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

A Comparison of Vancomycin Area Under the Curve and Trough Concentration in Specific Populations

Background: Vancomycin is an antibiotic known to cause nephrotoxicity, particularly when a vancomycin trough of 15 to 20 mg/L, a surrogate for an area under the curve (AUC) of at least 400 mgh/L, is targeted. Although monitoring vancomycin AUC is more resource intensive, it may especially benefit populations expected to be at higher risk of nephrotoxicity. Objective: To describe the proportion of discordance between vancomycin AUC and trough concentration in targeted high-risk populations. Methods: A prospective observational review was conducted on adults receiving intravenous vancomycin for more than 48 hours from May 9 to June 3, 2022. Patients included were elderly, obese, had renal dysfunction, and/or received 4 grams or more of vancomycin daily with a pending vancomycin trough concentration. A peak concentration was ordered by a project team member to calculate AUC to assess discordance. Results: A total of 47 patients were included with 87 vancomycin minimum concentration (Cmin)/AUC pairs analyzed. Discordance was observed in 52.9% of Cmin/AUC pairs in the entire cohort. The majority (79%) of the 43 Cmin levels <15 mg/L had an associated AUC >400 mgh/L and 57% of 21 Cmin levels within the 15 to 20 mg/L range had an AUC >600 mgh/L. Conclusion: A high degree of discordance between vancomycin Cmin and AUC was present in patients considered to be at high risk of nephrotoxicity. Monitoring vancomycin AUC in these patients may reduce the risk of nephrotoxicity.

Is it time to recommend AUC-based vancomycin therapeutic drug monitoring only? A cross-sectional survey in China

Background

The latest published therapeutic drug monitoring (TDM) guidelines for vancomycin recommend changing trough-based monitoring to area under the concentration-to-time curve (AUC)-based monitoring. This study aimed to evaluate the implementation status and perceptions of vancomycin AUC-based TDM in China and to determine the challenges in performing AUC-based TDM.

Methods

A nationwide cross-sectional survey was conducted in China using an online questionnaire. The questionnaire comprised a total of 25 questions with open- and closed-ended answers to collect information about the current implementation of vancomycin TDM and the participants' perceptions of these practices. The questionnaire responses were collected via the Questionnaire Star platform and analyzed.

Results

A total of 161 questionnaires were completed by 131 hospitals and were included. Approximately 59.5% (78/131) of the surveyed hospitals conducted vancomycin TDM; however, only 10.7% (14/131) of these hospitals performed AUC-based vancomycin TDM. Of the eligible participants, 58.4% (94/161) had experience with vancomycin TDM, and only 37 participants (37/161, 23.0%) had the ability to estimate the AUC, primarily through Bayesian simulation (33/161, 20.5%). The participants considered the following challenges to implementing AUC-based monitoring: (1) the high cost of AUC-based monitoring; (2) inadequate knowledge among pharmacists and/or physicians; (3) the complexity of AUC calculations; (4) difficulty obtaining AUC software; and (5) unclear benefit of AUC-based monitoring.

Conclusion

The majority of surveyed hospitals have not yet implemented AUC-based vancomycin TDM. Multiple challenges should be addressed before wide implementation of AUC-based monitoring, and guidance for trough-based monitoring is still needed.

A Deep Learning-Based Approach for Prediction of Vancomycin Treatment Monitoring: Retrospective Study Among Patients With Critical Illness

BACKGROUND

Vancomycin pharmacokinetics are highly variable in patients with critical illnesses, and clinicians commonly use population pharmacokinetic (PPK) models based on a Bayesian approach to dose. However, these models are population-dependent, may only sometimes meet the needs of individual patients, and are only used by experienced clinicians as a reference for making treatment decisions. To assist real-world clinicians, we developed a deep learning-based decision-making system that predicts vancomycin therapeutic drug monitoring (TDM) levels in patients in intensive care unit.

OBJECTIVE

This study aimed to establish joint multilayer perceptron (JointMLP), a new deep-learning model for predicting vancomycin TDM levels, and compare its performance with the PPK models, extreme gradient boosting (XGBoost), and TabNet.

