Determination of free vancomycin, ceftriaxone, cefazolin and ertapenem in plasma by ultrafiltration: Impact of experimental conditions

Free serum concentrations of antibiotics determined by ultrafiltration: extensive evaluation of experimental variables

Aim: To assess the impact of experimental conditions on free serum concentrations as determined by ultrafiltration and HPLC-DAD analysis in a wide range of antibiotics. Materials & methods: Relative centrifugation force (RCF), temperature, pH and buffer were varied and the results compared with the standard protocol (phosphate buffer pH 7.4, 37°C, 1000 × g). Results: Generally, at 10,000 × g the unbound fraction (fu) decreased with increasing molecular weight, and was lower at 22°C. In unbuffered serum, the fu of flucloxacillin or valproic acid was increased, that of basic or amphoteric drugs considerably decreased. Comparable results were obtained using phosphate or HEPES buffer except for drugs which form metal chelate complexes. Conclusion: Maintaining a physiological pH is more important than strictly maintaining body temperature.

Determination of unbound platinum concentrations in human plasma using ultrafiltration and precipitation methods

Quantification of the unbound portion of platinum (Pt) in human plasma is important for assessing the pharmacokinetics of the chemotherapeutic drug cisplatin. In this study, we sought to compare the recovery of unbound Pt using Nanosep® filters to 1) traditional filters (Centrifree®, Centrisart®, Amicon®) or trichloroacetic acid (TCA) protein precipitation, and 2) unbound, bound, and total Pt concentrations in clinical specimens. For the tested filters, the impact of 1) molecular weight cut-offs, 2) centrifugation force, and 3) total Pt concentration on Pt binding in human plasma was evaluated. Pt was quantified using inductively coupled-plasma mass spectrometry. In human plasma spiked with 0.9 μg/mL Pt, the percent of unbound Pt increased at higher centrifugation speeds. By comparison, the percent of unbound Pt was highest (42.1%) following TCA protein precipitation. When total Pt was ≤0.9 μg/mL, unbound Pt (∼20-30%) was consistent across filters. Conversely, when plasma was spiked with Pt exceeding 0.9 μg/mL, the percent of unbound Pt increased from 36.5 to 48% using ultrafiltration, compared to 63.4% to 79% with TCA precipitation. In patients receiving cisplatin-containing chemotherapy, the fraction of unbound Pt at concentrations exceeding 0.9 μg/mL ranged between 35 and 90%. Moreover, the unbound fraction of Pt in plasma correlated with the concentration of unbound (R2 = 0.738) and total Pt (R2 = 0.335). In summary, this study demonstrates that 1) the percent of unbound Pt is influenced by total and unbound Pt levels in vitro and in clinical specimens, and 2) ultrafiltration with Nanosep® filters is a feasible method for quantifying unbound Pt concentrations in human plasma.

Influence of ultrafiltration conditions on the measurement of unbound drug concentrations: flucloxacillin as an example

BACKGROUND

When performing therapeutic drug monitoring (TDM) for flucloxacillin, it is advised to measure the unbound, not the total, flucloxacillin concentration. To be able to accurately quantify unbound flucloxacillin concentrations, a reliable analytical method is indispensable.

OBJECTIVE

To determine the influence of temperature and pH of the sample during ultrafiltration on the measured unbound fraction of flucloxacillin.

MATERIALS AND METHODS

We performed three different experiments. In a single laboratory experiment, we investigated the influence of ultrafiltration temperature (10°C, room temperature and 37°C) on the measured unbound fraction of flucloxacillin for three concentration levels. In a multiple laboratory experiment, the results of eight laboratories participating in an international quality control programme measuring unbound flucloxacillin concentrations were analysed. In the third experiment, patient samples were ultrafiltrated using four different conditions: (i) physiological pH and room temperature; (ii) unadjusted pH (pH 9 after freezing) and room temperature; (iii) physiological pH and 37°C and (iv) unadjusted pH and 37°C.

RESULTS

For all experiments, measurement of samples that were ultrafiltrated at room temperature resulted in a substantially lower unbound fraction compared to samples that were ultrafiltrated at 37°C. Adjusting the pH to physiological pH only had a minimal impact on the measured unbound fraction.

CONCLUSIONS

On the basis of these findings and considering the need for fast, simple and reproducible sample pretreatment for TDM purposes, we conclude that ultrafiltration of flucloxacillin should be performed at physiological temperature (37°C), but adjustment of pH does not seem to be necessary.

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.

Mechanisms of Drug Solubility Enhancement Induced by β-Lactoglobulin-Based Amorphous Solid Dispersions

Protein-based amorphous solid dispersions (ASDs) have emerged as a promising approach for enhancing solubility in comparison to crystalline drugs. The dissolution behavior of protein-based amorphous solid dispersions (ASDs) was investigated in various pH media. ASDs of four poorly soluble model drugs with acidic (furosemide and indomethacin), basic (carvedilol), and neutral (celecoxib) properties were prepared by spray drying at 30 wt % drug loading with the protein β-lactoglobulin (BLG). The effect of spray-dried BLG (SD-BLG) solubility and protein binding ability with dissolved drugs in solution were investigated to retrieve the mechanisms governing the improvement of drug solubility from the BLG-based ASDs. Powder dissolution results showed that all ASDs obtained a higher maximum concentration (Cmax) compared to the respective pure crystalline drugs. It was found that the solubility increase of the drugs from the ASDs was to a large extent dependent on the solubility of the pure SD-BLG at the investigated pH values (low solubility at pH near the isoelectric point (pI) of BLG). Furthermore, drug-protein interactions in a solution were observed, in particular at pH values where the drugs were neutral. These drug-protein interactions also resulted, to some extent, in the stabilization of the drug in supersaturation.

