Innovative approaches to optimizing the delivery of vancomycin in individual patients

Vancomycin Dosing and Monitoring: Critical Evaluation of the Current Practice

After more than six decades of its use as the mainstay antibiotic for the treatment of multidrug-resistant Gram-positive bacterial infections, dosing and monitoring of vancomycin therapy have not been optimized. The current vancomycin therapeutic guidelines recommend empiric doses of 15-20 mg/kg administered by intermittent infusion every 8-12 h in patients with normal kidney function. Additionally, the guidelines recommend trough concentration of 15-20 mg/L as a therapeutic goal for adult patients with severe infections. This review critically discusses the current guidelines considering the basic pharmacokinetics and pharmacodynamics of vancomycin and the recent published reports from clinical studies. More in-depth discussion will be focused on (1) providing evidence of advantages of administering vancomycin by continuous infusion compared to intermittent infusion; (2) revising the current practice of trough-only monitoring versus the area under concentration-time curve (AUC); and (3) assessing the current practice of weight-based dosing versus AUC-based dosing. Using the gathered information presented in this paper, two user-friendly and scientifically based dosing strategies are proposed to improve the efficiency of vancomycin dosing while avoiding the risk of nephrotoxicity and minimizing the cost of therapeutic drug monitoring.

Optimizing Vancomycin Monitoring in Pediatric Patients

BACKGROUND

Several studies have reported that trough levels may not be optimal for monitoring vancomycin therapy, because of overexposure and nephrotoxicity risks. Therefore, we developed a population pharmacokinetic model to optimize vancomycin dosing and monitoring in pediatrics.

METHODS

Data were retrospectively collected on 76 pediatric patients 1-12 years of age, admitted to general pediatric wards or intensive care units at King Saud University Medical City, Riyadh, Saudi Arabia. The predictability of 3 methods for calculating the area under the curve (AUC) at steady state was assessed for optimum vancomycin therapy monitoring. The 3 methods were simple linear regression, Bayesian approach and the 2-sample pharmacokinetic equation method. We also used Monet Carlo simulations to evaluate the dosing of vancomycin.

RESULTS

A 1-compartment model adequately described the data. A strong correlation occurred between the observed and predicted AUC from 0 to 24 hours (AUC0-24h) calculated using the Bayesian approach with a trough sample only or pharmacokinetic equations based on 2 measured samples (R = 0.93 and 0.92, respectively). For the simple linear regression method with a trough sample only, the predicted AUC0-24h at steady state with vancomycin trough levels of 10, 15 and 20 µg/mL were 413, 548 and 714 µg·hour/mL, respectively. The target AUC0-24h above 400 was achieved in 46% and 95% of individuals with trough values of 7-11 and 11-15 µg/mL, respectively. Monte Carlo simulations showed that 60-80 mg/kg/d doses are needed to optimize vancomycin therapy.

CONCLUSIONS

In conclusion, targeting vancomycin trough levels above 15 µg/mL in pediatrics would overshoot the target AUC0-24h above 400 and expose them to unnecessary adverse events.

Prospective evaluation of vancomycin pharmacokinetics in a heterogeneous critically ill population

Rich pharmacokinetic data on vancomycin in critically ill patients are lacking. The purpose of this study was to evaluate the pharmacokinetics of vancomycin in this population using rich pharmacokinetic sampling. Nineteen critically ill patients received individualized vancomycin doses by intermittent infusion to achieve target trough concentrations (15-20 mg/L). Blood samples were collected following the third or later dose of vancomycin. Serial blood samples were collected at 30 min following initiation of the vancomycin infusion; at the end of the infusion; serially at 60, 120, 300, and 480 min after the infusion finished; and immediately prior to the next dose. Vancomycin concentration-time profiles at steady state were fit to a noncompartmental model to determine the pharmacokinetic parameters. Vancomycin trough concentration was correlated to AUC_0-24 (r = 0.83, P < 0.001). Total body weight was a predictor of volume of distribution (r = 0.43, P = 0.03). Age, serum creatinine, and creatinine clearance (CrCl) were found to be predictors for vancomycin clearance (r = -0.67, -0.52, and, 0.72, respectively). CrCl was the best predictor of vancomycin systemic clearance, and addition of other variables to a multivariate model failed to improve model fit. Vancomycin trough concentration may not be an adequate surrogate of AUC_0-24. Additional research is needed to determine dosing strategies to optimize AUC_0-24 while limiting toxicity.

