Serum protein-binding characteristics of vancomycin

Pharmacokinetics and pharmacodynamics of peptide antibiotics

Antimicrobial resistance is a major global health challenge. As few new efficacious antibiotics will become available in the near future, peptide antibiotics continue to be major therapeutic options for treating infections caused by multidrug-resistant pathogens. Rational use of antibiotics requires optimisation of the pharmacokinetics and pharmacodynamics for the treatment of different types of infections. Toxicodynamics must also be considered to improve the safety of antibiotic use and, where appropriate, to guide therapeutic drug monitoring. This review focuses on the pharmacokinetics/pharmacodynamics/toxicodynamics of peptide antibiotics against multidrug-resistant Gram-negative and Gram-positive pathogens. Optimising antibiotic exposure at the infection site is essential for improving their efficacy and minimising emergence of resistance.

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.

Compartmentalized Polymeric Nanoparticles Deliver Vancomycin in a pH-Responsive Manner

Vancomycin (VCM) is a last resort antibiotic in the treatment of severe Gram-positive infections. However, its administration is limited by several drawbacks such as: strong pH-dependent charge, tendency to aggregate, low bioavailability, and poor cellular uptake. These drawbacks were circumvented by engineering pH-responsive nanoparticles (NPs) capable to incorporate high VCM payload and deliver it specifically at slightly acidic pH corresponding to infection sites. Taking advantage of peculiar physicochemical properties of VCM, here we show how to incorporate VCM efficiently in biodegradable NPs made of poly(lactic-co-glycolic acid) and polylactic acid (co)polymers. The NPs were prepared by a simple and reproducible method, establishing strong electrostatic interactions between VCM and the (co)polymers’ end groups. VCM payloads reached up to 25 wt%. The drug loading mechanism was investigated by solid state nuclear magnetic resonance spectroscopy. The engineered NPs were characterized by a set of advanced physicochemical methods, which allowed examining their morphology, internal structures, and chemical composition on an individual NP basis. The compartmentalized structure of NPs was evidenced by cryogenic transmission electronic microscopy, whereas the chemical composition of the NPs’ top layers and core was obtained by electron microscopies associated with energy-dispersive X-ray spectroscopy. Noteworthy, atomic force microscopy coupled to infrared spectroscopy allowed mapping the drug location and gave semiquantitative information about the loadings of individual NPs. In addition, the NPs were stable upon storage and did not release the incorporated drug at neutral pH. Interestingly, a slight acidification of the medium induced a rapid VCM release. The compartmentalized NPs could find potential applications for controlled VCM release at an infected site with local acidic pH.

Unexpected Vancomycin Pharmacokinetic Profile Secondary to Macromolecular Complexing: A Case Series

BACKGROUND

The optimal dosing and monitoring of vancomycin has been largely debated for decades, with key guideline changes for recommended monitoring in 2009 and 2020. Current and past practices for pharmacokinetic dose optimization use serum drug assays to guide dose adjustment to effectively balance efficacy and the risks of toxicity. These assays detect both bound and unbound serum concentrations. Vancomycin is believed to be 50%-55% protein bound in most cases; however, some variability in this parameter has been previously published. The authors report 2 cases of abnormal vancomycin pharmacokinetics discovered based on unexpected serum levels during routine clinical care.

METHODS

Unexpected vancomycin levels, observed during clinical care for 2 separate patients, were further evaluated to determine the source of the abnormal pharmacokinetics. In case 1, serial dilution was performed to assure that assay interference was not associated with the significant elevation (>100 mg/L). In both cases, samples were filtered using a Millipore Centrifree 30 KDa centrifugal filter to separate bound vancomycin, with a Protein G spin kit used to bind IgG and remove IgG complexes from the patient sample. In case 2, a polyethylene glycol precipitation was also performed to precipitate large-molecular-weight complexes.

RESULTS

In both cases, laboratory analysis revealed abnormal vancomycin protein-binding profiles with macromolecular complex formation. Immunoglobulin G played a role in the macrocomplex in both patients.

CONCLUSIONS

In cases of unusual or unexpected vancomycin pharmacokinetics in the absence of renal dysfunction, an abnormal protein-binding profile should be considered. Bound vancomycin may yield elevated serum levels, leading to poorly informed dose adjustments and risk for treatment failure. Given implications for therapeutic drug monitoring and unknown impacts on efficacy and toxicity, further investigations into population incidence and risk factors for abnormal protein binding of vancomycin are warranted.

Association of Initial Trough Concentrations of Vancomycin with Outcomes in Pediatric Patients with Gram-Positive Bacterial Infection

Vancomycin is a glycopeptide antibiotic used for the treatment of Gram-positive infections. For adult patients, treatment with vancomycin requires effective therapeutic drug-monitoring (TDM) to achieve clinical outcomes and reduce the incidence of adverse effects. However, it remains still unclear whether the TDM with vancomycin is beneficial in yielding better clinical outcomes in pediatrics. The objective of our study was to evaluate whether the clinical response to treatment was associated with initial trough concentrations of vancomycin in pediatric patients. A retrospective observation study of 60 patients (age: 1 month-15 years) who had completed and qualified for analysis was conducted at Kyoto University Hospital. The response to treatment was assessed by the time to resolution of fever and time to 50% decline in C-reactive protein (CRP). In addition, we explored whether vancomycin trough level was associated with the baseline characteristics. Trend analysis showed that there were significant correlations between vancomycin trough level and age, body weight, estimated glomerular filtration rate, and serum albumin levels. The time to resolution of fever of the patients with higher initial trough level (≥ 5 µg/mL) was significantly lower than that of the patients with lower trough level (< 5 µg/mL). The higher vancomycin concentration tended to be associated with the shorter time to 50% decline in CRP. The findings suggest that initial trough concentration is important in achieving better outcomes with vancomycin treatment in pediatrics.

Prediction of Unbound Vancomycin Levels in Intensive Care Unit and Nonintensive Care Unit Patients: Total Bilirubin May Play an Important Role

Background

The mean unbound vancomycin fraction and whether the unbound vancomycin level could be predicted from the total vancomycin level are still controversial, especially for patients in different groups, such as intensive care unit (ICU) versus non-ICU patients. Other relevant potential patient characteristics that may predict unbound vancomycin levels have yet to be clearly determined.

Methods

We enrolled a relatively large study population and included widely comprehensive potential covariates to evaluate the unbound vancomycin fractions in a cohort of ICU (n=117 samples) and non-ICU patients (n=73 samples) by using a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method.

Results

The mean unbound vancomycin fraction was 45.80% ± 18.69% (median, 46.01%; range: 2.13–99.45%) in the samples from the total population. No significant differences in the unbound vancomycin fraction were found between the ICU patients and the non-ICU patients (P=0.359). A significant correlation was established between the unbound and total vancomycin levels. The unbound vancomycin level can be predicted with the following equations: unbound vancomycin level=0.395×total vancomycin level+0.019×total bilirubin level+0.468 (R²=0.771) for the ICU patients and unbound vancomycin level=0.526×total vancomycin level-0.527 (R²=0.749) for the non-ICU patients. Overall, the observed-versus-predicted plots were acceptable.

