Protein binding of vancomycin in a patient with immunoglobulin A myeloma

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.

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.

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.).

Review on Usage of Vancomycin in Livestock and Humans: Maintaining Its Efficacy, Prevention of Resistance and Alternative Therapy

Vancomycin is one of the “last-line” classes of antibiotics used in the treatment of life-threatening infections caused by Gram-positive bacteria. Even though vancomycin was discovered in the 1950s, it was widely used after the 1980s for the treatment of infections caused by methicillin-resistant Staphylococci, as the prevalence of these strains were increased. However, it is currently evident that vancomycin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci have developed for various reasons, including the use of avaparcin—an analog of vancomycin—as a feed additive in livestock. Therefore, prophylactic and empiric use of antibiotics and their analogues need to be minimized. Herein we discuss the rational use of vancomycin in treating humans, horses, farm animals, and pet animals such as dogs, cats, and rabbits. In present day context, more attention should be paid to the prevention of the emergence of resistance to antibiotics in order to maintain their efficacy. In order to prevent emergence of resistance, proper guidance for the responsible use of antimicrobials is indispensable. Therefore, almost all stakeholders who use antibiotics should have an in-depth understanding of the antibiotic that they use. As such, it is imperative to be aware of the important aspects of vancomycin. In the present review, efforts have been made to discuss the pharmacokinetics and pharmacodynamics, indications, emergence of resistance, control of resistance, adverse effects, and alternative therapy for vancomycin.

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.

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.

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.

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.

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.

Pharmacokinetics of vancomycin in adult cancer patients

Background and Objectives. Gram-positive infections are prevalent among cancer patients and vancomycin therapy is often initiated empirically. A typical vancomycin pharmacokinetics is observed in such patients. The aim of the study was to evaluate the pharmacokinetics of vancomycin in this patient population and compare it to that of normal population.

Method and Results. The pharmacokinetics of vancomycin was examined retrospectively in two groups of patients — 18 cancer patients (age 43.4 ± 22.1 years) and 13 patients without cancer (age 48.5 ± 20.2 years). Following the administration of intermittent intravenous infusion of 15 mg/kg of vancomycin, peak and trough vancomycin serum concentration were determined after the third dose or at steady state as per standard of care. Vancomycin data were analyzed according to a one-compartment open model. Pharmacokinetic parameters such as clearance (CL), volume of distribution (Vd), and K elimination (ke) were calculated. Both Vd and CL were significantly higher in the cancer group (Mean Vd was 70 ± 45 L in the cancer group and 31.1 ± 8.3 L in the noncancer group, p-value 0.002; CL mean was 110.1 ± 42 mL/min in the cancer group and 71.2 ± 22.2 mL/min in the noncancer group, p-value 0.005). There was no significant difference in K elimination and half-life (t1/2).

Conclusion. Cancer patients may require higher than usual dosing regimens to ensure optimal therapeutic concentrations, since vancomycin CL and Vd is significantly higher in these patients, a dosing schedule as high as 60 mg/kg/day may be needed for cancer patients.

The pharmacokinetic and pharmacodynamic properties of vancomycin

Vancomycin is one of only a few antibiotics available to treat patients infected with methicillin-resistant Staphylococcus aureus and methicillin-resistant, coagulase-negative Staphylococcus species. Therefore, understanding the clinical implications of the pharmacokinetic and pharmacodynamic properties of vancomycin is a necessity for clinicians. Vancomycin is a concentration-independent antibiotic (also referred to as a "time-dependent" antibiotic), and there are factors that affect its clinical activity, including variable tissue distribution, inoculum size, and emerging resistance. This article reviews the pharmacokinetic and pharmacodynamic data related to vancomycin and discusses such clinical issues as toxicities and serum concentration monitoring.

Impact of Monitoring Vancomycin Peak and Trough Concentrations versus Trough Concentrations Alone on Dose Adjustments: An Outcomes Analysis

Objective:

To determine whether monitoring both steady-state peak and trough serum vancomycin concentrations or steady-state trough serum vancomycin concentrations alone resulted in differences between two groups of patients in terms of dose adjustment, clinical outcome, and toxicity.

Design:

The study was a retrospective chart review of patients treated with vancomycin during two time periods. Group 1 represented patients hospitalized between July 1, 1996, and January 31, 1997. These patients routinely had vancomycin peak and trough concentrations measured. Group 2 represented patients hospitalized from July 1, 1997, to January 31, 1998, who were monitored with trough vancomycin concentrations only.

Setting:

A university teaching hospital.

Patients:

Adults at least 18 years of age who received a constant dose of intravenous vancomycin for at least three consecutive days were eligible for inclusion in the study. Patients were selected from lists generated by the Microbiology Department. The lists contained vancomycin serum concentrations measured during those time frames.

Main Outcome Measures:

The main outcome measure was to assess whether dose adjustments by prescribers were influenced by both vancomycin peak and trough concentrations or by the trough concentration alone.

Results:

Forty-nine and 37 patients met the criteria for inclusion into group 1 and group 2, respectively. The mean duration of therapy in group 1 (15 ± 10 d) was not statistically different from that of group 2 (14 ± 12 d). Patients in both groups received a mean daily vancomycin dose of approximately 1,500 mg. In analyzing treatment decisions, trough concentration was the only significant factor influencing a change in total daily dose of vancomycin (p = 0.038). Furthermore, although the method of vancomycin serum concentration monitoring varied between the two groups, the mean clinical outcome parameters were comparable.

Conclusions:

Prescribers tended to adjust vancomycin regimens based only on trough serum concentrations; monitoring peak serum vancomycin concentrations did not enhance patient care. Mean outcome parameters in the two groups were comparable.

