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

Simultaneous Determination of Methotrexate Concentrations in Human Plasma and Cerebrospinal Fluid Using Two-Dimensional Liquid Chromatography: Applications in Primary Central Nervous System Lymphoma

Background

In this study, we aimed to develop a method for the simultaneous quantification of methotrexate (MTX) samples extracted from human plasma and cerebrospinal fluid (CSF), using two-dimensional liquid chromatography (2D-LC). Furthermore, we intended to verify whether intravenous mannitol could increase MTX concentration in the CSF of patients.

Methods

The mobile phase of PUMP1 consisted of 10.0 mmol/L ammonium acetate and acetonitrile. PUMP2 solution consisted of an aqueous solution of 10.0 mmol/L ammonium acetate. The mobile phase of PUMP3 comprised 50.0 mmol/L ammonium acetate and acetonitrile, with a flow rate of 1.0 mL/min.

Results

The developed method was successfully employed to simultaneously determine drug levels in plasma and CSF from the patients treated with MTX. CSF samples were obtained by lumbar puncture 0.5 - 2 h after starting the high-dose methotrexate (HD-MTX) infusion (over 4 h) and immediately before the intrathecal (IT) administration of MTX. Venous blood samples were drawn 4 h after the start of infusion. The calibration curve was linear, with a range of 0.07 - 2.38 µmol/L for CSF samples and a range of 0.11 - 5.51 µmol/L for plasma samples. Precision (> 95%) and accuracy (> 97%) were within the acceptance criteria for each quality control (QC) level. Inter- and intra-day accuracy and precision values met the acceptance criteria for each QC level. The correlation between MTX concentrations in the plasma and CSF was moderate (r = 0.502). No significant difference was observed in MTX concentration in CSF between patients using intravenous mannitol and those not using intravenous mannitol (P = 0.682).

Conclusion

The developed method was useful for therapeutic drug monitoring of MTX and suitable for assessing the risks and benefits of chemotherapy in patients with primary central nervous system lymphoma. Intravenous mannitol did not increase MTX concentration in the CSF of patients.

Preanalytical Stability of 13 Antibiotics in Biological Samples: A Crucial Factor for Therapeutic Drug Monitoring

The stability of antibiotic preanalytical samples is a critical factor in therapeutic drug monitoring (TDM), a practice of undoubted importance for the proper therapeutic use of antibiotics, especially in complex management patients, such as pediatrics. This review aims to analyze the data in the literature regarding the preanalytical stability of some of the antibiotics for which TDM is most frequently requested. The literature regarding the preanalytical stability of amikacin, ampicillin, cefepime, ceftazidime, ciprofloxacin, daptomycin, gentamicin, levofloxacin, linezolid, meropenem, piperacillin, teicoplanin, and vancomycin in plasma, serum, whole blood, and dried blood/plasma spot samples was analyzed. Various storage temperatures (room temperature, 4 °C, -20 °C, and -80 °C) and various storage times (from 1 h up to 12 months) as well as subjecting to multiple freeze-thaw cycles were considered. The collected data showed that the non-beta-lactam antibiotics analyzed were generally stable under the normal storage conditions used in analytical laboratories. Beta-lactam antibiotics have more pronounced instability, particularly meropenem, piperacillin, cefepime, and ceftazidime. For this class of antibiotics, we suggest that storage at room temperature should be limited to a maximum of 4 h, storage at 2-8 °C should be limited to a maximum of 24 h, and storage at -20 °C should be limited to a maximum of 7 days; while, for longer storage, freezing at -80 °C is suggested.

Two-dimensional liquid chromatography with reversed phase in both dimensions: A review

Two-dimensional liquid chromatography (2D-LC), and in particular comprehensive two-dimensional liquid chromatography (LC×LC), offers increased peak capacity, resolution and selectivity compared to one-dimensional liquid chromatography. It is commonly accepted that the technique produces the best results when the separation mechanisms in the two dimensions are completely orthogonal; however, the use of similar separation mechanisms in both dimensions has been gaining popularity as it helps avoid difficulties related to mobile phase incompatibility and poor column efficiency. The remarkable advantages of using reversed phase in both dimensions (RPLC×RPLC) over other separation mechanisms made it a promising technique in the separation of complex samples. This review discusses some physical and practical considerations in method development for 2D-LC involving the use of RP in both dimensions. In addition, an extensive overview is presented of different applications that relied on RPLC×RPLC and 2D-LC with reversed phase column combinations to separate components of complex samples in different fields including food analysis, natural product analysis, environmental analysis, proteomics, lipidomics and metabolomics.