Reproducible Quantification of Unbound Fractions of Four Beta-Lactam Antibiotics: Ultrafiltration Versus Microdialysis of Spiked Healthy Donor Plasma

BACKGROUND

Ultrafiltration (UF) is a conventional method for isolating the protein-unbound plasma fractions of therapeutic drugs. However, the ideal UF conditions for specific compounds remain largely unexplored. By comparing UF-derived unbound concentrations with the corresponding results obtained using a reference method, the authors sought to identify appropriate UF conditions for cefotaxime, cloxacillin, flucloxacillin, and piperacillin.

METHODS

In vitro microdialysis (MD) with a no-net-flux approach was used as a reference method for plasma protein separation, for which UF performance was assessed. Four levels of relative centrifugal force (2500-11,290 g ) and 2 levels of temperature (37 vs. 22°C) during 10 minutes of UF centrifugation were evaluated. Ultrafiltrates and reference microdialysates were analyzed using liquid chromatography-tandem mass spectrometry to obtain unbound concentrations. After identifying the appropriate UF conditions in the spiked plasma samples, exploratory analyses of clinical samples (n = 10 per analyte) were performed.

RESULTS

Of the evaluated UF alternatives, the best overall agreement with the MD-derived reference concentrations was obtained with 11,290 g UF performed at 22°C. For cloxacillin specifically, 37°C UF yielded better agreement than 22°C UF at 11,290 g. Clinical sample analyses indicated minimal differences between 22°C and 37°C at 11,290 g UF for cefotaxime and piperacillin. However, consistently lower levels of unbound cloxacillin (median: -23%, IQR: -19% to -24%) and flucloxacillin (median: -27%, IQR: -21 to -34%) were observed after UF at 22°C versus 37°C.

CONCLUSIONS

For the evaluated UF device, 10 minutes of 11,290 g UF at 22°C is appropriate for flucloxacillin, cefotaxime, and piperacillin, and can arguably be justified for cloxacillin as well for laboratory practice purposes. Maintenance of 37°C during high-centrifugal UF may lead to overestimation, particularly for unbound flucloxacillin.

Determination of unbound piperaquine in human plasma by ultra-high performance liquid chromatography tandem mass spectrometry

Piperaquine (PQ) is an antimalarial drug that is highly protein-bound. Variation in plasma protein contents may affect the pharmacokinetic (PK) exposure of unbound drug, leading to alteration of clinical outcomes. All published methods for determination of PQ in human plasma measure the total PQ including both bound and unbound PQ to plasma proteins. There is no published method for unbound PQ determination. Here we report an ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method for determination of PQ in human plasma filtrate prepared by filtering human plasma through Millipore Microcon® centrifugal filters (10k NMWL). The filter cup had to be treated with 5% benzalkonium chloride to reduce non-specific binding to the filter devices before filtration of plasma samples. Multiple reactions monitoring (MRM) of the ion pairs m/z 535/288 for PQ and m/z 541/294 for the internal standard (IS) was selected for quantification. When electrospray ionization (ESI⁺) was used, paradoxical matrix effect was observed despite the structure similarity of the deuterated IS: Ion suppression for PQ versus ion enhancement for the PQ-d₆, even though they were closely eluted: 0.62 min versus 0.61 min. Separation was achieved on Evo C₁₈ column (50 × 2.1 mm, 1.7 μm, Phenomenex Inc.) eluted with 10 mM NH₄OH and MeCN. When atmospheric pressure chemical ionization in positive mode (APCI⁺) was used for ion source, matrix effect diminished. Separation was achieved on a PFP column (30 × 2.1 mm, 1.7 μm, Waters, Corp.) eluted with aqueous 20 mM ammonium formate 0.14% trifluoroacetic acid (A) and methanol-acetonitrile (4:1, v/v) containing 0.1% trifluoroacetic acid (B) at 0.8 mL/min flow rate in a gradient mode: 30–30–80–80–30–30%B (0–0.1–1.0–1.40–1.41–1.50 min). The retention time was 0.67 min for both PQ and the IS. The method was validated with a linear calibration range from 20 to 5,000 pg/mL and applied to clinical samples.

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.

A Review of Methods for Removal of Ceftriaxone from Wastewater

The presence of pharmaceuticals in surface water and wastewater poses a threat to public health and has significant effects on the ecosystem. Since most wastewater treatment plants are ineffective at removing molecules efficiently, some pharmaceuticals enter aquatic ecosystems, thus creating issues such as antibiotic resistance and toxicity. This review summarizes the methods used for the removal of ceftriaxone antibiotics from aquatic environments. Ceftriaxone is one of the most commonly prescribed antibiotics in many countries, including Tanzania. Ceftriaxone has been reported to be less or not degraded in traditional wastewater treatment of domestic sewage. This has piqued the interest of researchers in the monitoring and removal of ceftriaxone from wastewater. Its removal from aqueous systems has been studied using a variety of methods which include physical, biological, and chemical processes. As a result, information about ceftriaxone has been gathered from many sources with the searched themes being ceftriaxone in wastewater, ceftriaxone analysis, and ceftriaxone removal or degradation. The methods studied have been highlighted and the opportunities for future research have been described.

