The Role of PK/PD Analysis in the Development and Evaluation of Antimicrobials

Antimicrobial resistance and etiological dynamics affected by tropical climate variability on year-round diagnosis of upper respiratory infections in companion rabbits with snuffles

Upper respiratory infections (URIs) in rabbits are of significant concern, presenting diagnostic challenges and necessitating targeted antimicrobial stewardship. This study aimed to evaluate the etiological bacteria causing URIs in rabbits and their antimicrobial resistance (AMR) in Thailand during 2022, while exploring potential correlations between tropical meteorological factors and URI occurrence. For year-round diagnosis, seventy-eight companion rabbits with snuffles were confirmed infection based on bacterial culture. Antimicrobial susceptibility was tested using the Kirby-Bauer disk diffusion method according to Clinical and Laboratory Standards Institute guidelines. Meteorological data were obtained from the Meteorological Department of Thailand, Ministry of Digital Economy and Society and used for analyzing the climate influences. The results showed that highest URI occurrence could be found during the rainy season (46.15%, 95% CI 35.53-57.14%), with a significant correlation between URI occurrence and precipitation (r = 0.66, p = 0.02). Gram-negative bacteria were the predominant pathogens (67.95%, 95% CI 56.96-77.25%), particularly Pseudomonas spp., Acinetobacter spp., Enterobacter spp., and Pasteurella multocida. Consequently, AMR profiles revealed high resistance to penicillin and co-trimoxazole, with multidrug resistance common among major bacterial groups. These findings highlight the influence of tropical climate on URI occurrence and the growing AMR challenge in companion rabbits, underscoring the need for region-specific monitoring and antimicrobial stewardship.

Enhanced efficacy of sequential administration of fosfomycin and linezolid against methicillin-resistant Staphylococcus aureus

The aim of this study was to assess the superiority of sequential administration of fosfomycin and linezolid in combination on the efficacy of methicillin-resistant Staphylococcus aureus (MRSA). The antimicrobial activity was assessed using static and dynamic bactericidal assays, along with pharmacokinetics/pharmacodynamics in vitro simulation models. Transmission electron microscopy (TEM) was employed to observe ultrastructural changes in MRSA cell walls following both sequential and concomitant dosing strategies. The results indicated that in the static time-kill assay, at MIC levels (fosfomycin at 4-8 mg/L and linezolid at 2-4 mg/L), the combination effectively inhibited MRSA growth under both concurrent and sequential administration; however, the sequential dosing regimen exhibited significantly greater bactericidal activity. Similarly, in the dynamic sterilization test conducted at clinically relevant doses (linezolid 600 mg and fosfomycin 2 g), a comparable trend was observed, further supporting the superior efficacy of sequential administration. TEM analysis further revealed that sequential dosing caused more extensive damage to the bacterial cell wall and nucleus compared to concomitant administration. These findings suggest that sequential administration of fosfomycin and linezolid enhances in vitro efficacy against MRSA and may provide an improved approach for managing complicated and drug-resistant infections.

Enhanced Tear Film Concentrations of Cefazolin and Chloramphenicol Using Cross-Linked Hyaluronic Acid in Canine Eyes

OBJECTIVE

To evaluate the impact of two excipients, 1.4% polyvinyl alcohol (PVA) and 0.75% cross-linked hyaluronic acid (XHA), on tear film concentrations of cefazolin and chloramphenicol.

ANIMALS STUDIED

Ten ophthalmologically healthy dogs.

PROCEDURES

Cefazolin and chloramphenicol were compounded into 5.5% and 0.5% solutions, respectively, using either 1.4% PVA or 0.75% XHA. In the first trial, each dog received cefazolin-PVA in one randomly assigned eye and cefazolin-XHA in the contralateral eye. One month later, the experiment was repeated using chloramphenicol formulations. Tear fluid was sampled at 0, 1, 5, 10, 15, 30, 60, 120, 240, 360, and 480 min following eyedrop administration using 2 μL capillary tubes. Tear concentrations of cefazolin and chloramphenicol were measured using UV-Vis spectrophotometry.

RESULTS

Tear film concentrations of cefazolin and chloramphenicol were significantly higher with XHA compared to PVA at all time points (p ≤ 0.020), except for baseline (both antibiotics), times 1 min, 60 min, and 120 min for cefazolin. The tear film kinetics exhibited a biphasic pattern, with drug levels decreasing from 0 to 120 min, then slightly increasing between 120 and 360 min before declining again until 480 min. The area under the time-concentration curve (AUC0-480) was significantly greater with XHA versus PVA formulations (p = 0.002), with a median 2.4 and 4.2 times higher for cefazolin and chloramphenicol, respectively.

CONCLUSION

The cross-linked hyaluronic acid significantly enhanced the retention and overall exposure of both cefazolin and chloramphenicol in the canine tear film. These findings suggest that XHA could serve as a superior delivery vehicle for ocular antibiotics, potentially improving treatment outcomes for ophthalmic infections.

Predicting Antimicrobial Class Specificity of Small Molecules Using Machine Learning

While the useful armory of antibiotic drugs is continually depleted due to the emergence of drug-resistant pathogens, the development of novel therapeutics has also slowed down. In the era of advanced computational methods, approaches like machine learning (ML) could be one potential solution to help reduce the high costs and complexity of antibiotic drug discovery and attract collaboration across organizations. In our work, we developed a large antimicrobial knowledge graph (AntiMicrobial-KG) as a repository for collecting and visualizing public in vitro antibacterial assay. Utilizing this data, we build ML models to efficiently scan compound libraries to identify compounds with the potential to exhibit antimicrobial activity. Our strategy involved training seven classic ML models across six compound fingerprint representations, of which the Random Forest trained on the MHFP6 fingerprint outperformed, demonstrating an accuracy of 75.9% and Cohen's Kappa score of 0.68. Finally, we illustrated the model's applicability for predicting the antimicrobial properties of two small molecule screening libraries. First, the EU-OpenScreen library was tested against a panel of Gram-positive, Gram-negative, and Fungal pathogens. Here, we unveiled that the model was able to correctly predict more than 30% of active compounds for Gram-positive, Gram-negative, and Fungal pathogens. Second, with the Enamine library, a commercially available HTS compound collection with claimed antibacterial properties, we predicted its antimicrobial activity and pathogen class specificity. These results may provide a means for accelerating research in AMR drug discovery efforts by carefully filtering out compounds from commercial libraries with lower chances of being active.

Sampling from covariate distribution may not always be necessary in PK/PD simulations: illustrative examples with antibiotics

Pharmacokinetics (PK)/pharmacodynamics (PD) modeling and simulation is crucial for optimizing antimicrobial dosing. This study assessed covariate impact on PK variability and identified scenarios where fixing the covariate with median value proves effective PK/PD simulations for antibiotics with population PK (popPK) model including only one covariate effect. Three published popPK models were employed, with creatinine clearance (CRCL) identified as a covariate on clearance (CL) for meropenem and tobramycin, and total body weight (WT) associated with the volume of distributions for daptomycin. Given a fixed dose for Meropenem (1000 mg), and a WT based dose for tobramycin (7 mg/kg) and daptomycin (6 mg/kg), PK/PD simulation outcomes (e.g., percentage of PK/PD target attainment (PTA) and toxicity risk) were compared between fixed covariate-based and covariate distribution-based approaches. Covariate impact on PK was assessed through deterministic simulation using outer bounds of covariate versus simulation using median covariate value, with an overlap ratio calculated the percentage of overlapped area under concentration-time curve (AUC) between these two simulation approaches. Meropenem and tobramycin simulations showed a broader PK profiles and distinct PTA distribution with sampled covariate distribution, while daptomycin simulations exhibited consistency in PK/PD characteristics. CRCL had a relative strong impact on meropenem and tobramycin PK, while a weak impact of WT on daptomycin PK was observed from extensive overlap in simulated PK curves, with an overlap ratio of 99.5%. Regarding a weak covariate impact on PK with high overlap ratio, sampling from covariate distribution may not significantly enhance simulation performance, fixing covariate with median value could be efficient for antibiotic PK/PD simulations.