Conclusion

A significant correlation between the total and unbound vancomycin levels was found, and measurement of the unbound vancomycin level seems to have no added value over measurement of the total vancomycin level. The study developed parsimonious equations for predicting the unbound vancomycin level and provides a reference for clinicians to predict the unbound vancomycin level in adult populations.

A "Single-Use" Ceramic-Based Electrochemical Sensor Chip Using Molecularly Imprinted Carbon Paste Electrode

An inexpensive disposable electrochemical drug sensor for the detection of drugs (vancomycin, meropenem, theophylline, and phenobarbital) is described. Molecularly imprinted polymer (MIP) templated with the target drugs was immobilized on the surface of graphite particles using a simple radical polymerization method and packed into the working electrode of a three-electrode ceramic-based chip sensor. Differential pulse voltammetry (DPV) was used to determine the relationship between the response current and the concentration of the targeted drug while using one sensor chip for one single operation. The time required for each DPV measurement was less than 2 min. Concentrations corresponding to the therapeutic range of these drugs in plasma were taken into account while performing DPV. In all the cases, the single-used MIP sensor showed higher sensitivity and linearity than non-imprinted polymer. The selectivity test in drugs with a structure similar to that of the target drugs was performed, and it was found that MIP-based sensors were more selective than the untreated ones. Additionally, the test in whole blood showed that the presence of interfering species had an insignificant effect on the diagnostic responses of the sensor. These results demonstrate that the disposable MIP-sensor is promising for quick and straightforward therapeutic drug monitoring to prevent the toxic side effects and the insufficient therapeutic effect due to the overdose and underdose, respectively.

Augmented Renal Clearance of Vancomycin in Hematologic Malignancy Patients

The pharmacokinetics of vancomycin (VAN) was retrospectively examined based on trough concentrations at large scale to identify pharmacokinetic differences between Japanese hematologic malignancy and non-malignancy patients. Data from 261 hematologic malignancy patients and 261 non-malignancy patients, including the patient's background, VAN dose, and pharmacokinetics of VAN estimated by an empirical Bayesian method, were collected and analyzed. Our results showed significantly higher values for VAN clearance and shorter elimination half-lives in patients with hematologic malignancies than non-malignancy patients. In addition, multiple regression analysis under adjusting for confounding factors by propensity score, showed that VAN clearance significantly increased in relation to hematologic malignancies. In conclusion, since in hematologic cancer patients VAN clearance is increased, the blood concentration of VAN becomes lower than expected and this may contribute to the survival of resistant bacteria when VAN is administered at low doses. These results suggest that early monitoring of VAN levels in hematologic cancer patients might be recommended to maintain desired effects without side-effects.

Serum albumin saturation test based on non-esterified fatty acids imbalance for clinical employment

Fatty acids are fundamental as energy and structural source to the human cells. They are not usually found free in human circulation. Alteration in fatty acids metabolism is linked to diseases such as diabetes, preeclampsia, heart disease, and some infectious diseases. Increased levels of non-esterified fatty acids (NEFA) may cause cell dysfunction and lipotoxicity. Since physiologically fatty acids are transported bound to albumin, we propose here a simple and cheap test that consists of albumin isoelectric focusing determination to measure the potential systemic NEFA cytotoxicity. For validation of this method, albumin isoelectric focusing in 51 serum samples from 40 critically ill patients and 11 controls was compared with NEFA/albumin ratios measured by HPLC. We called this approach an albumin saturation test. This test may indicate to physicians the potential NEFA lipotoxicity guiding them throughout better patient management. The albumin saturation test can point out serum albumin-NEFA saturation through a cheap assay that could be performed by any care facility.

Prospective Cohort Study of the Tolerability of Prosthetic Joint Infection Empirical Antimicrobial Therapy

The empirical use of vancomycin in combination with a broad-spectrum beta-lactam is currently recommended after the initial surgery of prosthetic joint infection (PJI). However, the tolerability of such high-dose intravenous regimens is poorly known. Adult patients receiving an empirical antimicrobial therapy (EAT) for a PJI were enrolled in a prospective cohort study (2011 to 2016). EAT-related adverse events (AE) were described according to the common terminology criteria for AE (CTCAE), and their determinants were assessed by logistic regression and Kaplan-Meier curve analysis. The EAT of the 333 included patients (median age, 69.8 years; interquartile range [IQR], 59.3 to 79.1 years) mostly relies on vancomycin (n = 229, 68.8%), piperacillin-tazobactam (n = 131, 39.3%), and/or third-generation cephalosporins (n = 50, 15%). Forty-two patients (12.6%) experienced an EAT-related AE. Ten (20.4%) AE were severe (CTCAE grade ≥ 3). The use of vancomycin (odds ratio [OR], 6.9; 95% confidence interval [95%CI], 2.1 to 22.9), piperacillin-tazobactam (OR, 3.7; 95%CI, 1.8 to 7.2), or the combination of both (OR, 4.1; 95%CI, 2.1 to 8.2) were the only AE predictors. Acute kidney injury (AKI) was the most common AE (n = 25; 51.0% of AE) and was also associated with the use of the vancomycin and piperacillin-tazobactam combination (OR, 6.7; 95%CI, 2.6 to 17.3). A vancomycin plasma overexposure was noted in nine (37.5%) of the vancomycin-related AKIs only. Other vancomycin-based therapies were significantly less at risk for AE and AKI. The EAT of PJI is associated with an important rate of AE, linked with the use of the vancomycin and the piperacillin-tazobactam combination. These results corroborate recent findings suggesting a synergic toxicity of these drugs in comparison to vancomycin-cefepime, which remains to be evaluated in PJI. (This study has been registered at ClinicalTrials.gov under identifier NCT03010293.).

Recovery rates of combination antibiotic therapy using in vitro microdialysis simulating in vivo conditions

Microdialysis is a technique used to measure the unbound antibiotic concentration in the interstitial spaces, the target site of action. In vitro recovery studies are essential to calibrating the microdialysis system for in vivo studies. The effect of a combination of antibiotics on recovery into microdialysate requires investigation. In vitro microdialysis recovery studies were conducted on a combination of vancomycin and tobramycin, in a simulated in vivo model. Comparison was made between recoveries for three different concentrations and three different perfusate flow rates. The overall relative recovery for vancomycin was lower than that of tobramycin. For tobramycin, a concentration of 20μg/mL and flow rate of 1.0μL/min had the best recovery. A concentration of 5.0μg/mL and flow rate of 1.0μL/min yielded maximal recovery for vancomycin. Large molecular size and higher protein binding resulted in lower relative recoveries for vancomycin. Perfusate flow rates and drug concentrations affected the relative recovery when a combination of vancomycin and tobramycin was tested. Low perfusate flow rates were associated with higher recovery rates. For combination antibiotic measurement which includes agents that are highly protein bound, in vitro studies performed prior to in vivo studies may ensure the reliable measurement of unbound concentrations.