Liquid chromatography-tandem mass spectrometry methods for quantification of total and free antibiotic concentrations in serum and exudate from patients with post-sternotomy deep sternal wound infection receiving negative pressure wound therapy

BACKGROUND

Systemically administered antibiotics are thought to penetrate the wounds more effectively during negative pressure wound therapy (NPWT).To test this hypothesis total and free antibiotic concentrations were quantified in serum and wound exudate.

METHODS

UHPLC-MS/MS methods were developed and validated for the determination of ceftazidime, cefepime, cefotaxime, cefuroxime, cefazolin, meropenem, oxacillin, piperacillin with tazobactam, clindamycin, ciprofloxacin, sulfamethoxazole/trimethoprim (cotrimoxazole), gentamicin, vancomycin, and linezolid. The unbound antibiotic fraction was obtained by ultrafiltration using a Millipore Microcon-30kda Centrifugal Filter Unit. Analysis was performed on a 1.7-µm Acquity UPLC BEH C18 2.1 × 100-mm column with a gradient elution.

RESULTS

The validation was performed for serum, exudates and free fractions. For all matrices, requirements were met regarding linearity, precision, accuracy, limit of quantitation, and matrix effect. The coefficient of variation was in the range of 1.2-13.6%.and the recovery 87.6-115.6%, respectively. Among the 29 applications of antibiotics thus far, including vancomycin, clindamycin, ciprofloxacin, oxacillin, cefepime, cefotaxime, cotrimoxazole, and gentamicin, total and free antibiotic concentrations in serum and exudate were correlated.

CONCLUSION

This method can accurately quantify the total and free concentrations of 16 antibiotics. Comparison of concentration ratios between serum and exudates allows for monitoring individual antibiotics' penetration capacity in patients receiving NPWT.

An Overview of Analytical Methodologies for Determination of Vancomycin in Human Plasma

Vancomycin is regarded as the last resort of defense for a wide range of infections due to drug resistance and toxicity. The detection of vancomycin in plasma has always aroused particular concern because the performance of the assay affects the clinical treatment outcome. This article reviews various methods for vancomycin detection in human plasma and analyzes the advantages and disadvantages of each technique. Immunoassay has been the first choice for vancomycin concentration monitoring due to its simplicity and practicality, occasionally interfered with by other substances. Chromatographic methods have mainly been used for scientific research due to operational complexity and the particular requirement of the instrument. However, the advantages of a small amount of sample needed, high sensitivity, and specificity makes chromatography irreplaceable. Other methods are less commonly used in clinical applications because of the operational feasibility, clinical application, contamination, etc. Simplicity, good performance, economy, and environmental friendliness have been points of laboratory methodological concern. Unfortunately, no one method has met all of the elements so far.

Does Monitoring Total and Free Polymyxin B1 Plasma Concentrations Predict Polymyxin B-Induced Nephrotoxicity? A Retrospective Study in Critically Ill Patients

INTRODUCTION

The correlation between total and free polymyxin B (PMB including PMB1 and PMB2) exposure in vivo and acute kidney injury (AKI) remains obscure. This study explores the relationships between plasma exposure of PMB1 and PMB2 and nephrotoxicity, and investigates the risk factors for PMB-induced acute kidney injury (AKI) in critically ill patients.

METHODS

Critically ill patients who used PMB and met the criteria were enrolled. The total plasma concentration and plasma binding of PMB1 and PMB2 were analysed by liquid chromatography-tandem mass spectrometry and equilibrium dialysis.

RESULTS

A total of 89 patients were finally included, and AKI developed in 28.1% of them. The peak concentration of PMB1 (C_max (B1)) (adjusted odds ratio (AOR) = 1.68, 95% CI 1.08-2.62, p = 0.023), baseline BUN level (AOR = 1.08, 95% CI 1.01-1.16, p = 0.039) and hypertension (AOR = 3.73, 95% CI 1.21-11.54, p = 0.022) were independent risk factors for PMB-induced AKI. The area under the ROC curve of the model was 0.799. When C_max (B1) was 5.23 μg/ml or more, the probability of AKI was higher than 50%. The ratio of PMB1/PMB2 decreased after PMB preparation entered into the body. The protein binding rate in critically ill patients indicated significant individual differences. Free C_max (B) and free C_max (B1) levels in the AKI group were significantly (p < 0.05) higher than those in the non-AKI group. Total and free concentrations of PMB in patients showed a positive correlation.

