Creatinine reference values in ELBW infants: impact of quantification by Jaffe or enzymatic method

Population pharmacokinetics and dose rationale for aciclovir in term and pre-term neonates with herpes

Aciclovir is considered the first-line treatment against Herpes simplex virus (HSV) infections in new-borns and infants. As renal excretion is the major route of elimination, in renally-impaired patients, aciclovir doses are adjusted according to the degree of impairment. However, limited attention has been given to the implications of immature renal function or dysfunction due to the viral disease itself. The aim of this investigation was to characterize the pharmacokinetics of aciclovir taking into account maturation and disease processes in the neonatal population. Pharmacokinetic data obtained from 2 previously published clinical trials (n = 28) were analyzed using a nonlinear mixed effects modeling approach. Post-menstrual age (PMA) and creatinine clearance (CLCR) were assessed as descriptors of maturation and renal function. Simulation scenarios were also implemented to illustrate the use of pharmacokinetic data to extrapolate efficacy from adults. Aciclovir pharmacokinetics was described by a one-compartment model with first-order elimination. Body weight and diagnosis (systemic infection) were statistically significant covariates on the volume of distribution, whereas body weight, CLCR and PMA had a significant effect on clearance. Median clearance varied from 0.2 to 1.0 L/h in subjects with PMA <34 or ≥34 weeks, respectively. Population estimate for volume of distribution was 1.93 L with systemic infection increasing this value by almost 3-fold (2.67 times higher). A suitable model parameterization was identified, which discriminates the effects of developmental growth, maturation, and organ function. Exposure to aciclovir was found to increase with decreasing PMA and renal function (CLCR), suggesting different dosing requirement for pre-term neonates.

Duration of Simultaneous Exposure to High-Risk and Lower-Risk Nephrotoxic Antimicrobials in the Neonatal Intensive Care Unit (NICU) and Future Adolescent Kidney Health

OBJECTIVE

To determine whether greater duration of simultaneous exposure to antimicrobials with high nephrotoxicity risk combined with lower-risk antimicrobials (simultaneous exposure) in the neonatal intensive care unit (NICU) is associated with worse later kidney health in adolescents born preterm with very low birth weight (VLBW).

STUDY DESIGN

Prospective cohort study of participants born preterm with VLBW (<1500 g) as singletons between January 1, 1992, and June 30, 1996. We defined simultaneous exposure as a high-risk antimicrobial, such as vancomycin, administered with a lower-risk antimicrobial on the same date in the NICU. Outcomes were serum creatinine, estimated glomerular filtration rate (eGFR), and first-morning urine albumin-creatinine ratio (ACR) at age 14 years. We fit multivariable linear regression models with days of simultaneous exposure and days of nonsimultaneous exposure as main effects, adjusting for gestational age, birth weight, and birth weight z-score.

RESULTS

Of the 147 out of 177 participants who had exposure data, 97% received simultaneous antimicrobials for mean duration 7.2 days (SD 5.6). No participant had eGFR <90 ml/min/1.73 m2. The mean ACR was 15.2 mg/g (SD 38.7) and 7% had albuminuria (ACR >30 mg/g). Each day of simultaneous exposure was associated only with a 1.04-mg/g higher ACR (95% CI 1.01 to 1.06).

CONCLUSIONS

Despite frequent simultaneous exposure to high-risk combined with lower-risk nephrotoxic antimicrobials in the NICU, there were no clinically relevant associations with worse kidney health identified in adolescence. Although future studies are needed, these findings may provide reassurance in a population thought to be at increased risk of chronic kidney disease.

Characterizing dynamics of serum creatinine and creatinine clearance in extremely low birth weight neonates during the first 6 weeks of life

BACKGROUND

Characterizing the dynamics of serum creatinine concentrations (Scr) and associated creatinine clearance (CLcr) as a measure of kidney function in extremely low birth weight (≤ 1000 g; ELBW) neonates remains challenging.

METHODS

We performed a retrospective study that included longitudinal Scr (enzymatic assay) data from 148 ELBW neonates up to 6 weeks after birth. Change of Scr and inter-individual variability was characterized with nonlinear mixed-effect modeling. Key covariates such as gestational age (GA), mode of delivery (MOD), and treatment with ibuprofen or inotropic agents were investigated.

RESULTS

A total of 2814 Scr concentrations were analyzed. GA was associated with Scr at birth (higher with advancing GA), and GA and MOD showed an association with postnatal maturation of CLcr (faster clearance increase with advancing GA and after C-section). Small CLcr decrease (≤ 5%) was quantified during ibuprofen treatment. For a GA of 27 weeks, mean Scr (estimated CLcr) at birth was 0.61 mg/dl (0.23 ml/min), increasing to 0.87 mg/dl (0.27 ml/min) at day three, and decreasing to 0.36 mg/dl (0.67 ml/min) at day 42 after birth.

CONCLUSIONS

We report the first mathematical model able to characterize Scr and CLcr in ELBW neonates during the first 6 weeks of life in a quantitative manner as a function of GA, MOD, and ibuprofen treatment. This model allows the derivation of GA-adjusted reference ranges for ELBW neonates and provides a rationale for normative Scr concentrations, and as such will help clinicians to further optimize monitoring and treatment decisions in this vulnerable patient population.