Vancomycin Determination by Disrupting Electron-Transfer in a Fluorescence Turn-On Squaraine-Anthraquinone Triad

A highly sensitive and selective probe for Vancomycin (Van) in aqueous and serum samples is developed in this study. The probe is based on a triad consisting of a near-infrared squaraine dye (Seta-640) conjugated to two anthraquinone molecules via Lys-d-Ala-d-Ala peptides. In the absence of Van, the close proximity and efficient electron-transfer from the excited Seta-640 dye to anthraquinone result in significant fluorescence quenching of the dye ("off"-state). When Van is added, the antibiotic molecules bind with high affinity to the -d-Ala-d-Ala ligands in a 2:1 stoichiometry (Van:triad), resulting in fluorescence recovery that is as high as 30 times ("on"-state). Even though bound Van enhances the fluorescence by reducing the rate of (intrinsic) polarity-induced nonradiative decay process, this effect plays only a minor role. Instead, the main reason behind the observed fluorescence recovery after drug binding is the effective inhibition of electron-transfer; plausibly arising from a steric-induced lengthening of the spatial separation between electron donor and acceptor. The probe has detection limits of 7.0 and 96.9 nM in buffer and human serum, respectively, operates in the clinically relevant range, is insensitive to Van crystalline degradation product (CDP-1), and is easy to operate by using a commonly available fluorescence spectrometer.

Development of a Physiologically Based Pharmacokinetic Modelling Approach to Predict the Pharmacokinetics of Vancomycin in Critically Ill Septic Patients

BACKGROUND AND OBJECTIVES

Sepsis is characterised by an excessive release of inflammatory mediators substantially affecting body composition and physiology, which can be further affected by intensive care management. Consequently, drug pharmacokinetics can be substantially altered. This study aimed to extend a whole-body physiologically based pharmacokinetic (PBPK) model for healthy adults based on disease-related physiological changes of critically ill septic patients and to evaluate the accuracy of this PBPK model using vancomycin as a clinically relevant drug.

METHODS

The literature was searched for relevant information on physiological changes in critically ill patients with sepsis, severe sepsis and septic shock. Consolidated information was incorporated into a validated PBPK vancomycin model for healthy adults. In addition, the model was further individualised based on patient data from a study including ten septic patients treated with intravenous vancomycin. Models were evaluated comparing predicted concentrations with observed patient concentration-time data.

RESULTS

The literature-based PBPK model correctly predicted pharmacokinetic changes and observed plasma concentrations especially for the distribution phase as a result of a consideration of interstitial water accumulation. Incorporation of disease-related changes improved the model prediction from 55 to 88% within a threshold of 30% variability of predicted vs. observed concentrations. In particular, the consideration of individualised creatinine clearance data, which were highly variable in this patient population, had an influence on model performance.

CONCLUSION

PBPK modelling incorporating literature data and individual patient data is able to correctly predict vancomycin pharmacokinetics in septic patients. This study therefore provides essential key parameters for further development of PBPK models and dose optimisation strategies in critically ill patients with sepsis.

Development of a Novel Collagen Wound Model To Simulate the Activity and Distribution of Antimicrobials in Soft Tissue during Diabetic Foot Infection

Diabetes has major implications for public health, with diabetic foot ulcers (DFUs) being responsible for significant morbidity and mortality. A key factor in the development of nonhealing ulcers is infection, which often leads to the development of biofilm, gangrene, and amputation. A novel approach to treating DFUs is the local release of antibiotics from calcium sulfate beads. We have developed a novel model system to study and compare the release and efficacy of antibiotics released locally, using collagen as a substrate for biofilm growth and incorporating serum to mimic the biochemical complexity of the wound environment. We found that our soft-tissue model supports the growth of a robust Pseudomonas aeruginosa biofilm, and that this was completely eradicated by the introduction of calcium sulfate beads loaded with tobramycin or gentamicin. The model also enabled us to measure the concentration of these antibiotics at different distances from the beads and in simulated wound fluid bathing the collagen matrix. We additionally found that a multidrug-resistant Staphylococcus aureus biofilm, nonsusceptible to antibiotics, nonetheless showed an almost 1-log drop in viable counts when exposed to calcium sulfate beads combined with antibiotics. Together, these data suggest that locally applied antibiotics combined with calcium sulfate provide surprising efficacy in diabetic foot infections and offer an effective alternative approach to infection management. Our study additionally establishes our new system as a biochemically and histologically relevant model that may be used to study the effectiveness of a range of therapies locally or systemically for infected DFUs.

Measuring unbound versus total vancomycin concentrations in serum and plasma: methodological issues and relevance

BACKGROUND

Studies on the unbound fraction (fu) of vancomycin report highly variable results. Great controversy also exists about the correlation between unbound and total vancomycin concentrations. As differences in (pre-)analytic techniques may explain these findings, we investigated the impact of the procedure used to isolate unbound vancomycin in serum/plasma on fu and the correlation between total and unbound concentrations.

METHODS

Patient samples (n = 39) were analyzed for total and unbound vancomycin concentrations after ultrafiltration (UF, Centrifree at 4°C and 37°C) or equilibrium dialysis (ED, using a Fast Micro-Equilibrium Dialyzer at 37°C) on an Architect i2000SR. To investigate correlations with potential binding proteins, total protein, albumin, alpha-1-acid glycoprotein, and IgA concentrations were also measured.

RESULTS

The median fu after ED was 72.5% [interquartile range (IQR), 68.7%-75.0%]. Ultrafiltration at 4°C and 37°C resulted in a median fu of 51.6% (IQR, 48.6%-54.8%) and 75.2% (IQR, 69.3%-78.6%), respectively, with no significant difference between unbound vancomycin concentrations after ED and UF at 37°C (P = 0.13). Unbound concentrations obtained through ED and UF correlated linearly (4°C: r = 0.9457; 37°C: r = 0.9478; both P < 0.0001). Linear mixed-model regression showed that total vancomycin as such was the predominant determinant for the unbound concentration, allowing a reliable prediction (mean bias ± SD, 5.0% ± 7.6%). The studied protein concentrations were of no added value in predicting the unbound concentration.

CONCLUSIONS

Vancomycin fu after UF at 4°C was on average 30.6% lower than that after UF at 37°C, demonstrating the importance of temperature during UF. Ultrafiltration at 37°C resulted in unbound vancomycin concentrations equivalent with ED. As the unbound concentration could be reliably predicted based on total vancomycin concentrations as such, measurement of unbound vancomycin concentrations has little added value over measurements of total vancomycin concentrations.

External Evaluation of Population Pharmacokinetic Models of Vancomycin in Neonates: The transferability of published models to different clinical settings

BACKGROUND

Vancomycin is one of the most evaluated antibiotics in neonates using modeling and simulation approaches. However no clear consensus on optimal dosing has been achieved. The objective of the present study was to perform an external evaluation of published models, in order to test their predictive performances in an independent dataset and to identify the possible study-related factors influencing the transferability of pharmacokinetic models to different clinical settings.

METHOD

Published neonatal vancomycin pharmacokinetic models were screened from the literature. The predictive performance of 6 models was evaluated using an independent dataset (112 concentrations from 78 neonates). The evaluation procedures used simulation-based diagnostics (visual predictive check [VPC] and normalized prediction distribution errors [NPDE]).

RESULTS

Differences in predictive performances of models for vancomycin pharmacokinetics in neonates were found. The mean of NPDE for 6 evaluated models were 1.35, -0.22, -0.36, 0.24, 0.66, 0.48, respectively. These differences were explained, at least partly, by taking into account the method used to measure serum creatinine concentrations. The adult conversion factor of 1.3 (enzymatic to Jaffé) was tested with an improvement in the VPC and NPDE, but it still need to be evaluated and validated in neonates. Differences were also identified between analytical methods for vancomycin.

