The development of the Belgian paediatric clinical trial network.

Paediatric clinical trials are critical to ensure that medications prescribed to children are safe and effective. However, evidence-based dosing and labelling of such medications remain limited, and most clinical trials in paediatrics fail. Factors for lack of trial completion include performance at site level (limited patient recruitment, limited site staff experience and lack of infrastructure), the sponsor team (limited paediatric specific expertise in design, uncertainties on robustness of biomarkers or outcome variables) as well as regulatory and administrative burdens. As a result of the growing demand for site support, the Belgian Paediatric Clinical Research Network (BPCRN) established in 2009 has been relaunched in 2018 to improve paediatric clinical trials, with the support of innovative-medicines-initiative 2 (IMI2) pan-European network conect4children (c4c) and the transatlantic network I-ACT for Children (US).This paper highlights the formation of the BPCRN and the practical insights it offers for advancing paediatric clinical trials through national networks. A national network can improve trial quality, safety and efficiency, provide clinical research expertise, identify suitable sites, and help with troubleshooting of common trial issues. The BPCRN's centralized approach has advanced paediatric clinical trials by streamlining communication and standardizing trial conduct. Challenges and opportunities have arisen, including a relaunch in 2018, orphan medicine trials, and network sustainability. Collaboration between network activities, government support, site-level improvements, efficient communication, and interaction with industry are key to achieve lasting transformation in paediatric medicine research.

Highly Variable Paracetamol Pharmacokinetics After Multiple Oral Dosing in Frail Older People: A Population Pharmacokinetic Analysis.

INTRODUCTION: Paracetamol pharmacokinetics (PK) is highly variable in older fit adults after intravenous administration. Frailty and oral administration likely result in additional variability. The aim was to determine oral paracetamol PK and variability in geriatric inpatients. METHODS: A population PK analysis, using NONMEM 7.2, was performed on 245 paracetamol samples in 40 geriatric inpatients (median age 87 [range 80-95] years, bodyweight 66.4 [49.3-110] kg, 92.5% frail [Edmonton Frail Scale]). All subjects received paracetamol 1000 mg as tablet (72.5%) or granulate (27.5%) three times daily. Simulations of dosing regimens (1000 mg every 6 hours [q6h] or q8h) were performed to determine target attainment, using mean steady-state concentration (Css-mean) of 10 mg/L as target. RESULTS: A one-compartment model with first order absorption and lag time best described the data. The inter-individual variability was high, with absorption rate constant containing the highest variability. The inter-individual variability could not be explained by covariates. Simulations of 1000 mg q6h and q8h resulted in a Css-mean of 10.8 [25-75th percentiles 8.2-12.7] and 8.13 [6.3-9.6] mg/L, respectively, for the average geriatric inpatient. The majority of the population remained off-target (22.2% [q6h] and 52.2% [q8h] <8 mg/L; 31.3 [q6h] and 7.6% [q8h] >12 mg/L). CONCLUSION: A population of average geriatric inpatients achieved target Css-mean with paracetamol 1000 mg q6h, while q8h resulted in underexposure for the majority of them. Due to high unexplained variability, a relevant proportion remained either above or below the target concentration of 10 mg/L. Research focusing on PK, efficacy and safety is needed to recommend dosing regimens.

Ontogeny of Hepatic Transporters and Drug-Metabolizing Enzymes in Humans and in Nonclinical Species.

The liver represents a major eliminating and detoxifying organ, determining exposure to endogenous compounds, drugs, and other xenobiotics. Drug transporters (DTs) and drug-metabolizing enzymes (DMEs) are key determinants of disposition, efficacy, and toxicity of drugs. Changes in their mRNA and protein expression levels and associated functional activity between the perinatal period until adulthood impact drug disposition. However, high-resolution ontogeny profiles for hepatic DTs and DMEs in nonclinical species and humans are lacking. Meanwhile, increasing use of physiologically based pharmacokinetic (PBPK) models necessitates availability of underlying ontogeny profiles to reliably predict drug exposure in children. In addition, understanding of species similarities and differences in DT/DME ontogeny is crucial for selecting the most appropriate animal species when studying the impact of development on pharmacokinetics. Cross-species ontogeny mapping is also required for adequate translation of drug disposition data in developing nonclinical species to humans. This review presents a quantitative cross-species compilation of the ontogeny of DTs and DMEs relevant to hepatic drug disposition. A comprehensive literature search was conducted on PubMed Central: Tables and graphs (often after digitization) in original manuscripts were used to extract ontogeny data. Data from independent studies were standardized and normalized before being compiled in graphs and tables for further interpretation. New insights gained from these high-resolution ontogeny profiles will be indispensable to understand cross-species differences in maturation of hepatic DTs and DMEs. Integration of these ontogeny data into PBPK models will support improved predictions of pediatric hepatic drug disposition processes. SIGNIFICANCE STATEMENT: Hepatic drug transporters (DTs) and drug-metabolizing enzymes (DMEs) play pivotal roles in hepatic drug disposition. Developmental changes in expression levels and activities of these proteins drive age-dependent pharmacokinetics. This review compiles the currently available ontogeny profiles of DTs and DMEs expressed in livers of humans and nonclinical species, enabling robust interpretation of age-related changes in drug disposition and ultimately optimization of pediatric drug therapy.