Clinical Pharmacokinetics and Pharmacodynamics of Cefepime

Cefepime is a broad-spectrum fourth-generation cephalosporin with activity against Gram-positive and Gram-negative pathogens. It is generally administered as an infusion over 30-60 min or as a prolonged infusion with infusion times from 3 h to continuous administration. Cefepime is widely distributed in biological fluids and tissues with an average volume of distribution of ~ 0.2 L/kg in healthy adults with normal renal function. Protein binding is relatively low (20%), and elimination is mainly renal. About 85% of the dose is excreted unchanged in the urine, with an elimination half-life of 2-2.3 h. The pharmacokinetics of cefepime is altered under certain pathophysiological conditions, resulting in high inter-individual variability in cefepime volume of distribution and clearance, which poses challenges for population dosing approaches. Consequently, therapeutic drug monitoring of cefepime may be beneficial in certain patients including those who are critically ill, have life-threatening infections, or are infected with more resistant pathogens. Cefepime is generally safe and efficacious, with a goal exposure target of 70% time of the free drug concentration over the minimum inhibitory concentration for clinical efficacy. In recent years, reports of neurotoxicity have increased, specifically in patients with impaired renal function. This review summarizes the pharmacokinetics, pharmacodynamics, and toxicodynamics of cefepime contemporarily in the setting of increasing cefepime exposures. We explore the potential benefits of extended or continuous infusions and therapeutic drug monitoring in special populations.

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.

Effects of a fully enclosed hollow-fiber centrifugal ultrafiltration technique for laboratory biosafety improvement

Laboratory biosafety has become a core focus in biological analysis, owing to the frequent occurrence of laboratory-acquired infections caused by the leakage of pathogenic microorganisms. For this purpose, the authors developed a safe pretreatment device combining a sealing technique with a direct injection technique. In this study, several bacteria and viruses were used to validate the filtration effect of the invention. Data show that the new device can completely filter bacteria and that the filtration rates for hepatitis B virus and hepatitis C virus reached 94% and 96%, respectively. The results show that the new preparation device can effectively block these pathogens and can improve biological safety and provide powerful protection for technicians.

A meta-analysis of protein binding of flucloxacillin in healthy volunteers and hospitalized patients

OBJECTIVES

The aim of this study was to develop a mechanistic protein-binding model to predict the unbound flucloxacillin concentrations in different patient populations.

METHODS

A mechanistic protein-binding model was fitted to the data using non-linear mixed-effects modelling. Data were obtained from four datasets, containing 710 paired total and unbound flucloxacillin concentrations from healthy volunteers, non-critically ill and critically ill patients. A fifth dataset with data from hospitalized patients was used for evaluation of our model. The predictive performance of the mechanistic model was evaluated and compared with the calculation of the unbound concentration with a fixed unbound fraction of 5%. Finally, we performed a fit-for-use evaluation, verifying whether the model-predicted unbound flucloxacillin concentrations would lead to clinically incorrect dose adjustments.

RESULTS

The mechanistic protein-binding model predicted the unbound flucloxacillin concentrations more accurately than assuming an unbound fraction of 5%. The mean prediction error varied between -26.2% to 27.8% for the mechanistic model and between -30.8% to 83% for calculation with a fixed factor of 5%. The normalized root mean squared error varied between 36.8% and 69% respectively between 57.1% and 134%. Predicting the unbound concentration with the use of the mechanistic model resulted in 6.1% incorrect dose adjustments versus 19.4% if calculated with a fixed unbound fraction of 5%.

CONCLUSIONS

Estimating the unbound concentration with a mechanistic protein-binding model outperforms the calculation with the use of a fixed protein binding factor of 5%, but neither demonstrates acceptable performance. When performing dose individualization of flucloxacillin, this should be done based on measured unbound concentrations rather than on estimated unbound concentrations from the measured total concentrations. In the absence of an assay for unbound concentrations, the mechanistic binding model should be preferred over assuming a fixed unbound fraction of 5%.

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 Clean, Sustainable and Stability-Indicating Method for the Quantification of Ceftriaxone Sodium in Pharmaceutical Product by HPLC

Ceftriaxone sodium is a widely used antimicrobial, which is only available as a lyophilized powder. The presence of methods for evaluating the quality of this product is very important and helps to ensure its effectiveness, in addition to contributing to the fight against bacterial resistance. Therefore, a clean and sustainable high-performance liquid chromatography (HPLC) method has been developed for evaluating ceftriaxone stability in pharmaceutical product. A Zorbax SB C18 (150 × 4.6 mm, 5 μm) column was maintained at 25°C; the mobile phase consisted of purified water acidified with 0.2% orthophosphoric acid and ethanol (87: 13, v/v) at a flow rate of 0.9 mL min-1. The detection wavelength was set at 260 nm. The method was linear over a concentration range of 20-120 μg mL-1, precise with relative standard deviations <2%, robust in the event of minor changes to the original method conditions, accurate with recovery between 98% and 102% and specific to degradation products. The retention time for ceftriaxone sodium was ~4.6 minutes. This work shows an ecologically correct option by HPLC method for the evaluation of ceftriaxone sodium in pharmaceutical product, as well as its stability, which addresses the requirements of the current green and sustainable analytical chemistry.

The Role of Non-Enzymatic Degradation of Meropenem-Insights from the Bottle to the Body

Several studies have addressed the poor stability of meropenem in aqueous solutions, though not considering the main degradation product, the open-ring metabolite (ORM) form. In the present work, we elucidate the metabolic fate of meropenem and ORM from continuous infusion to the human bloodstream. We performed in vitro infusate stability tests at ambient temperature with 2% meropenem reconstituted in 0.9% normal saline, and body temperature warmed buffered human serum with 2, 10, and 50 mg/L meropenem, covering the therapeutic range. We also examined meropenem and ORM levels over several days in six critically ill patients receiving continuous infusions. Meropenem exhibited a constant degradation rate of 0.006/h and 0.025/h in normal saline at 22 °C and serum at 37 °C, respectively. Given that 2% meropenem remains stable for 17.5 h in normal saline (≥90% of the initial concentration), we recommend replacement of the infusate every 12 h. Our patients showed inter-individually highly variable, but intra-individually constant molar ORM/(meropenem + ORM) ratios of 0.21–0.52. Applying a population pharmacokinetic approach using the degradation rate in serum, spontaneous degradation accounted for only 6% of the total clearance.