CONCLUSIONS

Both the ROC curve and logistic regression model showed that C_max (B1) was a good predictor for the probability of PMB-induced AKI. Early therapeutic drug monitoring (TDM) of PMB should be considered in critically ill patients. Compared with C_min (B), C_max (B) and C_max (B1) may be helpful for the early prediction of PMB-induced AKI in critically ill patients.

Determination of Vancomycin and Norvancomycin Residues in Milk by Automated Online Solid-Phase Extraction Combined With Liquid Chromatography-High Resolution Mass Spectrometry

Background

Vancomycin and norvancomycin, as potent antibacterial retention drugs, were used illegally on animals bred for food, which directly affected the quality and safety of animal-derived food, and even harmed human health.

Objective

A fast analysis method, which was adopted to detect residues of vancomycin and norvancomycin in milk, was implemented on a chromatographic system containing online solid-phase extraction (SPE) device that combined with high-resolution mass spectrometer (HRMS).

Method

First, the analytes were added to the blank milk sample were extracted with water [containing 0.1% trifluoroacetic acid (TFA)]–acetonitrile (ACN) (8:2, v/v), and then were purified and enriched on a C18-XL column, whereafter eluted from the purification column onto the analytical column (Shiseido Capcell Pak ADME column) for chromatographic separation prior to hybrid quadrupole–Orbitrap (Q-Orbitrap) detection.

Results

The results showed that the limit of detection (LOD) for each analyte and the limit of quantitation (LOQ) were 0.15  and 0.5 μg/kg, respectively. The correlation coefficient(s) of vancomycin and norvancomycin ranged from 0 to 200 ng/mL were greater than 0.9983.

Conclusions

These validations reflected that it was suitable for the established method to rapidly analyze vancomycin and norvancomycin residues in milk.

Highlights

The method for detecting vancomycin and norvancomycin residues in milk by online SPE combined with LC-HRMS. Online SPE technology realized automation, and the application of HRMS greatly improved the reliability of qualitative and quantitative analyses. The developed method is fast, simple, and reliable; each methodological index can meet requirements of trace analyses of vancomycin and norvancomycin in milk.

Comparison of liquid-liquid extraction, microextraction and ultrafiltration for measuring free concentrations of testosterone and phenytoin

Aim: The purpose of the study was to find methods suitable for measuring the free concentrations of testosterone and phenytoin. Materials & methods: Sample solutions of the compounds in buffer and human albumin were processed using liquid-liquid extraction, microextraction and ultrafiltration and analyzed by LC-MS/MS. Results: Liquid-liquid extraction with dibutyl phthalate provided complete extraction from buffer solutions and partial extraction from albumin samples. Spintip C18 devices provided exhaustive extraction from buffer and albumin samples. Spintip C8 devices offered complete extraction from buffer and approximately 50% recovery from albumin samples. Centrifree ultrafiltration devices showed high recovery of free concentrations from all the samples, while Amicon and Nanosep devices provided partial recovery. Conclusion: Spintip C8 and Centrifree devices proved useful for measuring free concentrations.

Nemonoxacin enhances antibacterial activity and anti-resistant mutation ability of vancomycin against methicillin-resistant Staphylococcus aureus in an in vitro dynamic pharmacokinetic/pharmacodynamic model