Enhancing antibiotic therapy through comprehensive pharmacokinetic/pharmacodynamic principles

Antibiotic therapy relies on understanding both pharmacokinetics (PK) and pharmacodynamics (PD), which respectively address drug absorption, distribution, and elimination, and the relationship between drug concentration and antimicrobial efficacy. This review synthesizes decades of research, drawing from in-vitro studies, in-vivo models, and clinical observations, to elucidate the temporal dynamics of antibiotic activity. We explore how these dynamics, including concentration-effect relationships and post antibiotic effects, inform the classification of antibiotics based on their PD profiles. Additionally, we discuss the pivotal role of PK/PD principles in determining optimal dosage regimens. By providing a comprehensive overview of PK/PD principles in antibiotic therapy, this review aims to enhance understanding and improve treatment outcomes in clinical practice.

Multidose Dalbavancin Population Pharmacokinetic Analysis for Prolonged Target Attainment in Patients Requiring Long-Term Treatment

Introduction: Dalbavancin (DAL) is a long-acting lipoglycopeptide active against Gram-positive bacteria, including multidrug-resistant isolates. A growing body of evidence supports its efficacy in various difficult-to-treat infections. DAL shows time-dependent bactericidal activity in vitro at free drug concentrations equal to 4×MIC values. However, the optimal dosing scheme for achieving the PK/PD target in multidose treatment has not been fully established. Methods: Pharmacokinetic analysis was based on a nonlinear mixed effects modelling approach performed in NONMEM v7.5/Pirana, while R was used for data management and graphical summaries. Final model parameters were used to simulate the plasma disposition of DAL by Monte Carlo simulations to determine the multidose DAL regimen associated with a 90% target attainment of 100% fT > 4×MIC. Results: A two-compartmental model with first-order elimination and allometric-scaled bodyweight best described DAL disposition in patients with CLcr > 30 mL/min. Monte Carlo simulations showed that two 1500 mg DAL doses 7 days apart granted an optimal PTA > 90% of 100% fT > 4×MIC up to 5, 4, and 3 weeks in patients weighting from 40-80 kg, 80-120 kg and 120-200 kg, respectively. An additional third 1500 mg dose at the above time points by weight bands may extend the optimal PTA up to 9, 7, and 6 weeks of total treatment. Conclusions: Two 1500 mg DAL doses administered 7 days apart could be a valuable starting strategy for patients of all weight classes with CLcr > 30 mL/min. In patients requiring long-term DAL treatment, the optimal timing of additional administrations should be guided by routine TDM or empirically through patients' total body weight when TDM is unavailable.

Applications of pharmacometrics in drug development

The last two decades have witnessed profound changes in how advanced computational tools can help leverage tons of data to improve our knowledge, and ultimately reduce cost and increase productivity in drug development. Pharmacometrics has demonstrated its impact through model-informed drug development (MIDD) approaches. It is now an indispensable component throughout the whole continuum of drug discovery, development, regulatory review, and approval. Today, applications of pharmacometrics are common in designing better trials and accelerating evidence-based decisions. Newly emerging technologies, especially those from data and computer sciences, are being integrated with existing computational tools used in the pharmaceutical industry at a remarkably fast pace. The new challenges faced by the pharmacometrics community are not what or how to contribute, but which optimal MIDD strategy should be adopted to maximize its value in the decision-making process. While we are embracing new innovative approaches and tools, this article discusses how a variety of existing modeling tools, with differentiated advantages and focus, can work in concert to inform drug development.

Factoring fu Variability Into Estimates of Unbound Drug Concentrations Negatively Biases the MIC Versus % Probability of Target Attainment Relationship of Antimicrobial Agents

The clinical breakpoint for a drug-pathogen combination reflects the drug susceptibility of the pathogen wild-type population, the location of the infection, the integrity of the host immune response, and the drug-pathogen pharmacokinetic (PK)/pharmacodynamic (PD) relationship. That PK/PD relationship, along with the population variability in drug exposure, is used to determine the probability of target attainment (PTA) of the PK/PD index at a specified minimum inhibitory concentration (MIC) for a selected target value. The PTA is used to identify the pharmacodynamic cutoff value (COPD), which is one of the three components used to establish the clinical breakpoint. A challenge encountered when defining the COPD is that the available PK information typically reflects total (free plus protein-bound) plasma concentrations. However, it is the unbound drug concentrations that exert the therapeutic effects and how the population fraction unbound (fu) incorporated into the COPD assessments can markedly influence the COPD. Factors examined included the estimated population fu mean (risk of bias) and the incorporation of estimated fu population variability into the Monte Carlo simulations when converting total to unbound plasma concentrations (risk of inflating variability). In this in silico study, the drug fu, systemic clearance, and the variability of both were altered so that the relative impact of each could be explored. We demonstrate that incorporating fu variability into the estimation of fAUCback can bias the COPD assessment and that the magnitude of bias reflects the relative variability in systemic clearance and fu.

PK/PD-Guided Strategies for Appropriate Antibiotic Use in the Era of Antimicrobial Resistance

Antimicrobial resistance (AMR) poses a critical global health threat, necessitating the optimal use of existing antibiotics. Pharmacokinetic/pharmacodynamic (PK/PD) principles provide a scientific framework for optimizing antimicrobial therapy, particularly to respond to evolving resistance patterns. This review examines PK/PD strategies for antimicrobial dosing optimization, focusing on three key aspects. First, we discuss the importance of drug concentration management for enhancing efficacy while preventing toxicity, considering various patient populations, including pediatric and elderly patients with their unique physiological characteristics. Second, we analyze different PK modeling approaches: the classic top-down approach exemplified by population PK analysis, the bottom-up approach represented by physiologically based PK modeling, and hybrid models combining both approaches for enhanced predictive performance. Third, we explore clinical applications, including nomogram-based dosing strategies, Bayesian estimation, and emerging artificial intelligence applications, for real-time dose optimization. Critical challenges in implementing PK/PD simulation are addressed, particularly the selection of appropriate PK models, the optimization of PK/PD indices, and considerations concerning antimicrobial concentrations at infection sites. Understanding these principles and challenges is crucial for optimizing antimicrobial therapy and combating AMR through improved dosing strategies.

In vivo pharmacokinetic and pharmacodynamic study and cutoff of florfenicol against Riemerella anatipestifer in ducks

Riemerella anatipestifer causes serious infections, characterized by septicemia and serositis, in ducks and geese. R. anatipestifer is mainly controlled through antimicrobial chemotherapy. This study investigated the pharmacokinetic/pharmacodynamic (PK/PD) integration of florfenicol (FF) against R. anatipestifer by establishing a systemic infection model in ducks. For PK studies, FF was administrated intramuscularly (i.m.) at single doses of 2.5, 10, 20, and 40 mg/kg body weight. The concentrations of FF in blood, lung, and liver were determined. FF was rapidly eliminated in R. anatipestifer-infected ducks with T1/2kel values of 1.67, 2.2, and 1.62 h in the plasma, lung, and liver, respectively. For PD analysis, the infected ducks were administered FF via the i.m. route at doses of 5-80 mg/kg body weight, using 2 dosing regimens involving the administration of FF either once or twice over 24 h. The bacteria were counted 24 h after drug administration. Bactericidal effects in tissues (including those of the heart, liver, spleen, lung, kidney, and brain) were achieved at doses of ≥20 mg/kg following 2 i.m. injections of FF within 24 h. The data obtained were fitted to a sigmoidal Emax model. The results demonstrated that AUC24h/minimum inhibitory concentration (MIC) (R2 = 0.930) and Cmax/MIC (R2 = 0.930) were the optimal PK/PD parameters for describing the antibacterial activity of FF. The magnitudes of AUC24h/MIC and Cmax/MIC required to produce a drop of 3 Log10CFU/mL in the bacterial count were 58.56 h and 15.10, respectively. The MIC distribution of 164 R. anatipestifer strains for FF ranged from 0.25 to 16 μg/mL. Both the values of COWT derived from the ECOFFinder program and the COPD based on a 10,000-subject Monte Carlo simulation of FF against R. anatipestifer were 1 μg/mL, confirming that infections caused by strains with MIC ≤ 1 μg/mL could be effectively treated. Our study results may prove useful in optimizing FF regimens to treat R. anatipestifer infections.