Measurement of Free Plasma Concentrations of Beta-Lactam Antibiotics: An Applicability Study in Intensive Care Unit Patients

BACKGROUND

The antibacterial effect of antibiotics is linked to the free drug concentration. This study investigated the applicability of an ultrafiltration method to determine free plasma concentrations of beta-lactam antibiotics in ICU patients.

METHODS

Eligible patients included adult ICU patients treated with ceftazidime (CAZ), meropenem (MEM), piperacillin (PIP)/tazobactam (TAZ), or flucloxacillin (FXN) by continuous infusion. Up to 2 arterial blood samples were drawn at steady state. Patients could be included more than once if they received another antibiotic. Free drug concentrations were determined by high-performance liquid chromatography with ultraviolet detection after ultrafiltration, using a method that maintained physiological conditions (pH 7.4/37°C). Total drug concentrations were determined to calculate the unbound fraction. In a post-hoc analysis, free concentrations were compared with the target value of 4× the epidemiological cut-off value (ECOFF) for Pseudomonas aeruginosa as a worst-case scenario for empirical therapy with CAZ, MEM or PIP/tazobactam and against methicillin-sensitive Staphylococcus aureus for targeted therapy with FXN.

RESULTS

Fifty different antibiotic treatment periods in 38 patients were evaluated. The concentrations of the antibiotics showed a wide range because of the fixed dosing regimen in a mixed population with variable kidney function. The mean unbound fractions (fu) of CAZ, MEM, and PIP were 102.5%, 98.4%, and 95.7%, with interpatient variability of <6%. The mean fu of FXN was 11.6%, with interpatient variability of 39%. It was observed that 2 of 12 free concentrations of CAZ, 1 of 40 concentrations of MEM, and 11 of 23 concentrations of PIP were below the applied target concentration of 4 × ECOFF for P. aeruginosa. All concentrations of FXN (9 samples from 6 patients) were >8 × ECOFF for methicillin-sensitive Staphylococcus aureus.

CONCLUSIONS

For therapeutic drug monitoring purposes, measuring total or free concentrations of CAZ, MEM, or PIP is seemingly adequate. For highly protein-bound beta-lactams such as FXN, free concentrations should be favored in ICU patients with prevalent hypoalbuminemia.

Turbidimetric Method: A Multi-Advantageous Option for Assessing the Potency of Ceftriaxone Sodium in Powder for Injection

BACKGROUND

Ceftriaxone sodium, an antimicrobial used in parenteral form, does not have a microbiological method by turbidimetry described in the literature. For drugs from antimicrobial class, the existence of a microbiological method for assessing their potency is essential. Not only are the results from the physical-chemical methods enough, but microbiological analyzes are also necessary.

OBJECTIVE AND METHODS

Thus, this paper reports the development and validation of an efficient, accurate, reproducible, fast, and low-cost microbiological assay by turbidimetry to quantify ceftriaxone sodium in powder for injection. Water was used as the diluent to prepare the ceftriaxone solutions. BHI broth as used as culture media for the growth of the S. aureus ATCC 6538 at 9%.

RESULTS

The method was linear in the range of 100-196 µg/mL, selective against the sample adjuvants and the forced degradation test, precise (intraday RSD 4.53%, interday RSD 3.85% and between analysts tcalculated 0.14 < 2.23 tcritical), accurate with recovery of 100.33% and robust against minor changes in the volume of culture medium used, wavelength, incubation time, and inoculum concentration.

CONCLUSIONS AND HIGHLIGHTS

The turbidimetric method developed in this paper is a convenient and valuable alternative to the routine quality control of ceftriaxone sodium in powder for injection, since it allows a reliable quantification and can be used to complement the physical-chemical analysis.

Ultrafiltration Method for Plasma Protein Binding Studies and Its Limitations

Plasma protein binding plays a critical role in drug therapy, being a key part in the characterization of any compound. Among other methods, this process is largely studied by ultrafiltration based on its advantages. However, the method also has some limitations that could negatively influence the experimental results. The aim of this study was to underline key aspects regarding the limitations of the ultrafiltration method, and the potential ways to overcome them. The main limitations are given by the non-specific binding of the substances, the effect of the volume ratio obtained, and the need of a rigorous control of the experimental conditions, especially pH and temperature. This review presents a variety of methods that can hypothetically reduce the limitations, and concludes that ultrafiltration remains a reliable method for the study of protein binding. However, the methodology of the study should be carefully chosen.

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.

LC-MS/MS method for nine different antibiotics

BACKGROUND AND AIMS

TDM of antibiotics can bring benefits to patients and healthcare systems by providing better treatment and saving healthcare resources. We aimed to develop a multi-analyte method for several diverse antibiotics using LC-MS/MS.

MATERIALS AND METHODS

Sample preparation consisted of protein precipitation with methanol, dilution and online extraction using a Turboflow Cyclone column. Separation was performed on a Synergi 4 µm Max RP column and deuterated forms of three antibiotics were used as internal standards.

RESULTS

We present a LC-MS/MS method for the quantitative determination of nine antibiotics, including five cephalosporins, the carbapenem ertapenem, the fluoroquinolone ciprofloxacin as well as the combination drug trimethoprim-sulfamethoxazole from plasma. Additionally, unbound ertapenem and cefazolin were analyzed in plasma water after ultrafiltration using plasma calibrators. Results from routine TDM show the applicability of the method.

CONCLUSION

The presented method is precise and accurate and was introduced in a university hospital, permitting fast TDM of all nine analytes. It was also used in a clinical study for measuring cefazolin free and total concentrations.

