The pharmacokinetics of vancomycin during the initial loading dose in patients with septic shock

Population Pharmacokinetic Analysis of Vancomycin in Patients with Solid or Hematological Malignancy in Relation to the Quick Sequential Organ Failure Assessment Scores

BACKGROUND AND OBJECTIVE

It remains unclear whether sepsis in patients with malignancy interferes with the predictive performance of the dose-estimation formulas. The quick sequential organ failure assessment (qSOFA) score can help identify patients with poor outcomes because of sepsis-associated organ damage. Vancomycin, an important antibiotic, treats systemic infections (sepsis) caused by methicillin-resistant Staphylococcus aureus. We aimed to clarify whether including the qSOFA score in a standard population pharmacokinetic (PopPK) assessment may improve the predictive performance of vancomycin doses in patients with malignancy.

METHODS

This was a retrospective, observational study. Serum vancomycin concentration-time datasets were obtained from the therapeutic drug monitoring records of St. Luke's International Hospital (Tokyo, Japan) from January 2011 to August 2016. Clinical and laboratory data of the relevant patients were retrieved from electronic health records. PopPK analysis was performed using the NONMEM program, which includes creatinine clearance (CLCr), blood neutrophil counts, qSOFA scores, and type of malignancy as covariates. We examined the validity of the final PopPK model using bootstrapping, goodness-of-fit plots, and prediction-corrected visual predictive checks.

RESULTS

Six hundred and eight blood samples were obtained from 325 patients. In the final PopPK model, the CLCr and qSOFA scores were selected as covariates of systemic vancomycin clearance (p < 0.05): the population mean value was 2.8 (L/h). Regardless of the CLCr, a qSOFA score of greater than 1 was associated with an approximately 10% reduction in vancomycin clearance.

CONCLUSIONS

qSOFA scores might be an additional covariate to CLCr for estimating vancomycin concentrations with a PopPK model in patients with malignancy.

Use of a common spreadsheet program to demonstrate the ability of Bayesian forecasting to estimate the pharmacokinetic parameters of antibiotics

OBJECTIVES

Recent guidelines for vancomycin have incorporated the use of Bayesian forecasting, reinforcing the need to inform students in pharmacy and clinical pharmacology of its use in therapeutic drug monitoring. The goal was to devise a PharmD research project that could demonstrate to students through simulation and data generation the utility of the Bayesian approach in estimating the pharmacokinetics of gentamicin and vancomycin.

METHODS

A series of steps were devised using Microsoft Excel to simulate patient data based on study-derived means and variances, pharmacokinetic modelling, random selection of sparse blood samples, introduce random error into the selected concentrations based on assay variability measure, and finally, inputting of the information into an add-in computer program to find the pharmacokinetic estimates using Bayesian forecasting.

KEY FINDINGS

Excellent correlations were seen between Bayesian estimates and true clearances. Lower assay variability tended to provide better estimates than larger assay variability for gentamicin, and for vancomycin, selecting a sample during the distribution phase and near the trough values tended to provide estimates with less bias and greater precision.

CONCLUSIONS

The approach used was able to demonstrate all aspects involved in Bayesian forecasting, and the results supported its use for these antibiotics.

A Systematic Review on Antimicrobial Pharmacokinetic Differences between Asian and Non-Asian Adult Populations