Reduced susceptibility and emergence of resistance to vancomycin in methicillin-resistant Staphylococcus aureus (MRSA) have led to the development of various vancomycin based combinations. Nemonoxacin is a novel nonfluorinated quinolone with antibacterial activity against MRSA. The present study aimed to investigate the effects of nemonoxacin on antibacterial activity and the anti-resistant mutation ability of vancomycin for MRSA and explore whether quinolone resistance genes are associated with a reduction in the vancomycin minimal inhibitory concentration (MIC) and mutant prevention concentration (MPC) when combined with nemonoxacin. Four isolates, all with a vancomycin MIC of 2 μg/mL, were used in a modified in vitro dynamic pharmacokinetic/pharmacodynamic model to investigate the effects of nemonoxacin on antibacterial activity (M04, M23 and M24) and anti-resistant mutation ability (M04, M23 and M25, all with MPC ≥19.2 μg/mL) of vancomycin. The mutation sites of gyrA, gyrB, parC, and parE of 55 clinical MRSA isolates were sequenced. We observed that in M04 and M23, the combination of vancomycin (1g q12h) and nemonoxacin (0.5g qd) showed a synergistic bactericidal activity and resistance enrichment suppression. All clinical isolates resistant to nemonoxacin harbored gyrA (S84→L) mutation; gyrA (S84→L) and parC (E84→K) mutations were the two independent risk factors for the unchanged vancomycin MPC in combination. Nemonoxacin enhances the bactericidal activity and suppresses resistance enrichment ability of vancomycin against MRSA with a MIC of 2 μg/mL. Our in vitro data support the combination of nemonoxacin and vancomycin for the treatment of MRSA infection with a high MIC.

[Integrated multi-column two-dimensional liquid chromatographic system for determination of amisulpride in serum]

快速准确的治疗药物监测对于临床上确保患者用药有效性及安全性至关重要,同时也能够确定患者用药依从性,制定个性化给药方案。该文以两支疏水性略有差异的反相分离柱Supersil ODS2和SinoChrom ODS-BP,及强阳离子交换捕集柱Supersil SCX构建了基于集成化的多柱二维液相色谱系统。通过二维色谱接口,以pH 3.0的磷酸缓冲液调整第一维分离后的洗脱液组成,降低有机相含量并维持pH,改善了中心切割模式下样品转移和捕集的效率。利用该多柱二维液相色谱系统发展了血清中氨磺必利的二维液相色谱检测方法,血清样品经过高氯酸和甲醇混合液沉淀蛋白质并离心后直接300 μL大体积进样,以乙腈/磷酸缓冲液(25 mmol/L, pH 3.0)(20/80, v/v)作为第一维分离流动相,磷酸缓冲液(25 mmol/L, pH 3.0)作为捕集过程的稀释流动相,乙腈/磷酸缓冲液(25 mmol/L, pH 7.0)(25/75, v/v)作为第二维分离流动相,12 min内即可完成分析。方法在10~200 ng/mL的范围内线性相关性良好(r=0.9998)。样品在50 ng/mL和100 ng/mL两个加标浓度下的回收率稳定,在73.7%~76.8%之间。方法的检出限为7.28 ng/mL,定量限为24.27 ng/mL,能够满足《神经精神药理学治疗药物检测共识指南》中推荐的药物监控范围要求。由于该系统日常使用及维护成本较低,且能够实现自动化分析,故该方法适合在临床上用于治疗药物监测研究。

A novel method for the quantification of anlotinib in human plasma using two-dimensional liquid chromatography

A simple, efficient, and stable detection method of two-dimensional liquid chromatography (2D-LC) was established and validated to determine anlotinib in the human plasma. The 2D-LC system comprises a first-dimensional column (LC1), an intermediate transfer column, and a second-dimensional column (LC2). With simple protein precipitation treatment, the samples were processed directly for detection. The analysis cycle time was completed within 9.50 min. For the anlotinib concentrations, the calibration curve was linear over the 5.00-320.00 ng/mL range. The intra-day and inter-day precision ranges were 0.77-6.22% and 1.92-4.26%, respectively, for anlotinib concentrations. The recoveries were in the range of 97.85-102.50%. A total of 135 plasma samples from 94 patients were analyzed by our method. The plasma concentrations of patients were in the range of 5.17-106.38 ng/mL, in which the female had a higher plasma concentration (6.44-106.38 ng/mL). The simultaneous application of dexamethasone can increase the anlotinib concentration in the plasma. In our clinical application, we found that the factors that affect the plasma concentration include the time and dose of the medication, gender, and drug interactions. The method appears to be sensitive, precise, selective, and suitable for determining the concentration of anlotinib in the plasma sample.