Exposure to an Extended-Interval, High-Dose Gentamicin Regimen in the Neonatal Period Is Not Associated With Long-Term Nephrotoxicity

Objectives: To assess the association between gentamicin exposure and subclinical signs of nephrotoxicity in school children who were exposed to a high-dose gentamicin regimen in the neonatal period. Methods: Children receiving three or more doses (6 mg/kg) of gentamicin as neonates were invited to a follow-up in school age. We evaluated potential signs of subclinical nephrotoxicity with four validated urine biomarkers: protein-creatinine ratio (PCR), albumin-creatinine ratio (ACR), kidney injury molecule-1 (KIM-1), and N-acetyl-beta-D-glucosaminidase (NAG) normalized for urine creatinine (NAG-Cr). In addition, blood pressure was measured. The measures of gentamicin exposure were cumulative dose (mg/kg) and highest trough plasma concentration (TPC) in mg/L. We used logistic and linear regression and non-parametric kernel regression to analyze the relationship between gentamicin exposure and the urine biomarkers. Results: A total of 222 gentamicin exposed children were included. As neonates, the children were exposed to a median (interquartile range-IQR) cumulative gentamicin dose of 36 (26-42) mg/kg and the median (IQR) TPC was 1.0 (0.7-1.3) mg/L. At follow-up, 15 children (6.8%) had either one abnormal urine biomarker value (13 children) or two abnormal urine biomarker values (2 children). These 17 biomarker values were all marginally above the suggested upper cutoff, and included the following markers; KIM-1 (n = 2), NAC-Cr (n = 5), ACR (n = 6), and PCR (n = 4). All other 207 children had normal sets of all four urine biomarkers. One child had hypertension. There were no differences in gentamicin exposure, gestational age (GA) at birth or birth weight between the group of 15 children with one or two abnormal urine biomarker values compared to the other 207 children who had normal biomarker values. Using different regression analyses, we did not find any association between gentamicin exposure (cumulative dose and/or TPC) and the urine biomarker values. Conclusions: Exposure to an extended-interval, high-dose gentamicin regimen in the neonatal period was not associated with signs of subclinical nephrotoxicity in schoolchildren. We therefore suggest that the gentamicin treatment regimen evaluated in this study is safe in terms of long-term nephrotoxicity. Clinical Trial Registration: ClinicalTrials.gov, identifier: NCT03253614.

Measurement of serum creatinine levels with liquid chromatography-tandem mass spectrometry: comparison with Jaffe and enzymatic methods

Objectives

Our aim was to validate a mass spectrometric creatinine method and compare this method with Jaffe and enzymatic serum creatinine methods.

Methods

90 samples were included. The levels were classified into three groups according to serum creatinine results as Group 1: Lower (n=30) (0.16–0.59 mg/dL), Group 2: Normal (n=30) (0.62–1.18 mg/dL) and Group 3: Higher (n=30) (1.33–3.88 mg/dL). Jaffe and enzymatic creatinine measurements were performed on the Beckman Coulter AU5800 autoanalyzer.

Results

Serum creatinine was linear from 0.039 up to 10 mg/dL, CV and bias values were ranged between 1.9–3.8% and 2–15%. Correlation coefficients were 0.990 (95% confidence interval 0.984–0.993), 0.992 (95% confidence interval 0.988–0.995) and 0.994 (95% confidence interval 0.991–0.996) for LC-MS/MS-Enzymatic, LC-MS/MS-Jaffe and Enzymatic-Jaffe, respectively.

Conclusions

Although, Jaffe method for serum creatinine measurement is still much more practical and cheap, so in use for routine practice, tandem mass spectrometric detection of serum creatinine can be used as an accurate and specific method for verification of discordant clinical results, existence of possible interferences and serum levels under 0.5 mg/dL creatinine results such as pediatric or pregnant populations.

Population Pharmacokinetics of Teicoplanin in Preterm and Term Neonates: Is It Time for a New Dosing Regimen?

Our objective was to develop a population pharmacokinetic (PK) model in order to evaluate the currently recommended dosing regimen in term and preterm neonates. By using an optimal design approach, a prospective PK study was designed and implemented in 60 neonates with postmenstrual ages (PMA) of 26 to 43 weeks. A loading dose of 16 mg/kg was administered at day 1, followed by a maintenance dose of 8 mg/kg daily. Plasma concentrations were quantified by high-pressure liquid chromatography-mass spectrometry. Population PK (popPK) analysis was performed using NONMEM software. Monte-Carlo (MC) simulations were performed to evaluate currently recommended dosing based on a pharmacodynamic index of area under the concentration-time curve (AUC)/MIC ratio of ≥400. A two-compartment model with linear elimination best described the data by the following equations: clearance (CL) = 0.0227 × (weight [wt]/1,765)^0.75 × (estimated creatinine clearance [eCRCL]/22)^0.672, central compartment volume of distribution (V1) = 0.283 (wt/1,765), intercompartmental clearance (Q) = 0.151 (wt/1,765)^0.75, and peripheral compartment volume (V2) = 0.541 (wt/1,765). The interindividual variability estimates for CL, V1, and V2 were 36.5%, 45.7%, and 51.4%, respectively. Current weight (wt) and estimated creatinine clearance (eCRCL) significantly explained the observed variability. MC simulation demonstrated that, with the current dosing regimen, an AUC/MIC ratio of ≥400 was reached by only 68.5% of neonates with wt of <1 kg when the MIC was equal to 1 mg/kg, versus 82.2%, 89.7%, and 92.7% of neonates with wt of 1 to <2, 2 to <3, or ≥3 kg, respectively. Augmentation of a maintenance dose up to 10 or 11 mg/kg for preterm neonates with wt of 1 to <2 or <1 kg, respectively, increases the probability of reaching the therapeutic target; the recommended doses seem to be adequate for neonates with wt of ≥2 kg. Teicoplanin PK are variable in neonates, with wt and eCRCL having the most significant impact. Neonates with wt of <2 kg need higher doses, especially for Staphylococcus spp. with an MIC value of ≥1 mg/liter.

Renal Precision Medicine in Neonates and Acute Kidney Injury: How to Convert a Cloud of Creatinine Observations to Support Clinical Decisions

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.