Population Pharmacokinetic Model for Vancomycin Used in Open Heart Surgery: Model-Based Evaluation of Standard Dosing Regimens

The purpose of this study was to investigate the population pharmacokinetics of vancomycin in patients undergoing open heart surgery. In this observational pharmacokinetic study, multiple blood samples were drawn over a 48-h period of intravenous vancomycin in patients who were undergoing open heart surgery. Blood samples were analyzed using an Architect i4000SR immunoassay analyzer. Population pharmacokinetic models were developed using Monolix 4.4 software. Pharmacokinetic-pharmacodynamic (PK-PD) simulations were performed to explore the ability of different dosage regimens to achieve the pharmacodynamic targets. A total of 168 blood samples were analyzed from 28 patients. The pharmacokinetics of vancomycin are best described by a two-compartment model with between-subject variability in clearance (CL), the volume of distribution of the central compartment (V₁), and volume of distribution of the peripheral compartment (V₂). The CL and the V₁ of vancomycin were related to creatinine CL (CL_CR), body weight, and albumin concentration. Dosing simulations showed that standard dosing regimens of 1 and 1.5 g failed to achieve the PK-PD target of AUC_0-24/MIC > 400 for an MIC of 1 mg/liter, while high weight-based dosing regimens were able to achieve the PK-PD target. In summary, the administration of standard doses of 1 and 1.5 g of vancomycin two times daily provided inadequate antibiotic prophylaxis in patients undergoing open heart surgery. The same findings were obtained when 15- and 20-mg/kg doses of vancomycin were administered. Achieving the PK-PD target required higher doses (25 and 30 mg/kg) of vancomycin.

The Relationship Between Vancomycin Trough Concentrations and AUC/MIC Ratios in Pediatric Patients: A Qualitative Systematic Review

BACKGROUND

In adults, the area under the concentration-time curve (AUC) divided by the minimum inhibitory concentration (MIC) is associated with better clinical and bacteriological response to vancomycin in patients with methicillin-resistant Staphylococcus aureus who achieve target AUC/MIC ≥ 400. This target is often extrapolated to pediatric patients despite the lack of similar evidence. The impracticalities of calculating the AUC in practice means vancomycin trough concentrations are used to predict the AUC/MIC.

OBJECTIVE

This review aimed to determine the relationship between vancomycin trough concentrations and AUC/MIC in pediatric patients.

METHODS

We searched the MEDLINE and Embase databases, the Cochrane Database of Systematic Reviews, and the Cochrane Central Register of Controlled Trials using the medical subject heading (MeSH) terms vancomycin and AUC and pediatric* or paediatric*. Articles were included if they were published in English and reported a relationship between vancomycin trough concentrations and AUC/MIC.

RESULTS

Of 122 articles retrieved, 11 met the inclusion criteria. One trial reported a relationship between vancomycin trough concentrations, AUC/MIC, and clinical outcomes but was likely underpowered. Five studies found troughs 6-10 mg/l were sufficient to attain an AUC/MIC > 400 in most general hospitalized pediatric patients. One study in patients undergoing cardiothoracic surgery found a trough of 18.4 mg/l achieved an AUC/MIC > 400. Two oncology studies reported troughs ≥ 15 mg/l likely attained an AUC/MIC ≥ 400. In critical care patients: one study found a trough of 9 mg/l did not attain the AUC/MIC target; another found 7 mg/l corresponded to an AUC/MIC of 400.

CONCLUSIONS

Potential vancomycin targets varied based on the population studied but, for general hospitalized pediatric patients, troughs of 6-10 mg/l are likely sufficient to achieve AUC/MIC ≥ 400. For MIC ≥ 2 mg/l, higher troughs are likely necessary to achieve an AUC/MIC ≥ 400. More research is needed to determine the relationships between vancomycin trough concentrations, AUC/MIC, and clinical outcomes.

The Impact of AUC-Based Monitoring on Pharmacist-Directed Vancomycin Dose Adjustments in Complicated Methicillin-Resistant Staphylococcus aureus Infection

OBJECTIVE

This study aimed to assess the impact of area under the curve (AUC)-based vancomycin monitoring on pharmacist-initiated dose adjustments after transitioning from a trough-only to an AUC-based monitoring method at our institution.

METHODS

A retrospective cohort study of patients treated with vancomycin for complicated methicillin-resistant Staphylococcus aureus (MRSA) infection between November 2013 and December 2016 was conducted. The frequency of pharmacist-initiated dose adjustments was assessed for patients monitored via trough-only and AUC-based approaches for trough ranges: 10 to 14.9 mg/L and 15 to 20 mg/L.

