Anne Smits

Primary ciliary dyskinesia: critical evaluation of clinical symptoms and diagnosis in patients with normal and abnormal ultrastructure

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.

Physiologically Based Pharmacokinetic Modeling in Pediatric Drug Development: A Clinician’s Request for a More Integrated Approach

1 Neonatal Intensive Care Unit, Division of Woman and Child, University Hospitals Leuven, Herestraat 49, 3000 Leuven, Belgium 2 Division of Pediatric Clinical Pharmacology, Children’s National Medical Center, Washington, DC, USA 3 Departments of Pediatrics, Pharmacology, and Physiology, The School of Medicine and Health Sciences George Washington University, Washington, DC, USA 4 Intensive Care Ward, Erasmus MC-Sophia Children’s Hospital, Rotterdam, The Netherlands

Novel LC–MS/MS method for plasma vancomycin: Comparison with immunoassays and clinical impact

BACKGROUND Accurate quantification of vancomycin in plasma is important for adequate dose-adjustment. As literature suggests between-method differences, our first objective was to develop a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for total vancomycin in human plasma and to compare frequently used immunoassays with this method. Secondly, we investigated the clinical impact of between-method quantification differences. METHODS For LC-MS/MS, lithium heparin plasma was extracted by adding a precipitation reagent containing the internal standard (vancomycin-des-leucine). Analysis was performed on an Acquity TQD mass spectrometer equipped with an Acquity UPLC 2795 separations module. Our method was analytically validated and compared with four frequently used immunoassays from four different manufacturers. Vancomycin concentrations were clinically classified as toxic, therapeutic and sub-therapeutic. Clinical discordance was calculated using LC-MS/MS as a reference. RESULTS A novel LC-MS/MS method using protein precipitation as sole pretreatment and an analysis time of 5.0 min 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 ranging from 101.4 to 111.2%. Using LC-MS/MS as reference, three immunoassays showed a mean proportional difference within 10% and one showed a substantial mean proportional difference of >20%. Clinical discordant interpretation of the obtained concentrations ranged from 6.1 to 22.2%. CONCLUSIONS We developed a novel LC-MS/MS method for rapid analysis of total vancomycin concentrations in human plasma. Correlation of the method with immunoassays showed a mean proportional difference >20% for one of the assays, causing discordant clinical interpretation in more than 1 out of 5 samples.

Pharmacokinetics of paracetamol and its metabolites in women at delivery and post‐partum

AIM A 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. METHODS Population 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. RESULTS Population 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⁻¹), to oxidative metabolites (4.95 vs. 2.77 l h⁻¹) and of unchanged paracetamol (1.15 vs. 0.75 l h⁻¹). In contrast, there was no difference in clearance to paracetamol sulphate. CONCLUSION The 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.

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

ABSTRACT 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.

Prospective validation of neonatal vancomycin dosing regimens is urgently needed

Background Although vancomycin is frequently used to treat neonatal late-onset sepsis, there is no consensus on the optimal dosing regimen. Because many neonates needed dosing adaptation due to suboptimal trough values, the vancomycin dosing regimen in our neonatal department was changed during 2012. Objective We aimed to document the need for validation of neonatal vancomycin dosing by exploring serum trough levels achieved using 2 published dosing regimens (previous regimen: based on postmenstrual age and serum creatinine and new regimen: based on postmenstrual age and postnatal age) and to identify covariates associated with suboptimal vancomycin trough levels (<10 mg/L). Methods Routine therapeutic drug monitoring serum trough levels quantified after initiation of intravenous vancomycin therapy and clinical covariates were retrospectively collected. Median vancomycin trough levels of both dosing regimens were compared using the Mann-Whitney U test. The influence of continuous and dichotomous covariates on achieving a suboptimal trough level was explored using the Van Elteren test (stratified Mann-Whitney U test) and Mantel-Haenszel test (stratified χ2 test), respectively. Covariates significant in monovariate analysis were subsequently included in a logistic regression analysis. Results In total, 294 observations (median current weight 1870 g [range = 420–4863 g] and median postmenstrual age 35.07 weeks [range = 25.14–56.00 weeks]) were included. Using the previous and new dosing regimens, 66.3% and 76.2% of trough levels, respectively, were below 10 mg/L. Overall, suboptimal vancomycin trough values were significantly associated with lower weight (birth weight and current weight) and age (gestational age and postmenstrual age). Conclusions The majority of vancomycin trough levels in neonates achieved using 2 published dosing regimens did not reach the target of 10 mg/L. This illustrates the urgent need for prospective validation of neonatal vancomycin dosing regimens. We anticipate that dosing regimens integrating covariates reflecting general physiological maturation and renal maturation, as well as disease characteristics, could improve vancomycin exposure in neonates.