While the relevance of inter-ethnic differences to the pharmacokinetic variabilities of antimicrobials has been reported in studies recruiting healthy subjects, differences in antimicrobial pharmacokinetics between Asian and non-Asian patients with severe pathologic conditions require further investigation. For the purpose of describing the potential differences in antimicrobial pharmacokinetics between Asian and non-Asian populations, a systematic review was performed using six journal databases and six theses/dissertation databases (PROSPERO record CRD42018090054). The pharmacokinetic data of healthy volunteers and non-critically ill and critically ill patients were reviewed. Thirty studies on meropenem, imipenem, doripenem, linezolid, and vancomycin were included in the final descriptive summaries. In studies recruiting hospitalised patients, inconsistent differences in the volume of distribution (V_d) and drug clearance (CL) of the studied antimicrobials between Asian and non-Asian patients were observed. Additionally, factors other than ethnicity, such as demographic (e.g., age) or clinical (e.g., sepsis) factors, were suggested to better characterise these pharmacokinetic differences. Inconsistent differences in pharmacokinetic parameters between Asian and non-Asian subjects/patients may suggest that ethnicity is not an important predictor to characterise interindividual pharmacokinetic differences between meropenem, imipenem, doripenem, linezolid, and vancomycin. Therefore, the dosing regimens of these antimicrobials should be adjusted according to patients' demographic or clinical characteristics that can better describe pharmacokinetic differences.

Predicting the Area under the Plasma Concentration-Time Curve (AUC) for First Dose Vancomycin Using First-Order Pharmacokinetic Equations

To treat critically ill patients, early achievement of the target area under the plasma concentration-time curve/minimum inhibitory concentration (AUC/MIC) in the first 24 h is recommended. However, accurately calculating the AUC before steady state is an obstacle to this goal. A first-order pharmacokinetic equation to calculate vancomycin AUC after a first dose of vancomycin has never been studied. We sought to estimate AUC using two first-order pharmacokinetic equations, with different paired concentration time points, and to compare these to the actual first dose vancomycin AUC calculated by the linear-log trapezoid rule as a reference. The equations were validated using two independent intensive first dose vancomycin concentration time data sets, one from 10 adults and another from 14 children with severe infection. The equation with compensation for the alpha distribution phase using a first vancomycin serum concentration from 60 to 90 min and the second concentration from 240 to 300 min after the completed infusion showed good agreement and low bias of calculated AUC, with mean differences <5% and Lin's correlation coefficient >0.96. Moreover, it gave an excellent correlation with Pearson's r > 0.96. Estimating the first dose vancomycin AUC calculated using this first-order pharmacokinetic equation is both reliable and reproducible in clinical practice settings.

A 600 mg of fixed-dose linezolid in renally impaired patients versus 15 mg/kg intermittent dose-optimized vancomycin in renally non-impaired patients: A single centre retrospective analysis for adult patients with hospital-acquired pneumonia due to methicillin-resistant Staphylococcus aureus

OBJECTIVES

Both linezolid and vancomycin are approved by USFDA and IDSA guidelines for the management of nosocomial pneumonia due to methicillin-resistant Staphylococcus aureus (MRSA) in clinical practice. Baseline creatinine clearance is the criterion for prescribing vancomycin or linezolid for hospital-acquired pneumonia in our institution. However, patients with renal function impairment are far more difficult to manage in intensive care. Thus, the objectives of the study were to compare the clinical efficacy and safety of 600 mg of fixed-dose linezolid with intermittent dose-optimised vancomycin in hospital-acquired pneumonia due to MRSA and to evaluate parameters of clinical cure.

METHODS

Analysis of a review of patients' charts. Patients with creatinine clearance <80 ml/min received 600 mg linezolid/12 h (n = 139, LN cohort), and patients with creatinine clearance ≥80 ml/min received intravenous 15 mg/kg vancomycin/12 h for 1-2 weeks consecutively or 3 weeks in case of bacteremia (n = 152, VC cohort) for management of hospital-acquired pneumonia due to MRSA.

RESULTS

A 59% of patients from the LN cohort and 47% of patients from the VC cohort were clinically cured. Administration of systemic steroids (p = 0.0412) and ≥ 80 ml/min creatinine clearance (p = 0.0498) were the independent parameters for the clinical cure of patients. Nephrotoxicity was higher among patients of the VC cohort than the LN cohort (p = 0.0464). Treatment failed in 41% of patients from the LN cohort and in 53% of patients from the VC cohort (p = 0.0200).