RESULTS

Fifty patients were included: 36 in the trough-based monitoring and 14 in the AUC-based-monitoring group. The vancomycin dose was increased in 71.4% of patients when troughs were 10 to 14.9 mg/L when a trough-only approach was used and in only 25% of patients when using AUC estimation (P = .048). In the AUC group, the dose was increased only when AUC/minimum inhibitory concentration (MIC) <400; unchanged regimens had an estimated AUC/MIC ≥400. The AUC-based monitoring did not significantly increase the frequency of dose reductions when trough concentrations were 15 to 20 mg/L (AUC: 33.3% vs trough: 4.6%; P = .107).

CONCLUSIONS

The AUC-based monitoring resulted in fewer patients with dose adjustments when trough levels were 10 to 14.9 mg/L. The AUC-based monitoring has the potential to reduce unnecessary vancomycin exposure and warrants further investigation.

Pharmacokinetic/Pharmacodynamic Determinants of Vancomycin Efficacy in Enterococcal Bacteremia

While pharmacokinetic-pharmacodynamic targets for vancomycin therapy are recognized for invasive methicillin-resistant Staphylococcus aureus infections, scant data are available to guide therapy for other Gram-positive infections. A retrospective single-center cohort of patients with Enterococcus bacteremia hospitalized between 1 January 2009 and 31 May 2015 were studied. The average vancomycin AUC_0-24 was computed using a Bayesian approach. The MIC was determined by gradient diffusion (Etest; bioMérieux), and the average AUC_0-24/MIC value over the initial 72 h of therapy was calculated. We assessed 30-day all-cause mortality as the primary outcome. Classification and regression tree analysis (CART) was used to identify the vancomycin AUC_0-24/MIC value associated with 30-day mortality. Fifty-seven patients with enterococcal bacteremia (32 E. faecium, 21 E. faecalis, and 4 other Enterococcus spp.) were studied. The median vancomycin MIC was 0.75 mg/liter (range, 0.38 to 3 mg/liter). All-cause 30-day mortality occurred in 10 of 57 patients (17.5%). A CART-derived vancomycin AUC/MIC_Etest value of ≥389 was associated with reduced mortality (P = 0.017); failure to achieve this independently predicted 30-day mortality (odds ratio, 6.83 [95% confidence interval = 1.51 to 30.84]; P = 0.01). We found that a vancomycin AUC/MIC_Etest value of ≥389 achieved within 72 h was associated with reduced mortality. Larger, prospective studies are warranted to verify the vancomycin pharmacodynamic targets associated with maximal clinical outcomes and acceptable safety.

Prospective Trial on the Use of Trough Concentration versus Area under the Curve To Determine Therapeutic Vancomycin Dosing

We hypothesized that dosing vancomycin to achieve trough concentrations of >15 mg/liter overdoses many adults compared to area under the concentration-time curve (AUC)-guided dosing. We conducted a 3-year, prospective study of vancomycin dosing, plasma concentrations, and outcomes. In year 1, nonstudy clinicians targeted trough concentrations of 10 to 20 mg/liter (infection dependent) and controlled dosing. In years 2 and 3, the study team controlled vancomycin dosing with BestDose Bayesian software to achieve a daily, steady-state AUC/MIC ratio of ≥400, with a maximum AUC value of 800 mg · h/liter, regardless of trough concentration. For Bayesian estimation of AUCs, we used trough samples in years 1 and 2 and optimally timed samples in year 3. We enrolled 252 adults who were ≥18 years old with ≥1 available vancomycin concentration. Only 19% of all trough concentrations were therapeutic versus 70% of AUCs (P < 0.0001). After enrollment, median trough concentrations by year were 14.4, 9.7, and 10.9 mg/liter (P = 0.005), with 36%, 7%, and 6% over 15 mg/liter (P < 0.0001). Bayesian AUC-guided dosing in years 2 and 3 was associated with fewer additional blood samples per subject (3.6, 2.0, and 2.4; P = 0.003), shorter therapy durations (8.2, 5.4, and 4.7 days; P = 0.03), and reduced nephrotoxicity (8%, 0%, and 2%; P = 0.01). The median inpatient stay was 20 days among nephrotoxic patients versus 6 days (P = 0.002). There was no difference in efficacy by year, with 42% of patients having microbiologically proven infections. Compared to trough concentration targets, AUC-guided, Bayesian estimation-assisted vancomycin dosing was associated with decreased nephrotoxicity, reduced per-patient blood sampling, and shorter length of therapy, without compromising efficacy. These benefits have the potential for substantial cost savings. (This study has been registered at ClinicalTrials.gov under registration no. NCT01932034.).