[COVID-19 during pregnancy and lactation: what do we already know?] / COVID-19 tijdens zwangerschap en borstvoeding.

SARS-CoV-2 has rapidly spread worldwide since December 2019. Obviously, pregnant and lactating women will also be infected with SARS-CoV-2. Pregnant women, however, are a risk population for developing severe respiratory infections. Currently, the knowledge on potential risks and consequences of COVID-19 during pregnancy and lactation is limited. Available data show that pregnant women suffer from similar symptoms compared to non-pregnant patients. There is no evidence as yet that COVID-19 has a more serious course during pregnancy. Although pregnant women might suffer from a wide variety of symptoms, most of them are asymptomatic. Maternal SARS-CoV-2 infection might lead to adverse neonatal outcomes, such as prematurity or respiratory symptoms. There is currently no conclusive evidence of absence of intrauterine transmission of the virus; the virus has not been detected in breastmilk in most studies, although passage into breastmilk cannot be completely excluded.

Larger Dose Reductions of Vancomycin Required in Neonates with Patent Ductus Arteriosus Receiving Indomethacin versus Ibuprofen.

Ibuprofen and indomethacin are commonly used to induce ductus arteriosus closure in preterm neonates. Our group previously reported that ibuprofen decreased vancomycin clearance by 16%. In this study, we quantified the impact of indomethacin coadministration on vancomycin clearance by extending our vancomycin population pharmacokinetic model with a data set containing vancomycin concentrations measured in preterm neonates comedicated with indomethacin. The modeling data set includes concentration-time data of vancomycin administered alone or in combination with either ibuprofen or indomethacin collected in the neonatal intensive care units of UZ Leuven (Leuven, Belgium) and São Francisco Xavier Hospital (Lisbon, Portugal). The derived vancomycin pharmacokinetic model was subsequently used to propose dose adjustments that yield effective vancomycin exposure (i.e., area under the concentration-time curve from 0 to 24 h [AUC0-24] between 300 to 550 mg·h/liter, with a probability of <0.1 of subtherapeutic exposure) in preterm neonates with patent ductus arteriosus. We found that indomethacin coadministration reduced vancomycin clearance by 55%. Model simulations showed that the most recent vancomycin dosing regimen, which was based on an externally validated model, requires 20% and 60% decreases of the loading and maintenance doses of vancomycin, respectively, when aiming for optimized exposure in the neonatal population. By analyzing vancomycin data from preterm neonates comedicated with indomethacin, we found a substantial decrease in vancomycin clearance of 55% versus a previously reported 16% for ibuprofen. This decrease in clearance impacts vancomycin dosing, and we anticipate that other drugs eliminated by glomerular filtration are likely to be affected to a similar extent as vancomycin.

Population Pharmacokinetic Modeling of Acetaminophen and Metabolites in Children After Cardiac Surgery With Cardiopulmonary Bypass.