Pharmacokinetics and Pharmacodynamics Evaluation of Amoxicillin Against Staphylococcus pseudintermedius in Dogs

Antibiotic resistance in bacteria from companion animals poses significant public health risks. Prudent antibiotic use, particularly through pharmacokinetics/pharmacodynamics modeling, is crucial for minimizing resistance. We investigated the pharmacokinetics/pharmacodynamics of amoxicillin (AMX) against Staphylococcus pseudintermedius. A pharmacokinetic study was conducted on healthy dogs subcutaneously injected with a dose of 15 mg/kg AMX. The antibacterial efficacy of AMX was evaluated against a standard strain from animals (KCTC 3344) and clinical isolates from dogs (B-2, B-7, and B-8), with minimum inhibitory concentrations (MICs) of 0.25, 0.5, 64, and 16 μg/mL, respectively. The half-life of AMX was 7 h, allowing for extended drug efficacy. The time above MIC (%T > MIC) values indicated that the AMX concentrations were maintained above MICs of the two susceptible strains (KCTC 3344 and B-2) for more than 80% of the time when dosed at a one-day interval, suggesting an effective treatment. The area under the curve over 24 h/MIC ratios confirmed the bacteriostatic, bactericidal, and bacterial eradication effects of AMX against S. pseudintermedius strains, except for B-7 (the most resistant strain). These results support improved clinical dosing strategies for AMX against S. pseudintermedius infections in dogs.

Dynamic In Vitro PK/PD Infection Models for the Development and Optimisation of Antimicrobial Regimens: A Narrative Review

The antimicrobial concentration-time profile in humans affects antimicrobial activity, and as such, it is critical for preclinical infection models to simulate human-like dynamic concentration-time profiles for maximal translatability. This review discusses the setup, principle, and application of various dynamic in vitro PK/PD infection models commonly used in the development and optimisation of antimicrobial treatment regimens. It covers the commonly used dynamic in vitro infection models, including the one-compartment model, hollow fibre infection model, biofilm model, bladder infection model, and aspergillus infection model. It summarises the mathematical methods for the simulation of the pharmacokinetic profile of single or multiple antimicrobials when using the serial or parallel configurations of in vitro systems. Dynamic in vitro models offer reliable pharmacokinetic/pharmacodynamic data to help define the initial dosing regimens of new antimicrobials that can be developed further in clinical trials. They can also help in the optimisation of dosing regimens for existing antimicrobials, especially in the presence of emerging antimicrobial resistance. In conclusion, dynamic in vitro infection models replicate the interactions that occur between microorganisms and dynamic antimicrobial exposures in the human body to generate data highly predictive of the clinical efficacy. They are particularly useful for the development new treatment strategies against antimicrobial-resistant pathogens.

Pharmacokinetic/pharmacodynamic analysis of sulbactam against Acinetobacter baumannii pneumonia: establishing in vivo efficacy targets in the epithelial lining fluid

Background

Sulbactam is an effective therapy for Acinetobacter baumannii infections. Previous sulbactam pharmacokinetics/pharmacodynamics (PK/PD) analyses established exposure efficacy targets in plasma against A. baumannii pneumonia. Herein, we established sulbactam efficacy targets in epithelial lining fluid (ELF). The PTA following clinical sulbactam regimens was estimated.

Methods

Sulbactam (dosed as ampicillin-sulbactam) bronchopulmonary PK was assessed in the neutropenic murine pneumonia model. The percentage of the dosing interval during which the free drug concentration remained above the MIC (%fT > MIC) required to achieve different efficacy endpoints was estimated in 21 clinical A. baumannii isolates. PTA was assessed using Monte Carlo Simulations and utilizing previously published healthy volunteers sulbactam ELF pharmacokinetics.

Results

Median (IQR) %fT > MIC required to achieve 1-log kill in isolates resistant to both sulbactam and meropenem was 47.51 (39.7-54.2). This target was much higher than isolates with other phenotypes (i.e. sulbactam-susceptible/intermediate and sulbactam-resistant but meropenem susceptible) that required 16.62 (5.3-22.0). The PTA following sulbactam 1 g q6h 0.5h infusion regimen was >90% up to MIC of 2 mg/L while the PTA for MIC 4 mg/L (susceptibility breakpoint) was 81%. Conversely, previous assessment in plasma demonstrated the same regimen exceeded 90% PTA up to MIC of 4 mg/L. Sulbactam 3 g q8h 4h infusion provided PTA >90% for MIC 8 mg/L (sulbactam-intermediate), similar to previous assessment in plasma.

Conclusion

Based on the ELF assessment, the maximum FDA approved dose of sulbactam (1 g q6h 0.5h infusion) provided >90% PTA for isolates with sulbactam MIC only up to 2 mg/L. Nevertheless, sulbactam 3 g q8h for 4 hours of infusion achieved higher PTA and conferred additional benefit against sulbactam-susceptible/intermediate isolates.

Clinical pharmacokinetics of antimicrobials in critical care: a narrative review

INTRODUCTION

The management of critically ill septic patients presents considerable challenges due to multifaceted physiological alterations. Rapid changes such as fluid shifts, hyperdynamic states, and altered renal clearance often require special attention for better clinical outcomes. Vital organ dysfunction, with or without MODS, often necessitates supportive management like RRT, ventilatory support, and ECMO. These interventions can significantly affect the PK/PD of administered antimicrobials, complicating effective treatment.

AREA COVERED

Patient-specific parameters such as age, weight, and comorbid illnesses (e.g. cystic fibrosis, burns, and immunocompromised states) are critical determinants of antimicrobial pharmacokinetics. Understanding PK/PD determinants is crucial for developing optimized dosing regimens that enhance therapeutic efficacy and minimize toxicity in critically ill patients.

EXPERT OPINION

Incorporating pharmacometrics approaches in dose optimization can significantly improve patient outcomes. This review focuses on the nuances of PK/PD for optimized antimicrobial dosing in critically ill septic patients, emphasizing the importance of individualized treatment plans to address the complex and dynamic needs of this patient population. The adoption of these advanced pharmacokinetic and pharmacodynamic principles into clinical practice is essential for advancing patient care and optimizing therapeutic outcomes in critically ill patients.

Antibiotic dose optimisation in the critically ill: targets, evidence and future strategies

PURPOSE OF REVIEW

To highlight the recent evidence for antibiotic pharmacokinetics and pharmacodynamics (PK/PD) in enhancing patient outcomes in sepsis and septic shock. We also summarise the limitations of available data and describe future directions for research to support translation of antibiotic dose optimisation to the clinical setting.

RECENT FINDINGS

Sepsis and septic shock are associated with poor outcomes and require antibiotic dose optimisation, mostly due to significantly altered pharmacokinetics. Many studies, including some randomised controlled trials have been conducted to measure the clinical outcome effects of antibiotic dose optimisation interventions including use of therapeutic drug monitoring. Current data support antibiotic dose optimisation for the critically ill. Further investigation is required to evolve more timely and robust precision antibiotic dose optimisation approaches, and to clearly quantify whether any clinical and health-economic benefits support expanded use of this treatment intervention.

SUMMARY

Antibiotic dose optimisation appears to improve outcomes in critically ill patients with sepsis and septic shock, however further research is required to quantify the level of benefit and develop a stronger knowledge of the role of new technologies to facilitate optimised dosing.

Dose Individualisation of Antimicrobials from a Pharmacometric Standpoint: The Current Landscape

Successful antimicrobial therapy depends on achieving optimal drug concentrations within individual patients. Inter-patient variability in pharmacokinetics (PK) and differences in pathogen susceptibility (reflected in the minimum inhibitory concentration, [MIC]) necessitate personalised approaches. Dose individualisation strategies aim to address this challenge, improving treatment outcomes and minimising the risk of toxicity and antimicrobial resistance. Therapeutic drug monitoring (TDM), with the application of population pharmacokinetic (popPK) models, enables model-informed precision dosing (MIPD). PopPK models mathematically describe drug behaviour across populations and can be combined with patient-specific TDM data to optimise dosing regimens. The integration of machine learning (ML) techniques promises to further enhance dose individualisation by identifying complex patterns within extensive datasets. Implementing these approaches involves challenges, including rigorous model selection and validation to ensure suitability for target populations. Understanding the relationship between drug exposure and clinical outcomes is crucial, as is striking a balance between model complexity and clinical usability. Additionally, regulatory compliance, outcome measurement, and practical considerations for software implementation will be addressed. Emerging technologies, such as real-time biosensors, hold the potential for revolutionising TDM by enabling continuous monitoring, immediate and frequent dose adjustments, and near patient testing. The ongoing integration of TDM, advanced modelling techniques, and ML within the evolving digital health care landscape offers a potential for enhancing antimicrobial therapy. Careful attention to model development, validation, and ethical considerations of the applied techniques is paramount for successfully optimising antimicrobial treatment for the individual patient.