Clinical, demographic, and immunohistologic features of vancomycin-induced linear IgA bullous disease of the skin. Report of 2 cases and review of the literature

Administration of intravenous vancomycin has been associated with the development of linear IgA bullous disease (LABD). In contrast to the idiopathic variant, vancomycin-induced LABD (VILABD) appears to be more transient and to be associated with lower morbidity. The characteristics of this entity remain undefined. Our analysis of clinical, demographic, and immunopathologic features of 2 new and 14 previously reported patients with VILABD reveals that VILABD is clinically and immunopathologically indistinguishable from its idiopathic variant. A variety of premorbid conditions and concomitant medications were observed, none of which was consistently associated with the development of VILABD. VILABD occurs independently of vancomycin trough levels, resolves promptly upon discontinuation of vancomycin, and recurs more severely and with shorter onset latency with vancomycin rechallenge. This entity should be recognized as 1 of the adverse cutaneous effects of intravenous vancomycin, and warrants prompt diagnosis through direct immunofluorescence skin examination.

A closer look at vancomycin, teicoplanin, and antimicrobial resistance

The worldwide increase in the incidence of resistant Gram-positive infections has renewed interest in the glycopeptide class of antimicrobial agents. Two glycopeptides are available in many parts of the world--vancomycin and teicoplanin. These two agents appear to differ in several respects, including: potential for selecting microbial resistance, dosing convenience, safety, and efficacy in severe infection. Teicoplanin appears to have lower toxicity and greater convenience; however, its widespread acceptance has been plagued by concerns over antimicrobial resistance, efficacy, and appropriate dosing. A review of available studies suggests that teicoplanin, when dosed at 6 mg/kg/day, is better tolerated than vancomycin 15 mg/kg/q12h; however, at these doses, it appears to be somewhat less effective than vancomycin in serious Staphylococcus aureus infection, such as endocarditis. Although higher doses of teicoplanin, 12 mg/kg/day to 30 mg/kg/day, have been associated with efficacy comparable to that of vancomycin in serious S. aureus infections, such doses may eliminate some of the safety advantages conferred by lower teicoplanin doses. Teicoplanin has been associated with resistance among coagulase-negative staphylococci and the selection of resistance in S. aureus. There is some evidence that widespread use of teicoplanin might accelerate the development of S. aureus resistance to both teicoplanin and vancomycin. The selection of an appropriate glycopeptide in an individual patient should be based not only on convenience, but also on a determination of optimal efficacy, safety at an efficacious dose, and the potential for resistance.

Serum protein-binding characteristics of vancomycin

A synthesis of studies of serum protein binding of vancomycin and its reported abnormal binding in serum with very high concentrations of immunoglobulin A (IgA) suggests that this antibiotic may be bound to more than one serum protein. Using an ultrafiltration method for separating free from bound drug and high-performance liquid chromatography to measure drug concentration, we studied the binding characteristics of vancomycin for alpha-1 acid glycoprotein, IgG, IgM, IgA, and albumin. The results showed that vancomycin does not bind to alpha-1 acid glycoprotein, IgG, or IgM. Major binding to albumin and IgA occurs, and total drug binding to serum proteins can be fully explained by binding to these two proteins. We calculated an N (number of binding sites per molecule) of 1.3 +/- 0.4 and a K (association constant) of 3.3 x 10(5) +/- 6.3 x 10(4) M-1 (NK = 4.3 x 10(5) M-1) for binding to IgA, whereas the corresponding NK value for albumin was only 527.5 M-1, indicating that vancomycin preferentially binds to IgA. Very high concentrations of IgA in serum (i.e., grams per deciliter), such as in patients with IgA myeloma, may result in the paradox of high (total) concentrations of vancomycin in serum that may be clinically ineffective.

The influence of vancomycin concentration and the pH of plasma on vancomycin protein binding

A review of numerous studies of the protein binding of vancomycin suggests major discrepancies among their results. The reported percent protein binding of vancomycin varies from 0% to 98%. The influence of pH and concentration on the protein binding of vancomycin was investigated in this study. There was a significant difference (p < 0.001) in percent protein binding in vancomycin-spiked plasma samples across the pH range of 7.0-8.0. There was no significant difference (p > 0.05) in percent protein binding in vancomycin-spiked plasma samples across the concentration range of 2-80 mg/L. It is likely that some of the variation reported to date may be due to a lack of control of pH during the measurement of protein binding of vancomycin.

Characteristics of ceftriaxone binding to immunoglobulin G and potential clinical significance

The interaction between immunoglobulin G (IgG) and ceftriaxone was studied. Using an ultrafiltration method, we performed dose ranging studies at a ceftriaxone concentration range of 1 to 720 micrograms/ml in the presence of various concentrations of human IgG, human serum albumin (HSA), and combinations of IgG and HSA at pH 7.4 and 37 degrees C. The results showed that ceftriaxone binding to IgG was nonlinear and was consistent with the presence of two binding sites that possess different binding capacities and affinities. Except for increased peak percent binding as the IgG concentration increased, the binding characteristics did not change with IgG concentration. Binding to HSA was consistent, with the presence of only one high-affinity binding site. A mathematical model based on the observed data was constructed; this model was used to predict protein binding at various concentrations of drug, IgG, HSA, or combinations of IgG and HSA in buffer and in plasma medium. Correlations between the observed versus the predicted values were excellent in both media. Simulations with the model indicated that patients with hypergammaglobulinemia have an increased potential of being exposed to prolonged subinhibitory concentrations of ceftriaxone if the drug is given once every 24 h.