Children undergoing cardiac surgery often receive acetaminophen (paracetamol) as part of their postoperative pain treatment. To date, there is no information on the pharmacokinetics (PK) of acetaminophen in this special population, even though differences, as a result of altered hemodynamics and/or use of cardiopulmonary bypass, may be anticipated. Therefore, the aim of this study was to investigate the PK of intravenous acetaminophen in children after cardiac surgery with cardiopulmonary bypass. In the study, both children with and without Down syndrome were included. A population PK analysis, using NONMEM 7.2, was performed based on 161 concentrations of acetaminophen, acetaminophen sulfate, acetaminophen glucuronide, and oxidative metabolites from 17 children with Down syndrome and 13 children without Down syndrome of a previously published study (median age, 177 days [range, 92-944], body weight, 6.1 kg [4.0-12.9]). All children received 3 intravenous acetaminophen doses of 7.5 mg/kg (<10 kg) or 15 mg/kg (≥10 kg) at 8-hour intervals after cardiac surgery. For acetaminophen and its metabolites, 1-compartment models were identified. Clearance of acetaminophen and metabolites increased linearly with body weight. Acetaminophen clearance in a typical child of 6.1 kg is 0.96 L/h and volume of distribution 7.96 L. Down syndrome did not statistically significantly impact any of the PK parameters for acetaminophen, nor did any other remaining covariate. When comparing the PK parameters of acetaminophen in children after cardiac surgery with cardiopulmonary bypass with those from children of the same age following noncardiac surgery reported in the literature, clearance of acetaminophen was lower and volume of distribution higher.

Population pharmacokinetic modelling of intravenous paracetamol in fit older people displays extensive unexplained variability.

AIMS: Paracetamol is the analgesic most used by older people. The physiological changes occurring with ageing influence the pharmacokinetics (PK) of paracetamol and its variability. We performed a population PK-analysis to describe the PK of intravenous (IV) paracetamol in fit older people. Simulations were performed to illustrate target attainment and variability of paracetamol exposure following current dosing regimens (1000 mg every 6 h, every 8 h) using steady-state concentration (Css-mean ) of 10 mg l-1 as target for effective analgesia. METHODS: A population PK-analysis, using NONMEM 7.2, was performed based on 601 concentrations of paracetamol from 30 fit older people (median age 77.3 years, range [61.8-88.5], body weight 79 kg [60-107]). All had received an IV paracetamol dose of 1000 mg (over 15 min) after elective knee surgery. RESULTS: A two-compartment PK-model best described the data. Volume of distribution of paracetamol increased exponentially with body weight. Clearance was not influenced by any covariate. Simulations of the standardized dosing regimens resulted in a Css of 9.2 mg l-1 and 7.2 mg l-1 , for every 6 h and every 8 h respectively. Variability in paracetamol PK resulted in Css above 5.4 and 4.1 mg l-1 , respectively, in 90% of the population and above 15.5 and 11.7, respectively, in 10% at these dosing regimens. CONCLUSIONS: The target concentration was achieved in the average patient with 1000 mg every 6 h, while every 8 h resulted in underdosing for the majority of the population. Furthermore, due to a large (unexplained) interindividual variability in paracetamol PK a relevant proportion of the fit older people remained either under- or over exposed.

Monitoring of Brain Hemodynamics Coupling in Neonates using Updated Tensor Decompositions.

In this paper we explore the use of updated tensor decompositions for the monitoring of brain hemodynamics in neonates. For this study, we used concomitant measurements of heart rate, mean arterial blood pressure, arterial oxygen saturation, EEG, and brain oxygenation - measured using near-infrared spectroscopy. These measurements were obtained from 22 neonates undergoing an INSURE procedure (INtubation, SURfactant and Extubation) and sedation using propofol. To develop the monitoring framework using tensors, we used radial basis kernel function (RBF) to construct a similarity matrix for consecutive segments of the signals. These matrices were concatenated forming a tensor. Updating canonical polyadic decomposition was used to evaluate the impact of propofol in the coupling between the different signals. Results indicate, as previously reported, a drop in the interaction between signals due to propofol administration. This shows that tensor decompositions can be useful in order to monitor the coupling between different physiological signals.

Analgesics and Sedatives in Critically Ill Newborns and Infants: The Impact on Long-Term Neurodevelopment.

Inadequate pain and/or stress management in preterm- and term-born infants has been associated with increased morbidity and even mortality. However, exposure to analgosedatives during early infancy may also be one of the risk factors for subsequent neurodevelopmental impairment, at least in animal studies. Because infants admitted to neonatal or pediatric intensive care units may receive high amounts of these drugs for prolonged periods of time and the majority of these infants nowadays survive to discharge, this is of major concern. A balanced approach that incorporates the assessment and quantification of both wanted effects as well as unwanted side effects is therefore needed. In this article, the optimal dose determination of commonly used analgosedative drugs as well as their potential long-term effects on the developing human brain and neuropsychological functioning are reviewed.

Intravenous Paracetamol Dosing Guidelines for Pain Management in (pre)term Neonates Using the Paediatric Study Decision Tree.