Is Trough Concentration of Vancomycin Predictive of the Area Under the Curve? A Clinical Study in Elderly Patients

BACKGROUND

Current guidelines suggest that vancomycin trough concentrations (Cmin) between 15 and 20 mg/L should be achieved to optimize vancomycin exposure and effect. The objective of this study was to analyze the correlation between vancomycin Cmin and the area under the concentration-time curve (AUC) and assess the ability to predict an AUC target of 400 mg·h/L based on Cmin.

METHODS

A retrospective analysis of vancomycin therapeutic drug monitoring data collected in 95 elderly patients treated with intermittent intravenous vancomycin was performed. For each patient, individual pharmacokinetic parameters of vancomycin and AUC24 were estimated from concentration measurements using a Bayesian approach. The relationship between vancomycin Cmin and AUC was studied using global and local correlation analysis as well as logistic regression with Receiver Operating Characteristic curve analysis.

RESULTS

The overall correlation between AUC24 and Cmin was significant but moderate (R = 0.51). When vancomycin Cmin was greater than 15 mg/L, the corresponding AUC24 was >400 mg·h/L in 95% of cases. However, AUC24 values >400 mg·h/L were obtained with Cmin < 15 mg/L in more than 30% of the cases. The logistic regression analysis identified a Cmin value of 10.8 mg/L as the optimal predictor of AUC24 > 400 mg·h/L.

CONCLUSIONS

The results of this study indicate that the recommended target range of 15-20 mg/L for vancomycin Cmin seems acceptable for controlling vancomycin exposure, although a value of approximately 11 mg/L appears to be optimal and may be safer.

A Quasi-Experiment To Study the Impact of Vancomycin Area under the Concentration-Time Curve-Guided Dosing on Vancomycin-Associated Nephrotoxicity

Evidence suggests that maintenance of vancomycin trough concentrations at between 15 and 20 mg/liter, as currently recommended, is frequently unnecessary to achieve the daily area under the concentration-time curve (AUC₂₄) target of ≥400 mg · h/liter. Many patients with trough concentrations in this range have AUC₂₄ values in excess of the therapeutic threshold and within the exposure range associated with nephrotoxicity. On the basis of this, the Detroit Medical Center switched from trough concentration-guided dosing to AUC-guided dosing to minimize potentially unnecessary vancomycin exposure. The primary objective of this analysis was to assess the impact of this intervention on vancomycin-associated nephrotoxicity in a single-center, retrospective quasi-experiment of hospitalized adult patients receiving intravenous vancomycin from 2014 to 2015. The primary analysis compared the incidence of nephrotoxicity between patients monitored by assessment of the AUC₂₄ and those monitored by assessment of the trough concentration. Multivariable logistic and Cox proportional hazards regression examined the independent association between the monitoring strategy and nephrotoxicity. Secondary analysis compared vancomycin exposures (total daily dose, AUC, and trough concentrations) between monitoring strategies. Overall, 1,280 patients were included in the analysis. After adjusting for severity of illness, comorbidity, duration of vancomycin therapy, and concomitant receipt of nephrotoxins, AUC-guided dosing was independently associated with lower nephrotoxicity by both logistic regression (odds ratio, 0.52; 95% confidence interval [CI], 0.34 to 0.80; P = 0.003) and Cox proportional hazards regression (hazard ratio, 0.53; 95% CI, 0.35 to 0.78; P = 0.002). AUC-guided dosing was associated with lower total daily vancomycin doses, AUC values, and trough concentrations. Vancomycin AUC-guided dosing was associated with reduced nephrotoxicity, which appeared to be a result of reduced vancomycin exposure.