CONCLUSIONS

A 600 mg of fixed-dose linezolid is an ideal alternative to intermittent dose-optimised vancomycin for better clinical outcomes for patients with hospital-acquired pneumonia due to MRSA, especially for patients with renal impairment.

Dose optimization of vancomycin in obese patients: A systematic review

Background: Dose optimization of vancomycin plays a substantial role in drug pharmacokinetics because of the increased incidence of obesity worldwide. This systematic review was aimed to highlight the current dosing strategy of vancomycin among obese patients. Methods: This systematic review was in concordance with Preferred Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The literature search was carried out on various databases such as Scopus, PubMed/MEDLINE, ScienceDirect and EMBASE using Keywords and MeSH terms related to vancomycin dosing among obese patients. Google Scholar was also searched for additional articles. The English language articles published after January, 2000 were included in this study. The quality of the study was assessed using different assessment tools for cohort, and case reports. Results: A total of 1,029 records were identified. After screening, 18 studies were included for the final review. Of total, twelve studies are retrospective and remaining six are case-control studies. A total of eight studies were conducted in pediatrics while remaining studies were conducted in adult population. Most of the studies reported the dosing interval every 6-8 h. Differences in target trough concentration exist with respect to target ranges. The administration of loading dose (20-25 mg/kg) followed by maintenance dose (15-25 mg/kg) of vancomycin is recommended in adult patients to target therapeutic outcomes. Moreover, a dose of 40-60 mg/kg/day appears appropriate for pediatric patients. Conclusion: The initial dosing of vancomycin based on TBW could be better predictor of vancomycin trough concentration. However, the clinical significance is uncertain. Therefore, more studies are needed to evaluate the dosing strategy of vancomycin in overweight or obese patients.

Antimicrobial safety considerations in critically ill patients: part I: focused on acute kidney injury

INTRODUCTION

Antibiotic prescription is a challenging issue in critical care settings. Different pharmacokinetic and pharmacodynamic properties, polypharmacy, drug interactions, and high incidence of multidrug-resistant microorganisms in this population can influence the selection, safety, and efficacy of prescribed antibiotics.

AREAS COVERED

In the current article, we searched PubMed, Scopus, and Google Scholar for estimating renal function in acute kidney injury, nephrotoxicity of commonly used antibiotics, and nephrotoxin stewardship in intensive care units.

EXPERT OPINION

Early estimation of kidney function with an accurate method may be helpful to optimize antimicrobial treatment in critically ill patients. Different antibiotic dosing regimens may be required for patients with acute kidney injury. In many low-resource settings, therapeutic drug monitoring is not available for antibiotics. Acute kidney injury may influence treatment effectiveness and patient outcome.

Vancomycin dosing in an obese patient with acute renal failure: A case report and review of literature

BACKGROUND

Vancomycin is the most commonly used drug for methicillin-resistant Staphylococcus aureus. The empirical clinical doses of vancomycin based on non-obese patients may not be optimal for obese ones.

CASE SUMMARY

This study reports a case of vancomycin dosing adjustment in an obese patient (body mass index 78.4 kg/m²) with necrotizing fasciitis of the scrotum and left lower extremity accompanied with acute renal failure. Dosing adjustment was performed based on literature review and factors that influence pharmacokinetic parameters are analyzed. The results of the blood drug concentration monitoring confirmed the successful application of our dosing adjustment strategy in this obese patient. Total body weight is an important consideration for vancomycin administration in obese patients, which affects the volume of distribution and clearance of vancomycin. The alterations of pharmacokinetic parameters dictate that vancomycin should be dose-adjusted when applied to obese patients. At the same time, the pathophysiological status of patients, such as renal function, which also affects the dose adjustment of the patient, should be considered.

CONCLUSION

Monitoring vancomycin blood levels in obese patients is critical to help adjust the dosing regimen to ensure that vancomycin concentrations are within the effective therapeutic range and to reduce the incidence of renal injury.