BACKGROUND: Intravenous paracetamol (acetaminophen) has not been licensed for analgesia in preterm neonates or infants < 2 years, respectively, in Europe and the United States. A variety of dosing regimens is therefore used off-label. Because evidence supports the use of the same target mean steady state paracetamol concentration (Cssmean, 9-11 mg/L) for pain relief in neonates compared to older children and adults, dosing regimens based on this Cssmean were evaluated in a two-step approach. METHODS: First, a systematic search was performed to provide pharmacokinetic (PK)-based dosing guidelines for pain in neonates (with subsequent searches on safety in these papers). Second, concentration-time profiles based on these dosing guidelines were generated to provide a dosing advice for paracetamol to treat neonatal pain. RESULTS: Of 2334 potentially relevant articles, 9 studies were included. For typical term neonates, dosages specified in packaging (labels) resulted in Cssmean below target (7.65 mg/L), while dosages from investigator-initiated studies resulted in either a Cssmean above (15.31), or around the target (11.78 and 10.21) for (pre)term neonates >32 weeks. Only one study suggested a dosing resulting in a tailored concentration (8.7) in preterm neonates <32 weeks. CONCLUSION: A loading dose 20 mg/kg, followed by 10 mg/kg/6h is recommended for 32-44 weeks' neonates, which is supported by short-term safety. For neonates < 32 weeks, a loading dose of 12 mg/kg and a maintenance dose of 6mg/kg/6h seems to lead to the target Cssmean, though additional clinical studies are needed to support its safety.

Therapeutic Drug Monitoring in Neonates: What Makes them Unique?

INTRODUCTION: Therapeutic drug monitoring (TDM) refers to the interpretation of quantified drug concentrations in strategically timed samples of bodily fluids, with the aim to maximize therapeutic benefit, while minimizing toxicity. In essence, TDM criteria for neonates are similar to those for adults, but specific issues should be considered. This review focusses on the relevance of these specific issues: larger variability in pharmacokinetics (PK), and non-PK related factors, sampling opportunities, analytical techniques, therapeutic range. Specific issues: Larger variability in PK, and non-PK related factors in neonates compared to adults result in a less clear relation between the administered dose and the concentration measured. Sophisticated dosing regimens derived from population PK-models can partly overcome this variability, thereby reducing the need for TDM. Dosing can be further individualized using Bayesian forecasting as a tool for TDM. Besides PK related factors, concentrations of endogenous substances (e.g. immunoglobulin A, plasma protein) in neonates differ from those in adults, which may complicate interpretation of measured drug concentrations. Blood sampling opportunities in neonates are limited by the small blood volume and the need to minimize painful procedures. Dried blood spot sampling may be less invasive. This method has been facilitated by more sensitive analytical techniques, such as chromatography followed by mass spectrometry. For the same reason, saliva is gaining attention as an alternative non-invasive bodily fluid. Lastly, reference values for therapeutic ranges of drugs in neonates are mostly adapted from adult studies, although pharmacodynamics may be quite different in neonates. This review concludes with recommendations for future research on these specific issues.

Hepatic cyst penetration of cefazolin in patients receiving aspiration sclerotherapy.

BACKGROUND: Hepatic cyst infection is a potentially severe complication in cystic disease. Treatment demands effective antibiotic concentrations within the infected cyst. OBJECTIVES: The aim of this study was to use elective hepatic cyst drainage as a unique pharmacokinetic model to investigate whether cefazolin, a first-generation cephalosporin, is able to penetrate hepatic cysts. PATIENTS AND METHODS: Patients scheduled to undergo percutaneous aspiration sclerotherapy of a symptomatic non-infected, non-neoplastic hepatic cyst were eligible for this study. All participants received a single perioperative prophylactic dose of cefazolin (1000 mg, intravenously). We collected blood and cyst fluid samples to determine total and unbound cefazolin concentrations using HPLC. The primary outcome was hepatic cyst penetration, expressed as the ratio (%) of unbound concentration of cefazolin in cyst fluid to plasma (both in mg/L). RESULTS: We included eight patients [male = 25%, median age = 60 years (IQR 54-75), median estimated glomerular filtration rate = 97 mL/min/1.73 m(2) (IQR 67-102) and median serum albumin = 40 g/L (IQR 37-40)]. We detected low concentrations of unbound cefazolin in cyst fluid (≤1.0 mg/L). The median plasma unbound cefazolin peak level (immediately after cefazolin administration) was 36.6 mg/L (IQR 23.7-54.1) and the level at the time of cyst fluid aspiration was 16.1 mg/L (IQR 13.0-20.1). In total, the hepatic cyst penetration of free cefazolin was only 2.2% (IQR 0.7-5.2). CONCLUSIONS: We developed a study model to investigate the penetration of antibiotics into hepatic cysts. Cefazolin did not reach adequate intracystic concentrations. Future studies should explore alternatives.