Disposition kinetics and tissue residues of tilmicosin following intravenous, subcutaneous, single and multiple oral dosing in geese (Anser anser domesticus)

Tilmicosin (TMC), a semi-synthetic macrolide antibiotic, is widely used in veterinary medicine due to its broad-spectrum, bacteriostatic properties. Frequently administered in various birds species, it is likely used off-label in geese as well. The study sought to investigate TMC's pharmacokinetics, tissue residues, in geese through in vivo experiments. The study involved longitudinal open studies on 15 healthy adult males, with three phases separated by one-month washout periods. Geese were administered TMC through intravenous (IV, 5 mg/kg), subcutaneous (SC, 10 mg/kg), and oral (PO, 25 mg/kg for five consecutive days) routes, with blood samples drawn at specific intervals. Tissue samples were also collected for subsequent analysis at pre-assigned times. TMC in goose plasma was quantified by a fully validated HPLC method. Plasma concentrations were quantified up to 4 hr for the PO and IV routes, and up to 10 hr in the SC route. Significant variations in bioavailability were observed between SC (87%) and PO (4%) routes. The body extraction ratio was low at 0.03, suggesting minimal ability of the liver and kidneys to eliminate TMC. Multiple oral doses showed no plasma accumulation, but tissue data revealed extensive distribution and prolonged residence, up to 120 h, suggesting a sustained therapeutic effect despite the brief plasma half-life. Regarding the multiple PO doses, provisional withdrawal times of 6, 7.5, and 8 days were suggested for the liver, muscles, and kidneys, respectively, according to the MRL set for these matrices in chickens by EMA. In conclusion, while the practical oral administration is discouraged at the population level, SC administration of TMC may be appropriate for geese, albeit impractical for flock therapy.

The Vehicle of Administration and Prandial State May Reduce the Spectrum of Oral Broad-Spectrum Antibiotics (Oxytetracycline, Fosfomycin and Amoxicillin) Administered to Piglets: A Pharmacokinetic/Pharmacodynamic Approach

The objective of this study was to assess the impact of the vehicle of administration and the prandial state of post weaning piglets on the indices of therapeutic efficacy for different broad-spectrum antibiotic/pathogen combinations. Pharmacokinetic data were retrieved from previous studies, in which we orally administered oxytetracycline (OTC), fosfomycin (FOS), or amoxicillin (AMX) according to the following treatments: dissolved in soft water to fasted or non-fasted piglets, dissolved in hard water to fasted or non-fasted piglets, and mixed with feed. Minimum inhibitory concentration (MIC) values for susceptible strains of bacteria causing swine diseases were obtained from the database of European Committee on Antimicrobial Susceptibility Testing (EUCAST) for each antibiotic. Pharmacokinetic/pharmacodynamic (PK/PD) indices of therapeutic efficacy-drug exposure over the dosing interval (fAUC/MIC) for OTC and FOS; time that free drug concentration remains above MIC (%fT>MIC) for AMX-were calculated for each antibiotic/pathogen combination under each treatment. After all OTC and in-feed FOS and AMX treatments, the indices of therapeutic efficacy were below the target value for all the study microorganisms. When FOS or AMX were delivered dissolved in soft or hard water, the indices were above the target value over which therapeutic efficacy would be expected for Escherichia coli treated with FOS and, Glaesserella parasuis, Pasteurella multocida, and Actinobacillus pleuropneumoniae treated with AMX. The prandial state of piglets showed no influence on the indices of therapeutic efficacy. Pharmacokinetic profiles of broad-spectrum antibiotics, specifically the ability to achieve target concentrations, may be largely reduced due to drug interactions with components present in feed or water resulting in a discrepancy with PK/PD principles of prudent and responsible use of antibiotics.

Susceptibility evaluation and PK/PD integration of tulathromycin against Actinobacillus pleuropneumoniae during the mutant selection window

Introduction

Actinobacillus pleuropneumoniae (APP) is a serious pathogen that affects the development of livestock breeding. Due to excessive use of antimicrobial drugs, many multidrug-resistant bacteria have emerged and spread, which have threatened the livestock industry. Therefore, we established a peristaltic pump infection model (PPIM) to evaluate the susceptibility change and pharmacokinetic/pharmacodynamic (PK/PD) integration of tulathromycin against APP during the mutant selection window (MSW) for preventing the emergence of mutant-resistant bacteria.

Methods

The 99% minimum inhibitory concentration (MIC99) and mutant prevention concentration (MPC) of tulathromycin against APP were measured using the agar-plate method. After the model of dynamic infection had been established based on tulathromycin data in lungs, different dosages were administered to make the drug concentrations located in different parts of the MSW. The population and sensitivity of APP were monitored. Tulathromycin concentrations were measured by high-performance liquid chromatography-tandem mass spectrometry. Finally, a sigmoid Emax model was used to analyze the relationships between PK/PD parameters and antibacterial effects.

Results and discussion

The values of MIC, MIC99, and MPC of tulathromycin against APP were 2, 1.4, and 44.8 μg/mL, respectively. The PPIM was stable. An elimination effect without regrowth was observed at 5.6 to 44.8 μg/mL (-4.48 to -7.05 Log10 CFU/mL, respectively). The MIC of APP increased 32-fold at 8 MIC99. AUC168 h/MIC99 had the best fit with the antibacterial effect (R 2 = 0.9867). The AUC168 h/MIC99 required to achieve bacteriostatic, bactericidal, and clearance effects were 1.80, 87.42, and 198 h, respectively. Our results could provide guidance for the clinical application of tulathromycin to treat APP infection and avoid the generation of drug-resistant bacteria.

Optimizing Antibiotic Therapy for Stenotrophomonas maltophilia Infections in Critically Ill Patients: A Pharmacokinetic/Pharmacodynamic Approach

Stenotrophomonas maltophilia is an opportunistic, multidrug-resistant non-fermentative Gram-negative bacillus, posing a significant challenge in clinical treatment due to its numerous intrinsic and acquired resistance mechanisms. This study aimed to evaluate the adequacy of antibiotics used for the treatment of S. maltophilia infections in critically ill patients using a pharmacokinetic/pharmacodynamic (PK/PD) approach. The antibiotics studied included cotrimoxazole, levofloxacin, minocycline, tigecycline, cefiderocol, and the new combination aztreonam/avibactam, which is not yet approved. By Monte Carlo simulations, the probability of target attainment (PTA), the PK/PD breakpoints, and the cumulative fraction of response (CFR) were estimated. PK parameters and MIC distributions were sourced from the literature, the European Committee on Antimicrobial Susceptibility Testing (EUCAST), and the SENTRY Antimicrobial Surveillance Program collection. Cefiderocol 2 g q8h, minocycline 200 mg q12h, tigecycline 100 mg q12h, and aztreonam/avibactam 1500/500 mg q6h were the best options to treat empirically infections due to S. maltophilia. Cotrimoxazole provided a higher probability of treatment success for the U.S. isolates than for European isolates. For all antibiotics, discrepancies between the PK/PD breakpoints and the clinical breakpoints defined by EUCAST (or the ECOFF) and CLSI were detected.

Evaluation the kill rate and mutant selection window of danofloxacin against Actinobacillus pleuropneumoniae in a peristaltic pump model

BACKGROUND

Actinobacillus pleuropneumoniae is a serious pathogen in pigs. The abundant application of antibiotics has resulted in the gradual emergence of drugresistant bacteria, which has seriously affected treatment of disease. To aid measures to prevent the emergence and spread of drug-resistant bacteria, herein, the kill rate and mutant selection window (MSW) of danofloxacin (DAN) against A. pleuropneumoniae were evaluated.

METHODS

For the kill rate study, the minimum inhibitory concentration (MIC) was tested using the micro dilution broth method and time-killing curves of DAN against A. pleuropneumoniae grown in tryptic soy broth (TSB) at a series drug concentrations (from 0 to 64 MIC) were constructed. The relationships between the kill rate and drug concentrations were analyzed using a Sigmoid Emax model during different time periods. For the MSW study, the MIC99 (the lowest concentration that inhibited the growth of the bacteria by ≥ 99%) and mutant prevention concentration (MPC) of DAN against A. pleuropneumoniae were measured using the agar plate method. Then, a peristaltic pump infection model was established to simulate the dynamic changes of DAN concentrations in pig lungs. The changes in number and sensitivity of A. pleuropneumoniae were measured. The relationships between pharmacokinetic/pharmacodynamic parameters and the antibacterial effect were analyzed using the Sigmoid Emax model.