Comparison of Race and Non-Race Based Equations for Kidney Function Estimation in Critically Ill Thai Patients for Vancomycin Dosing

Empiric antibiotic dosing frequently relies on an estimate of kidney function based on age, serum creatinine (SCr), sex, and race (on occasion). New non-Race based estimated glomerular filtration rate (eGFR) equations have been published but their role to support dosing is not known. Here, we report on a population pharmacokinetic model of vancomycin that serves as a useful probe substrate of eGFR in critically ill Thai patients. Data were obtained from medical records during a 10-year period. A nonlinear mixed-effects modeling approach was conducted to estimate vancomycin parameters. Data from 208 critically ill patients (58.2% male and 36.0% septic shock) with 398 vancomycin concentrations were collected. Twenty-three covariates including 12 kidney function estimates were tested and ranked based on the model performance. The median [min, max] age, weight, and SCr was 69 [18, 97] years, 60.0 [27, 120] kg, and 1.53 [0.18, 7.15] mg/dL. The best base model was a one-compartment linear with zero-order input and proportional error model. A Thai specific eGFR equation not indexed to body surface area (BSA) model best predicted vancomycin clearance (CL). The typical value for volume of distribution and CL was 67.5 L and 1.22 L/h, respectively. A loading dose of 2000 mg followed by maintenance dose regimens based on eGFR is suggested. The Thai-GFR not indexed to BSA model best predicts vancomycin CL and dosing in the critically ill Thai population. A 5-10% absolute gain in the vancomycin probability of target attainment is expected with the use of this population specific GFR equation. This article is protected by copyright. All rights reserved.

Antibiotic Stewardship Related to Delayed Diagnosis and Poor Prognosis of Critically Ill Patients with Vancomycin-Resistant Enterococcal Bacteremia: A Retrospective Cohort Study

Purpose

Patients with septicemia caused by vancomycin-resistant Enterococcus (VRE) bacteremia have higher mortality rates than patients infected by VSE. Vancomycin or teicoplanin is selected as the antibiotic stewardship intervention to cover methicillin-resistant Staphylococcus aureus infections before blood culture reveals VRE bacteremia in critically ill patients with Gram-positive cocci (GPC) bacteremia; this may require linezolid or daptomycin treatment instead. We thus evaluated antibiotic stewardship practices, such as appropriate timing of antibiotic use in GPC bacteremia, and clinical outcomes of critically ill patients with VRE infection.

Patients and Methods

This retrospective study enrolled 191 critically ill patients with enterococcal bacteremia at the Taipei Tzu Chi Hospital during January 1, 2019–December 31, 2020. Demographic and clinical characteristics, as well as disease outcomes and appropriate antibiotic use after GPC bacteremia diagnosis, were compared between the VRE and VSE groups.

Results

Of 191 patients, 55 had VRE bacteremia (case group) and 136 had VSE bacteremia (control group). The rate of antibiotic change after initial antibiotic use for GPC bacteremia was higher in the VRE bacteremia group (100% vs 10.3%; p<0.001). The time to appropriate antibiotic administration after GPC bacteremia diagnosis was longer in the VRE bacteremia group (3.3±2.1 vs 1.5±1.8 days; p<0.001). Patients with VRE bacteremia had higher 28-day mortality rates (relative risk, 1.997; 95% confidence interval [CI], 1.041–3.83). Multivariate Cox regression analysis showed that delayed appropriate antibiotic administration of >3 days after GPC bacteremia diagnosis increased the risks of 28-day all-cause mortality (adjusted hazard ratio, 2.045; 95% CI, 1.089–3.84; p=0.026) in patients with VRE infection.

Conclusion

Patients with VRE bacteremia with delayed appropriate antibiotic administration of >3 days after GPC bacteremia diagnosis had increased 28-day mortality risks. New strategies for early VRE detection in GPC bacteremia may shorten the time to administer appropriate antibiotics and lower mortality rates.