Pharmacokinetic modelling and Bayesian estimation-assisted decision tools to optimize vancomycin dosage in neonates: only one piece of the puzzle

Introduction: Vancomycin is commonly administered to neonates, while observational data on therapeutic drug monitoring (TDM, trough levels) suggest that vancomycin exposure and dosage remain substandard. Area covered: Data on vancomycin pharmacokinetics (PK) and its covariates are abundant. Consequently, modeling is an obvious tool to improve targeted exposure, with a shift from TDM trough levels to area under the curve (AUC_24h) targets, as in adults. Continuous administration appeared as a practice to facilitate AUC_24h target attainment, while Bayesian model-supported targeting emerged as a novel tool. However, the AUC_24h/MIC (minimal inhibitory concentration) target itself should consider neonate-specific aspects (bloodstream infections, coagulase-negative staphylococci, protein binding, underexplored causes of variability, like assays, preparation and administration inaccuracies, or missing covariates). Expert opinion: To improve targeted exposure in neonates, initial vancomycin prescription should be based on 'a priori model-based individual dosing' using validated dosing regimens, followed by further tailoring by dosing optimization applying Bayesian estimation-assisted TDM. Future research should focus on the feasibility to integrate these tools (individualized dosing, Bayesian models) in clinical practice, and to perform PK/PD studies in the relevant animal models and human neonatal setting (coagulase-negative staphylococci, bloodstream infections).

Caffeine exposure and acute kidney injury in premature infants with necrotizing enterocolitis and spontaneous intestinal perforation

BACKGROUND

Acute kidney injury (AKI) is common in preterm infants, but specific therapies remain scarce. Recent studies have demonstrated an association between caffeine exposure and less frequent AKI in the first 7-10 days after birth. We hypothesized that patients with necrotizing enterocolitis (NEC) and spontaneous intestinal perforation (SIP) would provide a better natural model of AKI to evaluate this association.

METHODS

We reviewed all premature patients diagnosed with NEC or SIP at our institution from 2008 to 2014. AKI was defined by change in serum creatinine using the neonatal Kidney Disease: Improving Global Outcomes definition. Caffeine was prescribed for apnea of prematurity and caffeine exposure was determined by chart review.

RESULTS

A total of 146 patients with NEC/SIP were reviewed. Of these, 119 (81.5%) received caffeine, and 91 (62.3%) developed AKI. AKI occurred less frequently in patients who received caffeine than in those who did not (55.5% vs. 92.6%; odds ratio (OR) 0.10; 95% confidence interval (CI) 0.02-0.44). This association persisted in multivariable models after adjustment for potential confounders (adjusted OR 0.08; 95% CI 0.01-0.42; number needed to be exposed to caffeine to prevent one case of AKI = 2.6). Although baseline serum creatinine did not differ by caffeine exposure, patients receiving caffeine had lower peak creatinine (median 1.0 mg/dl vs. 1.5 mg/dl; p = 0.008) and absolute creatinine change (median 0.42 mg/dl vs. 0.68 mg/dl; p = 0.003) than those who did not.

CONCLUSIONS

Caffeine exposure in preterm infants with NEC/SIP is associated with decreased incidence and severity of AKI.

Renal Clearance in Newborns and Infants: Predictive Performance of Population-Based Modeling for Drug Development

The objective of this study was to evaluate the predictive performance of population models to predict renal clearance in newborns and infants. Pharmacokinetic (PK) data from eight drugs in 788 newborns and infants were used to evaluate the predictive performance of the population models based on postmenstrual age (PMA), postnatal age, gestational age, and body weight. For the PMA model, the average fold error for clearance (CL)_predicted /CL_observed was within a twofold range for each drug in all subgroups. For drugs with > 90% renal elimination, the prediction bias ranged from 0.7-1.3. For drugs with 60-80% renal elimination, the prediction bias ranged 0.6-2.0. Our results suggest that PMA-based sigmoidal maximum effect (E_max ) model, in combination with bodyweight-based scaling and kidney function assessment, can be used in population PK (PopPK) modeling for drugs that are primarily eliminated via renal pathway to inform initial dose selection for newborns and infants with normal renal function in clinical trials.

Risk factor analysis for a complicated postoperative course after neonatal arterial switch operation: The role of troponin T

OBJECTIVE

To find risk factors for a complicated early postoperative course after arterial switch operation (ASO) in neonates with d-transposition of the great arteries (dTGA). In addition to anatomical and surgical parameters, the predictive value of early postoperative troponin T (TnT) values in correlation to the early postoperative course after ASO is analyzed.

METHODS

Seventy-nine neonates (57 (72%) male) with simple dTGA treated by ASO between 2009 and 2016 were included in the analysis. A complicated early postoperative course (30 days) was defined by one of the following criteria: (A) moderate to severe cardiac dysfunction without rhythm disturbances, (B) rhythm disturbances causing hemodynamic instability with the need for medical treatment, (C) signs for ischemia in ECG, (D) need for surgical or catheter interventional reinterventions other than diagnostic, or (E) other reasons.

RESULTS

Forty of 79 patients (51%) showed a complicated early postoperative course after ASO, with 2 patients dying after 13 and 16 days. Patients with a complicated early postoperative course had a longer PICU stay (P < .001), needed longer mechanical ventilator support (P = .001) and longer inotropic support (P = .03), and more reinterventions (surgical or catheter interventional) were necessary (P = .001). Only the presence of a VSD (P = .001) and longer surgery duration (P = .026) were associated to a complicated postoperative course. TnT values only showed a trend toward higher values in patients with a complicated postoperative course (P = .06). A secondary rise in TnT was seen in 10 patients, ranging from 11.6% to 410.2%, of whom 7 could be classified in the complicated postoperative group.