CONCLUSION

The importance of analytical techniques for serum creatinine concentrations and vancomycin as a predictor of vancomycin concentrations in neonates has been confirmed. Dosage individualisation of vancomycin in neonates should consider not only patients' characteristics and clinical conditions, but also the methods used to measure serum creatinine and vancomycin.

Factors impacting unbound vancomycin concentrations in different patient populations

The unbound drug hypothesis states that only unbound drug concentrations are active and available for clearance, and highly variable results regarding unbound vancomycin fractions have been reported in the literature. We have determined the unbound vancomycin fractions in four different patient groups by a liquid chromatography tandem mass spectrometry (LC-MS/MS) method and identified factors that modulate vancomycin binding. We have further developed and validated a prediction model to estimate unbound vancomycin concentrations. Vancomycin (unbound and total) concentrations were measured in 90 patients in four different hospital wards (hematology [n = 33 samples], intensive care unit [ICU] [n = 51], orthopedics [n = 44], and pediatrics [age range, 6 months to 14 years; n = 18]) by a validated LC-MS/MS method. Multiple linear mixed model analysis was performed to identify patient variables that were predictive of unbound vancomycin fractions and concentrations. The variables included in the model were patient age, ward, number of coadministered drugs with high protein binding, kidney function (estimated glomerular filtration rate [determined by Chronic Kidney Disease Epidemiology Collaboration formula]), alpha-1-acid glycoprotein, albumin, total bilirubin, IgA, IgM, urea, and total vancomycin concentrations. In the pediatric cohort, the median unbound vancomycin fraction was 81.3% (range, 61.9 to 95.9%), which was significantly higher (P < 0.01) than the unbound fraction found in the three adult patient cohorts (hematology, 60.6% [48.7 to 90.6%]; ICU, 61.7% [47.0 to 87.6%]; orthopedics, 56.4% [45.9 to 78.0%]). The strongest significant predictor of the unbound vancomycin concentration was the total drug concentration, completed by albumin in the pediatric cohort and albumin and IgA in the adult cohorts. Validation of our model was performed with data from 13 adult patients. A mean difference of 0.3 mg/liter (95% confidence interval [CI], -1.3 to 0.7 mg/liter; R(2) = 0.99 [95% CI, 0.95 to 0.99]) between measured and calculated unbound vancomycin concentrations demonstrated that the predictive performance of our model was favorable. Unbound vancomycin fractions vary significantly between pediatric and adult patients. We developed a formula to estimate the unbound fraction derived from total vancomycin, albumin, and IgA concentrations in adult 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.

Extracellular DNA impedes the transport of vancomycin in Staphylococcus epidermidis biofilms preexposed to subinhibitory concentrations of vancomycin

Staphylococcus epidermidis biofilm formation is responsible for the persistence of orthopedic implant infections. Previous studies have shown that exposure of S. epidermidis biofilms to sub-MICs of antibiotics induced an increased level of biofilm persistence. BODIPY FL-vancomycin (a fluorescent vancomycin conjugate) and confocal microscopy were used to show that the penetration of vancomycin through sub-MIC-vancomycin-treated S. epidermidis biofilms was impeded compared to that of control, untreated biofilms. Further experiments showed an increase in the extracellular DNA (eDNA) concentration in biofilms preexposed to sub-MIC vancomycin, suggesting a potential role for eDNA in the hindrance of vancomycin activity. Exogenously added, S. epidermidis DNA increased the planktonic vancomycin MIC and protected biofilm cells from lethal vancomycin concentrations. Finally, isothermal titration calorimetry (ITC) revealed that the binding constant of DNA and vancomycin was 100-fold higher than the previously reported binding constant of vancomycin and its intended cellular d-Ala-d-Ala peptide target. This study provides an explanation of the eDNA-based mechanism of antibiotic tolerance in sub-MIC-vancomycin-treated S. epidermidis biofilms, which might be an important factor for the persistence of biofilm infections.

Determination of the free and total concentrations of vancomycin by two-dimensional liquid chromatography and its application in elderly patients

A robust two-dimensional liquid chromatography (2D-LC) method for determining the free and total concentrations of vancomycin in plasma was developed and validated. The 2D-LC system, which exhibited a strong capacity for inhibiting interference, comprised a unique RP1-IEX-RP2 column system and an "Assistant Flow" configuration. Ultrafiltration technology was employed to separate free vancomycin from the protein-bound fraction in human plasma. The influence of ultrafiltration conditions on the free vancomycin concentration was evaluated. The calibration curve was linear over the 0.195-49.92μg/ml range for the free and total vancomycin concentrations. The within- and between-run precision ranges were 1.5-3.9% and 2.0-4.7% for the total concentration, 1.4-3.3% and 2.4-4.0% for the free concentration, respectively. Ultrafiltration was susceptible to variations in the experimental conditions, including the centrifugation time, the centrifugal force, and the nominal molecular weight limit of the ultrafiltration membrane. A total of 101 serum samples from 84 elderly patients were analyzed by this method. The free vancomycin concentration was 5.88±3.75μg/ml (range: 0.240-16.79μg/ml), the total concentration was 12.36±5.36μg/ml (range: 2.16-27.14μg/ml), and the unbound fraction was 45.6±18.8% (range: 11.1-96.9%). There was a poor correlation between the free and total vancomycin concentrations (R(2)=0.596, p<0.05). This method appears to be sensitive, precise, selective, and suitable for use in protein-binding studies of vancomycin.

Surface-stress sensors for rapid and ultrasensitive detection of active free drugs in human serum

There is a growing appreciation that mechanical signals can be as important as chemical and electrical signals in biology. To include such signals in a systems biology description for understanding pathobiology and developing therapies, quantitative experiments on how solution-phase and surface chemistry together produce biologically relevant mechanical signals are needed. Because of the appearance of drug-resistant hospital 'superbugs', there is currently great interest in the destruction of bacteria by bound drug-target complexes that stress bacterial cell membranes. Here, we use nanomechanical cantilevers as surface-stress sensors, together with equilibrium theory, to describe quantitatively the mechanical response of a surface receptor to different antibiotics in the presence of competing ligands in solution. The antibiotics examined are the standard, Food and Drug Administration-approved drug of last resort, vancomycin, and the yet-to-be approved oritavancin, which shows promise for controlling vancomycin-resistant infections. The work reveals variations among strong and weak competing ligands, such as proteins in human serum, that determine dosages in drug therapies. The findings further enhance our understanding of the biophysical mode of action of the antibiotics and will help develop better treatments, including choice of drugs as well as dosages, against pathogens.

Vancomycin: does it still have a role as an antistaphylococcal agent?