A Strategy for Dosing Vancomycin to Therapeutic Targets Using Only Trough Concentrations

Effective treatment of complicated methicillin-resistant Staphylococcus aureus (MRSA) infections with vancomycin requires a 24-h area under the concentration-time curve (AUC₂₄) to minimum inhibitory concentration (MIC) ratio of at least 400. To ensure goal AUC₂₄ has been reached requires either dosing to concentrations strongly associated with nephrotoxicity, measurement of patient-specific pharmacokinetics, or use of Bayesian statistics. In this study, we show a method of determining patient-specific pharmacokinetics and dosing to therapeutic AUC₂₄ while minimizing potentially toxic concentrations, guided by only trough measurements. A Monte-Carlo simulation of 10,000 patients with complicated MRSA infections was prepared from two-compartment pharmacokinetic parameters using patient data extracted from the literature. The proposed method of determining patient-specific pharmacokinetics using consecutive trough concentrations was found to be more accurate than the conventional peak-trough method for peaks measured up to 4 h after infusion. Simulated human error in trough timing was found to reduce accuracy of the consecutive trough method, but an approach to resolve timing errors during a loading sequence or at steady-state using iteration is proposed. Both the simulated minimized concentration strategy and trough-based dosing to 15-20 mg/L had a high probability of achieving AUC₂₄ at least 400 mg·h/L, but conventional trough-based dosing was associated with higher probability of potentially toxic 24-h doses and trough concentrations. The proposed strategy must be validated in real patients, with outcomes assessed before it is used in daily practice, but the theoretical benefits found in the simulation suggest this simple strategy should be considered with other AUC₂₄-based approaches.

Pilot Study of a Bayesian Approach To Estimate Vancomycin Exposure in Obese Patients with Limited Pharmacokinetic Sampling

This study evaluated the predictive performance of a Bayesian PK estimation method (ADAPT V) to estimate the 24-h vancomycin area under the curve (AUC) with limited pharmacokinetic (PK) sampling in adult obese patients receiving vancomycin for suspected or confirmed Gram-positive infections. This was an Albany Medical Center Institutional Review Board-approved prospective evaluation of 12 patients. Patients had a median (95% confidence interval) age of 61 years (39 to 71 years), a median creatinine clearance of 86 ml/min (75 to 120 ml/min), and a median body mass index of 45 kg/m² (40 to 52 kg/m²). For each patient, five PK concentrations were measured, and four different vancomycin population PK models were used as Bayesian priors to estimate the vancomycin AUC (AUC_FULL). Using each PK model as a prior, data-depleted PK subsets were used to estimate the 24-h AUC (i.e., peak and trough data [AUC_PT], midpoint and trough data [AUC_MT], and trough-only data [AUC_T]). The 24-h AUC derived from the full data set (AUC_FULL) was compared to the AUC derived from data-depleted subsets (AUC_PT, AUC_MT, and AUC_T) for each model. For the four sets of analyses, AUC_FULL estimates ranged from 437 to 489 mg·h/liter. The AUC_PT provided the best approximation of the AUC_FULL; AUC_MT and AUC_T tended to overestimate AUC_FULL Further prospective studies are needed to evaluate the impact of AUC monitoring in clinical practice, but the findings from this study suggest that the vancomycin AUC can be estimated with good precision and accuracy with limited PK sampling using Bayesian PK estimation software.

Relationship between vancomycin exposure and outcomes among patients with MRSA bloodstream infections with vancomycin Etest® MIC values of 1.5mg/L: A pilot study

Data suggest that vancomycin is less effective for methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infection (BSI) with vancomycin Etest® MIC (MIC_Etest) ≥1.5 mg/L. No published studies have evaluated the relationship between vancomycin exposure and outcomes among patients with MRSA BSIs vancomycin MIC_Etest ≥1.5 mg/L. This study was a retrospective cohort of 71 hospitalized, adult, non-dialysis patients with MRSA BSIs treated with vancomycin. All but three patients had a vancomycin MIC_Etest of 1.5 mg/L. Achievement of CART-derived AUC_24-48h of at least 550 mg*h/L (AUC_24-48h/MIC of 366 mg*h/L) was associated with a lower incidence of treatment failure. In multivariate analyses, the risk ratio was 0.45 for the CART-derived AUC_24-48h threshold, indicating that achievement of the CART-derived AUC_24-48h threshold of 550 was associated with a 2-fold decrease in treatment failure. These findings suggest a potential association between vancomycin exposure and outcomes in patients with MRSA BSIs with MIC_Etest ≥1.5 mg/L. As this study was retrospective, these findings provide the basis for a future large-scale, multi-center prospective study.

Peak Measurement for Vancomycin AUC Estimation in Obese Adults Improves Precision and Lowers Bias

Vancomycin area under the curve (AUC) estimates may be skewed in obese adults due to weight-dependent pharmacokinetic parameters. We demonstrate that peak and trough measurements reduce bias and improve the precision of vancomycin AUC estimates in obese adults (n = 75) and validate this in an independent cohort (n = 31). The precision and mean percent bias of Bayesian vancomycin AUC estimates are comparable between covariate-dependent (R² = 0.774, 3.55%) and covariate-independent (R² = 0.804, 3.28%) models when peaks and troughs are measured but not when measurements are restricted to troughs only (R² = 0.557, 15.5%).

