in early life although other covariables (e.g. polymorphisms, co-administration of drugs, first pass metabolism, disease characteristics) further contribute to the interindividual variability in drug disposition. Documentation of these maturational processes based on in vivo 'case' studies is of value since these drug-specific observations can subsequently be extrapolated to other drugs which are either already being prescribed or even considered for use in neonates by the introduction of these observations in 'generic physiologically-based pharmacokinetic' models.

Covariates of tramadol disposition in the first months of life.

BACKGROUND: Data on contributors to between-individual variability in overall tramadol clearance and O-demethyl tramadol (M1) formation in preterm neonates and young infants are limited. METHODS: A population pharmacokinetic analysis of tramadol and M1 was undertaken using non-linear mixed effects model. Covariate analysis included weight, postmenstrual age (PMA), postnatal age (PNA), creatinaemia, (cardiac) surgery, cardiac defect, and cytochrome (CYP)2D6 polymorphisms, classified by CYP2D6 activity score. RESULTS: In 57 patients (25-54 weeks PMA), 593 observations were collected. Tramadol clearance was described using a two-compartment, zero-order input, first-order elimination linear model. An additional compartment was used to characterize M1. Tramadol clearance at term age was 17.1 litre h(-1) (70 kg)(-1) (CV, 37.2%). Size (37.8%) and PMA (27.3%) contribute to this variability. M1 formation clearance (CL2M1, i.e. the contribution of M1 synthesis to M clearance) was 4.11 litre h(-1) (70 kg)(-1) (CV, 110.9%) at term age. Size and PMA were the major contributors to the variability (52.7%); the CYP2D6 activity score contributes 6.4% to this variability. CONCLUSIONS: Overall tramadol clearance estimates confirm earlier reports while CL2M1 variability is explained by size, PMA, and CYP2D6 polymorphisms. The CL2M1 is very low in preterm neonates, irrespective of the CYP2D6 polymorphism with subsequent rapid maturation. The slope of this increase depends on the CYP2D6 activity score. The current pharmacokinetic observations suggest a limited micro-opioid receptor-mediated analgesic effect of M1 in preterm neonates and a potential CYP2D6 polymorphism-dependent effect beyond term age.

Urinary metabolites to assess in vivo ontogeny of hepatic drug metabolism in early neonatal life.

In addition to size-dependent allometric metabolic activity, most isoenzymes display age-dependent isoenzyme-specific ontogeny. We therefore need probe drugs to describe isoenzyme-specific ontogeny to develop more sophisticated, physiologically based models. We illustrate the feasibility and the relevance of in vivo assessment of hepatic metabolism, based on observations on urinary elimination of paracetamol and tramadol metabolites in neonates. On the basis of the observations on tramadol disposition, we were able to document that O-demethylation phenotypic activity developed sooner when compared with N-demethylation. During repeated administration of intravenous paracetamol, it was documented that, in addition to postmenstrual and postnatal age (PNA), repeated administration also contributed to the urinary excretion of glucuronidated paracetamol. In both probe drugs evaluated, age only in part explained the interindividual variability observed. Urine metabolites to assess in vivo metabolism of drugs routinely administered in neonates likely increase both the feasibility and clinical relevance of studies on in vivo isoenzyme-specific ontogeny in neonates.

Cardiorespiratory events recorded on home monitors: the effect of prematurity on later serious events.

OBJECTIVE: To describe severe alarms on home-documented monitoring in infants born prematurely. METHODS: In infants born at a post-menstrual age (PMA) less than 35 weeks, a polysomnography was performed before discharge. A heart rate less than 50 beats per minute (bpm) for more than 3 seconds or an apnea lasting for more than 15 seconds with a heart rate less than 60 bpm were defined as abnormal. These babies were given cardiorespiratory home monitoring with memory. Serious alarms on the home monitor were defined as heart rate less than 50 bpm for more than 3 seconds. RESULTS: Of 1058 infants, 96 infants needed cardiorespiratory home monitoring. Sixty-one infants showed alarms at home. The mean post-conceptional age (PCA) when alarms stopped was 46 weeks. Seventeen patients had serious alarms above the PCA of 50 weeks. There was a significant negative correlation (r = -0.46 and p = 0.0002 by Spearman's rank correlation) between the PMA at birth and the PCA at which the last alarm was noted CONCLUSION: Prematurely born infants with an abnormal polysomnography at discharge are at high risk for developing acute events at home. A younger PMA at birth correlates with a higher risk of alarms at a later PCA.

Maturational changes in the in vivo activity of CYP3A4 in the first months of life.