Characterization of positional isomers of drug intermediates by off-line RPLC x SFC hyphenated to high resolution MS

Many steps are needed in the synthesis of a new active pharmaceutical ingredient (API). In a practical case proposed by a French pharmaceutical company, an intermediate synthesis step, needed to protect 8 hydroxyl groups before oxidation, could produce a mixture of neutral compounds containing up to 652 structures being positional isomers of 18 molecular formulas. Some mixtures allowed obtaining the desired API, others did not. An efficient analytical method was needed to characterize these neutral positional isomers and identify the mixtures to reject. Two samples were provided by the pharmaceutical company: Sample A was conform, Sample B was not. 8 RPLC columns were used with different gradients to screen Sample A. Next, the best RPLC separation was used as the second dimension fast analysis in a comprehensive 2D-RPLC systems. Two columns were used as first dimension: a fluorinated one and a zirconium based one. An order of magnitude was gained in peak capacity, but a better sample characterization was still needed. An off-line RPLC x SFC x Q-TOF/MS analysis was performed collecting 96 RPLC fractions and analyzing them by SFC with Q-TOF/MS detection. A home-made software associated the 96 SFC MS chromatograms to produce either base peak (BPC) or extract ion (EIC) contour plots that allowed for a satisfying characterization of the samples. Subtracting the EIC of expected m/z compounds from the Sample B BPC contour plot produced a unique new contour plot clearly pointing out unexpected compounds explaining the failure of the synthesis and possibly allowing improving the synthesis process.

An Ensemble Model for Prediction of Vancomycin Trough Concentrations in Pediatric Patients

Purpose

This study aimed to establish an optimal model to predict vancomycin trough concentrations by using machine learning.

Patients and Methods

We enrolled 407 pediatric patients (age < 18 years) who received vancomycin intravenously and underwent therapeutic drug monitoring from June 2013 to April 2020 at Xinhua Hospital affiliated to Shanghai Jiaotong University School of Medicine. The median (interquartile range) age and weight of the patients were 2 (0.63–5) years and 12 (7.8–19) kg. Vancomycin trough concentrations were considered as the target variable, and eight different algorithms were used for predictive performance comparison. The whole dataset (407 cases) was divided into training group and testing group at the ratio of 80%: 20%, which were 325 and 82 cases, respectively.

Results

Ultimately, five algorithms (XGBoost, GBRT, Bagging, ExtraTree and decision tree) with high R² (0.657, 0.514, 0.468, 0.425 and 0.450, respectively) were selected and further ensembled to establish the final model and achieve an optimal result. For missing data, through filling the missing values and model ensemble, we obtained R²=0.614, MAE=3.32, MSE=24.39, RMSE=4.94 and a prediction accuracy of 51.22% (predicted trough concentration within ±30% of the actual trough concentration). In comparison with the pharmacokinetic models (R²=0.3), the machine learning model works better in model fitting and has better prediction accuracy.

Conclusion

Therefore, the ensemble model is useful for the vancomycin concentration prediction, especially in the population of children with great individual variation. As machine learning methods evolve, the clinical value of the ensemble model will be demonstrated in the clinical practice.

Application of the Westgard Multi-rule Theory to Internal Quality Control Evaluation of Voriconazole for Therapeutic Drug Monitoring

Background:

There is no worldwide recognized reference internal quality control method for Therapeutic Drug Monitoring (TDM) of voriconazole (VCZ) by Liquid Chromatography (LC). In this study, we aimed to develop an internal quality control method for TDM of VCZ, evaluate it by the Westgard multi-rule theory, and guarantee the analytical quality of the assays.

Methods:

The plasma concentration of VCZ was detected by two-dimensional liquid chromatography with ultraviolet detection (2D-LC-UV) method. The internal quality control results accompanying with TDM of VCZ in our laboratory from July 2019 to January 2020 were collected and retrospectively studied. The Levey-Jennings quality chart and Z-score quality chart were drawn and Westgard multirules of 12s/13s/22s/R4s/41s/10x were applied to assess the suitable quality control method for TDM of VCZ.

Results:

The 2D-LC-UV method was well suited to monitor the plasma concentration of VCZ and increase the real-time capability of TDM for VCZ. Combined with Westgard multi-rules, the quality control charts of Levery-Jennings and Z-score both can timely discover and judge the systematic errors and random errors for the internal quality control results. 86 batches of quality control products were assessed and 7 times warnings and 6 times out of control were detected.

Conclusion:

The Westgard multi-rules, with high efficacy in determining detection errors, has important application value in the internal quality control for TDM of VCZ. The developed quality control method can improve the accuracy and reliability for VCZ measurement by the 2D-LC-UV method and further promote the clinical rational use of the drug.