Simultaneous determination of six antibiotics in human serum by high-performance liquid chromatography with UV detection

Antibiotics are widely used in intensive care patients to treat severe infections. To avoid bacterial resistance or toxic side effects, the determination of serum concentration of ABs is advisable. Therefore, in this study, we developed and validated a simple and fast high-performance liquid chromatography method with UV detection for the simultaneous determination of four β-lactam ABs (meropenem, imipenem, ceftazidime, and piperacillin) and two coadministered substances (cilastatin and tazobactam) in human serum. Sample preparation required a simple protein precipitation by methanol. The separation of the ABs occurred within a timeframe of 17 min. For this purpose, we used a Kinetex F5 column with a linear gradient of acetonitrile and phosphate buffer (pH 6.9). The UV detector recorded two separate chromatograms at 220 and 295 nm simultaneously. Validation has demonstrated that the method is linear, accurate, and precise within the clinically relevant range for each substance.

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.

Insights on Ultrafiltration-Based Separation for the Purification and Quantification of Methotrexate in Nanocarriers

The evaluation of encapsulation efficiency is a regulatory requirement for the characterization of drug delivery systems. However, the difficulties in efficiently separating nanomedicines from the free drug may compromise the achievement of accurate determinations. Herein, ultrafiltration was exploited as a separative strategy towards the evaluation of methotrexate (MTX) encapsulation efficiency in nanostructured lipid carriers and polymeric nanoparticles. The effect of experimental conditions such as pH and the amount of surfactant present in the ultrafiltration media was addressed aiming at the selection of suitable conditions for the effective purification of nanocarriers. MTX-loaded nanoparticles were then submitted to ultrafiltration and the portions remaining in the upper compartment of the filtering device and in the ultrafiltrate were collected and analyzed by HPLC-UV using a reversed-phase (C18) monolithic column. A short centrifugation time (5 min) was suitable for establishing the amount of encapsulated MTX in nanostructured lipid carriers, based on the assumption that the free MTX concentration was the same in the upper compartment and in the ultrafiltrate. The defined conditions allowed the efficient separation of nanocarriers from the free drug, with recoveries of >85% even when nanoparticles were present in cell culture media and in pig skin surrogate from permeation assays.

Determination of free clindamycin, flucloxacillin or tedizolid in plasma: Pay attention to physiological conditions when using ultrafiltration

Pharmacokinetic/pharmacodynamic indices of anti-infective drugs should be referenced to free drug concentrations. In the present study, clindamycin, flucloxacillin and tedizolid have been determined in human plasma by HPLC-UV. The drugs were separated isocratically within 3-6 min on a C₁₈ column using mixtures of phosphate buffer-acetonitrile of pH 7.1-7.2. Sample treatment for the determination of total drug concentrations in plasma included extraction/back-extraction (clindamycin) or protein precipitation (flucloxacillin, tedizolid). The free drug concentrations were determined after ultrafiltration. An ultrafiltration device with a membrane consisting of regenerated cellulose proved to be suitable for all drugs. Maintaining a physiological pH was crucial for clindamycin, whereas maintaining body temperature was essential for tedizolid. The methods were applied to the analysis of total and free drug concentrations in clinical samples and were sufficiently sensitive for pharmacokinetic studies and therapeutic drug monitoring.

A 2D HPLC-MS/MS method for several antibiotics in blood plasma, plasma water, and diverse tissue samples

An analytical method using 2D high-performance liquid chromatography followed by tandem mass spectrometry for the quantification of the beta-lactam antibiotics amoxicillin, flucloxacillin, piperacillin, benzylpenicillin, the beta-lactamase inhibitors clavulanic acid, and tazobactam, as well as the macrolide antibiotic clindamycin, is presented. All analytes were measured in human plasma, while amoxicillin, clavulanic acid, flucloxacillin, and clindamycin were also analyzed in human tissue samples. Because of its high-protein binding, additionally, the free fraction of flucloxacillin was measured after ultrafiltration. As internal standards, deuterated forms of the beta-lactams were used. Sample preparation for all matrices was protein precipitation followed by online extraction on a TurboFlow MAX column, while sample separation was performed on an Accucore XL C18 column. Calibration curves were linear over 0.2-25 mg/kg for the tissue samples and 0.05-20 mg/l for the free fraction of flucloxacillin. In plasma, the calibration curves for amoxicillin and piperacillin were linear over 3.125-125 mg/l, for clavulanic acid and tazobactam over 1-40 mg/l, for benzylpenicillin 0.25-40 mg/l, and for flucloxacillin and clindamycin over 1.5-60 mg/l and 0.05-8 mg/l respectively. In plasma and plasma ultrafiltrate, inaccuracy and imprecision for any analyte were always less than 15%. In tissue, the accuracy and precision varied up to 16%, respectively, 20%, when various tissues were analyzed using a calibration in water. Graphical abstract.

Nonlinear Protein Binding: Not What You Think

Nonlinear protein binding is traditionally thought of as an increasing fraction unbound with increasing total drug concentration. In the past several years, research into the protein binding of several tetracyclines has shown that an unexpected and counterintuitive phenomenon has been observed, specifically that of decreasing unbound drug fraction with increasing total concentrations of drug over certain concentration ranges. Although several studies of tigecycline have shown the importance calcium and its chelation may play in the protein-drug interaction, the potential clinical implications and relevance have not been explored. Here, we define typical and atypical nonlinear protein binding, overview protein binding theory, and discuss theoretical implications on pharmacokinetics. Using tigecycline as an example, in silico simulations and calculations show how when atypical nonlinear protein binding is not accounted for free drug exposure, and drug tissue penetration may be overestimated. It is important to revisit the impacts of nonlinearity in protein binding on clinical pharmacokinetics and pharmacodynamics, and ultimately, clinical efficacy. Although this phenomenon could potentially warrant clinical dose adjustment for certain compounds, it also presents a potential opportunity to exploit underlying mechanisms to develop new therapies and better understand molecular interactions of xenobiotics within the physiological system.