The recognition of the shortcomings of vancomycin as an antistaphylococcal agent, together with the burgeoning availability of alternative effective antistaphylococcal antibiotics, has led to a reassessment of the role of this glycopeptide antimicrobial in clinical therapeutics. Evidence indicates that vancomycin is inferior to semisynthetic penicillins in the treatment of infections due to methicillin-susceptible Staphylococcus aureus. Additional evidence suggests that vancomycin may be inferior to some comparator agents in the treatment of infections due to methicillin-resistant S. aureus (MRSA). While high-level resistance remains rare, data from some centers suggest an evolutionary change in S. aureus, evidenced by reduced susceptibility to vancomycin. This, together with the problem of heteroresistance to vancomycin, as well as poor tissue penetration after its systemic administration, presents potential obstacles to the successful therapy of S. aureus infections with this glycopeptide. While it has been suggested that these problems may be overcome by administration of vancomycin in much higher doses, the efficacy and safety of this approach remains to be determined and will require randomized clinical trials for its demonstration. A number of novel agents with activity against MRSA have been introduced to clinical practice in the last 2 years and others are still in the investigational stage. Despite the fact that these newer agents have been compared with vancomycin in trials only designed to demonstrate noninferiority, some potential evidence of superiority over vancomycin has emerged. While the relative roles of each of these newer agents and vancomycin can only be determined definitively by performance of adequately powered randomized clinical trials, current evidence suggests that vancomycin may be an inferior therapeutic agent.

Unbound fraction of vancomycin in intensive care unit patients

Published data on the unbound fraction of vancomycin in patient samples exhibit high variability. In the present study, a robust ultrafiltration method was developed and applied to 102 clinical samples from 22 intensive care unit patients who were treated with continuous infusion of vancomycin. A validated HPLC method was used for determination of total and unbound concentrations. The mean unbound fraction was 67.2% (standard deviation 7.5%, range 47.2-92.1%) and independent of total concentration of vancomycin or of albumin. The unbound fraction was significantly correlated (r = +0.67, P = .0009) with the renally filtered fraction (drug clearance/creatinine clearance), providing functional evidence for the validity of the measurements. Ultrafiltration proved to be susceptible to variations in the experimental conditions such as pH, temperature and centrifugal force. The measured unbound fraction increased from 60% at pH 6 to 100% at pH 9, from 57% at 4°C to 80% at 37°C, and was 76% at 1,000 g compared with 45% at 10,000 g. Lack of standardization may therefore partly explain the variable results reported in the literature.

The effect of paraproteins and rheumatoid factor on four commercial immunoassays for vancomycin: implications for laboratorians and other health care professionals

BACKGROUND

Paraproteins, immunoglobulins (Igs), which are elevated in various autoimmune disorders, are known to interfere with various laboratory immunoassays, including vancomycin (VANC). Rheumatoid factor (RF), a known immunoassay interferant, may cause falsely elevated results.

OBJECTIVES

The aims of this study were to (1) evaluate the effect of 3 paraproteins (IgA, IgG, and IgM) on 4 commercial VANC immunoassays [fluorescence polarization immunoassay; enzyme multiplied immunoassay; 2 particle-enhanced turbidimetric inhibition immunoassays]; (2) determine the concentration at which the effect is obtained, and (3) examine the influence of RF on the VANC methods.

METHOD

Serum and plasma pools from patients prescribed VANC and a spiked VANC pool (20 mg/L) were each mixed 1:1 with individual patient specimens containing IgA (6-63 g/L), IgG (6-54 g/L), IgM (3-30 g/L) (n = 4 for each Ig), and a patient RF pool (196 IU/L). The mixtures (n = 39) were split and distributed for VANC analysis.

RESULTS

IgA and IgG in serum and plasma did not affect any of the VANC immunoassays. RF added to plasma specimens did not interfere, but in serum, elevated VAN results were observed. IgM did not affect the fluorescence polarization immunoassay and enzyme multiplied immunoassay methods but did attenuate VANC concentrations by both particle-enhanced turbidimetric inhibition immunoassays (Siemens, Beckman Coulter), with a more pronounced effect on the latter, producing concentrations >20% lower than expected in the patient serum and spiked plasma pools. The effect was progressively negative at effective IgM concentrations of 10 and 15 mg/L.

CONCLUSIONS

This phenomenon is a major analytical and clinical issue that must be communicated to health care professionals caring for patients receiving VANC, so optimal therapy is achieved.

Use of antibacterial agents in the neonate: 50 years of experience with vancomycin administration

Neonatal sepsis, classified as either early or late onset, has specific pathogen distribution and infection rates in the different neonatal age groups. It is a major cause of mortality and morbidity and administration of antibiotics is urgently required for suspected or proven infection. Vancomycin is the first choice treatment of late onset sepsis due to resistant staphylococci. Although it has been used for more than 50 years, prescription remains a challenge in neonatal intensive care units for many reasons, including: high pharmacokinetic variability, numerous presentations, lack of consensus on dosing regimen and therapeutic drug monitoring. In addition, recent concerns about the increase in minimal inhibition concentration and other more generic problems have prompted reappraisal of the rational use of vancomycin. This article highlights the goal of optimising vancomycin therapy in the neonate and discusses future research directions. Specific attention is given to dosing optimisation of vancomycin to avoid resistance and maximise the likelihood of achieving the therapeutic target. Modelling and simulation approaches have clear advantages in dosing optimisation of antimicrobial agents in the neonate. Neonatologists and paediatric pharmacologists should work closely together to achieve this goal.

Subtherapeutic serum vancomycin concentrations during on-line hemodiafiltration

The aim of the study is to study vancomycin serum concentration changes during on-line hemodiafiltration (OL-HDF) and determine whether administration of vancomycin during the last hour of OL-HDF provides therapeutic serum concentrations. Vancomycin was administered intravenously at a dose of 15 mg/kg to 17 chronic hemodialysis patients who were enrolled into two study groups (A and B). In group A patients (n = 11), vancomycin was administered immediately postdialysis. Forty-three hours later, a 4-hour OL-HDF session was performed. Blood samples (S) for vancomycin measurement were drawn before, during, and after the session. In group B patients (n = 6), vancomycin was administered during the last hour of a 4-hour OL-HDF session on Monday. Vancomycin serum concentrations were measured postdialysis, as well as before and after the next two dialysis sessions of the week. In group A patients, mean vancomycin concentrations were reduced by 50% (S(pre): 10.2 ± 1.4 μg/ml, S(post): 5.0 ± 0.9 μg/ml). Vancomycin dialysance was 74.6 ± 29.3 ml/min, while the volume of distribution was 0.42 L/kg. In group B patients, mean vancomycin concentrations before the beginning of Wednesday and Friday dialysis sessions were 3.1 ± 0.7 and 1.4 ± 0.4 μg/ml, respectively. Postdialysis administration of vancomycin followed by OL-HDF resulted in a 50% reduction of vancomycin serum concentrations. Administration during the last treatment hour of OL-HDF results in subtherapeutic vancomycin serum concentrations over the course of the subsequent inter- and intradialytic intervals.

