BackgroundPrimary ciliary dyskinesia (PCD) is a rare disorder with variable disease progression. To date, mutations in more than 20 different genes have been found. At present, PCD subtypes are described according to the ultrastructural defect on transmission electron microscopy (TEM) of the motile cilia. PCD with normal ultrastructure (NU) is rarely reported because it requires additional testing. Biallelic mutations in DNAH11 have been described as one cause of PCD with NU.The aim of our study was to describe the clinical characteristics of a large population of patients with PCD, in relation to the ultrastructural defect. Additionally, we aimed to demonstrate the need for biopsy and cell culture to reliably diagnose PCD, especially the NU subtype.MethodsWe retrospectively analyzed data from 206 patients with PCD. We compared the clinical characteristics, lung function, microbiology and imaging results of 68 patients with PCD and NU to those of 90 patients with dynein deficiencies and 41 patients with central pair abnormalities. In addition, we aimed to demonstrate the robustness of the diagnosis of the NU subtype in cell culture by data from genetic analysis.ResultsPCD with NU comprised 33% (68/206) of all patients with PCD. Compared to other subtypes, patients with PCD and NU had a similar frequency of upper and lower respiratory tract problems, as well as similar lung function and imaging. With the currently widely applied approach, without cell culture, the diagnosis would have been missed in 16% (11/68) of patients with NU. Genetic analysis was performed in 29/68 patients with PCD and NU, and biallelic mutations were found in 79% (23/29) of tested patients.ConclusionsWe reported on the clinical characteristics of a large population of patients with PCD and NU. We have shown that systematic performance of biopsy and cell culture increases sensitivity to detect PCD, especially the subtype with NU.PCD with NU has similar clinical characteristics as other PCD types and requires biopsy plus ciliogenesis in culture for optimal diagnostic yield.

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Although the principles of drug disposition also apply in neonates, their specific characteristics warrant focussed assessment. Children display maturation in drug disposition, but this is most prominent in the first year of life. Besides maturational aspects of drug absorption and distribution, maturation mainly relates to (renal) elimination and (hepatic) metabolic clearance. Renal elimination clearance in early life is low and almost completely depends on glomerular filtration. Despite the overall low clearance, interindividual variability is already extensive and can be predicted by covariates like postmenstrual age, postnatal age, co-administration of a non-selective cyclo-oxygenase inhibitor, growth restriction or peripartal asphyxia. These findings are illustrated by observations on amikacin and vancomycin. Variation in phenotypic metabolic clearance is based on constitutional, environmental and genetic characteristics. In early life, it mainly reflects ontogeny, but other covariates may also become relevant. Almost all phase I and phase II metabolic processes display ontogeny in a iso-enzyme specific pattern. The impact of covariates like postmenstrual age, postnatal age, disease state characteristics and polymorphisms are illustrated based or 'probe' drugs (paracetamol, tramadol, propofol) administered as part of their medical treatment in critically ill neonates. The description of a compound specific pattern is beyond compound specific relevance. The maturational patterns described and the extent of the impact of covariates can subsequently be applied to predict in vivo time-concentration profiles for compounds that undergo similar routes of elimination. Through improved predictability, such maturational models can serve to improve both the clinical care and feasibility and safety of clinical studies in neonates.