CONCLUSIONS

The postoperative course after ASO in dTGA neonates is influenced by other cardiac comorbidities like a VSD with the need for surgical treatment, influencing surgery duration. Postoperative higher TnT values reflect a longer and more vulnerable intraoperative course with limited predictive value on the early postoperative course.

Drug evaluation studies in neonates: how to overcome the current limitations

INTRODUCTION

Regulatory initiatives have stimulated drug research in infants, but the potential impact of drugs to improve health outcome in neonates remains underexplored. Areas covered: In this review, we focus on current limitations in drug evaluation studies and how to overcome these. The low volume of studies has additional weaknesses such as single center studies, non-commercial sponsorship, overrepresentation of high postulated risk reductions, and underrepresentation of therapeutic exploratory studies. Master protocols and selection criteria for neonatal centers to participate in studies are useful to improve logistics related to performance. Limitations also relate to inaccurate assessment of drug effects (efficacy/safety). This is because of poor symptom recognition, case definitions, and suboptimal data on adverse drug reactions (ADRs) epidemiology. To overcome these limitations, it is necessary to develop core outcome sets, reference values, and specific ADR tools. The limitations identified and approaches suggested to improve drug evaluation are illustrated using neonatal abstinence syndrome as an example. Expert commentary: We anticipate to see an evolving neonatal clinical pharmacology discipline driven by neonatal pathophysiology and knowledge. Multidisciplinary collaborative efforts between health care providers, academia, pharmaceutical industry, advocacy groups and regulatory agencies are crucial to improve the impact of drug evaluation studies in neonates.

The diagnostic value of serum creatinine and cystatin c in evaluating glomerular filtration rate in patients with chronic kidney disease: a systematic literature review and meta-analysis

BACKGROUND

Serum biomarkers, such as serum creatinine (SCr) and serum cystatin C (SCysC), have been widely used to evaluate renal function in patients who have chronic kidney disease (CKD).

OBJECTIVE

This article aims to assess the value of determining SCr and SCysC levels in patients that have long-term kidney disease. Approaches: MEDLINE, EmBase, the Cochrane Library and other databases were searched using both MeSH terms and text words to collect research that assessed the diagnostic value of using SCr and SCysC to evaluate Glomerular Filtration Rate (GFR) in patients with CKD. Data were converted into fourfold tables. Summary Receiver Operating Characteristic Curves and meta-analyses were accomplished via Meta-Disc version 1.4.

RESULTS

In total, 21 relevant articles involving 3112 study subjects were included in our review. Results showed that the collective sensitivity for SCr and SCysC was 0.77 (95% CI: 0.69-0.84) and 0.87 (95% CI: 0.82-0.91), respectively. The pooled specificity for SCr and SCysC was 0.91 (95% CI: 0.86-0.94) and 0.87 (95% CI: 0.82-0.91), respectively. Subgroup analyses demonstrated that when GFR cut-off values are set to 60 (ml/min/1.73 m²), the pooled sensitivity is 0.94 (95% CI: 0.90-0.96) for SCysC and 0.75 (95% CI: 0.68-0.82) for SCr.

CONCLUSIONS

The diagnostical accuracy for impaired kidney function favors SCysC. Confidence intervals for the pooled sensitivity and specificity for SCr and SCysC overlap. However, SCysC is more sensitive for estimating GFR than SCr when GFR cut-off values are set to 60 (ml/min/1.73 m²).

Diagnosis and Risk Factors of Acute Kidney Injury in Very Low Birth Weight Infants

BACKGROUND

Acute kidney injury (AKI) is common in critically ill premature infants. There is a lack of consensus on the diagnostic definition of AKI in very low birth weight (VLBW) infants. The primary aim of this study was to determine the incidence and risk factors for AKI in VLBW infants using the AKI network (AKIN) and pRIFLE (pediatric Risk, Injury, Failure, Loss, End-Stage) criteria and to evaluate whether Clinical Risk Index for Babies (CRIB II) score is a predictor of AKI. The secondary objective was to determine the extent of agreement between the AKIN and pRIFLE criteria in the diagnosis of AKI in VLBW infants.

METHODS

This was a retrospective chart review of 115 VLBW (< 1500 g) infants born in an academic center with a Level 3B neonatal intensive care unit. Multiple congenital anomalies, transfer to other centers, or death within the first 2 weeks were the exclusion criteria. Relevant data were collected and analyzed in the first 2 weeks postnatally.

RESULTS

AKI incidence, according to AKIN and pRIFLE criteria, was 20.1% and 22.6%, respectively. As per the interrater reliability analysis, there was a fair agreement between the two criteria (kappa = 0.217). AKI was nonoliguric. The length of stay was significantly longer in the AKI group. Prenatal nonsteroidal anti-inflammatory drug exposure, lower gestational age, lower birth weight, respiratory distress syndrome, mechanical ventilation, patent ductus arteriosus, hypotension, late onset sepsis, and higher CRIB II scores were significantly associated with AKI. Our regression analysis found CRIB II scores to be an independent risk factor for AKI (odds ratio = 1.621; 95% confidence interval, 1.230-2.167; p = 0.001).

CONCLUSION

The determination of AKI using the pRIFLE and AKIN criteria yielded different results. pRIFLE appears to be more sensitive in VLBW infants. A high CRIB II score was recorded for AKI. Future studies are necessary to develop a uniform definition and identify the risk factors to improve the outcomes in this population.