A Critical Review of Analytical Methods for Determination of Ceftriaxone Sodium

Ceftriaxone sodium is a third-generation semi-synthetic antibiotic belonging to the class of cephalosporins. Is administered only by parenteral route and has the ability to cross the blood-brain barrier. It has bactericidal action; its main activity is related to the Gram-negative bacteria, being also able to act against Gram-negative bacilli resistant to the first- and second-generation cephalosporins. The present study presents a survey of the characteristics, properties and analytical methods used for the determination of ceftriaxone sodium, for the gathering of data searches were carried out in scientific articles in the world literature, as well as in the official compendia. It is necessary to create awareness about the importance of developing effective and reliable analytical methods for quality control and consequently for conducting pharmacokinetic, bioavailability, bioequivalence studies as well as for the therapeutic monitoring of this drug. Most of the methods found use high-performance liquid chromatography, but also methods that use absorption spectroscopy ultraviolet, infrared spectroscopy, spectrofluorimetry and microbiological methods have been presented. A discussion was presented highlighting the need to develop new ecological methods using less toxic solvents, rapid analysis and miniaturization of the samples.

Microdialysis as a tool to determine the local tissue concentration of dicloxacillin in man

AIMS

The most common pathogen to cause postoperative infections in Denmark is Staphylococcus aureus. Despite using prophylactic antibiotics, infections are still seen. Whether the tissue concentration is above the minimal inhibitory concentration (MIC) for the pathogen is unknown. Thus, the concentration of dicloxacillin in muscle and adipose tissue was measured after intravenous administration, in healthy men.

METHODS

MIC for dicloxacillin against S. aureus was determined using the broth macrodilution method. A microdialysis (MD) catheter was placed in the subcutaneous tissue of the abdomen and in the lateral vastus muscle of the thigh of six healthy male volunteers. They were given 2 g dicloxacillin intravenously. Samples from blood and MD fluid were collected. The unbound dicloxacillin was isolated from plasma. Samples were analysed with high performance liquid chromatography (HPLC).

RESULTS

The maximum concentration was reached in muscle tissue after 0.5 h and in adipose tissue after 0.8 h. AUC_0-6h for the dicloxacillin concentration in adipose tissue was significantly lower when compared to the unbound dicloxacillin concentration in plasma. The dicloxacillin concentration was above the MIC for sensitive S. aureus for a minimum of 2.3 h and a median of 4.1 h in muscle tissue and a minimum of 1.8 h and a median of 3.2 h in adipose tissue.

CONCLUSIONS

The unbound dicloxacillin concentration in adipose and muscle tissue remained above the MIC for sensitive S. aureus, for a period sufficient for many orthopaedic procedures. Whether this is true in patients with compromised circulation remains to be investigated.

Variable Linezolid Exposure in Intensive Care Unit Patients-Possible Role of Drug-Drug Interactions

BACKGROUND

Standard doses of linezolid may not be suitable for all patient groups. Intensive care unit (ICU) patients in particular may be at risk of inadequate concentrations. This study investigated variability of drug exposure and its potential sources in this population.

METHODS

Plasma concentrations of linezolid were determined by high-performance liquid chromatography in a convenience sample of 20 ICU patients treated with intravenous linezolid 600 mg twice daily. Ultrafiltration applying physiological conditions (pH 7.4/37°C) was used to determine the unbound fraction. Individual pharmacokinetic (PK) parameters were estimated by population PK modeling. As measures of exposure to linezolid, area under the concentration-time curve (AUC) and trough concentrations (Cmin) were calculated and compared with published therapeutic ranges (AUC 200-400 mg*h/L, Cmin 2-10 mg/L). Coadministered inhibitors or inducers of cytochrome P450 and/or P-glycoprotein were noted.

RESULTS

Data from 18 patients were included into the PK evaluation. Drug exposure was highly variable (median, range: AUC 185, 48-618 mg*h/L, calculated Cmin 2.92, 0.0062-18.9 mg/L), and only a minority of patients had values within the target ranges (6 and 7, respectively). AUC and Cmin were linearly correlated (R = 0.98), and classification of patients (underexposed/within therapeutic range/overexposed) according to AUC or Cmin was concordant in 15 cases. Coadministration of inhibitors was associated with a trend to higher drug exposure, whereas 3 patients treated with levothyroxine showed exceedingly low drug exposure (AUC ∼60 mg*h/L, Cmin <0.4 mg/L). The median unbound fraction in all 20 patients was 90.9%.

CONCLUSIONS

Drug exposure after standard doses of linezolid is highly variable and difficult to predict in ICU patients, and therapeutic drug monitoring seems advisable. PK drug-drug interactions might partly be responsible and should be further investigated; protein binding appears to be stable and irrelevant.

Impact of Experimental Variables on the Protein Binding of Tigecycline in Human Plasma as Determined by Ultrafiltration

Tigecycline, a tetracycline derivative, shows atypical plasma protein binding behavior. The unbound fraction decreases with increasing concentration at therapeutic concentrations. Moreover, uncertainty exists about the magnitude of tigecyline's protein binding in man. Unbound fractions between 2.5% and 35% have been reported in plasma from healthy volunteers, and between 25% and 100% in patients, respectively. In the present study, the protein binding of tigecycline has been investigated by ultrafiltration using different experimental conditions. Whereas temperature had only a marginal influence, the unbound fraction at 0.3/3.0 mg/L was low at pH 8.2 (9.4%/1.9%) or in unbuffered pooled plasma (6.3%/1.2%), compared with plasma buffered with HEPES to pH 7.4 (65.9%/39.7%). In experiments with phosphate buffer and EDTA, the concentration dependency was markedly attenuated or abolished, which is compatible with a cooperative binding mechanism involving divalent cations such as calcium. The unbound fraction in clinical plasma samples from patients treated with tigecycline was determined to 66.3 ± 13.7% at concentrations <0.3 mg/L compared with 41.3 ± 16.0% at >1 to <5 mg/L. To summarize, tigecycline appears to be only moderately bound to plasma proteins as determined by ultrafiltration, when a physiological pH is maintained.