[Factor analysis of outcomes during drug-resistant bacterial infection treatment]

Factors related to poor outcome in drug-resistant bacterial infection treatment were analyzed based on surveys at 54 National Hospital Organization facilities. Results showed common etiological causes of Methicillin-resistant Staphylococcus aureus (MRSA) and Penicillin-resistant Streptococcus pneumoniae (PRSP). Specifically, the odds ratio in the elderly, aged 75 years and older, was 1.473 (p=0.006) for MRSA and 6.401 (p=0.0001) for PRSP. Among those undergoing tracheal intubation, the odds ratio was 1.767 (p=0.021) for MRSA and 4.185 (p=0.0001) for PRSP, showing that advanced age and tracheal intubation tended to aggravate disease. MRSA-specific causes were pneumonia with an odds ratio of 2.426 (p=0.0001) and sepsis with one of 1.417 (p=0.013). Causes specific to Multi-drug resistant Pseudomonas aeruginosa (MDRP) were Intravenous hyperalimentation (IVH) with an odds ratio of 2.078 (p=0.0001) and urinary-tract infection with one of 0.566 (p=0.027). The individual roles of these factors in poor outcomes must thus be clarified to develop preventive measures against them.

PEGylated liposome encapsulation increases the lung tissue concentration of vancomycin

Pneumonia due to methicillin-resistant Staphylococcus aureus (MRSA) often cannot be cured by vancomycin treatment. Poor lung tissue and intracellular penetration limits the ability to achieve effective bactericidal levels, particularly in alveolar macrophages, where MRSA can evade phagocytic killing. Compared to standard formulations, liposome encapsulation has been shown to enhance vancomycin intracellular killing of MRSA. In this murine pharmacokinetic and biodistribution study, PEGylated liposomal vancomycin, compared to standard and non-PEGylated formulations, significantly prolonged blood circulation time and increased deposition in lung, liver, and spleen and yet reduced accumulation in kidney tissue. As a result of optimizing antimicrobial targeting of infected lung tissue and limiting renal parenchymal exposure, administration of PEGylated liposomal vancomycin may improve the efficacy of treatment of MRSA pneumonia and reduce the risk of nephrotoxicity.

Refining vancomycin protein binding estimates: identification of clinical factors that influence protein binding

While current data indicate only free (unbound) drug is pharmacologically active and is most predictive of response, pharmacodynamic studies of vancomycin have been limited to measurement of total concentrations. The protein binding of vancomycin is thought to be approximately 50%, but considerable variability surrounds this estimate. The present study sought to determine the extent of vancomycin protein binding, to identify factors that modulate its binding, and to create and validate a prediction tool to estimate the extent of protein binding based on individual clinical factors. This single-site prospective cohort study included hospitalized adult patients treated with vancomycin and with a vancomycin serum concentration determination available. Linear regression was used to predict the free vancomycin concentration (f[vanco]) and to determine the clinical factors modulating vancomycin protein binding. Among the 50 patients in the study, the mean protein binding was 41.5%. The strongest predictor of f[vanco] was the total vancomycin concentration (total [vanco]), and this was modified by dialysis and total protein of ≥6.7 g/dl as covariates. The algebraic expression from the final prediction model was f[vanco] = 0.643 + 0.560 × total [vanco] - {0.067 × total [vanco] × D} - {0.071 × total [vanco] × TP} where D = 1 if dialysis dependent or 0 if not dialysis dependent, and TP = 1 if total protein is ≥6.7 g/dl or 0 if total protein is <6.7 g/dl. The R(2) of the final prediction model was 0.959 (P < 0.001). Validation of our model was performed in 13 patients, and the predictive performance was highly favorable (R(2) was 0.9, and bias and precision were 0.18 and 0.18, respectively). Prediction models such as ours can be utilized in future pharmacokinetics and pharmacodynamics studies evaluating the exposure-response profile and to determine the pharmacodynamic target of interest as it relates to the free concentration.

Class-dependent relevance of tissue distribution in the interpretation of anti-infective pharmacokinetic/pharmacodynamic indices

The pharmacokinetic/pharmacodynamic (PK/PD) indices useful for predicting antimicrobial clinical efficacy are well established. The most common indices include the time free drug concentration in plasma is above the minimum inhibitory concentration (MIC) (fT(>MIC)) expressed as a percent of the dosing interval, the ratio of maximum concentration to MIC (C(max)/MIC), and the ratio of the area under the 24-h concentration-time curve to MIC (AUC(0-24)/MIC). A single PK/PD index may correlate well with an entire antimicrobial class. For example, the beta-lactams correlate well with the fT(>MIC). However, other classes may be more complex and a single index cannot be generalised to the class, e.g. the macrolides. The rationale behind which PK/PD index best correlates with efficacy depends on several factors, including the mechanism of action, the microbial kill kinetics, the degree of protein binding and the degree of tissue distribution. Studies have traditionally emphasised the first two factors, whilst the significance of protein binding and tissue distribution is increasingly appreciated. In fact, the latter two factors may partially elucidate why the magnitude of reported target indices are not always as expected. For example, tigecycline and telithromycin are clinically efficacious with average serum concentrations below their MICs over a 24-h period. Therefore, to understand more fully the PK/PD relationship of antibiotics and to better predict the clinical efficacy of antibiotic dosing regimens, assessment of free drug concentrations at the site of action is warranted.

The importance of tissue penetration in achieving successful antimicrobial treatment of nosocomial pneumonia and complicated skin and soft-tissue infections caused by methicillin-resistant Staphylococcus aureus: vancomycin and linezolid

BACKGROUND

The rising prevalence of nosocomial methicillin-resistant Staphylococcus aureus (MRSA) and the recent emergence of community-associated MRSA are major clinical, public health, and economic challenges. MRSA is a leading cause of nosocomial pneumonia and complicated skin and soft-tissue infections (cSSTI). Vancomycin and linezolid are two commonly used antimicrobial agents with activity against Gram-positive pathogens, particularly MRSA, that are used to treat both nosocomial pneumonia and cSSTI. Recently, the therapeutic efficacy of vancomycin in the treatment of hospitalized patients with MRSA infections has been questioned due to the emergence of MRSA strains with reduced susceptibility to vancomycin together with concerns related to inadequate dosing and poor tissue penetration of the drug.

SCOPE

A literature review was conducted to investigate the pharmacokinetics and pulmonary and tissue penetration of vancomycin and linezolid. Using MEDLINE and EMBASE, the most relevant articles in English published over the past 25 years (up to October 2008) were identified and summarized. Studies in human volunteers and adult patients that measured concentrations of antibiotic in serum, epithelial lining fluid (ELF), and tissue were selected for further review.

FINDINGS

For both drugs, pharmacokinetic studies were conducted in diverse patient populations and employed varying techniques to measure tissue concentrations. Vancomycin concentrations in ELF ranged from 5 to 25% of simultaneous plasma levels, while concentrations in whole homogenized lung tissue were slightly higher (24-41%). Distribution of vancomycin into soft tissue was variable. For linezolid, overall mean concentrations in ELF and in soft tissue were generally similar or higher than simultaneous plasma levels, although variability in tissue penetration across studies in healthy volunteers and patients was seen.

LIMITATIONS

The studies included in this review vary greatly in their designs and patient populations; this, together with methodologic difficulties, limits the interpretation of the data.