Drug-induced renal injury in neonates: challenges in clinical practice and perspectives in drug development

INTRODUCTION

Acute kidney injury (AKI) is frequently diagnosed in the neonatal population, especially in those admitted to intensive care units, and poses several challenges for clinicians mainly because of difficulties in timely identification of renal impairment and the need to administer drugs with potential nephrotoxicity. In this context, research on biomarkers is growing for their implication in the early detection of renal damage and their higher sensitivity in monitoring renal activity, but also as an important tool for drug development. Areas covered: We described the tools currently used to detect renal damage in neonatal settings, their limits and applicability, as well as the role of drugs on renal toxicity occurrence. Subsequently, we discuss current knowledge on new biomarkers for the detection of kidney injury and drug-induced kidney injury in neonates, and the qualification programs developed by regulatory agencies for biomarkers intended as tools in drug development. Expert opinion: Some molecules are emerging as potential biomarkers for early detection of AKI: promising data has demonstrated higher sensitivity and accuracy compared with tools currently used in the clinical setting. In addition, novel techniques (e.g. high power magnetic resonance imaging) to assess long-term consequences of AKI in neonates are in early steps of development.

Evaluation of Vancomycin Use in Late-Onset Neonatal Sepsis Using the Area Under the Concentration-Time Curve to the Minimum Inhibitory Concentration ≥400 Target

AIM

To develop a vancomycin population pharmacokinetic model and assess the probability of attaining a pharmacodynamic target associated with clinical and microbiological success, a ratio of the 24-hour area under the concentration-time curve to the minimum inhibitory concentration (MIC) ≥ 400, in a 5-year clinical cohort of preterm and term neonatal patients with late-onset staphylococcal sepsis.

METHODS

Therapeutic drug monitoring data were obtained from septic neonates with ≥1 vancomycin concentration(s) from January 2006 to September 2011. Only neonates with a postnatal age of >72 hours and a positive microbiological culture were included. Population pharmacokinetic model was developed using nonlinear mixed effects modeling (NONMEM 7.2). Eleven demographic characteristics were evaluated as covariates. Probabilities of achieving the pharmacodynamic target were evaluated.

RESULTS

A 1-compartment model with first-order elimination was constructed from 528 vancomycin concentrations collected from 152 preterm and term neonates. Body weight, creatinine clearance (CL), and postmenstrual age were identified as significant covariates. Estimated vancomycin CL and volume of distribution for typical neonates were 0.068 ± 0.03 L·h·kg and 0.62 ± 0.13 L/kg, respectively. Coagulase-negative staphylococci (85.5%) and Staphylococcus aureus (14.5%) were the common pathogenic organisms. The distribution of vancomycin MIC breakpoints was composed of approximately 70% MIC breakpoint of ≤2 mcg/mL. Approximately 54% of neonates, with a median serum creatinine concentration of 0.44 mg/dL, achieved the target ratio of 24-hour area under the concentration-time curve to the MIC ≥ 400 with a median daily dose of 30 (interquartile range, 21-42) mg/kg.

CONCLUSIONS

Body weight, creatinine CL, and postmenstrual age significantly influenced vancomycin CL. The current vancomycin doses are acceptable at MICs ≤1 mcg/mL because they are likely to achieve the pharmacodynamic target in the majority of neonatal patients, although higher doses may be considered for more resistant staphylococcal infections.

Caffeine Exposure and Risk of Acute Kidney Injury in a Retrospective Cohort of Very Low Birth Weight Neonates

OBJECTIVE

To evaluate the association between caffeine exposure and acute kidney injury (AKI) in very low birth weight (VLBW; ≤1500 g) neonates.

STUDY DESIGN

We retrospectively reviewed a cohort of 140 VLBW neonates consecutively admitted to the University of Virginia's neonatal intensive care unit from March 2011 to June 2012, excluding only those admitted >2 days of age or who died at <2 days after birth. We separately analyzed a subgroup of 44 neonates who received prolonged invasive respiratory support (mechanical ventilation for first 7 days after birth). The exposure of interest was caffeine exposure in the first week after birth. The primary outcome was AKI within the first 10 days after birth according to the Kidney Disease: Improving Global Outcomes system, modified to include only serum creatinine.

RESULTS

Caffeine exposure occurred in 72.1% of all patients and 54.5% of those who received prolonged invasive respiratory support. AKI occurred less frequently in neonates who received caffeine (all patients: 17.8% vs 43.6%; P = .002; prolonged invasive respiratory support: 29.2% vs 75.0%; P = .002). Caffeine exposure was associated with decreased odds for AKI in logistic regression models adjusted for sex, birth weight, gestational age, small for gestational age status, illness severity on admission, and receipt of indomethacin, invasive ventilation, dopamine, aminoglycosides, and vancomycin (all patients: OR 0.22; 95% CI 0.07-0.75, P = .02; prolonged invasive respiratory support subgroup: OR 0.06; 95% CI 0.01-0.57, P = .02).

CONCLUSIONS

In a cohort of VLBW neonates, those exposed to caffeine were less likely to experience AKI.

Assessment of glomerular filtration rate in the neonate: is creatinine the best tool?

PURPOSE OF REVIEW

This article answers the question of whether creatinine is the best biomarker for monitoring neonatal glomerular filtration rate (GFR) in view of recent advances in measuring neonatal renal function.

RECENT FINDINGS

We rely largely on serum creatinine for the estimation of GFR in the newborn, even though creatinine is freely exchanged through the placenta. During the first few days of life, the serum creatinine reflects maternal renal function or the maternal creatinine. Back filtration of creatinine in preterm newborns is also a serious limitation. This review summarizes current knowledge on the prenatal and postnatal handling of creatinine as well as that of other, more novel biomarkers of GFR, such as cystatin C (CysC) and β-trace protein (BTP). Only small amounts of CysC cross the placenta, whereas BTP does not cross the placenta at all. However, BTP measurements are not widely available. Recent studies on renal volumetry are also discussed.