Dosing strategies to optimize currently available anti-MRSA treatment options (Part 1: IV options)

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) continues to be a predominant pathogen resulting in significant morbidity and mortality. Optimal dosing of anti-MRSA agents is needed to help prevent the development of antimicrobial resistance and to increase the likelihood of a favorable clinical outcome. Areas covered: This review summarizes the available data for antimicrobials routinely used for MRSA infections that are not administered orally or topically. We make recommendations and highlight the current gaps in the literature. A PubMed (1966 - Present) search was performed to identify relevant literature for this review. Expert commentary: Improvements in MIC determination and therapeutic drug monitoring are needed to fully implement individualized dosing that optimizes antimicrobial pharmacodynamics.Additional data will become available for these agents in regards to effectiveness for severe MRSA infections and pharmacokinetic data for special patient populations.

Neutropenia is independently associated with sub-therapeutic serum concentration of vancomycin

BACKGROUND

We aimed to identify the impact of the presence of neutropenia on serum vancomycin concentration (SVC).

METHODS

A retrospective study was conducted from January 2005 to December 2015. The study population was comprised of adult patients who were performed serum concentration of vancomycin. Patients with renal failure or using non-conventional dosages of vancomycin were excluded.

RESULTS

A total of 1307 adult patients were included in this study, of whom 163 (12.4%) were neutropenic. Patients with neutropenia presented significantly lower SVCs than non-neutropenic patients (P<0.0001). Multiple linear regressions showed significant association between neutropenia and trough SVC (beta coefficients, -2.351; P=0.004). Multiple logistic regression analysis also revealed a significant association between sub-therapeutic vancomycin concentrations (trough SVC values<10mg/l) and neutropenia (odds ratio, 1.75, P=0.029) CONCLUSIONS: The presence of neutropenia is significantly associated with low SVC, even after adjusting for other variables. Therefore, neutropenic patients had a higher risk of sub-therapeutic SVC compared with non-neutropenic patients. We recommended that vancomycin therapy should be monitored with TDM-guided optimization of dosage and intervals, especially in neutropenic patients.

Intravenous Vancomycin Dosing in the Elderly: A Focus on Clinical Issues and Practical Application

The elderly population can be divided into three distinct age groups: 65-74 years (young-old), 75-84 years (middle-old), and 85+ years (old-old). Despite evidence of a shift in leading causes for mortality in the elderly from infectious diseases to chronic conditions, infections are still a serious cause of death in this population. These patients are at increased risk due to weakened immune systems, an increased prevalence of underlying comorbidities, and decreased physiologic reserves to fight infection. Additionally, elderly patients, especially adults in institutional settings, are at an increased risk of colonization and subsequent infection with methicillin-resistant Staphylococcus aureus at a rate that is five times higher than in younger individuals, causing an increase in empiric and definitive vancomycin use. Elderly patients have unique characteristics that make dosing vancomycin a challenge for clinicians, such as increased volume of distribution and decreased renal function. Using the best available evidence, it is recommended to initiate lower empiric maintenance doses and monitor vancomycin serum concentrations earlier than steady state to accurately calculate drug elimination and make appropriate dose adjustments.

Daptomycin Improves Outcomes Regardless of Vancomycin MIC in a Propensity-Matched Analysis of Methicillin-Resistant Staphylococcus aureus Bloodstream Infections