RESULTS

In kill rate study, the MIC of DAN against A. pleuropneumoniae was 0.016 µg/mL. According to the kill rate, DAN exhibited concentration-dependent antibacterial activity against A. pleuropneumoniae. A bactericidal effect was observed when the DAN concentration reached 4-8 MIC. The kill rate increased constantly with the increase in DAN concentration, with a maximum value of 3.23 Log10 colony forming units (CFU)/mL/h during the 0-1 h period. When the drug concentration was in the middle part of the MSW, drugresistant bacteria might be induced. Therefore, the dosage should be avoided to produce a mean value of AUC24h/MIC99 (between 31.29 and 62.59 h. The values of AUC24h/MIC99 to achieve bacteriostatic, bactericidal, and eradication effects were 9.46, 25.14, and > 62.59 h, respectively.

CONCLUSION

These kill rate and MSW results will provide valuable guidance for the use of DAN to treat A. pleuropneumoniae infections.

Antibacterial and Antibiofilm Potential of Bacterial Cellulose Hydrogel Containing Vancomycin against Multidrug-Resistant Staphylococcus aureus and Staphylococcus epidermidis

The present study aimed to evaluate the in vitro antibacterial and antibiofilm activity of bacterial cellulose hydrogel produced by Zoogloea sp. (HYDROGEL) containing vancomycin (VAN) against bacterial strains that cause wound infections, such as multidrug-resistant (MDR) Staphylococcus aureus and Staphylococcus epidermidis. Initially, HYDROGEL was obtained from sugar cane molasses, and scanning electron microscopy (SEM) was performed to determine morphological characteristics. Then, VAN was incorporated into HYDROGEL (VAN-HYDROGEL). The antibacterial activity of VAN, HYDROGEL, and VAN-HYDROGEL was assessed using the broth microdilution method to determine the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) against methicillin-sensitive S. aureus (MSSA) ATCC 25923, methicillin-resistant S. aureus (MRSA) ATCC 33591, S. epidermidis INCQS 00016 (ATCC 12228), five clinical isolates of MRSA, and nine clinical isolates of methicillin-resistant S. epidermidis, following the Clinical and Laboratory Standards Institute (CLSI) guidelines. Additionally, the antibacterial activity of VAN, HYDROGEL, and VAN-HYDROGEL was studied using the time-kill assay. Subsequently, the antibiofilm activity of VAN, HYDROGEL, and VAN-HYDROGEL was evaluated using crystal violet and Congo red methods, as well as SEM analysis. VAN and VAN-HYDROGEL showed bacteriostatic and bactericidal activity against MRSA and methicillin-resistant S. epidermidis strains. HYDROGEL did not show any antibacterial activity. Analysis of the time-kill assay indicated that HYDROGEL maintained the antibacterial efficacy of VAN, highlighting its efficiency as a promising carrier. Regarding antibiofilm activity, VAN and HYDROGEL inhibited biofilm formation but did not demonstrate biofilm eradication activity against methicillin-resistant S. aureus and S. epidermidis strains. However, it was observed that the biofilm eradication potential of VAN was enhanced after incorporation into HYDROGEL, a result also proven through images obtained by SEM. From the methods carried out in this study, it was possible to observe that HYDROGEL preserved the antibacterial activity of vancomycin, aside from exhibiting antibiofilm activity and enhancing the antibiofilm effect of VAN. In conclusion, this study demonstrated the potential of HYDROGEL as a candidate and/or vehicle for antibiotics against MDR bacteria that cause wound infections.

Pharmacokinetic-Pharmacodynamic Correlation Analysis of Rhodiola crenulata in Rats with Myocardial Ischemia

The pharmacokinetics (PK) of Rhodiola crenulata in rats were studied, and pharmacokinetic-pharmacodynamic (PK-PD) correlation analysis was performed to elucidate their time-concentration-effect relationship. The myocardial ischemia model was made with pituitrin. Rats were divided into sham operation, sham operation administration, model, and model administration groups (SG, SDG, MG, and MDG, respectively; n = 6). Blood was collected from the fundus venous plexus at different time points after oral administration. The HPLC-QQQ-MS/MS method was established for the quantification of five components of Rhodiola crenulata. CK, HBDH, SOD, LDH, and AST at different time points were detected via an automatic biochemical analyzer. DAS software was used to analyze PK parameters and PK-PD correlation. The myocardial ischemia model was established successfully. There were significant differences in the PK parameters (AUC0-t, AUC0-∞, Cmax) in MDG when compared with SDG. Two PD indicators, CK and HBDH, conforming to the sigmoid-Emax model, had high correlation with the five components, which indicated a delay in the pharmacological effect relative to the drug concentration in plasma. The difference in the PK parameters between modeled and normal rats was studied, and the time-concentration-effect of composition and effect indicators were investigated. This study can provide reference for the rational clinical application of Rhodiola crenulata and for related studies of other anti-myocardial ischemia drugs.

Updated antimicrobial dosing recommendations for obese patients

The prevalence of obesity has increased considerably in the last few decades. Pathophysiological changes in obese patients lead to pharmacokinetic (PK) and pharmacodynamic (PD) alterations that can condition the correct exposure to antimicrobials if standard dosages are used. Inadequate dosing in obese patients can lead to toxicity or therapeutic failure. In recent years, additional antimicrobial PK/PD data, extended infusion strategies, and studies in critically ill patients have made it possible to obtain data to provide a better dosage in obese patients. Despite this, it is usually difficult to find information on drug dosing in this population, which is sometimes contradictory. This is a comprehensive review of the dosing of different types of antimicrobials (antibiotics, antifungals, antivirals, and antituberculosis drugs) in obese patients, where the literature on PK and possible dosing strategies in obese adults was critically assessed.

What are the optimal pharmacokinetic/pharmacodynamic targets for β-lactamase inhibitors? A systematic review

BACKGROUND

Pharmacokinetic/pharmacodynamic (PK/PD) indices are widely used for the selection of optimum antibiotic doses. For β-lactam antibiotics, fT>MIC, best relates antibiotic exposure to efficacy and is widely used to guide the dosing of β-lactam/β-lactamase inhibitor (BLI) combinations, often without considering any PK/PD exposure requirements for BLIs.

OBJECTIVES

This systematic review aimed to describe the PK/PD exposure requirements of BLIs for optimal microbiological efficacy when used in combination with β-lactam antibiotics.

METHODS

Literature was searched online through PubMed, Embase, Web of Science, Scopus and Cochrane Library databases up to 5 June 2023. Studies that report the PK/PD index and threshold concentration of BLIs approved for clinical use were included. Narrative data synthesis was carried out to assimilate the available evidence.

RESULTS

Twenty-three studies were included. The PK/PD index that described the efficacy of BLIs was fT>CT for tazobactam, avibactam and clavulanic acid and fAUC0-24/MIC for relebactam and vaborbactam. The optimal magnitude of the PK/PD index is variable for each BLI based on the companion β-lactam antibiotics, type of bacteria and β-lactamase enzyme gene transcription levels.

CONCLUSIONS

The PK/PD index that describes the efficacy of BLIs and the exposure measure required for their efficacy is variable among inhibitors; as a result, it is difficult to make clear inference on what the optimum index is. Further PK/PD profiling of BLI, using preclinical infection models that simulate the anticipated mode(s) of clinical use, is warranted to streamline the exposure targets for use in the optimization of dosing regimens.

Pharmacokinetic behaviour and pharmacokinetic-pharmacodynamic integration of doxycycline in rainbow trout (Oncorhynchus mykiss) after intravascular, intramuscular and oral administrations

OBJECTIVE

Doxycycline (DO) has been used in fish for a long time, but there are some factors that have not yet been clarified regarding its pharmacokinetic (PK) and pharmacodynamic (PD) properties. Therefore, the aim of this study was to investigate the PK and PK/PD targets of DO after 20 mg/kg intravascular (IV), intramuscular (IM) and oral (OR) gavage administration in rainbow trout (Oncorhynchus mykiss).