Clinical Practice Guidelines for Therapeutic Drug Monitoring of Vancomycin in the Framework of Model-Informed Precision Dosing: A Consensus Review by the Japanese Society of Chemotherapy and the Japanese Society of Therapeutic Drug Monitoring

Background: To promote model-informed precision dosing (MIPD) for vancomycin (VCM), we developed statements for therapeutic drug monitoring (TDM). Methods: Ten clinical questions were selected. The committee conducted a systematic review and meta-analysis as well as clinical studies to establish recommendations for area under the concentration-time curve (AUC)-guided dosing. Results: AUC-guided dosing tended to more strongly decrease the risk of acute kidney injury (AKI) than trough-guided dosing, and a lower risk of treatment failure was demonstrated for higher AUC/minimum inhibitory concentration (MIC) ratios (cut-off of 400). Higher AUCs (cut-off of 600 μg·h/mL) significantly increased the risk of AKI. Although Bayesian estimation with two-point measurement was recommended, the trough concentration alone may be used in patients with mild infections in whom VCM was administered with q12h. To increase the concentration on days 1–2, the routine use of a loading dose is required. TDM on day 2 before steady state is reached should be considered to optimize the dose in patients with serious infections and a high risk of AKI. Conclusions: These VCM TDM guidelines provide recommendations based on MIPD to increase treatment response while preventing adverse effects.

Analysis of Risk Factors Associated with Reduced Trough Concentrations of Vancomycin in Relation to Renal Function in a Tertiary Hospital in Japan

BACKGROUND

Low trough concentrations of vancomycin (VCM) are common in patients receiving the drug, because patients are often administered relatively low doses of VCM due to its high potential for renal toxicity. However, the clinical risk factors associated with low VCM trough concentration in relation to renal function are unclear.

METHODS

Patients at our hospital who received VCM intravenously from January 2018 to December 2020 were analyzed. The patients were divided into two groups based on their renal function: normal and lower renal function, such as estimated glomerular filtration rate (eGFR) ≧60 and <60 mL/min/1.73 m2, respectively. In each renal function group, patients' background characteristics, laboratory data and treatments were compared between lower VCM concentration (<10 mg/L) and appropriate VCM concentration (10-20 mg/L) subgroups.

RESULTS

Among 101 patients with normal renal function, 47 and 54 patients, respectively, showed lower and appropriate VCM trough concentrations. Elderly age, short stature, and higher C-reactive protein (CRP) level were significantly more common in the lower VCM concentration group compared with appropriate VCM concentration group. Among the 45 patients with renal dysfunction, 20 and 25 patients, respectively, showed lower and appropriate VCM trough concentrations. CRP levels were significantly higher in lower VCM concentration than appropriate VCM concentration subgroups. Multivariate analysis showed that insufficient total VCM doses and higher CRP might have affected the lower VCM trough concentration in patients with normal renal function.

CONCLUSION

The results of this study suggest that higher CRP might be one of the risk factors associated with lower VCM concentration in both normal and low renal function patients. Severely ill and emergency patients might receive a lower VCM dose due to underestimation of the acceptable VCM dose.

Vancomycin pharmacokinetics in patients treated with intermittent haemodialysis based on therapeutic drug monitoring

Vancomycin is frequently used in haemodialysis (HD) patients but generally accepted target serum ranges and dosing strategy are still lacking in this group. Based on retrospective analysis of data from 118 HD patients treated with vancomycin the interdialytic elimination constant (K_e), apparent volume of distribution (Vd) and dialysis efficacy were calculated. The influence of possible clinical variables on the pharmacokinetic parameters of vancomycin have been tested. The median of K_e in interdialytic periods, corresponding half-life and Vd were 0.0073 h^-1, 95.0 h and 0.87 L/kg, respectively. We found significant positive correlation between time in dialysis program and K_e. The Vd correlated best with lean body mass (LBM). For high- and low flux membrane HD of 4 hours duration the decline in vancomycin levels was 20.88% and 12.86%, respectively. Based on these data loading dose for vancomycin in HD patient should be calculated as 24.483 × LBM (kg) + 455 mg. The utility of this equation for entire HD population should be also verified prospectively.

