Accuracy of measured vancomycin serum concentrations in patients with end-stage renal disease

Long-Acting Lipoglycopeptides Can Interfere With Vancomycin Therapeutic Drug Monitoring

Oritavancin and dalbavancin are long-acting lipoglycopeptides with activity against susceptible gram-positive bacteria, including methicillin-resistant Staphylococcus aureus. Though similar in structure to traditional glycopeptide antibiotics like vancomycin, these antibiotics have terminal half-lives >10 days, and, as a result, there is potential for administration of vancomycin to a patient while oritavancin or dalbavancin are still appreciably present in serum. Given the structural similarities, this creates an opportunity for lab assay interference when performing therapeutic drug monitoring for vancomycin. Following higher-than-expected serum vancomycin concentrations in a patient who received both oritavancin and vancomycin within a short time frame, we evaluated the potential for lipoglycopeptide interference with clinical vancomycin assays. Five platforms covering 3 immunoassay technologies were used to quantify vancomycin concentrations in serum spiked with oritavancin or dalbavancin. Oritavancin generated spurious vancomycin concentrations (20%-84% increase) in both enzyme-multiplied immunoassay technique and a particle-enhanced turbidimetric inhibition immunoassay. However, the improper detection of oritavancin was not consistent across all particle-enhanced turbidimetric inhibition immunoassay platforms. Dalbavancin interference was not detected on any of the platforms tested. The interference from oritavancin may result in falsely elevated vancomycin concentrations and, subsequently, inappropriately adjusted vancomycin doses.

Measurement and Calculation of the Extracorporeal Elimination of Vancomycin During Continuous Venovenous Hemodiafiltration and Continuous Venovenous Hemofiltration in Critically Ill Patients

Six surgical intensive care patients with continuous renal replacement therapy and therapy with vancomycin entered the prospective clinical study. The first day the patients were treated with continuous venovenous hemodiafiltration (CVVHDF) and the second day with continuous venovenous hemofiltration (CVVH). Three patients received 500 mg and three patients received 1000 mg of vancomycin every 12 hours. Monoclonal fluorescence polarization immunoassay (AxSYM) of vancomycin levels was performed from serum and dialysate/ultrafiltrate (during CVVHDF) or ultrafiltrate (during CVVH). Blood flow was 90 ml/hr, substitution 1 L/hr predilution, dialysate flow 1 L/hr (CVVHDF). The extracorporeal elimination of vancomycin during CVVHDF and CVVH is nearly linear but shows wide interindividual variation. The extracorporeal clearance of vancomycin was 24.2 ± 3.1 ml/min during CVVHDF (total clearance 60.4 ±18.1 ml/min) and 14.5 ± 2.4 ml/min during CVVH (total clearance 50.2 ± 14.9 ml/min). Intraindividual comparison revealed a significantly higher elimination of vancomycin by CVVHDF (p < 0.028). Peak serum vancomycin levels in patients receiving vancomycin 1g/day were 24.7 ± 5.3 μg/ml (CVVH) and 23.1 ± 5.2 μg/ml (CVVHDF), and with 2 g/day were 33.5 ± 2.7 μg/ml (CVVH) and 27.3 ±4.1 μg/ml (CVVHDF). The daily excreted amount of vancomycin during CVVHDF (r2 = 0.950, p = 0.01) and CVVH (r2 = 0.947, p = 0.01) can be calculated from a vancomycin level in the ultrafiltrate/dialysate outlet (CVVHDF) or the ultrafiltrate (CVVH) 8 hours after dosing. The 8-hour concentration of vancomycin in the ultrafiltrate from CVVH (or ultrafiltrate/dialysate from CVVHDF) during continuous renal replacement therapy serves as a basis for predicting extracorporeal elimination within 24 hours for the individual patient. Since critically ill patients show wide interindividual and intraindividual differences in the volume of distribution, clearance, and elimination half-life of vancomycin during therapy, the estimation of serum levels remains a necessity.

Unexplained increases in serum vancomycin concentration in a morbidly obese patient

INTRODUCTION

To report a case of increases in vancomycin concentrations without additional vancomycin doses being given.

CASE STUDY

A 64 year-old morbidly obese female received three total doses of vancomycin for surgical prophylaxis and for ventilator-associated pneumonia. Subsequent vancomycin concentrations from the patient's central venous catheter (CVC) demonstrated increasing drug levels from 27.1 to 45.9mcg/mL despite no additional vancomycin being given and proper line flushing prior to sample collection. There is no clear explanation for the increase in the patient's vancomycin concentration. Drug leaching from the CVC, enterohepatic recycling, drug redistribution from adipose or other tissues, and assay cross-reactivity with other medications are all potential explanations for the increased vancomycin concentrations.