Propofol Dose-Finding to Reach Optimal Effect for (Semi-)Elective Intubation in Neonates

OBJECTIVE To define the effective dose for 50% of patients (ED50) of propofol for successful intubation and to determine the rate of successful extubation in those patients with planned intubation, surfactant administration, and immediate extubation (INSURE procedure). In addition, pharmacodynamic effects were assessed. STUDY DESIGN Neonates (n = 50) treated with propofol for (semi-)elective endotracheal intubation were stratified in 8 strata by postmenstrual and postnatal age. The first patient in each stratum received an intravenous bolus of 1 mg/kg propofol. Dosing for the next patient was determined using the up-and-down method. A propofol ED50 dose was calculated in each stratum with an effective sample size of at least 6, via the Dixon-Masey method, with simultaneous assessment of clinical scores and continuous vital sign monitoring. RESULTS Propofol ED50 values for preterm neonates <10 days of age varied between 0.713 and 1.350 mg/kg. Clinical recovery was not attained at the end of the 21-minute scoring period. Mean arterial blood pressure showed a median decrease between 28.5% and 39.1% from baseline with a brief decrease in peripheral and regional cerebral oxygen saturation. Variability in mean arterial blood pressure area under the curve could not be explained by weight or age. CONCLUSIONS Low propofol doses were sufficient to sedate neonates for intubation. Clinical recovery was accompanied by permissive hypotension (no clinical shock and no treatment). The propofol ED50 doses can be administered at induction, with subsequent up-titration if needed, while monitoring blood pressure. They can be used for further dosing optimalization and validation studies. TRIAL REGISTRATION ClinicalTrials.gov: NCT01621373; EudraCT: 2012-002648-26.

Population pharmacokinetic modelling of total and unbound cefazolin plasma concentrations as a guide for dosing in preterm and term neonates

OBJECTIVES Cefazolin is frequently administered for antimicrobial prophylaxis and treatment of infections. In neonates, pharmacokinetic observations are limited and dosing regimens variable. The aim of this study was to describe the pharmacokinetics of cefazolin in neonates based on total and unbound concentrations to optimize cefazolin dosing. METHODS Thirty-six neonates [median birth body weight 2720 (range 540-4200) g, current body weight (cBW) 2755 (830-4200) g and postnatal age (PNA) 9 (1-30) days] receiving intravenous cefazolin (50 mg/kg/8 h) were included. Based on 119 total and unbound plasma concentrations, a population pharmacokinetic analysis with a covariate analysis was performed. Monte Carlo simulations were performed aiming for unbound concentrations above an MIC of 8 mg/L (>60% of the time) in all patients. RESULTS A one-compartment pharmacokinetic model was developed in which total and unbound concentrations were linked by maximum protein binding (Bmax) of 136 mg/L and a dissociation constant (KD) for cefazolin protein binding of 46.5 mg/L. cBW was identified as covariate for volume of distribution (V), bBW and PNA for clearance and albumin plasma concentration for Bmax, explaining 50%, 58% and 41% of inter-individual variability in V, clearance and Bmax, respectively. Based on Monte Carlo simulations, a body weight- and PNA-adapted dosing regimen that resulted in similar exposure across different weight and age groups was proposed. CONCLUSIONS A neonatal pharmacokinetic model taking into account total and unbound cefazolin concentrations with saturable plasma protein binding was identified. As cBW and PNA were the most important covariates, these may be used for individualized dosing in neonates.