CONCLUSIONS

In the absence of clinical data correlating ELF concentrations and clinical outcome, the clinical significance of differences in pulmonary penetration of vancomycin and linezolid is unknown. Higher vancomycin serum concentrations may be necessary to achieve appropriate lung concentrations to optimize treatment outcomes. Linezolid demonstrates adequate penetration into lung and other soft issues with sustained concentrations above the minimum inhibitory concentrations for susceptible pathogens, including MRSA, for the majority of the dosing interval. Examination of the pharmacokinetic data adds insights not provided by the clinical trial data and together provides clinicians with a more comprehensive basis for selecting appropriate antimicrobial therapy for the treatment of serious MRSA infections.

pH-triggered release of vancomycin from protein-capped porous silicon films

Objective: An in vitro model system for pH-triggered release of the antibiotic vancomycin from porous Si films is studied. Method: Vancomycin is infused into a mesoporous Si film from a mixed aqueous/acetonitrile solution and trapped by a capping layer containing the protein bovine serum albumin (BSA). The protein effectively traps vancomycin in the porous nanostructure at pH 4.0; the protein dissolves and vancomycin is released into solution when the pH increases to 7.4. The surface chemistry of porous Si exerts a substantial effect on the efficacy of drug loading. The amount of drug loading is larger in freshly-etched (hydrophobic, hydrogen-terminated) porous Si and smaller in methyl-modified, undecylenic acid-modified and thermally oxidized samples. The quantity of drug loaded in a freshly etched porous Si chip is proportional to the thickness of the porous layer, which exhibits a constant volume loading efficiency of 31% (v/v). Flow-cell experiments designed to mimic the transition from pH 4 to 7 that occurs when material moves from the stomach to the upper intestinal tract were performed on the freshly etched films and vancomycin- and BSA-release rates were quantified from the effluent of the flow cell by high-pressure liquid chromatography analysis. Results & conclusion: There is a small, constant rate of vancomycin release at pH 4 that is independent of the amount of drug loaded in the pores. This is attributed to diffusion of vancomycin from the BSA-capping layer. The release rate increases five- to tenfold when the pH of the solution in the flow cell increases to 7.4; 100% of the drug is released within 3 h of this increase.

Impaired target site penetration of vancomycin in diabetic patients following cardiac surgery

Soft tissue infections constitute a serious complication following surgery in diabetic patients and frequently require the administration of vancomycin. However, despite antibiotic treatment, mortality of patients with postoperative infections remains high and might be related to an impaired penetration of anti-infective agents to target tissues. Therefore, the present study was designed to measure vancomycin tissue concentrations in six diabetic and six nondiabetic patients after cardiac surgery. Vancomycin was administered as a continuous intravenous infusion at an infusion rate of 80 to 120 mg/h. Vancomycin concentrations in soft tissues and plasma were measured in all patients during steady state as "therapeutic window" concentrations in plasma by microdialysis on day 8+/-4 after initiation of vancomycin treatment. Vancomycin tissue concentrations in diabetic patients were significantly lower than in nondiabetics (3.7 mg/liter versus 11.9 mg/liter; P=0.002). The median vancomycintissue/vancomycinplasma concentration ratio was 0.1 in diabetic patients and 0.3 in nondiabetics (P=0.002). Our study demonstrated that vancomycin penetration into target tissues is substantially impaired in diabetic patients versus nondiabetics. Insufficient tissue concentrations could therefore possibly contribute to failure of antibiotic treatment and the development of antimicrobial resistance in diabetic patients.

Successful management of discovered pH dependence in vancomycin recovery studies: novel HPLC method for microdialysis and plasma samples

Vancomycin is a glycopeptide antibiotic approved for the treatment of serious infections or patients allergic to beta-lactams. A rapid HPLC assay using UV detection for the determination in microdialysate and human plasma was developed. After sample preparation, using methanol and trichloroacetic acid for plasma and water for microdialysate, 20 microL were injected and separated on a RP(18) column. Overall, the assay exhibited good precision and accuracy. The diffusion properties of vancomycin investigated in in vitro microdialysis experiments revealed an unfavourable concentration dependence avertable by keeping a constant pH using phosphate buffer as perfusate. The mean relative recoveries were 27.8% [coefficient of variation (CV) 11.1%] and 33.2% (CV 8.3%) for retrodialysis and recovery experiments, respectively. Following characterization of vancomycin in in vitro microdialysis, the developed setting is suitable for application in (pre-)clinical studies.

Antistaphylococcal activity of WCK 771, a tricyclic fluoroquinolone, in animal infection models

WCK 771, the arginine salt of S-(-)-nadifloxacin, was evaluated in animal models of staphylococcal infection and in vitro. For 302 methicillin-susceptible strains the MIC at which 50% of isolates are inhibited (MIC50) and the MIC90 of WCK 771 were 0.03 and 0.03 microg/ml, respectively, and for 198 methicillin-resistant strains the MIC50 and the MIC90 were 0.5 and 1.0 microg/ml, respectively. All methicillin-susceptible staphylococci were quinolone susceptible, and almost all methicillin-resistant staphylococci were quinolone resistant. WCK 771 was more potent than moxifloxacin, trovafloxacin, levofloxacin, and ciprofloxacin and had potency comparable to that of clinafloxacin. Only WCK 771 and clinafloxacin demonstrated strong potencies against vancomycin-intermediate Staphylococcus aureus strains (MICs = 1 microg/ml). WCK 771 is not a substrate of the NorA pump, as evident from the lack of an effect of reserpine on the MICs and similar protective doses against infections caused by efflux-positive and -negative staphylococci. WCK 771 was effective by both the oral and the subcutaneous routes in mice infected intraperitoneally with quinolone-susceptible methicillin-susceptible S. aureus (MSSA) strains. For infections caused by quinolone-resistant methicillin-resistant S. aureus (MRSA) strains, the activity of WCK 771 administered subcutaneously was superior to those of trovafloxacin and sparfloxacin, with a 50% effective dose range of 27.8 to 46.8 mg/kg of body weight. The activity of WCK 771 was superior to those of moxifloxacin, vancomycin, and linezolid in a mouse cellulitis model of infection caused by one MSSA and two MRSA strains, with effective doses of 2.5 and 5 mg/kg for the MSSA strain and 10-fold higher effective doses for MRSA strains. WCK 771, like vancomycin and linezolid, eradicated MRSA from mouse liver, spleen, kidney, and lung when it was administered subcutaneously at a dose of 50 mg/kg for four doses. These studies have demonstrated the effectiveness of WCK 771, administered orally and parenterally, for the treatment of diverse staphylococcal infections in mice, including those caused by quinolone-resistant strains.

Vancomycin removal during a plasma exchange transfusion

OBJECTIVE

To report a case of clinically significant removal of vancomycin during a plasma exchange transfusion in a patient with sickle-cell anemia.

CASE SUMMARY

A 46-year-old African American woman with sickle-cell disease was admitted on three separate occasions and treated with vancomycin. Vancomycin serum drug concentrations were obtained on all three admissions. During one of the admissions, a plasma exchange transfusion was performed the same day vancomycin concentrations were obtained. The vancomycin serum drug concentrations were considerably lower than predicted, resulting in potentially subtherapeutic vancomycin concentrations. Bayesian pharmacokinetic forecasting was used in interpreting the vancomycin concentrations.

DISCUSSION

Searches from MEDLINE (1966-September 2000) and Drugs and Pharmacology (1990-September 2000) were performed to obtain pertinent published literature.