SUMMARY

Currently, CysC may be the most suitable marker of neonatal renal function, but its availability is still limited, it is more costly, and the best method of reporting acute kidney injury and neonatal estimated GFR remains to be established.

Pharmacometric Approaches to Personalize Use of Primarily Renally Eliminated Antibiotics in Preterm and Term Neonates

Sepsis remains a major cause of mortality and morbidity in neonates, and, as a consequence, antibiotics are the most frequently prescribed drugs in this vulnerable patient population. Growth and dynamic maturation processes during the first weeks of life result in large inter- and intrasubject variability in the pharmacokinetics (PK) and pharmacodynamics (PD) of antibiotics. In this review we (1) summarize the available population PK data and models for primarily renally eliminated antibiotics, (2) discuss quantitative approaches to account for effects of growth and maturation processes on drug exposure and response, (3) evaluate current dose recommendations, and (4) identify opportunities to further optimize and personalize dosing strategies of these antibiotics in preterm and term neonates. Although population PK models have been developed for several of these drugs, exposure-response relationships of primarily renally eliminated antibiotics in these fragile infants are not well understood, monitoring strategies remain inconsistent, and consensus on optimal, personalized dosing of these drugs in these patients is absent. Tailored PK/PD studies and models are useful to better understand relationships between drug exposures and microbiological or clinical outcomes. Pharmacometric modeling and simulation approaches facilitate quantitative evaluation and optimization of treatment strategies. National and international collaborations and platforms are essential to standardize and harmonize not only studies and models but also monitoring and dosing strategies. Simple bedside decision tools assist clinical pharmacologists and neonatologists in their efforts to fine-tune and personalize the use of primarily renally eliminated antibiotics in term and preterm neonates.

Renal Function Descriptors in Neonates: Which Creatinine-Based Formula Best Describes Vancomycin Clearance?

Growth and maturational changes have been identified as significant covariates in describing variability in clearance of renally excreted drugs such as vancomycin. Because of immaturity of clearance mechanisms, quantification of renal function in neonates is of importance. Several serum creatinine (SCr)-based renal function descriptors have been developed in adults and children, but none are selectively derived for neonates. This review summarizes development of the neonatal kidney and discusses assessment of the renal function regarding estimation of glomerular filtration rate using renal function descriptors. Furthermore, identification of the renal function descriptors that best describe the variability of vancomycin clearance was performed in a sample study of a septic neonatal cohort. Population pharmacokinetic models were developed applying a combination of age-weight, renal function descriptors, or SCr alone. In addition to age and weight, SCr or renal function descriptors significantly reduced variability of vancomycin clearance. The population pharmacokinetic models with Léger and modified Schwartz formulas were selected as the optimal final models, although the other renal function descriptors and SCr provided reasonably good fit to the data, suggesting further evaluation of the final models using external data sets and cross validation. The present study supports incorporation of renal function descriptors in the estimation of vancomycin clearance in neonates.

External Evaluation of Population Pharmacokinetic Models of Vancomycin in Neonates: The transferability of published models to different clinical settings

BACKGROUND

Vancomycin is one of the most evaluated antibiotics in neonates using modeling and simulation approaches. However no clear consensus on optimal dosing has been achieved. The objective of the present study was to perform an external evaluation of published models, in order to test their predictive performances in an independent dataset and to identify the possible study-related factors influencing the transferability of pharmacokinetic models to different clinical settings.

METHOD

Published neonatal vancomycin pharmacokinetic models were screened from the literature. The predictive performance of 6 models was evaluated using an independent dataset (112 concentrations from 78 neonates). The evaluation procedures used simulation-based diagnostics (visual predictive check [VPC] and normalized prediction distribution errors [NPDE]).

RESULTS

Differences in predictive performances of models for vancomycin pharmacokinetics in neonates were found. The mean of NPDE for 6 evaluated models were 1.35, -0.22, -0.36, 0.24, 0.66, 0.48, respectively. These differences were explained, at least partly, by taking into account the method used to measure serum creatinine concentrations. The adult conversion factor of 1.3 (enzymatic to Jaffé) was tested with an improvement in the VPC and NPDE, but it still need to be evaluated and validated in neonates. Differences were also identified between analytical methods for vancomycin.

CONCLUSION

The importance of analytical techniques for serum creatinine concentrations and vancomycin as a predictor of vancomycin concentrations in neonates has been confirmed. Dosage individualisation of vancomycin in neonates should consider not only patients' characteristics and clinical conditions, but also the methods used to measure serum creatinine and vancomycin.

LC-MS/MS Method for Serum Creatinine: Comparison with Enzymatic Method and Jaffe Method

Accurate quantification of creatinine (Cre) is important to estimate glomerular filtration rate (GFR). Differences among various methods of Cre quantification were previously noted. This study aims to develop a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for serum Cre and compare this method with clinical routine methods. LC-MS/MS analysis was performed on API 4000 triple quadrupole mass spectrometer coupled with an Agilent 1200 liquid chromatography system. After adding isotope-labeled Cre-d3 as internal standard, serum samples were prepared via a one-step protein precipitation with methanol. The LC-MS/MS method was compared with frequently used enzymatic method and Jaffe method. This developed method, with a total run time of 3 min, had a lower limit of quantification of 4.4 μmol/L, a total imprecision of 1.15%–3.84%, and an average bias of 1.06%. No significant matrix effect, carryover, and interference were observed for the LC-MS/MS method. The reference intervals of serum Cre measured by LC-MS/MS assay were 41–79 μmol/L for adult women, and 46–101 μmol/L for adult men. Using LC-MS/MS as a reference, the enzymatic method showed an average bias of -2.1% and the Jaffe method showed a substantial average bias of 11.7%. Compared with the LC-MS/MS method, significant negative bias was observed for the enzymatic and Jaffe methods in hemolytic and lipimic samples. We developed a simple, specific, and accurate LC-MS/MS method to analyze serum Cre. Discordance existed among different methods.