Method for Simultaneous Determination of Free Concentration, Total Concentration, and Plasma Binding Capacity in Clinical Samples

Most quantitative research methods are based on measuring either the total or the free concentration of an analyte in a sample. However, this is often insufficient for the study of complex biological systems. The main objective of this research was to develop new methods for providing more information from samples: the free concentration (C_f), the total concentration (C_t), and the plasma binding capacity (PBC). Samples were processed using microextraction and ultrafiltration. For each of these techniques, two quantification procedures were used: addition of isotopically labeled standard and repeated analysis of the same sample. The new methods were validated by analyzing clinical samples and samples with known concentrations. Methods based on addition of labeled compound were found to be the fastest, and most reproducible. For analysis of clinical samples, methods based on microextraction were more sensitive and more accurate than those based on ultrafiltration. For analysis of pooled plasma samples, the overall accuracy of all approaches to determine PBC, testosterone C_f, and testosterone C_t was between 94 and 109%, 87-113%, and 94-122% respectively. The new approach goes beyond a simple concentration measurement, giving more information from clinical samples, with great potential for personalizing drug dosage and therapy to the needs of individual patients.

A systematic review on chromatography-based method validation for quantification of vancomycin in biological matrices

A fully validated bioanalytical methods are prerequisite for pharmacokinetic and bioequivalence studies as well as for therapeutic drug monitoring. Due to high pharmacokinetic variability and narrow therapeutic index, vancomycin requires reliable quantification methods for therapeutic drug monitoring. To identify published chromatographic based bioanalytical methods for vancomycin in current systematic review, PubMed and ScienceDirect databases were searched. The selected records were evaluated against the method validation criteria derived from international guidelines for critical assessment. The major deficiencies were identified in method validation parameters specifically for accuracy, precision and number of calibration and validation standards, which compromised the reliability of the validated bioanalytical methods. The systematic review enacts to adapt the recommended international guidelines for suggested validation parameters to make bioanalysis reliable.

Comparing ultrafiltration and equilibrium dialysis to measure unbound plasma dolutegravir concentrations based on a design of experiment approach

Dolutegravir therapeutic drug monitoring (TDM) could be improved by measuring the unbound dolutegravir plasma concentration (Cu), particularly in patients experiencing virological failure or toxicity despite achieving appropriate DTG total plasma concentrations. Equilibrium dialysis (ED) is the gold standard to measure Cu, but ED is time consuming, precluding its use in clinical practice. In contrast, ultrafiltration is applicable to TDM, but is sensitive to numerous analytical conditions. In order to evaluate measurements of Cu by ultrafiltration, ultrafiltration conditions were validated by comparison with ED. DTG concentrations were measured by LC–MS/MS. Three ultrafiltration factors (temperature, duration and relative centrifugal force [RCF]) were evaluated and compared to ED (25/37 °C), using a design of experiment strategy. Temperature was found to influence Cu results by ED (p = 0.036) and UF (p = 0.002) when results were analysed with ANOVA. Relative centrifugal force (2000 g) and time (20 min) interacted to influence Cu (p = 0.006), while individually they did not influence Cu (p = 0.88 and p = 0.42 for RCF and time). Ultrafiltration conditions which yielded the most comparable results to ED were 37 °C, 1000 g for 20 min. Ultrafiltration results greatly depended on analytical conditions, confirming the need to validate the method by comparison with ED in order to correctly interpret DTG Cu.

Pretreatment and non-specific binding in ultrafiltration device: Impact on protease inhibitor quantification

INTRODUCTION

Ultrafiltration (UF) is used to separate unbound drugs; however, non-specific binding (NSB) may be a limiting factor of this technique. Pretreatment of UF devices has been suggested to reduce NSB. Therefore, the pretreatment methodologies for UF devices were evaluated in order to test their effectiveness in reducing NSB of protease inhibitors (PIs).

METHODOLOGY

Two PIs (lopinavir-LPV and ritonavir-RTV) were tested. UF devices were pretreated with ultrapure water, Tween-20 or Tween-80. To evaluate the NSB, after UF devices being pretreated, ultrafiltrate solutions containing the analytes at two concentrations (low and high) were used. Samples were quantified by LC-MS/MS.

RESULTS

UF devices pretreated with Tween-5% had the lowest NSB for both analytes. NSB values varied between 7 and 11% at low concentration 16-34% at high LPV concentration, respectively. For RTV, NSB was approximately 6% for low concentration and 18% for high concentration. Failure to completely remove Tween in UF devices could results in an overestimation of NSB.