CONCLUSION

This case report describes an unexplained increase in vancomycin concentrations and reinforces both the fallibility of laboratory testing and that unusual circumstances do occur. Several potential causes are hypothesised with CVC drug leaching being the most likely. Nurses and other healthcare providers with similar scenarios should consider a peripheral blood sample to rule out the potential for CVC drug leaching as a possible explanation.

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.

How to use vancomycin optimally in neonates: remaining questions

In neonates, vancomycin, a narrow-spectrum antibiotic, is the first choice of treatment of late-onset sepsis predominantly caused by Gram-positive bacteria (coagulase-negative staphylococci and enterococci). Although it has been used for >50 years, prescribing the right dose and dosing regimen remains a challenge in neonatal intensive care units for many reasons including high pharmacokinetic variability, increase in the minimal inhibition concentration against staphylococci, lack of consensus on dosing regimen and way of administration (continuous or intermittent), duration of treatment, use of therapeutic drug monitoring, limited data on short- and long-term toxicity, risk of mutant selection and errors of administration linked to concentrated formulations. This article highlights and discusses future research directions, with specific attention given to dosing optimization of vancomycin, including the advantages of modeling and simulation approaches.

Intraperitoneal vancomycin concentrations during peritoneal dialysis-associated peritonitis: correlation with serum levels

BACKGROUND

For the treatment of peritoneal dialysis-associated peritonitis (PDP), it has been suggested that serum concentrations of vancomycin be kept above 12 mg/L-15 mg/L. However, studies correlating vancomycin concentrations in serum and peritoneal dialysate effluent (PDE) during active infection are sparse. We undertook the present study to investigate this issue and to determine whether achieving the recommended serum level of vancomycin results in therapeutic levels intraperitoneally.

METHODS

We studied patients treated with intraperitoneal (i.p.) vancomycin for non-gram-negative PDP. We gave a single dose (approximately 30 mg/kg) at presentation, and we subsequently measured vancomycin levels in PDE on day 5; we wanted to determine if efflux of vancomycin from serum to PDE during a 4-hour dwell was consistent and resulted in therapeutic levels.

RESULTS

Of the 48 episodes of PDP studied, serum vancomycin concentrations exceeding 12 mg/L were achieved in 98% of patients, but in 11 patients (23%), a PDE vancomycin level below 4 mg/L--the minimal inhibitory concentration (MIC) of many gram-positive organisms--was observed at the end of a 4-hour dwell on day 5. The correlation between the concentrations of vancomycin in serum and PDE (from efflux of antibiotic over 4 hours) was statistically significant, but poor (R(2) = 0.18).

CONCLUSIONS

Our data support the International Society for Peritoneal Dialysis statement that adequate serum vancomycin concentrations can be achieved with intermittent dosing (single dose every 5 days), but cannot guarantee therapeutic PDE levels in the treatment of PDP. Intermittent dosing of vancomycin may not consistently result in PDE concentrations markedly greater than MIC of many important pathogens. Although the clinical significance of this finding remains to be determined, it may be preferable to give smaller but more frequent doses of PDE vancomycin (continuous dosing) for adults with PDP (as is currently recommended for children).

Vancomycin assay performance in patients with end-stage renal disease receiving hemodialysis

STUDY OBJECTIVE

To compare the performance of polyclonal fluorescence polarization immunoassay (pFPIA) with that of enzyme-multiplied immunoassay technique (EMIT) in patients receiving vancomycin and hemodialysis.

SETTING

Outpatient hemodialysis center.

PATIENTS

Seven subjects with end-stage renal disease treated with hemodialysis 3 times/week with a cellulose triacetate hemodialyzer.

INTERVENTION

Subjects received vancomycin 1000 mg intradialytically during the first study session and 750 mg every other hemodialysis session thereafter for 4 weeks.

MEASUREMENTS AND MAIN RESULTS

Blood samples were obtained throughout the study, and vancomycin serum concentrations were determined by pFPIA and EMIT. The mean +/- SD difference (estimate of bias) between assays was -1.10 +/- 1.35 mg/L. The limits of agreement (mean difference +/- 1.96 x SD) between them were -3.80-1.60 mg/L.

CONCLUSION

Our data suggest that the manufacturer's changes in the vancomycin pFPIA eliminated overestimation of drug concentrations in patients undergoing high-permeability hemodialysis.