METHODS

Plasma samples were collected at specific time points and subsequently analysed by HPLC-ultraviolet. The PK/PD indices were calculated based on the MIC90 (Aeromonas hydrophila and Aeromonas sobria) values obtained for the respective bacteria and the PK parameters obtained for DO following both IM and OR administration.

RESULTS

After IV administration, the elimination half-life (t1/2 ʎz), area under the concentration vs. time curve (AUC), apparent volume of distribution at steady-state and total body clearance of DO were 34.81 h, 723.82 h µg/mL, 1.24 L/kg and 0.03 L/kg/h, respectively. The t1/2λz of the DO was found to be 37.39 and 39.78 h after IM, and OR administration, respectively. The bioavailability was calculated 57.02% and 32.29%, respectively, after IM and OR administration. The MIC90 of DO against A. hydrophila and A. sobria was 4 µg/mL. The PK/PD integration showed that DO (20 mg/kg dose) for A. hydrophila and A. sobria with MIC90 ≤4 µg/mL achieved target AUC/MIC value after IM administration.

CONCLUSIONS

These results suggest that when rainbow trout was treated with 20 mg/kg IV and IM administered DO, therapeutically effective concentrations were reached in the control of infections caused by A. hydrophila and A. sobria.

Revisiting the Checkerboard to Inform Development of β-Lactam/β-Lactamase Inhibitor Combinations

A two-dimensional "checkerboard" array employing systematic titration (e.g., serial two-fold dilutions) is a well-established in vitro method for exploring the antibacterial effects of novel drug combinations. Minimum inhibitory concentrations (MICs) on the checkerboard are isoeffective points at which the antibiotic potency is the same. Representations of checkerboard MIC curves for a β-lactam and β-lactamase inhibitor combination are used in hypothetical "thought experiments" and reveal the ways in which current practices can be improved. Because different types of response (i.e., independence vs. additivity vs. one effective agent; interaction vs. noninteraction) produce different MIC curves, data from different strains/isolates should not be pooled indiscriminately, as the composition of a pooled dataset will influence any derived pharmacokinetic/pharmacodynamic (PK/PD) index. Because the β-lactamase inhibitor threshold concentration (CT) parameter is a function of the β-lactam partner dosing regimen, it is not possible to derive a universal PK/PD index target based on CT. Alternative susceptibility testing methods represent different planes through the checkerboard; a fixed ratio method is less prone to bias for all β-lactam and β-lactamase inhibitor combinations. Susceptibility test MICs will often not reflect the sensitivity of the strain/isolate to the β-lactamase inhibitor, so the use of these MICs to normalize PK/PD indices is inappropriate.

Antimicrobial Resistance Genes in Respiratory Bacteria from Weaned Dairy Heifers

Bovine respiratory disease (BRD) is the leading cause of mortality and antimicrobial drug (AMD) use in weaned dairy heifers. Limited information is available regarding antimicrobial resistance (AMR) in respiratory bacteria in this population. This study determined AMR gene presence in 326 respiratory isolates (Pasteurella multocida, Mannheimia haemolytica, and Histophilus somni) from weaned dairy heifers using whole genome sequencing. Concordance between AMR genotype and phenotype was determined. Twenty-six AMR genes for 8 broad classes of AMD were identified. The most prevalent, medically important AMD classes used in calf rearing, to which these genes predict AMR among study isolates were tetracycline (95%), aminoglycoside (94%), sulfonamide (94%), beta-lactam (77%), phenicol (50%), and macrolide (44%). The co-occurrence of AMR genes within an isolate was common; the largest cluster of gene co-occurrence encodes AMR to phenicol, macrolide, elfamycin, β-lactam (cephalosporin, penam cephamycin), aminoglycoside, tetracycline, and sulfonamide class AMD. Concordance between genotype and phenotype varied (Matthew's Correlation Coefficient ranged from -0.57 to 1) by bacterial species, gene, and AMD tested, and was particularly poor for fluoroquinolones (no AMR genes detected) and ceftiofur (no phenotypic AMR classified while AMR genes present). These findings suggest a high genetic potential for AMR in weaned dairy heifers; preventing BRD and decreasing AMD reliance may be important in this population.

Oral linezolid compared with benzathine penicillin G for treatment of early syphilis in adults (Trep-AB Study) in Spain: a prospective, open-label, non-inferiority, randomised controlled trial

BACKGROUND

Management of syphilis, a sexually transmitted infection (STI) with increasing incidence, is challenged by drug shortages, scarcity of randomised trial data, an absence of non-penicillin alternatives for pregnant women with penicillin allergy (other than desensitisation), extended parenteral administration for neurosyphilis and congenital syphilis, and macrolide resistance. Linezolid was shown to be active against Treponema pallidum, the causative agent of syphilis, in vitro and in the rabbit model. We aimed to assess the efficacy of linezolid for treating early syphilis in adults compared with the standard of care benzathine penicillin G (BPG).

METHODS

We did a multicentre, open-label, non-inferiority, randomised controlled trial to assess the efficacy of linezolid for treating early syphilis compared with BPG. We recruited participants with serological or molecular confirmation of syphilis (either primary, secondary, or early latent) at one STI unit in a public hospital and two STI community clinics in Catalonia (Spain). Participants were randomly allocated in a 1:1 ratio using a computer-generated block randomisation list with six participants per block, to receive either oral linezolid (600 mg once per day for 5 days) or intramuscular BPG (single dose of 2·4 million international units) and were assessed for signs and symptoms (once per week until week 6 and at week 12, week 24, and week 48) and reagin titres of non-treponemal antibodies (week 12, week 24, and week 48). The primary endpoint was treatment response, assessed using a composite endpoint that included clinical response, serological response, and absence of relapse. Clinical response was assessed at 2 weeks for primary syphilis and at 6 weeks for secondary syphilis following treatment initiation. Serological cure was defined as a four-fold decline in rapid plasma reagin titre or seroreversion at any of the 12-week, 24-week, or 48-week timepoints. The absence of relapse was defined as the presence of different molecular sequence types of T pallidum in recurrent syphilis. Non-inferiority was shown if the lower limit of the two-sided 95% CI for the difference in rates of treatment response was higher than -10%. The primary analysis was done in the per-protocol population. The trial is registered at ClinicalTrials.gov (NCT05069974) and was stopped for futility after interim analysis.

FINDINGS

Between Oct 20, 2021, and Sept 15, 2022, 62 patients were assessed for eligibility, and 59 were randomly assigned to linezolid (n=29) or BPG (n=30). In the per-protocol population, after 48 weeks' follow-up, 19 (70%) of 27 participants (95% CI 49·8 to 86·2) in the linezolid group had responded to treatment and 28 (100%) of 28 participants (87·7 to 100·0) in the BPG group (treatment difference -29·6, 95% CI -50·5 to -8·8), which did not meet the non-inferiority criterion. The number of drug-related adverse events (all mild or moderate) was similar in both treatment groups (five [17%] of 29, 95% CI 5·8 to 35·8 in the linezolid group vs five [17%] of 30, 5·6 to 34·7, in the BPG group). No serious adverse events were reported during follow-up.

INTERPRETATION

The efficacy of linezolid at a daily dose of 600 mg for 5 days did not meet the non-inferiority criteria compared with BPG and, as a result, this treatment regimen should not be used to treat patients with early syphilis.

FUNDING

European Research Council and Fondo de Investigaciones Sanitarias.

Anatomical, pathological, and histological features of experimental respiratory infection of birds by biofilm-forming bacteria Staphylococcus aureus

Background and Aim

The pathogenesis of staphylococcal infections is mediated by virulence factors, such as enzymes, toxins, and biofilms, which increase the resistance of microorganisms to host immune system evasion. Testing and searching for standardized multi-level algorithms for the indication and differentiation of biofilms at the early stages of diagnosis will contribute to the development of preventive measures to control the critical points of technology and manage dangerous risk factors for the spread of infectious diseases. This research aimed to study the main stages of Staphylococcus aureus biofilm formation in in vitro experiments and to analyze the dynamics of respiratory syndrome development in chickens infected with these bacteria.

Materials and Methods

Experimental reproduction of the infectious process was performed using laboratory models: 10-day-old White Leghorn chickens (n = 20). Before the experiments, the birds were divided into two groups according to the principle of analogs: Group I (control, n = 10): the birds were intranasally inoculated with 0.5 cm3 of 0.9% NaCl solution; Group II (experiment, n = 10): the birds were intranasally inoculated with a suspension of S. aureus bacteria, 0.5 cm3, concentration 1 billion/cm3.