Possible effects of repeated exposure to ibuprofen and acetaminophen on the intestinal immune response in young infants.

There has been an exponential increase in the frequency of immune deviations in young children. Consequently, research investigating environmental causes for this increase has become a Public Health priority. We have summarized the experimental observations and epidemiological data that could link repeated acetaminophen and ibuprofen exposure in early infancy to this increase. Recent observations on the maturational immunity of the intestinal sub-mucosal lamina propria underscore indeed the importance of prostaglandins (PGE2s). PGE2 appearing at this sub-mucosal level is a product of arachidonic acid metabolism mediated by type-2 cyclooxygenase (COX-2) situated on the membrane of many immune cells. Moreover, it seems that acetaminophen - like ibuprofen - also carries a non-selective inhibitory action on peripheral COXs, besides its central action. This inhibitory action of acetaminophen on COX2 only relates to physiological, low arachidonic acid concentrations. This explains the difference in anti-inflammatory effects. The impact of repeated inhibition of mucosal PGE2 synthesis due to COX-inhibitor exposure on maturational immunity has been demonstrated in animal experiments. Repeatedly exposed young animals do not develop tolerance to food antigens and exhibit autoimmune deviations. Several recent epidemiological studies have also reported on the magnitude of acetaminophen and ibuprofen exposure in children and the increase in immune deviations, it is important to better understand the potential negative impact of repeated inhibitions of prostaglandin synthesis by COX2s during infancy. Since acetaminophen and ibuprofen are commonly administered analgesics and antipyretics, a well-designed prospective strategy for pharmacovigilance and -epidemiology of COX-inhibitor exposure in infancy is urgently needed.

Postoperative recovery in children after outpatient ENT surgery.

OBJECTIVE: To provide a comprehensive description of postoperative recovery after routine outpatient ENT procedures in children and to compare parental estimations to the child's self-reported ratings of postoperative pain. METHODS: For 14 days after surgery, we monitored pain, nausea or vomiting, problems with eating and fluid intake, sleep disturbances, behavioral changes, emotional impact, other types of discomfort, rehospitalization, and duration to full recovery, based on diary entries and telephone calls. RESULTS: 69 children and their parents participated. After inserting ventilation tubes, the average recovery time was 4.6 days. Symptoms were most intense during the first three days. Participants mainly reported pain, behavioral changes, and emotional impact. After more extensive ENT surgery (adenoidectomy and/or tonsillectomy, with or without insertion of ventilation tubes), the average recovery time was 6.2 days, and pain was more severe and longer-lasting. Apart from nausea or vomiting during the first three days, participants frequently reported behavioral changes, emotional impact, and sleep disturbances. Problems with eating and fluid intake were most prevalent. Pain scores reported by parents differed from the scores reported by their children; parents both underestimated and overestimated their child's pain. CONCLUSION: This study provided descriptions of postoperative recovery after outpatient ENT surgery in children. This information is indispensable for preparing the child and parents and for ensuring accurate follow-up. Recovery varied with the type of surgery. Mainly, postoperative discomfort was most severe after adenoidectomy and/or tonsillectomy. Parents tended to give inaccurate estimates of their child's pain. Self-reports from children should be considered the gold standard.

Prospective Evaluation of a Model-Based Dosing Regimen for Amikacin in Preterm and Term Neonates in Clinical Practice.