20 LC-MS/MS 21 Vancomycin 22Tandem mass spectrometry 23Therapeutic drug monitoring 24 Background: Accurate quantification of vancomycin in plasma is important for adequate dose-adjustment.25 As literature suggests between-method differences, our first objective was to develop a novel liquid 26 chromatography-tandem mass spectrometry (LC-MS/MS) method for total vancomycin in human plasma and to 27 compare frequently used immunoassays with this method. Secondly, we investigated the clinical impact of 28 between-method quantification differences.29 Methods: For LC-MS/MS, lithium heparin plasma was extracted by adding a precipitation reagent containing the in-30 ternal standard (vancomycin-des-leucine). Analysis was performed on an Acquity TQD mass spectrometer 31 equipped with an Acquity UPLC 2795 separations module. Our method was analytically validated and compared 32 with four frequently used immunoassays from four different manufacturers. Vancomycin concentrations were 33 clinically classified as toxic, therapeutic and sub-therapeutic. Clinical discordance was calculated using LC-MS/MS 34 as a reference.35 Results: A novel LC-MS/MS method using protein precipitation as sole pretreatment and an analysis time of 5.0 min 36 was developed. The assay had a total imprecision of 2.6-8.5%, a limit of quantification of 0.3 mg/L and an accuracy 37 ranging from 101.4 to 111.2%. Using LC-MS/MS as reference, three immunoassays showed a mean proportional 38 difference within 10% and one showed a substantial mean proportional difference of N 20%. Clinical discordant 39 interpretation of the obtained concentrations ranged from 6.1 to 22.2%. 40 Conclusions: We developed a novel LC-MS/MS method for rapid analysis of total vancomycin concentrations in 41 human plasma. Correlation of the method with immunoassays showed a mean proportional difference N20% for 42 one of the assays, causing discordant clinical interpretation in more than 1 out of 5 samples.Q4 43

AIMA recent report on intravenous (i.v.) paracetamol pharmacokinetics (PK) showed a higher total clearance in women at delivery compared with non-pregnant women. To describe the paracetamol metabolic and elimination routes involved in this increase in clearance, we performed a population PK analysis in women at delivery and post-partum in which the different pathways were considered. METHODSPopulation PK parameters using non-linear mixed effect modelling were estimated in a two-period PK study in women to whom i.v. paracetamol (2 g loading dose followed by 1 g every 6 h up to 24 h) was administered immediately following Caesarean delivery and in a subgroup of the same women to whom single 2 g i.v.loading dose was administered 10-15 weeks post-partum. RESULTSPopulation PK analysis was performed based on 255 plasma and 71 urine samples collected in 39 women at delivery and in eight of these 39 women 12 weeks post-partum. Total clearance was higher in women at delivery compared with 12th post-partum week (21.1 vs. 11.7 l h -1 ) due to higher clearances to paracetamol glucuronide (11.6 vs. 4.76 l h ). In contrast, there was no difference in clearance to paracetamol sulphate. CONCLUSIONThe increased total paracetamol clearance at delivery is caused by a disproportional increase in glucuronidation clearance and a proportional increase in clearance of unchanged paracetamol and in oxidation clearance, of which the latter may potentially limit further dose increase in this patient group. WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• In adults, paracetamol is almost exclusively metabolized by the hepatic route and excreted into urine, with paracetamol glucuronide (47-62%) and paracetamol sulphate (25-36%) as the main metabolites. Between 8-10% of the paracetamol dose is oxidized by cytochrome P450 (CYP2E1) into 3-hydroxy-paracetamol and the toxic metabolite N-acetyl-p-benzoquinone-imine (NAPQI), while only 1-4% is excreted in urine as unchanged paracetamol.• Total clearance of paracetamol appears higher at Caesarean delivery compared with healthy female volunteers but it is unknown which pathways are affected. WHAT THIS STUDY ADDS• Population pharmacokinetic modelling showed a substantially higher paracetamol clearance in women at delivery compared with a subset of the same women 12 weeks post-partum.• The increase in total paracetamol clearance at delivery is due to a disproportional increase in glucuronidation clearance and a proportional increase in clearance of unchanged paracetamol and in oxidation clearance.• Compared with modelling based on metabolite fractions retrieved in urine only, population modelling based on both plasma and urine collections was of added value to gain insight into how different metabolic pathways of paracetamol contribute to changes in total clearance.