A Monocentric Retrospective Study of AUC/MIC Ratio of Vancomycin Associated with Clinical Outcomes and Nephrotoxicity in Patients with Enterococcal Infections

Vancomycin is an antibiotic commonly used for the treatment of enterococcal infections. However, there is no clear correlation regarding of vancomycin area under the curve/minimum inhibitory concentration (AUC/MIC) ratio and clinical outcomes for the treatment of enterococcal infections. The aims of this study were to evaluate the relationship of vancomycin AUC/MIC ratio in patients with clinical outcomes and nephrotoxicity for patients with documented enterococcal infections. A Bayesian technique was used to calculate the average vancomycin AUC_0–24. The MIC was determined using the VITEK 2 automated microbiology system, and the average AUC_0–24/MIC value was calculated for the first 72 h of therapy. All medical records of patients prescribed vancomycin with therapeutic drug monitoring were collected during January 2010–October 2020 at Chiang Mai University Hospital (CMUH). A retrospective single-center cohort of 312 participants were met the inclusion criteria. The results of this study showed that, a vancomycin AUC/MIC of ≥400 mg·h/L was associated with significant differences in clinical response compared to a vancomycin AUC/MIC of <400 mg·h/L (aHR: 0.50, 95% CI: 0.26–0.97; p = 0.042). Likewise, a vancomycin AUC/MIC of ≥400 mg·h/L was associated with significant differences in the microbiological response (aHR: 0.37, 95% CI: 0.14–0.94; p = 0.036), compared to a vancomycin AUC/MIC of <400 mg·h/L. However, nephrotoxicity in patients with a vancomycin AUC/MIC of ≥400 mg·h/L was higher than those with a vancomycin AUC/MIC of <400 mg·h/L (aHR: 3.96, 95% CI: 1.09–14.47; p = 0.037). Declining renal function may be a result of high vancomycin concentrations. In addition, declining renal function (e.g., failure to resolve the focus of infection, co-administration of other antibiotics) might result in higher AUC/MIC. We found a target vancomycin AUC/MIC of ≥400 mg·h/L and this AUC/MIC target value could be optimal for the use for monitoring treatment of enterococcal infections. Thus, vancomycin dosage must be adjusted to achieve the AUC/MIC target and closely monitored for renal function. These findings are not transferable to critically ill patients.

Vancomycin Advanced Therapeutic Drug Monitoring: Exercise in Futility or Virtuous Endeavor to Improve Drug Efficacy and Safety?

Vancomycin is commonly prescribed to hospitalized patients. Decades of pharmacokinetic/pharmacodynamic research culminated in recommendations to monitor the ratio of the area under the concentration-time curve (AUC) to the minimum inhibitory concentration in order to optimize vancomycin exposure and minimize toxicity in the revised 2020 guidelines. These guideline recommendations are based on limited data without high-quality evidence and limitations in strength. Despite considerable effort placed on vancomycin therapeutic drug monitoring (TDM), clinicians should recognize that the majority of vancomycin use is empiric. Most patients prescribed empiric vancomycin do not require it beyond a few days. For these patients, AUC determinations during the initial days of vancomycin exposure are futile. This added workload may detract from high-level patient care activities. Loading doses likely achieve AUC targets, so AUC monitoring after a loading dose is largely unnecessary for broad application. The excessive vancomycin TDM for decades has been propagated with limitations in evidence, and it should raise caution on contemporary vancomycin TDM recommendations.

