Pharmacokinetics of Cefuroxime in Synovial Fluid

Dynamic distribution of systemically administered antibiotics in orthopeadically relevant target tissues and settings

This review aimed to summarize the current literature on antibiotic distribution in orthopedically relevant tissues and settings where dynamic sampling methods have been used. PubMed and Embase databases were systematically searched. English-published studies between 2004 and 2024 involving systemic antibiotic administration in orthopedically relevant tissues and settings based on dynamic measurements were included. In total, 5385 titles were identified. After title and abstract screening, 97 eligible studies (43 different antibiotic drugs) were included. The studies covered both preclinical (42%) and clinical studies including healthy and infected tissues (21%) and prophylactic and steady-state situations (35%). Microdialysis emerged as the predominant sampling method in 98% of the studies. Most of the presented antibiotics (80%) were only assessed once or twice. Among the most extensively studied antibiotics were cefuroxime (18 studies), linezolid (9 studies) and vancomycin (9 studies). This review presents valuable insights into the microenvironmental distribution of antibiotics in orthopedically relevant target tissues and settings and seeks to provide a basis for improving dosing recommendations and treatment outcomes. However, it is important to acknowledge that our findings are limited to the specific drug, dosing regimens, administration method and target tissue, and are crucially linked to the selected PK/PD target.

Linezolid brain penetration in neurointensive care patients

BACKGROUND

Linezolid exposure in critically ill patients is associated with high inter-individual variability, potentially resulting in subtherapeutic antibiotic exposure. Linezolid exhibits good penetration into the CSF, but its penetration into cerebral interstitial fluid (ISF) is unknown.

OBJECTIVES

To determine linezolid penetration into CSF and cerebral ISF of neurointensive care patients.

PATIENTS AND METHODS

Five neurocritical care patients received 600 mg of linezolid IV twice daily for treatment of extracerebral infections. At steady state, blood and CSF samples were collected from arterial and ventricular catheters, and microdialysate was obtained from a cerebral intraparenchymal probe.

RESULTS

The median fAUC0-24 was 57.6 (24.9-365) mg·h/L in plasma, 64.1 (43.5-306.1) mg·h/L in CSF, and 27.0 (10.7-217.6) mg·h/L in cerebral ISF. The median penetration ratio (fAUCbrain_or_CSF/fAUCplasma) was 0.5 (0.25-0.81) for cerebral ISF and 0.92 (0.79-1) for CSF. Cerebral ISF concentrations correlated well with plasma (R = 0.93, P < 0.001) and CSF levels (R = 0.93, P < 0.001).The median fAUC0-24/MIC ratio was ≥100 in plasma and CSF for MICs of ≤0.5 mg/L, and in cerebral ISF for MICs of ≤0.25 mg/L. The median fT>MIC was ≥80% of the dosing interval in CSF for MICs of ≤0.5 mg/L, and in plasma and cerebral ISF for MICs of ≤0.25 mg/L.

CONCLUSIONS

Linezolid demonstrates a high degree of cerebral penetration, and brain concentrations correlate well with plasma and CSF levels. However, substantial variability in plasma levels, and thus cerebral concentrations, may result in subtherapeutic tissue concentrations in critically ill patients with standard dosing, necessitating therapeutic drug monitoring.

Predictive Performance of Physiologically Based Pharmacokinetic Modelling of Beta-Lactam Antibiotic Concentrations in Adipose, Bone, and Muscle Tissues

Physiologically based pharmacokinetic (PBPK) models consist of compartments representing different tissues. As most models are only verified based on plasma concentrations, it is unclear how reliable associated tissue profiles are. This study aimed to assess the accuracy of PBPK-predicted beta-lactam antibiotic concentrations in different tissues and assess the impact of using effect site concentrations for evaluation of target attainment. Adipose, bone, and muscle concentrations of five beta-lactams (piperacillin, cefazolin, cefuroxime, ceftazidime, and meropenem) in healthy adults were collected from literature and compared with PBPK predictions. Model performance was evaluated with average fold errors (AFEs) and absolute AFEs (AAFEs) between predicted and observed concentrations. In total, 26 studies were included, 14 of which reported total tissue concentrations and 12 unbound interstitial fluid (uISF) concentrations. Concurrent plasma concentrations, used as baseline verification of the models, were fairly accurate (AFE: 1.14, AAFE: 1.50). Predicted total tissue concentrations were less accurate (AFE: 0.68, AAFE: 1.89). A slight trend for underprediction was observed but none of the studies had AFE or AAFE values outside threefold. Similarly, predictions of microdialysis-derived uISF concentrations were less accurate than plasma concentration predictions (AFE: 1.52, AAFE: 2.32). uISF concentrations tended to be overpredicted and two studies had AFEs and AAFEs outside threefold. Pharmacodynamic simulations in our case showed only a limited impact of using uISF concentrations instead of unbound plasma concentrations on target attainment rates. The results of this study illustrate the limitations of current PBPK models to predict tissue concentrations and the associated need for more accurate models. SIGNIFICANCE STATEMENT: Clinical inaccessibility of local effect site concentrations precipitates a need for predictive methods for the estimation of tissue concentrations. This is the first study in which the accuracy of PBPK-predicted tissue concentrations of beta-lactam antibiotics in humans were assessed. Predicted tissue concentrations were found to be less accurate than concurrent predicted plasma concentrations. When using PBPK models to predict tissue concentrations, this potential relative loss of accuracy should be acknowledged when clinical tissue concentrations are unavailable to verify predictions.