METHODS

We used a 977-case data set split into training and testing groups in a 9:1 ratio. We performed external validation of the model using 1429 cases from Kangwon National University Hospital and 2394 cases from the Medical Information Mart for Intensive Care-IV (MIMIC-IV). In addition, we performed 10-fold cross-validation on the internal training data set and calculated the 95% CIs using the metric. Finally, we evaluated the generalization ability of the JointMLP model using the MIMIC-IV data set.

RESULTS

Our JointMLP model outperformed other models in predicting vancomycin TDM levels in internal and external data sets. Compared to PPK, the JointMLP model improved predictive power by up to 31% (mean absolute error [MAE] 6.68 vs 5.11) on the internal data set and 81% (MAE 11.87 vs 6.56) on the external data set. In addition, the JointMLP model significantly outperforms XGBoost and TabNet, with a 13% (MAE 5.75 vs 5.11) and 14% (MAE 5.85 vs 5.11) improvement in predictive accuracy on the inner data set, respectively. On both the internal and external data sets, our JointMLP model performed well compared to XGBoost and TabNet, achieving prediction accuracy improvements of 34% and 14%, respectively. Additionally, our JointMLP model showed higher robustness to outlier data than the other models, as evidenced by its higher root mean squared error performance across all data sets. The mean errors and variances of the JointMLP model were close to zero and smaller than those of the PPK model in internal and external data sets.

CONCLUSIONS

Our JointMLP approach can help optimize treatment outcomes in patients with critical illnesses in an intensive care unit setting, reducing side effects associated with suboptimal vancomycin administration. These include increased risk of bacterial resistance, extended hospital stays, and increased health care costs. In addition, the superior performance of our model compared to existing models highlights its potential to help real-world clinicians.

Analytical Validation of Aptamer-Based Serum Vancomycin Monitoring Relative to Automated Immunoassays

The practice of monitoring therapeutic drug concentrations in patient biofluids can significantly improve clinical outcomes while simultaneously minimizing adverse side effects. A model example of this practice is vancomycin dosing in intensive care units. If dosed correctly, vancomycin can effectively treat methicillin-resistant streptococcus aureus (MRSA) infections. However, it can also induce nephrotoxicity or fail to kill the bacteria if dosed too high or too low, respectively. Although undeniably important to achieve effectiveness, therapeutic drug monitoring remains inconvenient in practice due primarily to the lengthy process of sample collection, transport to a centralized facility, and analysis using costly instrumentation. Adding to this workflow is the possibility of backlogs at centralized clinical laboratories, which is not uncommon and may result in additional delays between biofluid sampling and concentration measurement, which can negatively affect clinical outcomes. Here, we explore the possibility of using point-of-care electrochemical aptamer-based (E-AB) sensors to minimize the time delay between biofluid sampling and drug measurement. Specifically, we conducted a clinical agreement study comparing the measurement outcomes of E-AB sensors to the benchmark automated competitive immunoassays for vancomycin monitoring in serum. Our results demonstrate that E-ABs are selective for free vancomycin─the active form of the drug, over total vancomycin. In contrast, competitive immunoassays measure total vancomycin, including both protein-bound and free drug. Accounting for these differences in a pilot study consisting of 85 clinical samples, we demonstrate that the E-AB vancomycin measurement achieved a 95% positive correlation rate with the benchmark immunoassays. Therefore, we conclude that E-AB sensors could provide clinically useful stratification of patient samples at trough sampling to guide effective vancomycin dose recommendations.

What Is the Best Vancomycin Therapeutic Drug Monitoring Parameter to Assess Efficacy? A Critical Review of Experimental Data and Assessment of the Need for Individual Patient Minimum Inhibitory Concentration Value