Open-Label Study To Evaluate the Single-Dose Pharmacokinetics, Safety, and Tolerability of Doripenem in Infants Less than 12 Weeks in Chronological Age

Doripenem, a parenteral carbapenem with broad-spectrum activity against aerobic Gram-negative and Gram-positive and anaerobic pathogens, is currently approved for use in adults in the United States and European Union. Single-dose doripenem pharmacokinetics in 52 infants <12 weeks in chronological age were investigated in this phase 1 study. Hospitalized, medically stable infants <12 weeks in chronological age were stratified into 6 groups based on chronological and gestational age designed to reflect increasing renal maturation and decreasing volume of distribution (Vz) for β-lactam antimicrobials during the first 3 months of life. Subjects received single-dose doripenem (5 mg/kg of body weight for <8 weeks and 8 mg/kg for ≥8 weeks in chronological age) administered intravenously over 1 h. Plasma samples were obtained immediately before the end of the infusion and 1.5, 3, and 7 h after the start of the infusion. Urine was obtained by indwelling catheter during the 8 h following infusion. Doripenem showed linear pharmacokinetics across the 6 age groups. Neonates (<4 weeks in chronological age) had increased mean exposure (area under the plasma concentration-time curve from time zero to infinite time [AUC∞], 45.7 versus 32.4 μg · h/ml), longer elimination half-life (2.98 versus 1.79 h), and lower clearance (2.03 versus 3.03 ml/min/kg) compared with infants >4 weeks. Mean Vz was highest in subjects with the earliest gestational age (<32 weeks): 0.564 liter/kg for neonates and 0.548 liter/kg for infants. Single-dose pharmacokinetics of doripenem administered as a 1-hour infusion in term and preterm infants <12 weeks in chronological age were similar to what has been observed in neonates and very young infants with other carbapenems. Single-dose doripenem was generally safe and well tolerated. (This study has been registered with ClinicalTrials.gov under registration no. NCT01381848 and with EudraCT under registration no. 2009-014387-20.).

Cystatin C in newborns: a promising renal biomarker in search for standardization and validation

OBJECTIVE

Neonatologists still commonly use creatinine as a proxy for renal clearance, despite issues related to neonatal (patho)physiology and methodology (assay variability). Cystatin C (CysC) has been suggested to be a more reliable biomarker, but assay related differences have also been reported in children and adults. We are unaware of any review on the assay related impact on CysC reference values in newborns.

METHODS

A structured literature search was performed on published CysC values in (pre)term neonates.

RESULTS

The extensive range (>5-fold) in serum CysC observations in neonates in part relates to the fact that CysC concentrations are higher at birth with subsequent decrease and that CysC concentrations are higher in preterm compared to term neonates. The CysC assay matters while disease characteristics also affect CysC values, but not always in the predicted direction.

CONCLUSIONS

Similar to creatinine, the extensive CysC range in neonates is only in part explained by renal (patho)physiology. Its applicability in neonatal medicine can be further improved by use of assay specific reference values, adapted to neonatal renal physiology (e.g. weight, age) and should be compared to a gold standard such as inulin clearance.

Recognition and reporting of AKI in very low birth weight infants

BACKGROUND AND OBJECTIVES

AKI is associated with both increased short-term morbidity and mortality and greater long-term risk for CKD. This study determined the prevalence of AKI among very low birth weight infants using a modern study definition, evaluated the frequency of AKI diagnosis reporting in the discharge summary, and determined whether infants were referred to a pediatric nephrologist for AKI follow-up.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Records of very low birth weight infants admitted to a level IV neonatal intensive care unit from 2008 to 2011 were reviewed. AKI was classified using the Kidney Disease: Improving Global Outcomes definition modified to include only serum creatinine.

RESULTS

AKI occurred in 39.8% of 455 infants; 75 (16.5%) infants experienced multiple episodes of AKI, and 8 (2%) infants were discharged with an abnormal last creatinine. Updated clinical risk index for babies score >10 (odds ratio, 12.9; 95% confidence interval, 7.8 to 21.4) and gestational age <28 weeks (odds ratio, 10.6; 95% confidence interval, 6.8 to 16.7) were strongly associated with AKI in univariate analyses. AKI was associated with increased mortality (odds ratio, 4.0; 95% confidence interval, 1.4 to 11.5) and length of stay (11.7 hospital days; 95% confidence interval, 5.1 to 18.4), even after accounting for gestational age, birth weight, and updated clinical risk index for babies score. AKI was recorded in the discharge summary for only 13.5% of AKI survivors. No infants were referred to a nephrologist for AKI follow-up.

CONCLUSIONS

AKI occurred in 40% of very low birth weight infants and was concentrated in the most premature and severely ill infants. One in six infants experienced multiple episodes of AKI, and a small number of infants was discharged with an elevated serum creatinine. Reporting a history of AKI in the discharge summary occurred infrequently, and referral to a nephrologist for AKI follow-up did not occur, highlighting areas for quality improvement.