Determination of protein-unbound, active rifampicin in serum by ultrafiltration and Ultra Performance Liquid Chromatography with UV detection. A method suitable for standard and high doses of rifampicin

Rifampicin is the most important antibiotic in use for the treatment of tuberculosis (TB). Preclinical and clinical data suggest that higher doses of rifampicin, resulting in disproportionally higher systemic exposures to the drug, are more effective. Serum concentrations of rifampicin are the intermediary link between the dose administered and eventual response and only protein-unbound (free) rifampicin is pharmacologically active. The objective of this work was to develop an ultra performance liquid chromatography assay for protein-unbound rifampicin in serum with ultrafiltration, carried out at a sample temperature of 37°C, suitable for measurement of concentrations achieved after currently used and higher doses of rifampicin. Human serum was equilibrated at 37°C and ultrafiltrated at the same temperature in a Centrifree YM-30 ultrafiltration device, followed by dilution of the ultrafiltrate with methanol and ascorbic acid. Unbound rifampicin was analyzed using ultra performance liquid chromatography with a BEH C18 column, isocratic elution and ultra-violet (UV) detection. The run time was 5min. The assay was linear over the concentration range of 0.065-26mg/L rifampicin in ultrafiltrate. Accuracies for measurement of rifampicin in ultrafiltrate were 97% and 102% at the higher and lower limits of quantitation. Accuracy of the ultrafiltration process cannot be established, as it is not possible to spike blank serum with known amounts of protein-unbound rifampicin. Within- and between-day precision of the method including ultrafiltration as well as after ultrafiltration were within prespecified limits (CV<10%). Dilution of the ultrafiltrate with methanol and ascorbic acid kept rifampicin in solution and prevented it from degradation. Rifampicin loss during the ultrafiltration process and variation in analytical results when using two different batches of ultrafiltration devices were both limited. Processed ultrafiltrate samples were stable for 3days in the autosampler. The developed method can be applied in pharmacokinetic research, studying exposure-response relationships for rifampicin when administered at higher than currently used doses.

Decreased protein binding of moxifloxacin in patients with sepsis?

The mean (SD) unbound fraction of moxifloxacin in plasma from patients with severe sepsis or septic shock was determined by ultrafiltration to 85.5±3.0% (range 81.9 and 91.6%) indicating a decreased protein binding of moxifloxacin in this population compared with the value of 58-60% provided in the Summary of Product Characteristics. However, previous investigations neglected the influence of pH and temperature on the protein binding of moxifloxacin. Maintaining physiological conditions (pH 7.4, 37°C) - as in the present study - the unbound fraction of moxifloxacin in plasma from healthy volunteers was 84%. In contrast, the unbound fraction of moxifloxacin was 77% at 4°C and 66-68% in unbuffered plasma or at pH 8.5 in fair agreement with previously published data. PK/PD parameters e.g. fAUC/MIC or ratios between interstitial fluid and free plasma concentrations, which were obtained assuming a protein binding rate of moxifloxacin of 40% or more, should be revised.

A novel pretreatment method combining sealing technique with direct injection technique applied for improving biosafety

AIM

People today have a stronger interest in the risk of biosafety in clinical bioanalysis. A safe, simple, effective method of preparation is needed urgently.

METHODOLOGY/RESULTS

To improve biosafety of clinical analysis, we used antiviral drugs of adefovir and tenofovir as model drugs and developed a safe pretreatment method combining sealing technique with direct injection technique. The inter- and intraday precision (RSD %) of the method were <4%, and the extraction recoveries ranged from 99.4 to 100.7%. Meanwhile, the results showed that standard solution could be used to prepare calibration curve instead of spiking plasma, acquiring more accuracy result.

CONCLUSION/DISCUSSION

Compared with traditional methods, the novel method not only improved biosecurity of the pretreatment method significantly, but also achieved several advantages including higher precision, favorable sensitivity and satisfactory recovery. With these highly practical and desirable characteristics, the novel method may become a feasible platform in bioanalysis.

Unbound fraction of fluconazole and linezolid in human plasma as determined by ultrafiltration: Impact of membrane type

Ultrafiltration is a rapid and convenient method to determine the free concentrations of drugs in plasma. Several ultrafiltration devices based on Eppendorf cups are commercially available, but are not validated for such use by the manufacturer. Plasma pH, temperature and relative centrifugal force as well as membrane type can influence the results. In the present work, we developed an ultrafiltration method in order to determine the free concentrations of linezolid or fluconazole, both neutral and moderately lipophilic antiinfective drugs for parenteral as well as oral administration, in plasma of patients. Whereas both substances behaved relatively insensitive in human plasma regarding variations in pH (7.0-8.5), temperature (5-37°C) or relative centrifugal force (1000-10.000xg), losses of linezolid were observed with the Nanosep Omega device due to adsorption onto the polyethersulfone membrane (unbound fraction 75% at 100mg/L and 45% at 0.1mg/L, respectively). No losses were observed with Vivacon which is equipped with a membrane of regenerated cellulose. With fluconazole no differences between Nanosep and Vivacon were observed. Applying standard conditions (pH 7.4/37°C/1000xg/20min), the mean unbound fraction of linezolid in pooled plasma from healthy volunteers was 81.5±2.8% using Vivacon, that of fluconazole was 87.9±3.5% using Nanosep or 89.4±3.3% using Vivacon. The unbound fraction of linezolid was 85.4±3.7% in plasma samples from surgical patients and 92.1±6.2% in ICU patients, respectively. The unbound fraction of fluconazole was 93.9±3.3% in plasma samples from ICU patients.