Therapeutic drug monitoring is recommended for the use of vancomycin, but a recent widely publicized US medical society consensus statement has changed the suggested optimal method(s) of dose adjustment. Specifically, 24 h area under the curve (AUC₂₄)-based monitoring is has been recommended for vancomycin in preference to monitoring of trough concentrations. One reason cited for this change is the claim that AUC₂₄ is a superior correlate to efficacy than trough (Cmin). Evidence from a number of retrospective analyses have been critically reviewed and determined to have weaknesses. This narrative review focuses on the experimental studies performed in vivo in animal models of infection and in vitro to determine the extent to which these data may provide a compelling distinction between pharmacokinetic/pharmacodynamics (PKPD) parameters that may translate to clinical use in therapeutic drug monitoring. Animal in vivo studies have been presented at conferences, but no original peer reviewed studies could be found that compare various PKPD parameters. These conference proceeding findings were supportive but unconvincing, even though they were favorably presented subsequently in review articles and clinical practice guidelines. In vitro data are somewhat conflicting, but the range of concentrations may play a role in the discrepancies found. It has been suggested that MIC may be assumed to have a value of 1 mg/L; however, it can be demonstrated that this assumption may lead to considerable discrepancy from results with an actual MIC value. The AUC₂₄ parameter has been weighed against the percentage of time above the MIC (%T > MIC) as a comparative PKPD parameter, yet this may be an inappropriate comparison for vancomycin since all clinically useful dosing provides 100% T > MIC. Regardless, there is a distinction between clinical TDM parameters and PKPD parameters, so, in practice, the change to AUC₂₄:MIC based on animal experiments and in vitro evidence for vancomycin may be premature.

Doing More With Less: Pragmatic Implementation of Vancomycin Area-Under-the-Curve (AUC) Monitoring

Universal area-under-the-curve (AUC) guided vancomycin therapeutic drug monitoring (TDM) is resource-intensive, cost-prohibitive, and presents a paradigm shift that leaves institutions with the quandary of defining the preferred and most practical method for TDM. We report a step-by-step quality improvement process using 4 plan-do-study-act (PDSA) cycles to provide a framework for development of a hybrid model of trough and AUC-based vancomycin monitoring. We found trough-based monitoring a pragmatic strategy as a first-tier approach when anticipated use is short-term. AUC-guided monitoring was most impactful and cost-effective when reserved for patients with high-risk for nephrotoxicity. We encourage others to consider quality improvement tools to locally adopt AUC-based monitoring.

Optimization of Vancomycin Aptamer Sequence Length Increases the Sensitivity of Electrochemical, Aptamer-Based Sensors In Vivo

The measurement of serum vancomycin levels at the clinic is critical to optimizing dosing given the narrow therapeutic window of this antibiotic. Current approaches to quantitate serum vancomycin levels are based on immunoassays, which are multistep methods requiring extensive processing of patient samples. As an alternative, vancomycin-binding electrochemical, aptamer-based sensors (E-ABs) were developed to simplify the workflow of vancomycin monitoring. E-ABs enable the instantaneous measurement of serum vancomycin concentrations without the need for sample dilution or other processing steps. However, the originally reported vancomycin-binding E-ABs had a dissociation constant of 45 μM, which is approximately 1 order of magnitude higher than the recommended trough concentrations of vancomycin measured in patients. This limited sensitivity hinders the ability of E-ABs to accurately support vancomycin monitoring. To overcome this problem, here we sought to optimize the length of the vancomycin-binding aptamer sequence to enable a broader dynamic range in the E-AB platform. Our results demonstrate, via isothermal calorimetry and E-AB calibrations in undiluted serum, that superior affinity and near-equal sensor gain in vitro can be achieved using a one-base-pair-longer aptamer than the truncated sequence originally reported. We validate the impact of the improved binding affinity in vivo by monitoring vancomycin levels in the brain cortex of live mice following intravenous administration. While the original sequence fails to resolve vancomycin concentrations from baseline noise (SNR = 1.03), our newly reported sequence provides an SNR of 1.62 at the same dose.

An area under the concentration-time curve threshold as a predictor of efficacy and nephrotoxicity for individualizing polymyxin B dosing in patients with carbapenem-resistant gram-negative bacteria

BACKGROUND

Evidence supports therapeutic drug monitoring of polymyxin B, but clinical data for establishing an area under the concentration-time curve across 24 h at steady state (AUC_ss,24 h) threshold are still limited. This study aimed to examine exposure-response/toxicity relationship for polymyxin B to establish an AUC_ss,24 h threshold in a real-world cohort of patients.

METHODS

Using a validated Bayesian approach to estimate AUC_ss,24 h from two samples, AUC_ss,24 h threshold that impacted the risk of polymyxin B-related nephrotoxicity and clinical response were derived by classification and regression tree (CART) analysis and validated by Cox regression analysis and logical regression analysis.