Vancomycin remains the mainstay treatment for methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSIs) despite increased treatment failures. Daptomycin has been shown to improve clinical outcomes in patients with BSIs caused by MRSA isolates with vancomycin MICs of >1 mg/liter, but these studies relied on automated testing systems. We evaluated the outcomes of BSIs caused by MRSA isolates for which vancomycin MICs were determined by standard broth microdilution (BMD). A retrospective, matched cohort of patients with MRSA BSIs treated with vancomycin or daptomycin from January 2010 to March 2015 was completed. Patients were matched using propensity-adjusted logistic regression, which included age, Pitt bacteremia score, primary BSI source, and hospital of care. The primary endpoint was clinical failure, which was a composite endpoint of the following metrics: 30-day mortality, bacteremia with a duration of ≥7 days, or a change in anti-MRSA therapy due to persistent or worsening signs or symptoms. Secondary endpoints included MRSA-attributable mortality and the number of days of MRSA bacteremia. Independent predictors of failure were determined through conditional backwards-stepwise logistic regression with vancomycin BMD MIC forced into the model. A total of 262 patients were matched. Clinical failure was significantly higher in the vancomycin cohort than in the daptomycin cohort (45.0% versus 29.0%; P = 0.007). All-cause 30-day mortality was significantly higher in the vancomycin cohort (15.3% versus 6.1%; P = 0.024). These outcomes remained significant when stratified by vancomycin BMD MIC. There was no significant difference in the length of MRSA bacteremia. Variables independently associated with treatment failure included vancomycin therapy (adjusted odds ratio [aOR] = 2.16, 95% confidence interval [CI] = 1.24 to 3.76), intensive care unit admission (aOR = 2.46, 95% CI = 1.34 to 4.54), and infective endocarditis as the primary source (aOR = 2.33, 95% CI = 1.16 to 4.68). Treatment of MRSA BSIs with daptomycin was associated with reduced clinical failure and 30-day mortality; these findings were independent of vancomycin BMD MIC.

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.

Vancomycin Dosing and Pharmacokinetics in Postoperative Pediatric Cardiothoracic Surgery Patients

OBJECTIVES

This study compared vancomycin trough concentrations and pharmacokinetic parameters in pediatric cardiothoracic surgery (CTS) patients versus those in controls receiving 20 mg/kg/dose, intravenously, every 8 hours.

METHODS

A retrospective study was conducted in children <18 years of age, following CTS, versus an age-and sex-matched control group. The primary objective was to determine differences in trough concentrations between groups. Secondary objectives included comparisons of pharmacokinetics between groups and development of vancomycin-associated acute kidney injury (AKI), defined as a doubling in serum creatinine from baseline. Also dosing projections were developed to target an area-under-the-curve-to-minimum inhibitory concentration (AUC:MIC) ratio of ≥400.

RESULTS

Twenty-seven patients in each group were evaluated. Mean trough concentrations were significantly different between groups (CTS: 18.4 mg/L; control: 8.8 mg/L; p < 0.01). Vancomycin-associated acute kidney injury AKI was significantly higher in the CTS group than in controls (25.9% versus 0%, respectively, p<0.01). There were significant differences in vancomycin elimination rates, with a high degree of variability, but no statistical differences in other parameters. Based on dosing projections, CTS patients would require 21 to 88 mg/kg/day, with a dosage interval determined by the child's glomerular filtration rate to achieve the target AUC:MIC ≥400.

CONCLUSIONS

Vancomycin dosage of 20 mg/kg/dose intravenously every 8 hours achieved significantly higher trough concentrations in CTS patients than in controls. Pharmacokinetic parameters were highly variable in CTS patients, indicating more individualization of dosage is needed. A future prospective study is needed to determine whether the revised dosage projections achieve the AUC:MIC target and to determine whether these regimens are associated with less vancomycin-associated AKI.

Achievement of Vancomycin Therapeutic Goals in Critically Ill Patients: Early Individualization May Be Beneficial

Objective. The aim of our study was to assess and validate the effectiveness of early dose adjustment of vancomycin based on first dose monitoring in achieving target recommended goal in critically ill patients. Methods. Twenty critically ill patients with sepsis received loading dose of 25 mg/kg of vancomycin and then were randomly assigned to 2 groups. Group 1 received maximum empirical doses of vancomycin of 15 mg/kg every 8 hrs. In group 2, the doses were individualized based on serum concentrations of vancomycin. First dose nonsteady state sampling was used to calculate pharmacokinetic parameters of the patients within 24 hours. Results. Steady state trough serum concentrations were significantly higher in group 2 in comparison with group 1 (19.4 ± 4.4 mg/L versus 14.4 ± 4.3 mg/L) (P = 0.03). Steady state AUCs were significantly higher in group 2 compared with group 1 (665.9 ± 136.5 mg·hr/L versus 490.7 ± 101.1 mg·hr/L) (P = 0.008). Conclusions. With early individualized dosing regimen, significantly more patients achieved peak and trough steady state concentrations. In the context of pharmacokinetic/pharmacodynamic goal of area under the time concentration curve to minimum inhibitory concentration (AUC/MIC) ≥400 and also to obtain trough serum concentration of vancomycin of ≥15 mg/L, it is necessary to individualize doses of vancomycin in critically ill patients.

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.