Plasma and intraprostatic concentrations of ertapenem following preoperative single dose administration: a single-centre prospective experience and clinical implications-the ERTAPRO study

The incidence of urinary tract infections caused by extended-spectrum β-lactamase (ESBL)-producing pathogens is increasing. These infections are associated with a long hospital stay in patients undergoing urological procedures. We aimed to demonstrate that significant intraprostatic diffusion of ertapenem is achieved after a single preoperative administration. A referred sample of 19 patients requiring surgery for benign prostatic hyperplasia was prospectively included. Patients received a 1 g intravenous (i.v.) dose of ertapenem 1 h (n = 10, group A) or 12 h (n = 9, group B) before blood and prostatic samples were collected. Plasma and intraprostatic concentrations of ertapenem were measured using LC-MS/MS. Intraprostatic concentrations were considered satisfactory when higher than the MIC90 value of urinary-targeted pathogens perioperatively and for 40% of the dosing interval. The Wilcoxon test and a pharmacokinetic predictive model were used. Median plasma concentrations of ertapenem were 144.3 mg/L (95% CI 126.5-157.9) in group A and 30.7 mg/L (95% CI 22.9-36.4) in group B (P < 0.001); median intraprostatic concentrations were 16.6 mg/L (95% CI 13.3-31.4 mg/L) and 4.2 mg/L (95% CI 3.1-4.9 mg/L), respectively (P < 0.001), which were above the MIC90 values of bacteria, including ESBL-producers, during surgery and for 40% of the dosing interval. The plasma-to-prostate concentration ratio was not significantly different between groups (P = 0.97). Single-dose i.v. ertapenem reached satisfactory intraprostatic concentrations, suggesting that it could be a relevant prophylactic strategy for carriers of ESBL-producing bacteria undergoing prostatic procedures, which needs to be confirmed by further prospective trials.

Assays for therapeutic drug monitoring of β-lactam antibiotics: A structured review

In some patient groups, including critically ill patients, the pharmacokinetics of β-lactam antibiotics may be profoundly disturbed due to pathophysiological changes in distribution and elimination. Therapeutic drug monitoring (TDM) is a strategy that may help to optimise dosing. The aim of this review was to identify and analyse the published literature on the methods used for β-lactam quantification in TDM programmes. Sixteen reports described methods for the simultaneous determination of three or more β-lactam antibiotics in plasma/serum. Measurement of these antibiotics, due to low frequency of usage relative to some other tests, is generally limited to in-house chromatographic methods coupled to ultraviolet or mass spectrometric detection. Although many published methods state they are fit for TDM, they are inconvenient because of intensive sample preparation and/or long run times. Ideally, methods used for routine TDM should have a short turnaround time (fast run-time and fast sample preparation), a low limit of quantification and a sufficiently high upper limit of quantification. The published assays included a median of 6 analytes [interquartile range (IQR) 4-10], with meropenem and piperacillin being the most frequently measured β-lactam antibiotics. The median run time was 8 min (IQR 5.9-21.3 min). There is also a growing number of methods measuring free concentrations. An assay that measures antibiotics without any sample preparation would be the next step towards real-time monitoring; no such method is currently available.

Protein binding characteristics and pharmacokinetics of ceftriaxone in intensive care unit patients

AIMS

The aim of the present study was to assess the pharmacokinetics of total and unbound ceftriaxone in intensive care unit (ICU) patients and its protein binding characteristics.

METHODS

Twenty patients (m/f 15/5, age 25-86 years, body weight 60-121 kg, APACHE II 7-40, estimated glomerular filtration rate 19-157 ml min(-1) , albumin 11.7-30.1 g l(-1) , total bilirubin <0.1-36.1 mg dl(-1) ) treated with intravenous ceftriaxone were recruited from two ICUs. Timed plasma samples were obtained using an opportunistic study protocol. Ceftriaxone concentrations were determined by high-performance liquid chromatography; unbound concentrations were determined after ultrafiltration using a new method which maintains physiological pH and temperature. The pharmacokinetics was described by a one-compartment model, the protein-binding characteristics by Michaelis-Menten kinetics.

RESULTS

For total drug, the volume of distribution was 20.2 l (median; interquartile range 15.6-24.5 l), the half-life 14.5 h (10.0-25.5 h) and the clearance 0.96 l h(-1) (0.55-1.28 l h(-1) ). The clearance of unbound drug was 1.91 l h(-1) (1.46-6.20 l h(-1) ) and linearly correlated with estimated glomerular filtration rate (slope 0.85, y-intercept 0.24 l h(-1) , r(2)  = 0.70). The unbound fraction was higher in ICU patients (33.0%; 20.2-44.5%) than reported in healthy volunteers, particularly when renal impairment or severe hyperbilirubinaemia was present. In all patients, unbound concentrations during treatment with ceftriaxone 2 g once daily remained above the EUCAST susceptibility breakpoint (≤1 mg l(-1) ) throughout the whole dosing interval.

CONCLUSIONS

Protein binding of ceftriaxone is reduced and variable in ICU patients due to hypoalbuminaemia, but also to altered binding characteristics. Despite these changes, the pharmacokinetics of unbound ceftriaxone is governed by renal function. For patients with normal or reduced renal function, standard doses are sufficient.