RESULTS

A total of 393 patients were included; acute kidney injury (AKI) was 29.0%, clinical response was 63.4%, and 30-day all-cause mortality was 35.4%. AUC_ss,24 h thresholds for AKI of > 99.4 mg h/L and clinical response of > 45.7 mg h/L were derived by CART analysis. Cox and logical regression analyses showed that AUC_ss,24 h of > 100 mg h/L was a significant predictor of AKI (HR 16.29, 95% CI 8.16-30.25, P < 0.001) and AUC_ss,24 h of ≥ 50 mg h/L (OR 4.39, 95% CI 2.56-7.47, P < 0.001) was independently associated with clinical response. However, these exposures were not associated with mortality. In addition, the correlation between trough concentration (1.2-2.8 mg/L) with outcomes was similar to AUC_ss,24 h.

CONCLUSIONS

For critically ill patients, AUC_ss,24 h threshold of 50-100 mg h/L was associated with decreased nephrotoxicity while assuring clinical efficacy. Therapeutic drug monitoring is recommended for individualizing polymyxin B dosing.

Metagenome Analysis Reveals a Response of the Antibiotic Resistome to Mars-like Extraterrestrial Conditions

The spread of antibiotic resistance is becoming a serious global health concern. Numerous studies have been done to investigate the dynamics of antibiotic resistance genes (ARGs) in both indoor and outdoor environments. Nonetheless, few studies are available about the dynamics of the antibiotic resistome (total content of ARGs in the microbial cultures or communities) under stress in outer space environments. In this study, we aimed to experimentally investigate the dynamics of ARGs and metal resistance genes (MRGs) in Kombucha Mutualistic Community (KMC) samples exposed to Mars-like conditions simulated during the BIOMEX experiment outside the International Space Station with analysis of the metagenomics data previously produced. Thus, we compared them with those of the respective non-exposed KMC samples. The antibiotic resistome responded to the Mars-like conditions by enriching its diversity with ARGs after exposure, which were not found in non-exposed samples (i.e., tet and van genes against tetracycline and vancomycin, respectively). Furthermore, ARGs and MRGs were correlated; therefore, their co-selection could be assumed as a mechanism for maintaining antibiotic resistance in Mars-like environments. Overall, these results highlight the high plasticity of the antibiotic resistome in response to extraterrestrial conditions and in the absence of anthropogenic stresses.

Microneedle Aptamer-Based Sensors for Continuous, Real-Time Therapeutic Drug Monitoring

The ability to continuously monitor the concentration of specific molecules in the body is a long-sought goal of biomedical research. For this purpose, interstitial fluid (ISF) was proposed as the ideal target biofluid because its composition can rapidly equilibrate with that of systemic blood, allowing the assessment of molecular concentrations that reflect full-body physiology. In the past, continuous monitoring in ISF was enabled by microneedle sensor arrays. Yet, benchmark microneedle sensors can only detect molecules that undergo redox reactions, which limits the ability to sense metabolites, biomarkers, and therapeutics that are not redox-active. To overcome this barrier, here, we expand the scope of these devices by demonstrating the first use of microneedle-supported electrochemical, aptamer-based (E-AB) sensors. This platform achieves molecular recognition based on affinity interactions, vastly expanding the scope of molecules that can be sensed. We report the fabrication of microneedle E-AB sensor arrays and a method to regenerate them for multiple uses. In addition, we demonstrate continuous molecular measurements using these sensors in flow systems in vitro using single and multiplexed microneedle array configurations. Translation of the platform to in vivo measurements is possible as we demonstrate with a first E-AB measurement in the ISF of a rodent. The encouraging results reported in this work should serve as the basis for future translation of microneedle E-AB sensor arrays to biomedical research in preclinical animal models.

Response to Rybak et al

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Optimal exposure targets for vancomycin in the treatment of neonatal coagulase-negative Staphylococcus infection: A retrospective study based on electronic medical records

BACKGROUND

The currently advocated ratio of area under the curve (AUC) over 24 h to minimum inhibitory concentration (AUC/MIC) > 400 and AUC < 600 mg h/L as the therapeutic drug monitoring (TDM) target of vancomycin is based on data from multiple observational studies in adult patients with methicillin-resistant Staphylococcus aureus (MRSA) infection. It may not be applicable to newborns with coagulase-negative Staphylococcus (CoNS) infection. We conducted a retrospective study to identify the optimal exposure targets for vancomycin in the treatment of neonatal CoNS infection.