Association between vancomycin trough concentration and area under the concentration-time curve in neonates

National treatment guidelines for invasive methicillin-resistant Staphylococcus aureus (MRSA) infections recommend targeting a vancomycin 24-h area under the concentration-time curve (AUC0-24)-to-MIC ratio of >400. The range of vancomycin trough concentrations that best predicts an AUC0-24 of >400 in neonates is not known. This understanding would help clarify target trough concentrations in neonates when treating MRSA. A retrospective chart review from a level III neonatal intensive care unit was performed to identify neonates treated with vancomycin over a 5-year period. Vancomycin concentrations and clinical covariates were utilized to develop a one-compartment population pharmacokinetic model and examine the relationships between trough and AUC0-24 in the study neonates. Monte Carlo simulations were performed to examine the effect of dose, postmenstrual age (PMA), and serum creatinine level on trough and AUC0-24 achievement. A total of 1,702 vancomycin concentrations from 249 neonates were available for analysis. The median (interquartile range) PMA was 39 weeks (32 to 42 weeks) and weight was 2.9 kg (1.6 to 3.7 kg). Vancomycin clearance was predicted by weight, PMA, and serum creatinine level. At a trough of 10 mg/liter, 89% of the study neonates had an AUC0-24 of >400. Monte Carlo simulations demonstrated that troughs ranging from 7 to 11 mg/liter were highly predictive of an AUC0-24 of >400 across a range of PMA, serum creatinine levels, and vancomycin doses. However, a trough of ≥10 mg/liter was not readily achieved in most simulated subgroups using routine starting doses. Higher starting doses frequently resulted in troughs of >20 mg/liter. A vancomycin trough of ∼10 mg/liter is likely adequate for most neonates with invasive MRSA infections based on considerations of the AUC0-24. Due to pharmacokinetic and clinical heterogeneity in neonates, consistently achieving this target vancomycin exposure with routine starting doses is difficult. More robust clinical dosing support tools are needed to help clinicians with dose individualization.

Tailored tools to improve pharmacotherapy in infants

INTRODUCTION

Extensive within-population variability is the essence of neonatal pharmacology. Despite this, infants remain one of the last therapeutic orphans. Together with additional legal initiatives, tailoring of already available tools (modeling, covariates, pharmacovigilance) may significantly improve pharmacotherapy in infants.

AREAS COVERED

Modeling approaches that hold the promise to improve pharmacotherapy in infants are between-compound extrapolation for compounds that undergo the same route of elimination and integration of time-varying physiology to adapt for the fast maturational changes. Besides these maturational covariates (size, age), newly emerging covariates relate to novel treatment modalities (extracorporeal circulation, hypothermia), environmental issues (microbiome, critical illness) or pharmacogenetics. All these covariates interact with the maturational variation. Finally, pharmacovigilance also needs to be tailored to the characteristics of this population. This relates to preventive strategies, signal detection and assessment of causality.

EXPERT OPINION

Knowledge on pharmacotherapy in infants is lagging. Tailoring available tools to the specific characteristics (maturation) and clinical needs (newly emerging covariates) of infants is feasible but needs creativity and a multidisciplinary collaboration between modelers, academia, clinical researchers and, obviously, the public, including parents.

Simultaneous pharmacokinetic modeling of gentamicin, tobramycin and vancomycin clearance from neonates to adults: towards a semi-physiological function for maturation in glomerular filtration

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.

High-dose gentamicin in newborn infants: is it safe?

Dosing regimens often recommend lower gentamicin doses in neonates (3-5 mg/kg) than in older children (7 mg/kg or more) despite the higher volume of distribution in neonates. We studied an extended-interval high-dose (6 mg/kg) gentamicin regimen in a single tertiary neonatal unit from 2004-2012. During the first week of life, dosing interval was 24 h for term infants, 36 h for preterm infants with gestational age (GA) 29-36 weeks and 48 h for preterm infants with GA <29 weeks. After the first week of life, dosing interval was 24 h if corrected age (GA + postnatal age) ≥29 weeks and 36 h if corrected age <29 weeks. Outcome measures were trough plasma concentration (TPC), ototoxicity and prescription errors. In 546 treatment episodes, TPC was measured prior to the third gentamicin dose. There were 37 episodes (6.7 %) of prescription errors, mainly a too long dosing interval. We included 509 treatment episodes (440 infants) in the final analysis. Mean (standard deviation) gentamicin TPC during the first week of life was 1.1 (0.5) mg/L and after the first week of life 0.8 (0.6) mg/L. In 31 (6 %) episodes, TPC was ≥2.0 mg/L, predominantly among term infants with renal impairment. Thirty-eight patients failed the neonatal hearing screening, but only four of these 38 had permanent hearing loss. All four had a TPC <2.0 mg/L. Conclusions: This extended-interval high-dose gentamicin regimen was associated with low numbers of elevated TPCs, low numbers of prescription errors and no evidence for ototoxicity.

Clinical evaluation of serum cystatin C and creatinine in patients with chronic kidney disease: A meta-analysis

Objective

Glomerular filtration rate (GFR) is an important indicator of renal function. This meta-analysis aimed to evaluate the diagnostic value of serum cystatin C (CysC) and serum creatinine (SCr) for estimating GFR in patients with chronic kidney disease.

Methods

Google Scholar, PubMed®, Cochrane Library and China National Knowledge Infrastructure databases were searched, to identify randomized controlled trials that determined the diagnostic value of CysC and SCr, for estimating GFR in patients with chronic kidney disease.

Results

The inclusion criteria were met by 17 studies (total number of patients with chronic kidney disease, 2521). Meta-analysis showed that when the diagnostic cut-off value of GFR was 80–90 ml/min/1.73 m2, the heterogeneity was modest for CysC ( I2 = 48%, summary sensitivity [SEN] = 0.803, summary specificity [SPE] = 0.821), but there was no heterogeneity for SCr ( I2 = 0.0%, SEN = 0.697, SPE = 0.787). Meta-analysis of the studies demonstrated a significant difference between patients with chronic kidney disease and controls, for CysC and SCr.

Conclusions

This meta-analysis demonstrated significant correlations between CysC, SCr and GFR. CysC was more sensitive, but less specific, than SCr for the estimation of GFR.