First-Dose Vancomycin Pharmacokinetics Versus Empiric Dosing on Area-Under-the-Curve Target Attainment in Critically Ill Patients

BACKGROUND

Early attainment of target area under the curve (AUC) to minimum inhibitory concentration (MIC) ratios have been associated with clinical success, as well as lower incidence of acute kidney injury (AKI), in patients receiving vancomycin for methicillin-resistant Staphylococcus aureus (MRSA). Critically ill patients are particularly vulnerable to poor outcomes from infection and face multiple risk factors for AKI, thus early precision dosing of vancomycin is vital in this population. We hypothesized that a personalized dosing approach, using vancomycin levels obtained after the first dose to guide further dosing, would be superior to empiric dosing in terms of AUC target attainment assessed at steady state (SS).

METHODS

A retrospective cohort study of 66 critically ill adult patients admitted to the medical intensive care unit without AKI and receiving vancomycin with at least two SS concentrations obtained for AUC calculation was performed. Patients were separated into cohorts based on whether they had two concentrations assessed after the first dose of vancomycin and were subsequently dosed based on personalized pharmacokinetic calculations (first-dose kinetics) or whether they were empirically dosed using population estimates. The primary outcome was AUC target attainment (400-600 mg hour/L) at SS.

RESULTS

Compared with patients receiving empiric dosing by population estimates, using first-dose kinetics to guide subsequent dosing resulted in significantly greater AUC target attainment at SS (58.6% first-dose vs 32.4% empiric; p=0.033). Patients dosed empirically yielded more variable AUC values across a wide range compared with the first-dose kinetics group (coefficient of variation 40.7% empiric vs 26.1% first-dose). There was no difference in AKI up to 48 hours after SS concentrations between the two dosing schemes.

CONCLUSIONS

A dosing strategy using two vancomycin serum concentrations after the first dose and calculating personalized pharmacokinetic parameters to guide subsequent dosing is associated with greater AUC target attainment at SS compared with empiric dosing of vancomycin in critically ill adults with relatively stable renal function.

Vancomycin Pharmacokinetics in Obese Patients with Sepsis or Septic Shock

STUDY OBJECTIVES

Obese patients with sepsis or septic shock may have altered vancomycin pharmacokinetics compared with the general population that may result in improper dosing or inadequate drug concentrations. The objective of this study was to characterize vancomycin pharmacokinetics in obese patients with sepsis or septic shock, and to develop a novel pharmacokinetic dosing model based on pharmacokinetic-pharmacodynamic target requirements.

DESIGN

Prospective observational pharmacokinetic study.

SETTING

Large quaternary academic medical center.

PATIENTS

Sixteen obese (body mass index [BMI] 30 kg/m² or higher) adults with sepsis and either a gram-positive bacteremia or requiring vasopressor support (septic shock), who were receiving vancomycin between November 2016 and June 2018, were included. Patients were excluded if they were receiving renal replacement therapy or extracorporeal membrane oxygenation, treatment for central nervous system infections, pregnant, or receiving vancomycin for surgical prophylaxis.

INTERVENTION

Four blood samples per patient were collected following a single dose of vancomycin: one peak serum vancomycin level (within 1-2 hrs of infusion completion), two random levels during the dosing interval, and one trough level (within 30-60 min of the next dose) were measured.

MEASUREMENTS AND MAIN RESULTS

A population pharmacokinetic model was developed to describe vancomycin concentrations over time. Simulations to determine optimal dosing were performed using the pharmacokinetic model with different ranges of creatinine clearance (Cl_cr ) and different vancomycin daily doses. Median age of the patients was 62 years; median BMI was 36.1 kg/m² , Acute Physiology and Chronic Health Evaluation II score was 26, and Sequential Organ Failure Assessment score was 11. Eleven patients (69%) had an acute kidney injury. Median initial vancomycin dose was 15 mg/kg; median vancomycin trough concentration was 17 mg/L. A one-compartment model best characterized the pharmacokinetics of vancomycin in obese patients with sepsis or septic shock. Volume of distribution was slightly increased in this population (0.8 L/kg) compared with the general population (0.7 L/kg). Only Cl_cr effect on drug clearance was found to be significant (decrease in the objective function value by 16.4 points), confirming that it is a strong predictor of vancomycin clearance.