SPILF update on bacterial arthritis in adults and children

In 2020 the French Society of Rhumatology (SFR) published an update of the 1990 recommendations for management of bacterial arthritis in adults. While we (French ID Society, SPILF) totally endorse this update, we wished to provide further information about specific antibiotic treatments. The present update focuses on antibiotics with good distribution in bone and joint. It is important to monitor their dosage, which should be maximized according to PK/PD parameters. Dosages proposed in this update are high, with the optimized mode of administration for intravenous betalactams (continuous or intermittent infusion). We give tools for the best dosage adaptation to conditions such as obesity or renal insufficiency. In case of enterobacter infection, with an antibiogram result "susceptible for high dosage", we recommend the requesting of specialized advice from an ID physician. More often than not, it is possible to prescribe antibiotics via the oral route as soon as blood cultures are sterile and clinical have symptoms shown improvement. Duration of antibiotic treatment is 6 weeks for Staphylococcus aureus, and 4 weeks for the other bacteria (except for Neisseria: 7 days).

The mysteries of target site concentrations of antibiotics in bone and joint infections: what is known? A narrative review

INTRODUCTION

Currently, antibiotic treatment is often a standard dosing regimen in bone and joint infections (BJI). However, it remains unknown if exposure at the target-site is adequate. The aim of this review is to gain more insight in the relationship between the target site concentration of antibiotic and the minimal inhibitory concentration to target the bacteria in bone and joint infections (BJI).

AREAS COVERED

A literature search was performed by Erasmus MC Medical library. Bone, bone tissue and synovial concentration of antibiotics were covered in humans. In addition, we reported number of patients, dose, sampling method, analytical method and tissue and plasma concentrations. We used the epidemiological cut-off value (ECOFF) values of the targeted micro-organisms. If more than 3 publications were available on the antibiotic, we graphically presented ECOFFS values against reported antibiotic concentrations.

EXPERT OPINION

For most antibiotics the literature is sparse. In addition, a lot of variable and total antibiotic concentrations are published. Ciprofloxacin, cefazolin, cefuroxime, vancomycin and linezolid seem to have adequate average exposure if correlating total concentration to ECOFF, when standard dosing is used. With regards to other antibiotics, results are inconclusive. More extensive pharmacokinetic/pharmacodynamic modeling in BJI is needed.

Pharmacokinetic Assessment of Staphylococcal Phage K Following Parenteral and Intra-articular Administration in Rabbits

The therapeutic value of phage as an alternative to antibiotics for the treatment of bacterial infections is being considered in the wake of mounting antibiotic resistance. In this study, the pharmacokinetic properties of Staphylococcus aureus phage K following intravenous and intra-articular administration were investigated in a rabbit model. Using a traditional plaque assay and a novel quantitative PCR assay to measure phage levels in specimens over time, it was found that intra-articularly administered phage enters the systemic circulation; that phage may be detected in synovial fluid up to 24 h following the intra-articular, but not intravenous, administration; and that qPCR-based enumeration is generally more sensitive than plaque enumeration, with fair to moderate correlation between the two methods. Findings presented should inform the design of phage therapy experiments and therapeutic drug monitoring in preclinical and human phage studies.

Quantification of beta-lactam antibiotics cefuroxime and flucloxacillin in human synovial fluid, using ultra-performance convergence chromatography-tandem mass spectrometry

Total hip- and knee arthroplasty generally result in successful outcomes. A small percentage of patients however suffer from periprosthetic joint infections (PJI) postoperatively, often with severe consequences. The standard treatment of chronic PJIs consists of a staged arthroplasty exchange during which antibiotic therapy plays a crucial role. For successful antibiotic treatment, adequate concentrations at the infection site are a prerequisite. Regarding the treatment of PJIs, knowledge is lacking with respect to the relationship between administered dosages and plasma- and infection site concentrations of the antibiotics. To gain insight into the antibiotic exposure at the infection site, validated analytical methods for analysis of the antibiotics in matrices at the site of the PJI are essential. We describe a validated ultra-performance convergence chromatography-tandem mass spectrometry (UPC2-MS/MS) method for quantification of the beta-lactam antibiotics cefuroxime and flucloxacillin in synovial fluid. This method was successfully validated for antibiotic quantification in synovial fluids according to the EMA guidelines and consists of a simple sample preparation. For both antibiotics, the accuracy and precision were within requirements (RSD < 15%). In addition, matrix effects and recovery were within the range of 80-120%. Carry over was less than 20% and stability in -80 °C was at least 2 months for standards and quality controls. The limits of quantification were adequate (1-100 mg/L) to cover potential cefuroxime and flucloxacillin concentrations in synovial fluid as described in literature (r > 0.995). The method has a run time of 4.5 min and 50 μL synovial fluid is needed and the validated method will be applied during a PK/PD study to determine the exposure of the study antibiotics in synovial fluid at the site of PJIs.