METHODS

Based on the inclusion and exclusion criteria, serum vancomycin concentration, demographics, clinical data, and related laboratory data of newborns who received vancomycin intravenous infusion from June 1, 2016 to February 1, 2021 were collected retrospectively. The AUC was calculated using the maximum a posteriori Bayesian (MAPB) method. The vancomycin exposure threshold of AUC/MIC for efficacy and AUC for toxicity (acute kidney injury, AKI) were determined based on receiver operating characteristic (ROC) curve analysis. The correlation between vancomycin exposure and both clinical effect and nephrotoxicity was analyzed using logistic multivariate regression.

RESULTS

In total, 153 patients and 245 vancomycin concentrations (160 trough and 85 peak concentrations) were included. The ROC curve analysis showed that the exposure thresholds of AUC/MIC for clinical efficacy and AUC for nephrotoxicity were 281 and 602 mg h/L, respectively. The multivariate regression analysis showed that AUC/MIC > 280 was a predictor of efficacy (OR: 13.960, 95% CI: 1.891-103.078, P < 0.05) and AUC > 600 mg h/L was associated with AKI (OR: 9.008, 95% CI: 2.706-29.983, P < 0.05). The vancomycin AUC/MIC threshold for treating neonatal CoNS infection with vancomycin is lower than the currently advocated AUC/MIC >400.

CONCLUSION

The optimal exposure targets for vancomycin in neonatal CoNS infection were AUC/MIC > 280 and AUC < 600 mg h/L.

Approaching 65 Years: Is it Time to Consider Retirement of Vancomycin for Treating Methicillin-Resistant Staphylococcus aureus Endovascular Infections?

Vancomycin was introduced nearly 65 years ago and remains the standard antibiotic for serious methicillin-resistant Staphylococcus aureus (MRSA) infections. Staphylococcus aureus remains highly susceptibility to vancomycin (>97%). Despite this, MRSA treatment failure with vancomycin is high in complicated bacteremia. Additionally, vancomycin can cause nephrotoxicity, leading to new therapeutic drug monitoring guidance. This demonstrates how difficult it is to dose vancomycin in a way that is both efficacious and safe, especially during long courses of therapy. Often underappreciated are the cost, resources, and complexity of vancomycin care at a time when alternative antibiotics are becoming cost comparable. This perspective highlights a bigger picture of how the treatment repertoires of many other diseases have changed and advanced since vancomycin’s introduction in the 1950s, yet the vancomycin MRSA treatment standard remains. While vancomycin can still have a role, 65 years may be a practical retirement age for vancomycin in highly complex endovascular infections.

Pharmacokinetic equations versus Bayesian guided vancomycin monitoring: Pharmacokinetic model and model-informed precision dosing trial simulations

The recently released revised vancomycin consensus guideline endorsed area under the concentration-time curve (AUC) guided monitoring. Means to AUC-guided monitoring include pharmacokinetic (PK) equations and Bayesian software programs, with the latter approach being preferable. We aimed to evaluate the predictive performance of these two methods when monitoring using troughs or peaks and troughs at varying single or mixed dosing intervals (DIs), and evaluate the significance of satisfying underlying assumptions of steady-state and model transferability. Methods included developing a vancomycin population PK model and conducting model-informed precision dosing clinical trial simulations. A one-compartment PK model with linear elimination, exponential between-subject variability, and mixed (additive and proportional) residual error model resulted in the best model fit. Conducted simulations demonstrated that Bayesian-guided AUC can, potentially, outperform that of equation-based AUC predictions depending on the quality of model diagnostics and met assumptions. Ideally, Bayesian-guided AUC predictive performance using a trough from the first DI was equivalent to that of PK equations using two measurements (peak and trough) from the fifth DI. Model transferability diagnostics can guide the selection of Bayesian priors but are not strong indicators of predictive performance. Mixed versus single fourth and/or fifth DI sampling seems indifferent. This study illustrated cases associated with the most reliable AUC predictions and showed that only proper Bayesian-guided monitoring is always faster and more reliable than equations-guided monitoring in pre-steady-state DIs in the absence of a loading dose. This supports rapid Bayesian monitoring using data as sparse and early as a trough at the first DI.