CONCLUSION

To our knowledge, this study provides the first population-based pharmacokinetic model in obese patients with sepsis or septic shock. The nomograms generated from this pharmacokinetic model provide a simplified approach to vancomycin dosing in this patient population.

In vitro Evaluation of Linezolid and Doripenem Clearance with Different Hemofilters

INTRODUCTION

Renal replacement therapy (RRT) is widely used in the treatment of septic acute kidney injury. However, little is known about how the adsorption properties of hemofilters used in RRT affect antibiotic concentration. Because a cytokine-adsorption membrane is frequently used in RRT, it is important to determine the antibiotic adsorption capacity of this membrane.

OBJECTIVE

The present study aimed to investigate the antibiotic adsorption capacity of different hemofilter membranes by in vitro experiments using 2 antibacterial agents (linezolid and doripenem).

METHODS

We performed experimental hemofiltration in vitro using polyacrylonitrile (AN69ST), polymethylmethacrylate (PMMA), and polysulfone (PS) hemofilters for 1,440 min. The test solution was a 1,000-mL substitution fluid containing 30 µg/mL linezolid and 120 µg/mL doripenem. We measured drug concentrations at the inlet, outlet, and filtrate ports of the hemofilters for 1,440 min and calculated the sieving coefficient (SC) and adsorption rate (Ra) of the drugs onto the hemofilters.

RESULTS

The amount of linezolid adsorbed onto AN69ST, PMMA, and PS membranes was decreased relative to that in the control group at 15 min (p < 0.05). However, no SC for linezolid was obtained thereafter. The Ra of linezolid onto AN69ST, PMMA, and PS membranes was higher than that in the control group (p < 0.05). In contrast, no significant differences were observed in the concentrations and Ra values of doripenem adsorbed onto AN69ST, PMMA, and PS membranes compared with those in the control group.

CONCLUSIONS

Doripenem was not adsorbed onto PMMA, PS, and AN69ST membranes. Linezolid was adsorbed onto PMMA, PS, and AN69ST membranes, but only temporarily, and this did not affect drug bioavailability.

Describing vancomycin serum levels in pediatric intensive care unit (ICU) patients: are expected goals being met

BACKGROUND

In the pediatric population, infections by methicillin-resistant Staphylococcus aureus (MRSA) are associated with significant morbidity and hospital costs. Vancomycin is a glycopeptide antibiotic, widely used for the treatment of serious infections by Gram-positive microorganisms, especially MRSA. It is recommended to keep the serum level of vancomycin between 10 and 20 mg/L, that correlates with AUC/MIC > 400 in adults. This pharmacodynamic target is extrapolated to pediatric patients despite the lack of similar evidence. However, recent studies suggest that serum levels between 7 and 10 mg/L are predictive of reaching the pharmacodynamic target in this population. In spite of widespread use, ideal information about dosage for the pediatric population remains limited.

METHODS

A retrospective study was conducted in patients admitted to the Pediatric Intensive Care Unit during the period between January 01, 2008 to December 31, 2014. We investigated variables such as age, positive fluid balance and use of vasoactive drugs on the ability of these patients to achieve the proposed recommended serum level target and the vancomycin serum levels.

RESULTS

Our study showed that only 26% of children reached the 10-20 mg/L serum level whereas the 7-20 mg/L serum level was reached by 51% of patients.

CONCLUSIONS

We observed no evidence of a significant association between the inadequacy of serum level and age. The positive fluid balance also had no influence on the vancomycin serum level but patients using vasoactive drugs had a greater serum level adequacy than patients not using vasoactive drugs.