CONCLUSIONS

Plasma exchange transfusions may result in clinically significant removal of vancomycin from the plasma. The potential exists of underdosing vancomycin in patients who are receiving frequent plasma exchange transfusions. Further research may be warranted to determine whether these patients may be candidates for more frequent and vigilant monitoring of vancomycin concentrations.

Non steady state and steady state PKS Bayesian forecasting and vancomycin pharmacokinetics in ICU adult patients

The pharmacokinetics of vancomycin was investigated in adult ICU patients after the first administration and at steady state. Then the predictive performance of a two-compartment Bayesian forecasting program was assessed in these patients by using population-based parameters and three non steady state vancomycin concentrations as feedback information. Finally a prospective investigation was carried out to search potential covariates. At steady state, a significant decrease (around 30%) in clearance (CL) was observed, while creatinine clearance (CLcr) was stable and a significant increase (around 30%) in volume of distribution (V(SS)) was observed. A two-fold increase in elimination half-life was found. CL was weakly correlated with CLcr at onset of therapy and at steady state. The Bayesian program tended to overpredict vancomycin peak and trough concentrations. A larger mean prediction error and a poorer precision were observed when population-based parameter estimates were used (no feedback) compared to feedback prediction, but the differences were not significant. Mechanical ventilation and concurrent opioid therapy may be pertinent covariates of vancomycin pharmacokinetics. The current work has shown that vancomycin pharmacokinetics in ICU patients displayed a significant variability and a significant change in both clearance and distribution during the course of therapy. Further investigation is necessary to clarify these findings. Moreover, the use of the Bayesian forecasting PKS program in our patients led to a prediction with low bias but rather poor precision. This outcome highlights the need to implement a population modeling approach, to determine the vancomycin pharmacokinetic parameters and covariates in our ICU patients, and to apply this information to provide more accurate concentration predictions.

Pharmacokinetics of drugs used in critically ill adults

Critically ill patients exhibit a range of organ dysfunctions and often require treatment with a variety of drugs including sedatives, analgesics, neuromuscular blockers, antimicrobials, inotropes and gastric acid suppressants. Understanding how organ dysfunction can alter the pharmacokinetics of drugs is a vital aspect of therapy in this patient group. Many drugs will need to be given intravenously because of gastrointestinal failure. For those occasions on which the oral route is possible, bioavailability may be altered by hypomotility, changes in gastrointestinal pH and enteral feeding. Hepatic and renal dysfunction are the primary determinants of drug clearance, and hence of steady-state drug concentrations, and of efficacy and toxicity in the individual patient. Oxidative metabolism is the main clearance mechanism for many drugs and there is increasing recognition of the importance of decreased activity of the hepatic cytochrome P450 system in critically ill patients. Renal failure is equally important with both filtration and secretion clearance mechanisms being required for the removal of parent drugs and their active metabolites. Changes in the steady-state volume of distribution are often secondary to renal failure and may lower the effective drug concentrations in the body. Failure of the central nervous system, muscle, the endothelial system and endocrine system may also affect the pharmacokinetics of specific drugs. Time-dependency of alterations in pharmacokinetic parameters is well documented for some drugs. Understanding the underlying pathophysiology in the critically ill and applying pharmacokinetic principles in selection of drug and dose regimen is, therefore, crucial to optimising the pharmacodynamic response and outcome.

Influence of biochemical parameters of liver function on vancomycin pharmacokinetics

The influence of biochemical parameters of hepatic function on vancomycin pharmacokinetics was retrospectively evaluated in 76 adult patients (age 18 to 81 years), from biochemistry data gathered during routine therapeutic drug monitoring. All subjects had normal serum creatinine levels. Vancomycin concentrations were determined by fluorescence polarization immunoassay in 101 paired serum samples. All data for vancomycin concentration versus time were fitted to a one-compartment model using the bayesian approach. Bilirubin, transaminases (n = 101), gamma-glutamyl transferase (n = 97), alkaline phosphatase (n = 95), albumin (n = 92) and lactate dehydrogenase (n = 42) were determined. No strong correlation was seen between any of the pharmacokinetic and biochemistry parameters studied. In patients with hyperbilirubinaemia, the mean Vss and t1/2 were increased (Vss: 0.75 +/- 0.31 versus 0.92 +/- 0.42 1.kg-1, p = 0.020; t1/2 5.93 +/- 3.30 versus 7.48 +/- 4.44 hr, p = 0.049). When liver function was evaluated according to hepatic profile (normal, mildly altered and severely altered), no significant differences were observed in vancomycin pharmacokinetics among the groups. In conclusion, vancomycin pharmacokinetics are only weakly influenced by the biochemistry parameters of liver function.

Changes in vancomycin pharmacokinetics during treatment

Using data gathered in routine monitoring, the pharmacokinetics of vancomycin during the first 10 days of treatment were compared with the pharmacokinetics after 10 days of treatment in 46 adult patients with normal renal function, ages 17-85 years old (mean +/- SD: 50.8 +/- 17.5). The mean time from initiation of treatment to the first sample determination was 5.5 days, and the mean time to the second determination was 13.4 days. Statistical differences between the two periods were observed for all pharmacokinetic parameters, except for the steady-state distribution volume. After 10 days of treatment, the mean +/- SD of the vancomycin clearance and elimination rate constant decreased from 1.31 +/- 0.82 to 1.13 +/- 0.72 ml/kg/min (p = 0.0044) and from 0.13 +/- 0.08 to 0.10 +/- 0.06 h-1 (p = 0.091), respectively. The half-life (t1/2) increased from 8.01 +/- 6.82 to 10.02 +/- 8.00 h (p = 0.012). The median percentage of the increment of t1/2 was 9.4%. The increase in t1/2 was > 50% in 12 patients and > 100% in nine cases. No association was found between the increment of t1/2 and the cumulative vancomycin dose. Frequent monitoring of serum vancomycin seems indicated, given the risk of decreased elimination during prolonged treatment.

Teicoplanin or vancomycin in the treatment of gram-positive infections?

The glycopeptide antibiotics vancomycin and teicoplanin have similar mechanisms of action on bacterial cell wall synthesis. Their spectra of activity are limited to Gram-positive bacteria, with the degree of bactericidal activity depending on the species of micro-organism. Staphylococcus aureus, Staphylococcus epidermis, enterococci and Clostridium difficile are generally sensitive, including methicillin-resistant strains of S. aureus and S. epidermidis. Glycopeptide resistance has recently emerged in staphylococci and enterococci. Vancomycin has a shorter half-life than teicoplanin and requires multiple dosing to maintain adequate serum levels. It can only be given by prolonged intravenous infusion over 1 h. In contrast, the pharmacokinetics of teicoplanin allow for once-daily dosing, either by rapid intravenous infusion or by the intramuscular route. The latter offers reliable absorption for patients with limited venous access and is also of benefit for out-patient therapy. Teicoplanin is a safer drug than vancomycin. It is associated with a lower incidence of nephrotoxicity or ototoxicity. Compared to vancomycin, the availability of the intramuscular route and the absence of a requirement for routine serum monitoring, together with the reduced need to treat drug-related side-effects make teicoplanin more cost-effective. It is as effective as vancomycin for most indications, is safe, easy to administer and an important agent for treating Gram-positive infections. Its role in hospitals is likely to increase if the price of drug acquisition is kept low.