Results

Colonization of individual areas of the substrate under study in vitro occurred gradually from the sedimentation and adhesion of single motile planktonic cells to the attachment stage of microcolony development. Staining preparations with gentian violet due to the "metachromosia" property of this dye are a quick and fairly simple way to differentiate cells and the intercellular matrix of biofilms. Fixation with vapors of glutaraldehyde and osmium tetroxide preserves the natural architecture of biofilms under optical and scanning electron microscopy. Pure cultures of S. aureus microorganisms were isolated from the blood, lungs, small intestine, liver, kidneys, and spleen after 5-10 days during experimental infection of chickens. Clinical signs of respiratory syndrome developed within 5-6 days after infection. Acute and subacute serous-fibrinous airsacculitis, characterized by edema and thickening of the membranes of the air sacs and the presence of turbid, watery, foamy contents in the cavity, was the most characteristic pathomorphological sign. The signs of acute congestive hyperemia and one-sided serous-fibrinous pneumonia developed with significant thickening of fibrinous deposits. In Garder's gland, there was an increase in the number of secretory sections, indicating hypersecretion of the glands. In the lymphoid follicles of Meckel's diverticulum, leukocytes, usually lymphocytes, and pseudoeosinophils were detected.

Conclusions

Hydration and heteromorphism of the internal environment of biofilms determine the localization of differentiated cells in a three-dimensional matrix for protection against adverse factors. The most characteristic pathomorphological sign was the development of acute and subacute serous-fibrinous airsacculitis when reproducing the infectious process in susceptible models. There was a significant thickening of fibrinous deposits and signs of acute congestive hyperemia and one or two serous-fibrinous pneumonia developed.

Concurrent determination of anti-microbial and anti-inflammatory drugs in lachrymal fluid and tissue by LC-MS/MS: A potential treatment for microbial keratitis and its PK-PD evaluation

Unforeseen surfacing of microbial keratitis (MKT) over the years has led to a requisite for promising treatment strategy involving combination of antifungal and antibacterial agents. Subsequently, symptoms associated with MKT including inflammation and watery eyes require treatment with anti-inflammatory agents. Thus, a requirement of functional clinical treatment strategy involving combination of anti-inflammatory corticosteroids (Betamethasone) with antifungal polyene (Amphotericin B, AmB) and antibacterials macrolide (Azithromycin, AZT) and aminoglycoside (Neomycin, NEO). In the ensuing pursuit, a sensitive and fast simultaneous LC-MS/MS method of four drastically different analytes in rabbit tear fluid and cornea was developed and validated as per US-FDA guidelines. The gradient LC set-up was used with C18 column and flow rate of 0.55 mL/min along with short run time of 7 min. The calibration curves showed good linearity over the concentration range of 0.07-300 ng/mL, 1.00-400 ng/mL, 3.00-600 ng/mL and 8.00-900 ng/mL for AZT, AmB, NEO and BEM respectively. The bioanalytical method requires only 10 µL of ocular sample and analytes were extracted with fast protein precipitation with acidic methanol. Finally, the developed method was validated for selectivity, linearity (r2 > 0.99), precision, accuracy, matrix effects, and stability. PK-PD indices and dosing frequency was predicted using Phoenix WinNonlin Software, based on single dose ocular pharmacokinetics and MIC values of AmB, AZT and NEO. According to the PK-PD simulation, S. aureus and E. coli required 6 and 12 instillations of AZT per 24 h, respectively whereas 12 instillation of NEO requires per 24 h for S. aureus. The result suggests that to minimize antimicrobial resistance; drug, dose and dosing schedule depend upon the pathogen as well as the strain.

Pharmacokinetic/pharmacodynamic integration of amphenmulin: a novel pleuromutilin derivative against Mycoplasma gallisepticum

Amphenmulin is a novel pleuromutilin derivative with great anti-mycoplasma potential. The present study evaluated the action characteristics of amphenmulin against Mycoplasma gallisepticum using pharmacokinetic/pharmacodynamic (PK/PD) modeling approaches. Following intravenous administration, amphenmulin exhibited an elimination half-life of 2.13 h and an apparent volume of distribution of 3.64 L/kg in healthy broiler chickens, demonstrating PK profiles of extensive distribution and rapid elimination. The minimum inhibitory concentration (MIC) of amphenmulin against M. gallisepticum was determined to be 0.0039 µg/mL using the broth microdilution method, and the analysis of the static time-kill curves through the sigmoid Emax model showed a highly correlated relationship (R ≥ 0.9649) between the kill rate and drug concentrations (1-64 MIC). A one-compartment open model with first-order elimination was implemented to simulate the in vivo anti-mycoplasma effect of amphenmulin, and it was found that bactericidal levels were reached with continuous administration for 3 days at doses exceeding 0.8 µg/mL. Furthermore, the area under the concentration-time curve divided by MIC (AUC/MIC) correlated well with the anti-mycoplasma effect of amphenmulin within 24 h after each administration, with a target value of 904.05 h for predicting a reduction of M. gallisepticum by 1 Log10CFU/mL. These investigations broadened the antibacterial spectrum of amphenmulin and revealed its characteristics of action against M. gallisepticum, providing a theoretical basis for further clinical development.IMPORTANCEMycoplasma has long been recognized as a significant pathogen causing global livestock production losses and public health concerns, and the use of antimicrobial agents is currently one of the mainstream strategies for its prevention and control. Amphenmulin is a promising candidate pleuromutilin derivative that was designed, synthesized, and screened by our laboratory in previous studies. Moreover, this study further confirms the excellent antibacterial activity of amphenmulin against Mycoplasma gallisepticum and reveals its action characteristics and model targets on M. gallisepticum by establishing an in vitro pharmacokinetic/pharmacodynamic synchronization model. These findings can further broaden the pharmacological theoretical basis of amphenmulin and serve as data support for its clinical development, which is of great significance for the discovery of new antimicrobial drugs and the control of bacterial diseases in humans and animals.

Pharmacokinetic and Pharmacodynamic Considerations of Antibiotic Use in Neonates

The selection of an appropriate dose of a given antibiotic for a neonate not only requires knowledge of the drug's basic pharmacokinetic (PK) and pharmacodynamic (PD) properties but also the profound effects that organ development might have on the volume of distribution and clearance, both of which may affect the PK/PD of a drug. Interest has grown in alternative antibiotic dosing strategies that are better aligned with the antibiotic's PK and PD properties. These strategies should be used in conjunction with minimum inhibitory concentration measurements and therapeutic drug monitoring to measure their potential success. They can also guide the clinician in tailoring the delivery of antibiotics to suit an individual patient's needs. Model-informed precision dosing, such as Bayesian forecasting dosing software (which incorporates PK/PD population models), may be utilized to optimize antibiotic exposure in neonatal populations. Consequently, optimizing the antibiotic dose and exposure in each newborn requires expertise in different fields. It drives the collaboration of physicians together with lab technicians and quantitative clinical pharmacologists.

Effective Antimicrobial Prophylaxis in Surgery: The Relevance and Role of Pharmacokinetics-Pharmacodynamics

Appropriate surgical antimicrobial prophylaxis (SAP) is an important measure in preventing surgical site infections (SSIs). Although antimicrobial pharmacokinetics-pharmacodynamics (PKPD) is integral to optimizing antibiotic dosing for the treatment of infections, there is less research on preventing infections postsurgery. Whereas clinical studies of SAP dose, preincision timing, and redosing are informative, it is difficult to isolate their effect on SSI outcomes. Antimicrobial PKPD aims to explain the complex relationship between antibiotic exposure during surgery and the subsequent development of SSI. It accounts for the many factors that influence the PKs and antibiotic concentrations in patients and considers the susceptibilities of bacteria most likely to contaminate the surgical site. This narrative review examines the relevance and role of PKPD in providing effective SAP. The dose-response relationship i.e., association between lower dose and SSI in cefazolin prophylaxis is discussed. A comprehensive review of the evidence for an antibiotic concentration-response (SSI) relationship in SAP is also presented. Finally, PKPD considerations for improving SAP are explored with a focus on cefazolin prophylaxis in adults and outstanding questions regarding its dose, preincision timing, and redosing during surgery.