Neurovascular coupling refers to the mechanism that links the transient neural activity to the subsequent change in cerebral blood flow, which is regulated by both chemical signals and mechanical effects. Recent studies suggest that neurovascular coupling in neonates and preterm born infants is different compared to adults. The hemodynamic response after a stimulus is later and less pronounced and the stimulus might even result in a negative (hypoxic) signal. In addition, studies both in animals and neonates confirm the presence of a short hypoxic period after a stimulus in preterm infants. In clinical practice, different methodologies exist to study neurovascular coupling. The combination of functional magnetic resonance imaging or functional near-infrared spectroscopy (brain hemodynamics) with EEG (brain function) is most commonly used in neonates. Especially near-infrared spectroscopy is of interest, since it is a non-invasive method that can be integrated easily in clinical care and is able to provide results concerning longer periods of time. Therefore, near-infrared spectroscopy can be used to develop a continuous non-invasive measurement system, that could be used to study neonates in different clinical settings, or neonates with different pathologies. The main challenge for the development of a continuous marker for neurovascular coupling is how the coupling between the signals can be described. In practice, a wide range of signal interaction measures exist. Moreover, biomedical signals often operate on different time scales. In a more general setting, other variables also have to be taken into account, such as oxygen saturation, carbon dioxide and blood pressure in order to describe neurovascular coupling in a concise manner. Recently, new mathematical techniques were developed to give an answer to these questions. This review discusses these recent developments.

Renal precision medicine in neonates is useful to support decision making on pharmacotherapy, signal detection of adverse (drug) events, and individual prediction of short- and long-term prognosis. To estimate kidney function or glomerular filtration rate (GFR), the most commonly measured and readily accessible biomarker is serum creatinine (S cr ). However, there is extensive variability in S cr observations and GFR estimates within the neonatal population, because of developmental physiology and superimposed pathology. Furthermore, assay related differences still matter for S cr , but also exist for Cystatin C. Observations in extreme low birth weight (ELBW) and term asphyxiated neonates will illustrate how renal precision medicine contributes to neonatal precision medicine. When the Kidney Disease Improving Global Outcome (KDIGO) definition of acute kidney injury (AKI) is used, this results in an incidence up to 50% in ELBW neonates, associated with increased mortality and morbidity. However, urine output criteria needed adaptations to broader time intervals or weight trends, while S cr and its trends do not provide sufficient detail on kidney function between ELBW neonates. Instead, we suggest to use assay-specific centile S cr values to better describe postnatal trends and have illustrated its relevance by quantifying an adverse drug event (ibuprofen) and by explaining individual amikacin clearance. Term asphyxiated neonates also commonly display AKI. While oliguria is a specific AKI indicator, the majority of term asphyxiated cases are non-oliguric. Asphyxia results in a clinical significant—commonly transient—mean GFR decrease (−50%) with a lower renal drug elimination. But there is still major (unexplained) inter-individual variability in GFR and subsequent renal drug elimination between these asphyxiated neonates. Recently, the Baby-NINJA (nephrotoxic injury negated by just-in-time action) study provided evidence on the concept that a focus on nephrotoxic injury negation has a significant impact on AKI incidence and severity. It is hereby important to realize that follow-up should not be discontinued at discharge, as there are concerns about long-term renal outcome. These illustrations suggest that integration of renal (patho)physiology into neonatal precision medicine are an important tool to improve contemporary neonatal care, not only for the short-term but also with a positive health impact throughout life.

Drug dosing in infants should be based on their physiological characteristics and the pharmacokinetic and -dynamic profile of the compound. Since maturational physiological changes are most prominent in infancy, variability is the key feature of clinical pharmacology in infancy: developmental physiology drives developmental pharmacology. This is illustrated by the link between renal physiology and renal drug clearance and between hepatic physiology and hepatic drug elimination for some specific compounds. However, the maturational profiles of the individual elimination processes differ substantially at the enzyme and transporter level. This implies that it is important to integrate all ontogeny-related knowledge of the different elimination routes to predict compound specific, phenotypic in vivo observations of infancy. In addition to the introduction of already available in vivo observations to validate mechanistic (estimated to in vivo observations) or physiology based pharmacokinetic (PBPK, developmental physiology related estimated to in vivo observations) models, a simultaneous use of both approaches (mechanistic and PBPK) to search for discrepancies between both approaches may also unveil 'missing' links in maturational physiology or clinical pharmacology (e.g. ontogeny renal or hepatic drug transporters): developmental pharmacology drives developmental pharmacology.