Based on a previously derived population pharmacokinetic model, a novel neonatal amikacin dosing regimen was developed. The aim of the current study was to prospectively evaluate this dosing regimen. First, early (before and after second dose) therapeutic drug monitoring (TDM) observations were evaluated for achieving target trough (<3 mg/liter) and peak (>24 mg/liter) levels. Second, all observed TDM concentrations were compared with model-predicted concentrations, whereby the results of a normalized prediction distribution error (NPDE) were considered. Subsequently, Monte Carlo simulations were performed. Finally, remaining causes limiting amikacin predictability (i.e., prescription errors and disease characteristics of outliers) were explored. In 579 neonates (median birth body weight, 2,285 [range, 420 to 4,850] g; postnatal age 2 days [range, 1 to 30 days]; gestational age, 34 weeks [range, 24 to 41 weeks]), 90.5% of the observed early peak levels reached 24 mg/liter, and 60.2% of the trough levels were <3 mg/liter (93.4% ≤5 mg/liter). Observations were accurately predicted by the model without bias, which was confirmed by the NPDE. Monte Carlo simulations showed that peak concentrations of >24 mg/liter were reached at steady state in almost all patients. Trough values of <3 mg/liter at steady state were documented in 78% to 100% and 45% to 96% of simulated cases with and without ibuprofen coadministration, respectively; suboptimal trough levels were found in patients with postnatal age <14 days and current weight of >2,000 g. Prospective evaluation of a model-based neonatal amikacin dosing regimen resulted in optimized peak and trough concentrations in almost all patients. Slightly adapted dosing for patient subgroups with suboptimal trough levels was proposed. This model-based approach improves neonatal dosing individualization.

Neonatal drug therapy: The first frontier of therapeutics for children.

Knowledge about the safe and effective use of medicines in neonates has increased substantially but has resulted in few label changes. Drugs developed for use in adults are reshaped and tailored to specific neonatal indications. However, the use of drugs in neonates should not only mirror adult pharmacotherapy, but should be driven by their own specific needs. Therefore, building collaborative networks may assist to develop a newborn-driven research agenda addressing their clinical needs and diseases.

Cognitive assessment of very low birth weight infants using the Dutch version of the PARCA-R parent questionnaire.

OBJECTIVE: Very low birth weight (VLBW) infants are at an increased risk of long-term cognitive impairment. Early identification and timely interventions are important. We aimed to validate the Dutch version of the revised Parent Report of Children's Abilities (PARCA-R) questionnaire. METHODS: The subjects were survivors from the Belgian participating centers to the NIRTURE trial. As part of a study-related follow-up, PARCA-R was sent out at the age of 2 years. As part of a normal hospital follow-up, these infants were assessed by the Bayley Scales of Infant Development - second edition (BSID-II) at the age of 9, 18 and 36 months. MRI was performed at term in the group of VLBW infants of ZOL Genk as standard care. RESULTS: PARCA-R was sent out to 193 surviving infants. BSID-II was performed in 36% (n=70) at 9 months, in 30% (n=58) at 18 months and in 12% (n=23) at 36 months. MRI was available for 32 infants. We received 86 responses to the PARCA-R. Parent report composite (PRC) scores were significantly correlated with the Mental Development Index (MDI) (p<0.0001 (9 months); p=0.003 (18 months); p=0.01 (36 months)). PRC scores were significantly lower in those with an abnormal MRI (92 vs.124; p=0.04). CONCLUSION: We support the use of the PARCA-R as a time and cost efficient alternative for identifying cognitive delay. PRACTICE IMPLICATIONS: We suggest that the combination of BSID-II, MRI at term and PARCA-R would be the ideal testing method for identifying VLBW infants at risk for cognitive developmental delay by two years of age.

Estradiol and weight are covariates of paracetamol clearance in young women.

AIM: Paracetamol clearance differs between pregnant and non-pregnant women and between women with or without specific oral contraceptives (OCs). However, an association between female sex hormones and paracetamol clearance has never been explored. METHODS: In total, 49 women at delivery, 8 female control subjects without OC use, historical data of 14 women taking OCs, and 15 postpartum observations with and without OCs were pooled to explore covariates of paracetamol clearance. All received a single intravenous 2-gram paracetamol dose, and blood samples were collected up to 6 h after dosing. High-performance liquid chromatography was used to quantify paracetamol. The area under the curve to time infinity (AUC0-∞) was determined and clearance (l/h·m(2)) was calculated by dose/ AUC0-∞. In addition, estradiol and progesterone were quantified by ELISA with electro-chemiluminescence. RESULTS: Median paracetamol clearance at delivery was significantly higher when compared to postpartum or non-pregnant women (11.9 vs. 6.42 and 8.4 l/h·m(2), at least p < 0.05), while an association between paracetamol clearance and estradiol was observed (R = 0.494, p < 0.0001). In non-pregnant subjects, there was no impact of OC exposure on paracetamol clearance. Multiple regression revealed a linear association (Radj = 0.41, p < 0.001) between paracetamol clearance and weight (p = 0.0462) and estradiol (p < 0.0001). CONCLUSION: Estradiol and weight in part explain the variation in paracetamol clearance in young women.