A Systematic Review on Clinical Safety and Efficacy of Vancomycin Loading Dose in Critically Ill Patients

Background: The clinical significance of utilizing a vancomycin loading dose in critically ill patients remains unclear. Objective: The main aim of this systematic review is to evaluate the clinical safety and efficacy of the vancomycin loading dose in critically ill patients. Methods: We performed a systematic review using PRISMA guidelines. PubMed, the Web of Science, MEDLINE, Scopus, Google Scholar, the Saudi Digital Library and other databases were searched. Studies that reported clinical outcomes among patients receiving the vancomycin LD were considered eligible. Data for this study were collected using PubMed, the Web of Science, MEDLINE, Scopus, Google Scholar and the Saudi Digital Library using the following terms: “vancomycin”, “safety”, “efficacy” and “loading dose” combined with the Boolean operator “AND” or “OR”. Results: A total of 17 articles, including 2 RCTs, 11 retrospective cohorts and 4 other studies, met the inclusion/exclusion criteria out of a total 1189 studies. Patients had different clinical characteristics representing a heterogenous group, including patients in critical condition, with renal impairment, sepsis, MRSA infection and hospitalized patients for hemodialysis or in the emergency department. Conclusions: The study shows that the target therapeutic level is achieved more easily among patients receiving a weight-based LD as compared to patients received the usual dose without an increased risk of new-onset adverse drug reactions.

Therapeutic drug monitoring of vancomycin in neurosurgery patients, from trough concentration to area under the curve: a retrospective single center cohort study in a tertiary hospital

OBJECTIVE

To evaluate the effect of therapeutic drug monitoring (TDM) of vancomycin in neurosurgery patients.

METHODS

In this retrospective, single-center cohort study, data were collected from patients administered vancomycin after neurosurgery during 2020. Intervention by a pharmacist using an area under the curve (AUC)-based strategy for TDM of vancomycin was started on 1 July 2020. The trough concentration was monitored previously. Data regarding basic demographics, vancomycin application, and TDM were collected and analyzed.

RESULTS

Ninety and 155 samples were included in the non-intervention and intervention groups, respectively. No difference in baseline characteristics was detected. After intervention, the attainment rate of vancomycin TDM was significantly increased from 36.7% to 52.3%. The intervention resulted in an increased daily vancomycin dose (28.9 vs. 26.7 mg/kg/day), a more reasonable sample extraction time (sixth vs. ninth dose), reductions in dose adjustments (37.4% vs. 54.4%) and preventative applications (66.7% vs. 52.3%), and no difference in kidney function impact. The intervention group had a shorter hospital stay.

CONCLUSIONS

Intervention by a clinical pharmacist using an AUC-based strategy for vancomycin TDM can provide benefits other than pharmacokinetic attainment in neurosurgery patients. Further prospective multi-center studies are needed to establish standardized intervention measures and evaluation indicators.

Assessment of an online calculator's vancomycin dosing and exposure appropriateness in persons who inject drugs with methicillin-resistant Staphylococcus aureus bloodstream infections

WHAT IS KNOWN AND OBJECTIVE

While the gold standard for calculating AUC involves two steady-state concentrations, online calculators can empirically estimate AUC and other pharmacokinetic (PK) parameters. In patients with potentially altered PK, such as persons who inject drugs (PWID), the reliability of these predictions is unclear. Our objectives were to characterize the PK of vancomycin in PWID with methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSI) and to assess the impact of these PK parameters on dosing regimens when compared to regimens generated by an online calculator.

METHODS

This descriptive pilot study included a retrospective chart review of 48 inpatient PWID with MRSA BSI from 30 April 2018 through 31 August 2020. Demographic and clinical data along with vancomycin dosing and serum concentrations were collected. Patient-specific PK parameters were used to calculate the AUC of each empiric regimen compared with the originally predicted AUC.