Factors Impacting Unbound Vancomycin Concentrations in Different Patient Populations

ABSTRACT The unbound drug hypothesis states that only unbound drug concentrations are active and available for clearance, and highly variable results regarding unbound vancomycin fractions have been reported in the literature. We have determined the unbound vancomycin fractions in four different patient groups by a liquid chromatography tandem mass spectrometry (LC-MS/MS) method and identified factors that modulate vancomycin binding. We have further developed and validated a prediction model to estimate unbound vancomycin concentrations. Vancomycin (unbound and total) concentrations were measured in 90 patients in four different hospital wards (hematology [n = 33 samples], intensive care unit [ICU] [n = 51], orthopedics [n = 44], and pediatrics [age range, 6 months to 14 years; n = 18]) by a validated LC-MS/MS method. Multiple linear mixed model analysis was performed to identify patient variables that were predictive of unbound vancomycin fractions and concentrations. The variables included in the model were patient age, ward, number of coadministered drugs with high protein binding, kidney function (estimated glomerular filtration rate [determined by Chronic Kidney Disease Epidemiology Collaboration formula]), alpha-1-acid glycoprotein, albumin, total bilirubin, IgA, IgM, urea, and total vancomycin concentrations. In the pediatric cohort, the median unbound vancomycin fraction was 81.3% (range, 61.9 to 95.9%), which was significantly higher (P < 0.01) than the unbound fraction found in the three adult patient cohorts (hematology, 60.6% [48.7 to 90.6%]; ICU, 61.7% [47.0 to 87.6%]; orthopedics, 56.4% [45.9 to 78.0%]). The strongest significant predictor of the unbound vancomycin concentration was the total drug concentration, completed by albumin in the pediatric cohort and albumin and IgA in the adult cohorts. Validation of our model was performed with data from 13 adult patients. A mean difference of 0.3 mg/liter (95% confidence interval [CI], −1.3 to 0.7 mg/liter; R2 = 0.99 [95% CI, 0.95 to 0.99]) between measured and calculated unbound vancomycin concentrations demonstrated that the predictive performance of our model was favorable. Unbound vancomycin fractions vary significantly between pediatric and adult patients. We developed a formula to estimate the unbound fraction derived from total vancomycin, albumin, and IgA concentrations in adult patients.

Enzymatic isotope dilution mass spectrometry (IDMS) traceable serum creatinine is preferable over Jaffe in neonates and young infants

*Corresponding author: Karel Allegaert, MD PhD, Neonatal Intensive Care Unit, University Hospitals Leuven, Herestraat 49, 3000 Leuven, Belgium, Phone: + 32 16 343850, Fax: + 32 16 343209, E-mail: karel.allegaert@uzleuven.be Steven Pauwels and Pieter Vermeersch: Clinical Department of Laboratory Medicine, University Hospitals Leuven, Belgium ; and Department of Cardiovascular Sciences, KU Leuven, Belgium Anne Smits and Kaat Cr e vecoeur: Neonatal Intensive Care Unit, University Hospitals Leuven, Leuven, Belgium ; and Department of Development and Regeneration, KU Leuven, Belgium John van den Anker: Division of Pediatric Clinical Pharmacology, Children ’ s National Medical Center, Washington, DC, USA ; Departments of Pediatrics, Pharmacology and Physiology, George Washington University School of Medicine and Health Sciences, Washington, DC, USA ; and Pediatric Intensive Care, Erasmus MC Sophia Children ’ s Hospital, Rotterdam, The Netherlands Djalila Mekahli: Department of Development and Regeneration, KU Leuven, Belgium ; and Department of Paediatric Nephrology, University Hospitals Leuven, Leuven, Belgium