CONCLUSION

Pretreatment of UF device with Tween and subsequent removal proved to be effective in reducing NSB of PI.

Current Status of Vancomycin Analytical Methods

BACKGROUND

The glycopeptide antibiotics are a class of antimicrobial drugs that are an important alternative for cases of bacterial infections resistant to penicillins, besides being able to be used to treat infections in people allergic to pencilin. They have great activity against Gram-positive microorganisms, including methicillin-resistant Staphylococcus aureus (MRSA), by inhibiting the cell wall synthesis.

OBJECTIVE

There are many analytical methods in the literature for determination of antimicrobial glycopeptide vancomycin in different matrixes that are very effective; however, all of them use toxic solvents, contributing to the generation of waste, causing damage to the environment and to the operator, as well as increased costs of analysis.

RESULTS

The most prevailing method found was high performance liquid chromatography (HPLC), followed by microbiological assays and, in less quantity, spectrometric methods. The chromatographic methods use organic solvents that are toxic, such as acetonitrile and methanol, and buffer solutions, that can damage the equipment and the column. In the microbiological assays the disc diffusion methods are still in the majority. The spectrophotometric methods were based in the UV-Vis region using buffer solutions as a diluent.

CONCLUSIONS

All these methods can become greener, following green analytical chemistry principles, which could bring benefits both to the environment and the operator, and reduce costs.

HIGHLIGHTS

In this paper, a literature review regarding analytical methods for determination of vancomycin was carried out with a suggestion of greener alternatives.

A novel two-dimensional liquid chromatography system for the simultaneous determination of three monoterpene indole alkaloids in biological matrices

The present paper describes a novel two-dimensional liquid chromatography (2D-LC) system, which is comprised of a first-dimensional ion exchange chromatography (IEX1) column, trap column, and second-dimensional reversed-phase chromatography (RP2) column system. The biological sample is separated by the first-dimensional LC using an IEX column to remove interferences. The analytes are transferred to the trap column after heart-cutting. Then, the analytes are transferred to the second-dimensional LC using an RP2 column for further separation and ultraviolet detection. This 2D-LC system can offer a large injection volume to provide sufficient sensitivity and exhibits a strong capacity for removing interferences. Here, the determination of three monoterpene indole alkaloids (MIAs; gelsemine, koumine, and humantenmine) from Gelsemium in biological matrices (plasma, tissue, and urine) was used this 2D-LC system. After a rapid and easy sample preparation method based on protein precipitation, the sample was injected into the 2D-LC. The method was developed and validated in terms of the selectivity, LOD, LOQ, linearity, precision, accuracy, and stability. The sample preparation time for the three MIAs was 15 min. The LOD for these compounds was 10 ng/mL, which was lower than the developed HPLC methods. The results showed that this method had good quantitation performance and allowed the determination of gelsemine, koumine, and humantenmine in biological matrices. The method is rapid, exhibits high selectivity, has good sensitivity, and is low-cost, thus making it well-suited for application in the pharmaceutical and toxicological analysis of Gelsemium. Graphical abstract.

An ultra-performance liquid chromatography–tandem mass spectrometry method to quantify vancomycin in human serum by minimizing the degradation product and matrix interference

Aim: This study aimed to develop and validate a method for better therapeutic monitoring of vancomycin serum concentration. Methods & results: An ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method was developed and validated to minimize the interference of crystalline degradation product and matrix. It was compared with chemiluminescence microparticle immunoassay (CMIA) and ultra-performance liquid chromatography with ultraviolet detection (UPLC-UV) in the performance of testing normal, on-dialysis and hemolytic serum samples. For on-dialysis samples, a moderate correlation (r = 0.534) was observed between UPLC-UV and UPLC–MS/MS. In testing hemolytic samples, ten (10/85, 11.8%) samples were overestimated by CMIA method. Conclusion: Vancomycin concentration determined by CMIA, UPLC-UV was more affected by various panels of serum samples than UPLC–MS/MS assay, suggesting that UPLC–MS/MS is a more reliable and promising tool for clinical vancomycin therapeutic drug monitoring.