RESULTS AND DISCUSSION

The study population had a median volume of distribution of 0.74 L/kg, clearance of 0.081 L/kg/h, elimination rate constant of 0.110/h and half-life of 6.3 h. The online calculator empirically predicted 6 subtherapeutic and 42 appropriate AUC values with its recommended empiric dosing regimens. Using the actual patient-specific PK parameters, the empiric vancomycin regimens actually resulted in 21 (43.75%) underexposures, 24 (50%) appropriate exposures and 3 (6.25%) overexposures.

WHAT IS NEW AND CONCLUSIONS

In PWID, empiric vancomycin dosing strategies suggested by an online calculator frequently resulted in lower-than-predicted vancomycin exposures. These findings suggest that PWID with MRSA BSI may require higher and/or more frequent vancomycin doses than those empirically recommended by the population-based methods of an online calculator.

How I manage a patient with MRSA bacteraemia

BACKGROUND

Staphylococcus aureus bloodstream infections are common and associated with a high mortality of 15-25%. Methicillin-resistant S. aureus (MRSA) bloodstream infection accounts for 10-40% of cases, and has an even higher mortality. Despite being the 'bread and butter' of clinical infectious diseases practice, robust evidence to guide optimal management is often lacking and there is wide variation in practice.

OBJECTIVES

To provide a real-world example of a case of MRSA bacteraemia and the thought processes of the authors as key management decision points are reached.

SOURCES

The discussion is based on recent literature searches of relevant topics. In making recommendations, randomized clinical trial data have been prioritized and highlighted, and where these are not available recommendations are based on the experience and opinions of the authors.

CONTENT

For a patient with MRSA bacteraemia and a primary bone and joint infection the following points are discussed: empirical antibiotic choice for suspected S. aureus bacteraemia; directed antibiotic choice for MRSA; monitoring and dosing of vancomycin; the role of combination therapy when bacteraemia is persistent; and the duration of therapy and role of switching to oral antibiotics.

IMPLICATIONS

While broad principles of aggressive source control and appropriate choice and duration of antibiotics are important, the heterogeneity of S. aureus bacteraemia means that a tailored rather than algorithmic approach to management is often required. Further randomized controlled trials are needed to strengthen the evidence base for the management of MRSA bacteraemia.

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.

Individualized Vancomycin Dosing with Therapeutic Drug Monitoring and Pharmacokinetic Consultation Service: A Large-Scale Retrospective Observational Study

Background

To date, outcome data with a large sample size and data regarding the clinical outcomes of pharmacokinetic-guided (PK) dosing of vancomycin are limited.

Aim

We evaluated the pharmacokinetic and clinical outcomes of a PK-guided dosing advisory program, pharmacokinetic consultation service (PKCS), in vancomycin treatment.

Methods

We investigated vancomycin therapeutic drug monitoring (TDM) and PKCS use through a retrospective review of patients who had serum vancomycin trough concentration data from October 2017 to November 2018. Among these patients, we selected non-critically ill adult patients satisfying our selection criteria to evaluate the effect of PKCS. Target trough attainment rate, time to target attainment, vancomycin-induced nephrotoxicity (VIN), vancomycin treatment failure rate, and duration of vancomycin therapy were compared between patients whose dosing was adjusted according to PKCS (PKCS group), and those whose dose was adjusted at the discretion of the attending physician (non-PKCS group).

Results

A total of 280 patients met the selection criteria for the VIN analysis (PKCS, n=134; non-PKCS, n=146). The incidence of VIN was similar between the two groups (PKCS, n=5; non-PKCS, n=5); however, the target attainment rate was higher in the PKCS group (75% vs 60%, P = 0.012). The time to target attainment was similar between the two groups. Further exclusions yielded 112 patients for the clinical outcome evaluation (PKCS, n=51; non-PKCS, n=61). The treatment failure rate was similar, and the duration of vancomycin therapy was longer in the PKCS group (12 vs 8 days, P = 0.008).

Conclusion

In non-critically ill patients, an increase in target trough achieved by PKCS did not lead to decreased vancomycin treatment failures, shorter vancomycin treatment, or decreased nephrotoxicity in vancomycin treatment. Considering the excessive amount of effort currently put into vancomycin dosing and monitoring, more selective criteria for individualized pharmacokinetic-guided dosing needs to be applied.