Vancomycin continuous infusion versus intermittent infusion during continuous venovenous hemofiltration: slow and steady may win the race

Background

Vancomycin during continuous venovenous hemofiltration (CVVH) is either administered by intermittent infusion (II) or continuous infusion (CI). In this patient population, the best method to rapidly achieve target serum concentrations of 15 mcg/ml to 25 mcg/ml remains to be elucidated. We hypothesized that CI would achieve a target serum level of 15 mcg/ml to 25 mcg/ml within 24 h of the initiation of therapy more consistently than II.

Methods

A retrospective cohort study of adult patients admitted to the intensive care unit (ICU) between 2011 and 2014 receiving intravenous vancomycin with 24-hour serum level while on CVVH was included. Patients were excluded from this review if they had residual renal function during CVVH, were concomitantly on extracorporeal membrane oxygenation, or if the first dose of vancomycin was received six or more hours prior to the initiation of CVVH. The primary outcome was the achievement of a therapeutic level of 15mcg/ml to 25 mcg/ml by 24 hours.

Results

Fifty-nine patients met the inclusion criteria and 14 received CI and 45 in II. Therapeutic 24-hour levels were achieved in 14/14 versus 2/45 in CI and II, respectively (p < 0.001). Mean 24-hour vancomycin levels were 20.35 ± 2.78 mcg/ml for CI compared to 9.7 ± 3.52 mcg/ml for II (p < 0.001). Mean loading dose was 26.65 ± 3.06 mg/kg for CI compared to 17.58 ± 5.72 mg/kg for II (p < 0.001). Daily maintenance doses were 15.66 ± 6.26 mg/kg for CI compared to 17.28 ± 4.96 mg/kg for II (p = 0.339). In the subgroup of 27 patients who received vancomycin-loading dose >20 mg/kg, mean 24-hour levels were 20.35 ± 2.78 mcg/ml for CI versus 11.8 ± 2.7 mcg/ml for II (p < 0.001). No significant differences were found between patients in the two groups with respect to CVVH rate and length of CVVH prior to vancomycin administration.

Conclusions

The results of our study suggest that critically ill patients on CVVH treated with CI achieved the target level faster than II and consistently keep the vancomycin level within target range.

Balancing vancomycin efficacy and nephrotoxicity: should we be aiming for trough or AUC/MIC?

Sixty years later, the question that still remains is how to appropriately utilize vancomycin in the pediatric population. The Infectious Diseases Society of America published guidelines in 2011 that provide guidance for dosing and monitoring of vancomycin in adults and pediatrics. However, goal vancomycin trough concentrations of 15-20 μg/mL for invasive infections caused by methicillin-resistant Staphylococcus aureus were based primarily on adult pharmacokinetic and pharmacodynamic data that achieved an area under the curve to minimum inhibitory concentration ratio (AUC/MIC) of ≥400. Recent pediatric literature shows that vancomycin trough concentrations needed to achieve the target AUC/MIC are different than the adult goal troughs cited in the guidelines. This paper addresses several thoughts, including the role of vancomycin AUC/MIC in dosing strategies and safety monitoring, consistency in laboratory reporting, and future directions for calculating AUC/MIC in pediatrics.

Influence of renal function estimation on pharmacokinetic modeling of vancomycin in elderly patients

Vancomycin is a renally excreted drug, and its body clearance correlates with creatinine clearance. However, the renal function estimation equation that best predicts vancomycin clearance has not been established yet. The objective of this study was to compare the abilities of different renal function estimation equations to describe vancomycin pharmacokinetics in elderly patients. The NPAG algorithm was used to perform population pharmacokinetic analysis of vancomycin concentrations in 78 elderly patients. Six pharmacokinetic models of vancomycin clearance were built, based on the following equations: Cockcroft-Gault (CG), Jelliffe (JEL), Modification of Diet in Renal Disease (MDRD), Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) (both in milliliters per minute per 1.73 m(2)), and modified MDRD and CKD-EPI equations (both in milliliters per minute). Goodness-of-fit and predictive performances of the six PK models were compared in a learning set (58 subjects) and a validation set (20 patients). Final analysis was performed to estimate population parameters in the entire population. In the learning step, the MDRD-based model best described the data, but the CG- and JEL-based models were the least biased. The mean weighted errors of prediction were significantly different between the six models (P = 0.0071). In the validation group, predictive performances were not significantly different. However, the use of a renal function estimation equation different from that used in the model building could significantly alter predictive performance. The final analysis showed important differences in parameter distributions and AUC estimation across the six models. This study shows that methods used to estimate renal function should not be considered interchangeable for pharmacokinetic modeling and model-based estimation of vancomycin concentrations in elderly patients.