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.