Simultaneous Retrodialysis by Drug for Cefuroxime Using Meropenem as an Internal Standard-A Microdialysis Validation Study

Microdialysis is a valuable pharmacokinetic tool for obtaining samples of drug concentrations from tissues of interest. When an absolute tissue concentration is needed, a calibration of the microdialysis catheter is required. The use of an internal standard offers a number of advantages compared to standard calibration methods. However, meticulous validation both in vitro and in vivo is needed, as this method requires an internal standard with physiochemical similarities to the analyte of interest with no interference. A series of in vitro and in vivo setups were conducted to determine the relative recovery by gain and by loss for cefuroxime, with and without a constant meropenem concentration. The cefuroxime and meropenem concentrations were determined using ultra-HPLC. The main finding was that cefuroxime and meropenem relative recovery behaved similarly both in vitro and in vivo, signifying that meropenem is a representative internal standard for cefuroxime. Furthermore, cefuroxime relative recovery in vitro was not affected by either the cefuroxime concentration or the presence of meropenem, and the in vivo meropenem relative recovery was constant over 6 h.

Plasma and tissue pharmacokinetics of fosfomycin in morbidly obese and non-obese surgical patients: a controlled clinical trial

Objectives

To assess the pharmacokinetics and tissue penetration of fosfomycin in obese and non-obese surgical patients.

Methods

Fifteen obese patients undergoing bariatric surgery and 15 non-obese patients undergoing major intra-abdominal surgery received an intravenous single short infusion of 8 g of fosfomycin. Fosfomycin concentrations were determined by LC-MS/MS in plasma and microdialysate from subcutaneous tissue up to 8 h after dosing. The pharmacokinetic analysis was performed in plasma and interstitial fluid (ISF) by non-compartmental methods.

Results

Thirteen obese patients (BMI 38–50 kg/m2) and 14 non-obese patients (BMI 0–29 kg/m2) were evaluable. The pharmacokinetics of fosfomycin in obese versus non-obese patients were characterized by lower peak plasma concentrations (468 ± 139 versus 594 ± 149 mg/L, P = 0.040) and higher V (24.4 ± 6.4 versus 19.0 ± 3.1 L, P = 0.010). The differences in AUC∞ were not significant (1275 ± 477 versus 1515 ± 352 mg·h/L, P = 0.16). The peak concentrations in subcutaneous tissue were reached rapidly and declined in parallel with the plasma concentrations. The drug exposure in tissue was nearly halved in obese compared with non-obese patients (AUC∞ 1052 ± 394 versus 1929 ± 725 mg·h/L, P = 0.0010). The tissue/plasma ratio (AUCISF/AUCplasma) was 0.86 ± 0.32 versus 1.27 ± 0.34 (P = 0.0047).

Conclusions

Whereas the pharmacokinetics of fosfomycin in plasma of surgical patients were only marginally different between obese and non-obese patients, the drug exposure in subcutaneous tissue was significantly lower in the obese patients.

High voriconazole target-site exposure after approved sequence dosing due to nonlinear pharmacokinetics assessed by long-term microdialysis

Voriconazole, a broad-spectrum antifungal drug used to prevent and treat invasive fungal infections, shows complex pharmacokinetics and is primarily metabolised by various CYP enzymes. An adequate unbound antibiotic concentration-time profile at the target-site of an infection is crucial for effective prophylaxis or therapy success. Therefore, the aim was to evaluate the pharmacokinetics of voriconazole after the approved sequence dosing in healthy volunteers in interstitial space fluid, assessed by microdialysis, and in plasma. Moreover, potential pharmacogenetic influences of CYP2C19 polymorphisms on pharmacokinetics were investigated. The prospective, open-labelled, uncontrolled long-term microdialysis study included 9 healthy male individuals receiving the approved sequence dosing regimen for voriconazole. Unbound voriconazole concentrations were sampled over 84 h in interstitial space fluid of subcutaneous adipose tissue and in plasma and subsequently quantified via high-performance liquid chromatography. For pharmacokinetic data analysis, non-compartmental analysis was used. High interindividual variability in voriconazole concentration-time profiles was detected although dosing was adapted to body weight for the first intravenous administrations. Due to nonlinear pharmacokinetics, target-site exposure of voriconazole in healthy volunteers was found to be highly comparable to plasma exposure, particularly after multiple dosing. Regarding the CYP2C19 genotype-predicted phenotype, the individuals revealed a broad spectrum, ranging from poor to rapid metaboliser status. A strong relation between CYP2C19 genotype-predicted phenotype and voriconazole clearance was identified.