The application of on-line two-dimensional liquid chromatography (2DLC) in the chemical analysis of herbal medicines

Herbal medicines are complicated chemical systems containing hundreds of small molecules of various polarities, structural types, and contents. Thus far, the chromatographic separation of herbal extracts is still a big challenge. Two-dimensional liquid chromatography (2DLC) has become an attractive separation tool in the past few years. Particularly, a lot of attention has been paid to on-line 2DLC. In this review, we aim to give an overview on applications of on-line 2DLC in the chemical analysis of herbal medicines since 2010. Firstly, classification and general configurations of on-line 2DLC were briefly introduced. Then, we summarized main applications in herbal medicines of heart-cutting 2DLC (LC-LC), comprehensive 2DLC (LC × LC), and their combinations, with emphasis on LC × LC. Mass spectrometry is the most popular detector coupled with 2DLC, which allows sensitive and accurate structural characterization of herbal compounds. Finally, future developments in on-line 2DLC techniques were also discussed.

Impact of vancomycin protein binding on target attainment in critically ill children: back to the drawing board?

Objectives

The objectives of this observational study were to investigate plasma protein binding and to evaluate target attainment rates of vancomycin therapy in critically ill children.

Patients and methods

Paediatric ICU patients, in whom intravenous intermittent dosing (ID) or continuous dosing (CD) with vancomycin was indicated, were included. Covariates on unbound vancomycin fraction and concentration were tested using a linear mixed model analysis and attainment of currently used pharmacokinetic/pharmacodynamic (PK/PD) targets was evaluated. Clinicaltrials.gov: NCT02456974.

Results

One hundred and eighty-eight plasma samples were collected from 32 patients. The unbound vancomycin fraction (median = 71.1%; IQR = 65.4%-79.7%) was highly variable within and between patients and significantly correlated with total protein and albumin concentration, which were both decreased in our population. Total trough concentration (ID) and total concentration (CD) were within the aimed target concentrations in 8% of patients. The targets of AUC/MIC ≥400 and f AUC/MIC ≥200 were achieved in 54% and 83% of patients, respectively. Unbound vancomycin concentrations were adequately predicted using the following equation: unbound vancomycin concentration (mg/L) = 5.38 + [0.71 × total vancomycin concentration (mg/L)] - [0.085 × total protein concentration (g/L)]. This final model was externally validated using 51 samples from another six patients.

Conclusions

The protein binding of vancomycin in our paediatric population was lower than reported in non-critically ill adults and exhibited large variability. Higher target attainment rates were achieved when using PK/PD indices based on unbound concentrations, when compared with total concentrations. These results highlight the need for protein binding assessment in future vancomycin PK/PD research.

An LC-MS/MS method to determine vancomycin in plasma (total and unbound), urine and renal replacement therapy effluent

AIM

Critical illness and medical interventions, such as renal replacement therapy, can cause changes to vancomycin pharmacokinetics and lead to suboptimal dosing. To comprehensively characterize vancomycin pharmacokinetic a method must measure vancomycin in a range of clinical matrices.

RESULTS

A LC-MS/MS method was developed using hydrophilic interaction liquid chromatography and microsample volumes, where possible. For all matrices, the linear concentration range was 1-100 μg/ml, interassay accuracy and precision was within 15%, and recovery above 80%. No matrix effects were observed. Calibration equivalence may be applied for some matrix combinations.

CONCLUSION

A method for the analysis of vancomycin in plasma (total, unbound), urine and renal replacement therapy effluent, suitable for use in any patient pharmacokinetic study, has been developed and validated.

Interaction of Citrinin with Human Serum Albumin

Citrinin (CIT) is a mycotoxin produced by several Aspergillus, Penicillium, and Monascus species. CIT occurs worldwide in different foods and drinks and causes health problems for humans and animals. Human serum albumin (HSA) is the most abundant plasma protein in human circulation. Albumin forms stable complexes with many drugs and xenobiotics; therefore, HSA commonly plays important role in the pharmacokinetics or toxicokinetics of numerous compounds. However, the interaction of CIT with HSA is poorly characterized yet. In this study, the complex formation of CIT with HSA was investigated using fluorescence spectroscopy and ultrafiltration techniques. For the deeper understanding of the interaction, thermodynamic, and molecular modeling studies were performed as well. Our results suggest that CIT forms stable complex with HSA (logK ~ 5.3) and its primary binding site is located in subdomain IIA (Sudlow’s Site I). In vitro cell experiments also recommend that CIT-HSA interaction may have biological relevance. Finally, the complex formations of CIT with bovine, porcine, and rat serum albumin were investigated, in order to test the potential species differences of CIT-albumin interactions.