Creatinine-Based Vancomycin Dosing Regimens in Neonates: There Is More to Consider Than the Variation in Drug Assay

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.

Different Vancomycin Immunoassays Contribute to the Variability in Vancomycin Trough Measurements in Neonates

Substantial interassay variability (up to 20%) has been described for vancomycin immunoassays in adults, but the impact of neonatal matrix is difficult to quantify because of blood volume constraints in neonates. However, we provide circumstantial evidence for a similar extent of variability. Using the same vancomycin dosing regimens and confirming similarity in clinical characteristics, vancomycin trough concentrations measured by PETINIA (2011-2012, n = 400) were 20% lower and the mean difference was 1.93 mg/L compared to COBAS (2012–2014, n = 352) measurements. The impact of vancomycin immunoassays in neonatal matrix was hereby suggested, supporting a switch to more advanced techniques (LC-MS/MS).

Quantitative clinical pharmacology practice for optimal use of antibiotics during the neonatal period

INTRODUCTION

For safe and effective neonatal antibiotic therapy, knowledge of the pharmacokinetic parameters of antibacterial agents in neonates is a prerequisite. Fast maturational changes during the neonatal period influence pharmacokinetic and pharmacodynamic parameters and their variability. Consequently, the need for applying quantitative clinical pharmacology and determining optimal drug dosing regimens in neonates has become increasingly recognized.

AREAS COVERED

Modern quantitative approaches, such as pharmacometrics, are increasingly utilized to characterize, understand and predict the pharmacokinetics of a drug and its effect, and to quantify the variability in the neonatal population. Individual factors, called covariates in modeling, are integrated in such approaches to explain inter-individual pharmacokinetic variability. Pharmacometrics has been shown to be a relevant tool to evaluate, optimize and individualize drug dosing regimens.

EXPERT OPINION

Challenges for optimal use of antibiotics in neonates can largely be overcome with quantitative clinical pharmacology practice. Clinicians should be aware that there is a next step to support the clinical decision-making based on clinical characteristics and therapeutic drug monitoring, through Bayesian-based modeling and simulation methods. Pharmacometric modeling and simulation approaches permit us to characterize population average, inter-subject and intra-subject variability of pharmacokinetic parameters such as clearance and volume of distribution, and to identify and quantify key factors that influence the pharmacokinetic behavior of antibiotics during the neonatal period.

Vancomycin monitoring in children using bayesian estimation

BACKGROUND

Optimal monitoring of vancomycin in children needs evaluation using the exposure target with area under the curve (AUC) of the serum concentrations versus time over 24 hours. Our study objectives were to: (1) compare the accuracy and precision of vancomycin AUC estimations using 2 sampling strategies-1 serum concentration sample (1S, near trough) versus 2 samples (2S, near peak and trough) against the rich sample (RS) method; and (2) determine the performance of these strategies in predicting future AUC against an internal validation sample (VS).

METHODS

This was a retrospective cohort study using population-based pharmacokinetic modeling with Bayesian post hoc individual estimations in nonlinear mixed effects modeling (version 7.2). Pediatric subjects 3 months-21 years of age who received vancomycin ≥48 hours and had more than 3 drug samples within the first ≤96 hours of therapy were enrolled. Outcome measures were the accuracy, precision, and internal predictive performance of AUC estimations using 2 monitoring strategies (ie, 1S versus 2S) against the RS (which was derived from modeling all serum vancomycin concentrations obtained anytime during therapy) and VS (from serum concentrations obtained after 96 hours of therapy).

RESULTS

Analysis included 138 subjects with 712 vancomycin serum concentrations. Median age was 6.1 (interquartile range, 2.2-12.2) years, weight 22 (13-38) kg, and baseline serum creatinine 0.37 (0.30-0.50) mg/dL. Both accuracy and precision were improved with the 2S, compared with 1S, for AUC estimations (-2.0% versus -7.6% and 10.3% versus 12.8%, respectively) against the RS. Improved accuracy and precision were also observed for 2S when evaluated against VS in predicting future AUC.

CONCLUSIONS

Compared with 1S, the 2S sampling strategy for vancomycin monitoring improved accuracy and precision in estimating and predicting future AUC. Evaluating 2 drug concentrations in children may be prudent to ensure adequate drug exposure.

Implications of serum creatinine measurements on GFR estimation and vancomycin dosing in children

BACKGROUND

Different serum creatinine (sCr) assays may obtain different values in the same patient, causing discrepancies in estimated glomerular filtration rate (eGFR) and sCr-based vancomycin dosing calculations.

OBJECTIVE

To identify potential discrepancies in sCr concentrations obtained by different assays, the compensated Jaffe (sCr-Jaffe) and the enzymatic (sCr-enz), and to compare between the eGFR and vancomycin daily dose, based on these sCr values.

METHOD

sCr-Jaffe and, sCr-enz concentrations of 890 healthy children, aged 1-18 years, were available from the Canadian Laboratory Initiative in Pediatric Reference Intervals study in Ontario. For each subject, eGFR (eGFR-Jaffe, eGFR-enz) was calculated using the revised Schwartz equation, and vancomycin daily dose (Vdose-Jaffe, Vdose-enz) was calculated using a sCr-based pharmacokinetic model.

RESULT

Significant, age-related differences were found in sCr concentrations, and in subsequent eGFR and Vdose, between the two assays. In children aged 1-5 years, mean sCr-Jaffe was higher than sCr-enz (44.0 ± 5.0 vs. 27.7 ± 7.3 μmol/L, P < 0.001), leading to lower eGFR-Jaffe (83.2 ± 9.0 vs. 137.9 ± 27.1 mL/min/1.73m2, P < 0.001) and lower Vdose-Jaffe (44.7 ± 2.5 vs. 53.5 ± 5.1 mg/kg/24 h, P < 0.001).

CONCLUSION

Based on these findings, young children may be at risk for vancomycin under-treatment. Further research is needed to define the more accurate sCr assay in young children treated with renally excreted drugs.