OBJECTIVE: To document maturational changes of the in vivo activity of CYP3A4 in the first months of life. METHODS: The contribution of tramadol (M), O-demethyl tramadol (M1, CYP2D6-mediated) and N-demethyl tramadol (M2, CYP3A4-mediated) to the overall elimination of tramadol and the log M/M2 was assessed in 24-hour urine collections during continuous intravenous tramadol administration. Correlations with perinatal characteristics (postnatal age (PNA) and postmenstrual age (PMA)) were studied. RESULTS: Of the total amount of tramadol administered in a 24-hour interval to 25 neonates and young infants (PMA 25 - 53 weeks), 34.5% (SD 6.1) were retrieved in the urine as parent compound or metabolite in a 24-hour interval. This retrieved material consisted primarily of tramadol 79% (SD 18), M1 10% (SD 17) and M2 3% (SD 3.4). The contribution of M (r2 = -0.53), M1 (r2 = 0.46) and M2 (r2 = 0.16) to overall M elimination correlated with increasing PMA. The mean log M/M2 was 1.44 (SD 0.46) and there was an inverse correlation between the log M/M2 ratio and PMA (r2 = -0.43, 95% CI for r = -0.84 to -0.34, p = 0.0006) and PNA (r2 = -0.25, 95% CI for r = -0.78 to -0.16, p = 0.008). The maturational half-life of the log M/M2 ratio was 16 - 20 weeks. In a multiple regression model, PMA was the only significant variable accounting for the interindividual variability in log M/M2. CONCLUSIONS: PMA was found to be the most important maturational change determing the in vivo activity of CYP3A4. The activity of CYP3A4 is relatively delayed in the first months of life compared to the developmental changes in CYP2D6 activity described earlier, however, the overall weak correlations reflect that PMA explains only in part the interindividual variability observed.

Cryotherapy versus laser photocoagulation for threshold retinopathy of prematurity: impact on early postoperative clinical recovery.

In a retrospective study in preterms treated with either cryotherapy (n= 16, 2000-2001) or laser photocoagulation (n= 19, 2002-2005) for threshold retinopathy, a significant decrease in duration of postoperative ventilation, in postoperative administration of analgesics and in time until regain of full enteral feeding was documented in infants who received laser photocoagulation. We therefore conclude that - compared to cryotherapy - laser treatment for threshold retinopathy is associated with a faster clinical postoperative recovery.

Scalp skin lesion in Turner syndrome: more than lymphoedema?

We present a case of a newborn with Turner syndrome (TS) and a scalp skin lesion resembling cutis verticis gyrata (CVG). Several reports on CVG in TS describe the lesions and correlate it with lymphoedema frequently seen in foetuses and infants with Turner syndrome. Histological examination in this case, however, shows a congenital mucinous nevus. Possibly an abnormal amount of proteoglycans in the skin of patients with TS can clarify the occurrence of this type of skin lesion.

Tramadol disposition in the very young: an attempt to assess in vivo cytochrome P-450 2D6 activity.

BACKGROUND: Tramadol is potentially a very useful pain relief medication in neonates and infants. It is primarily metabolized into O-demethyl tramadol (M1) by CYP2D6. Data concerning tramadol disposition and CYP2D6 activity in young infants are not available. METHODS: A population pharmacokinetic analysis of tramadol and M1 time-concentration profiles was undertaken using non-linear mixed-effects models (NONMEM), based on newly collected data on tramadol and M1 time-concentration profiles in neonates and young infants (n=20) and published studies on intravenous tramadol in children and adults. M1 formation served as a surrogate for CYP2D6 activity. RESULTS: Tramadol clearance was described using a two-compartment linear model with zero-order input and first-order elimination. Clearance increased from 25 weeks post-conception age (PCA) (5.52 litre h(-1) [70 kg](-1)) to reach 84% of the mature value by 44 weeks PCA (standardized to a 70 kg adult using allometric '1/4 power' models). The central volume of distribution decreased from 25 weeks PCA (256 litre [70 kg](-1)) to reach 120% of its mature value by 87 weeks PCA. Formation clearance to M1 contributed 43% of tramadol clearance, but had no relationship with PCA. There was a weak non-linear relationship between PCA and M1 metabolite clearance. CONCLUSIONS: Maturational clearance of tramadol is almost complete by 44 weeks PCA. A target concentration of 300 microg litre(-1) is achieved after a bolus of tramadol hydrochloride 1 mg kg(-1) and can be maintained by infusion of tramadol hydrochloride 0.09 mg kg(-1) h(-1) at 25 weeks PCA, 0.14 mg kg(-1) h(-1) at 30 weeks PCA, 0.17 mg kg(-1) h(-1) at 35 weeks PCA, 0.18 mg kg(-1) h(-1) at 40 weeks, 0.19 mg kg(-1) h(-1) at 50 weeks PCA to 1 yr, 0.18 mg kg(-1) h(-1) at 3 yr and 0.12 mg kg(-1) h(-1) in adulthood. CYP2D6 activity was observed as early as 25 weeks PCA, but the impact of CYP2D6 polymorphism on the variability in pharmacokinetics, metabolism and pharmacodynamics of tramadol remains to be established.