Amikacin clearance, reflecting the GFR in neonates, can be predicted by birthweight representing the antenatal state of maturation of the kidney, postnatal age representing postnatal maturation, and co-administration of ibuprofen. Finally, the model reflects maturation of the GFR, allowing for adjustments of dosing regimens for other renally excreted drugs in preterm and term neonates.

Elevated levels of extracellular glutamate cause excitotoxic oligodendrocyte cell death and contribute to progressive oligodendrocyte loss and demyelination in white matter disorders such as multiple sclerosis and periventricular leukomalacia. However, the mechanism by which glutamate homeostasis is altered in such conditions remains elusive. We show here that microglial cells, in their activated state, compromise glutamate homeostasis in cultured oligodendrocytes. Both activated and resting microglial cells release glutamate by the cystine-glutamate antiporter system xc−. In addition, activated microglial cells act to block glutamate transporters in oligodendrocytes, leading to a net increase in extracellular glutamate and subsequent oligodendrocyte death. The blocking of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors or the system xc− antiporter prevented the oligodendrocyte injury produced by exposure to LPS-activated microglial cells in mixed glial cultures. In a whole-mount rat optic nerve, LPS exposure produced wide-spread oligodendrocyte injury that was prevented by AMPA/kainate receptor block and greatly reduced by a system xc− antiporter block. The cell death was typified by swelling and disruption of mitochondria, a feature that was not found in closely associated axonal mitochondria. Our results reveal a novel mechanism by which reactive microglia can contribute to altering glutamate homeostasis and to the pathogenesis of white matter disorders.

Purpose Since glomerular filtration rate (GFR) is responsible for the elimination of a large number of water-soluble drugs, the aim of this study was to develop a semi-physiological function for GFR maturation from neonates to adults. Methods In the pharmacokinetic analysis (NONMEM VI) based on data of gentamicin, tobramycin and vancomycin collected in 1,760 patients (age 1 day–18 years, bodyweight 415 g–85 kg), a distinction was made between drug-specific and system-specific information. Since the maturational model for clearance is considered to contain system-specific information on the developmental changes in GFR, one GFR maturational function was derived for all three drugs. Results Simultaneous analysis of these three drugs showed that maturation of GFR mediated clearance from preterm neonates to adults was best described by a bodyweight-dependent exponent (BDE) function with an exponent varying from 1.4 in neonates to 1.0 in adults (ClGFR = Cldrug*(BW/4 kg)BDE with BDE = 2.23*BW−0.065). Population clearance values (Cldrug) for gentamicin, tobramycin and vancomycin were 0.21, 0.28 and 0.39 L/h for a full term neonate of 4 kg, respectively. Discussion Based on an integrated analysis of gentamicin, tobramycin and vancomycin, a semi-physiological function for GFR mediated clearance was derived that can potentially be used to establish evidence based dosing regimens of renally excreted drugs in children.

Purpose Recently, a covariate model characterizing developmental changes in clearance of amikacin in neonates has been developed using birth bodyweight and postnatal age. The aim of this study was to evaluate whether this covariate model can be used to predict maturation in clearance of other renally excreted drugs. Methods Five different neonatal datasets were available on netilmicin, vancomycin, tobramycin and gentamicin. The extensively validated covariate model for amikacin clearance was used to predict clearance of these drugs. In addition, independent reference models were developed based on a systematic covariate analysis. Results The descriptive and predictive properties of the models developed using the amikacin covariate model were good, and fairly similar to the independent reference models (goodness-of-fit plots, NPDE). Moreover, similar clearance values were obtained for both approaches. Finally, the same covariates as in the covariate model of amikacin, i.e. birth bodyweight and postnatal age, were identified on clearance in the independent reference models. Conclusions This study shows that pediatric covariate models may contain physiological information since information derived from one drug can be used to describe other drugs. This semi-physiological approach may be used to optimize sparse data analysis and to derive individualized dosing algorithms for drugs in children.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• Despite its increased use, the pharmacokinetics (PK) of mycophenolic acid (MPA) and the relationship between dose, plasma concentration and exposure are poorly understood, especially in children.• The PK of MPA are associated with high inter-and intra-individual variability.• MPA and its metabolites, like the inactive 7-O-MPA-b-glucuronide (MPAG) undergo enterohepatic circulation (EHC), which can contribute to an increase in exposure to MPA of 40% (range 10-60%). WHAT THIS STUDY ADDS• Thisis the first report of MPA PK in adolescents with childhood-onset systemic lupus erythematosus (cSLE).• The proposed final population PK model successfully incorporates the physiological aspects associated with MPA disposition, which includes MPA and its main metabolite MPAG, and adequately reflects the complex processes of absorption and enterohepatic circulation associated with mycophenolate mofetil (MMF) oral dosing in patients with cSLE.• This model provides a basis for further development of a model-based Bayesian estimator for individualized MPA dosing in paediatric patients treated for cSLE. AIMThis study aimed to develop a population pharmacokinetic (PK) enterohepatic recycling model for MPA in patients with childhood-onset systemic lupus erythematosus (cSLE). METHODSMPA concentration-time data were from outpatients on stable oral mycophenolate mofetil (MMF) and collected under fasting conditions, with standardized meals (1 and 4 h post-dose). Sampling times were pre-dose, 20, 40 min, 1, 1.5, 2, 3, 4, 6 and 9 h, post dose. The population PK analysis simultaneously modelled MPA and 7-O-MPA-b-glucuronide (MPAG) concentrations using nonlinear mixed effect modelling. RESULTSPK analysis included 186 MPA and MPAG concentrations (mg l -1) from 19 patients. cSLE patients, age range 10-28 years, median 16.5 years were included. Mean Ϯ SD disease duration was 3.8 Ϯ 3.7 years. The final PK model included a gallbladder compartment for enterohepatic recycling and bile release time related to meal times, with first order absorption and single series of transit compartments. The PK estimates for MPA were CL1/F 25