Optimizing tylosin dosage for co-infection of Actinobacillus pleuropneumoniae and Pasteurella multocida in pigs using pharmacokinetic/pharmacodynamic modeling

Formulating a therapeutic strategy that can effectively combat concurrent infections of Actinobacillus pleuropneumoniae (A. pleuropneumoniae) and Pasteurella multocida (P. multocida) can be challenging. This study aimed to 1) establish minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), time kill curve, and post-antibiotic effect (PAE) of tylosin against A. pleuropneumoniae and P. multocida pig isolates and employ the MIC data for the development of epidemiological cutoff (ECOFF) values; 2) estimate the pharmacokinetics (PKs) of tylosin following its intramuscular (IM) administration (20 mg/kg) in healthy and infected pigs; and 3) establish a PK-pharmacodynamic (PD) integrated model and predict optimal dosing regimens and PK/PD cutoff values for tylosin in healthy and infected pigs. The MIC of tylosin against both 89 and 363 isolates of A. pleuropneumoniae and P. multocida strains spread widely, ranging from 1 to 256 μg/mL and from 0.5 to 128 μg/mL, respectively. According to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) ECOFFinder analysis ECOFF value (≤64 µg/mL), 97.75% (87 strains) of the A. pleuropnumoniae isolates were wild-type, whereas with the same ECOFF value (≤64 µg/mL), 99.72% (363 strains) of the P. multicoda isolates were considered wild-type to tylosin. Area under the concentration time curve (AUC), T1/2, and Cmax values were significantly greater in healthy pigs than those in infected pigs (13.33 h × μg/mL, 1.99 h, and 5.79 μg/mL vs. 10.46 h × μg/mL, 1.83 h, and 3.59 μg/mL, respectively) (p < 0.05). In healthy pigs, AUC24 h/MIC values for the bacteriostatic activity were 0.98 and 1.10 h; for the bactericidal activity, AUC24 h/MIC values were 1.97 and 1.99 h for A. pleuropneumoniae and P. multocida, respectively. In infected pigs, AUC24 h/MIC values for the bacteriostatic activity were 1.03 and 1.12 h; for bactericidal activity, AUC24 h/MIC values were 2.54 and 2.36 h for A. pleuropneumoniae and P. multocida, respectively. Monte Carlo simulation lead to a 2 μg/mL calculated PK/PD cutoff. Managing co-infections can present challenges, as it often demands the administration of multiple antibiotics to address diverse pathogens. However, using tylosin, which effectively targets both A. pleuropneumoniae and P. multocida in pigs, may enhance the control of bacterial burden. By employing an optimized dosage of 11.94-15.37 mg/kg and 25.17-27.79 mg/kg of tylosin can result in achieving bacteriostatic and bactericidal effects in 90% of co-infected pigs.

Impact of Disease States on the Oral Pharmacokinetics of EIDD-1931 (an Active Form of Molnupiravir) in Rats for Implication in the Dose Adjustment

The pharmacokinetic alteration of an antimicrobial medication leading to sub-therapeutic plasma level can aid in the emergence of resistance, a global threat nowadays. In this context, molnupiravir (prodrug of EIDD-1931) is the most efficacious orally against corona virus disease (COVID-19). In addition to drug-drug interaction, the pharmacokinetics of a drug can significantly vary during any disease state, leading to disease-drug interaction. However, no information is available for such a recently approved drug. Therefore, we aimed to explore the oral pharmacokinetics of EIDD-1931 in seven chemically induced disease states individually compared to the normal state using various rat models. Induction of any disease situation was confirmed by the disease specific study(s) prior to pharmacokinetic investigations. Compared to the normal state, substantially lowered plasma exposure (0.47- and 0.63-fold) with notably enhanced clearance (2.00- and 1.56-fold) of EIDD-1931 was observed in rats of ethanol-induced gastric injury and carbon tetrachloride-induced liver injury states. Conversely, paclitaxel-induced neuropathic pain and cisplatin-induced kidney injury states exhibited opposite outcomes on oral exposure (1.43- and 1.50-fold) and clearance (0.69- and 0.65-fold) of EIDD-1931. Although the highest plasma concentration (2.26-fold) markedly augmented in the doxorubicin-induced cardiac injury state, streptozocin-induced diabetes and lipopolysaccharide-induced lung injury state did not substantially influence the pharmacokinetics of EIDD-1931. Exploring the possible phenomenon behind the reduced or boosted plasma exposure of EIDD-1931, results suggest the need for dose adjustment in respective diseased conditions in order to achieve desired efficacy during oral therapy of EIDD-1931.

Oral pharmacokinetics of a pharmaceutical preparation of florfenicol in broiler chickens

Introduction

The use of florfenicol must follow particular pharmacokinetic/pharmacodynamic (PK/PD) ratios, i.e., it requires achieving serum concentrations at or slightly above the pathogen's minimum inhibitory concentration (MIC) during the dosing interval and that the ratio of area under the concentration vs. time curve (AUC)/MIC should be as high as possible (still undetermined for poultry). As an alternative to the standard soluble florfenicol that is administered to the flock through drinking water, florfenicol premix is often recommended as feed medication in Latin America. However, no particular pharmaceutical design has been proposed.

Methods

This study compared the PK of two preparations of florfenicol in broiler chickens and pondered the possibility of each covering the referred PK-PD ratios as predictors of clinical efficacy. The preparations comprise a pharmaceutical form as FOLA pellets (F = bioavailability; O = optimum; and LA = long-acting) and the premix formulation. The former are small colored pellets with vehicles and absorption enhancers of florfenicol designed for long action, and the latter is the reference premix of the antibiotic. First, these two pharmaceutical forms of florfenicol were administered as oral boluses (30 mg/kg), aided by a probe. In a second trial of the dosing form, both pharmaceutical preparations of florfenicol were administered in feed and ad libitum (110 ppm; ~30 mg/kg).

Results

In both cases, FOLA-florfenicol presented much higher relative bioavailability (3.27 times higher) and mean better residence time than florfenicol premix (two times high when forced as bolus dose). Consequently, FOLA-florfenicol possesses better PK/PD ratios than less sensitive pathogens, i.e., E. coli. It is proposed that if a metaphylactic treatment of a bacterial outbreak in poultry is implemented with florfenicol prepared as FOLA, better PK/PD ratios will be obtained than those of standard florfenicol premix.

Discussion

Clinicians must confirm that feed consumption in the flock has not been affected by the particular disease if FOLA pellets of florfenicol are used.

Pharmacokinetic-pharmacodynamic (PK/PD) modeling to study the hepatoprotective effect of Perilla Folium on the acute hepatic injury rats

ETHNOPHARMACOLOGICAL RELEVANCE

Perilla Folium (PF), is a traditional medicinal material with the homology of medicine and food in China and has been widely used due to its rich nutritional content and medicinal value. The hepatoprotective effects of PF extract include their protection against acute hepatic injury, tert-butylhydroperoxide (t-BHP) induced oxidative damage, and Lipopolysaccharide (LPS) and D-galactosamine (D-GalN) induced hepatic injury have been well studied. However, there are few reports on the pharmacokinetics studies of PF extract in acute hepatic injury model rats, and the anti-hepatic injury activity of PF is still unclear.

AIM OF THE STUDY

The differences in the plasma pharmacokinetic of 21 active compounds between the normal and model groups were compared， and established pharmacokinetics/pharmacodynamics (PK/PD) modeling was to analyze the hepatoprotective effects of PF.

MATERIALS AND METHODS

The acute hepatic injury model was induced with an intraperitoneal injection of lipopolysaccharide (LPS) and D-galactosamine (D-GalN), and the plasma pharmacokinetics of 21 active compounds of PF were analyzed in the normal and model groups using ultra-high performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS). The correlation between plasma components and hepatoprotective effects indicators (the alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactic dehydrogenase (LDH)) in the model group was also investigated and established a Pharmacokinetic/pharmacodynamic (PK/PD) correlation analysis of the hepatoprotective effects of PF.

RESULTS

The results revealed that organic acid compounds possessed the characteristics of faster absorption, shorter peak time and slower metabolism, while the flavonoid compounds had slower absorption and longer peak time, and the pharmacokinetics of various components were significantly affected after modeling. The results of PK/PD modeling analysis demonstrated that the plasma drug concentration of each component existed a good correlation with the three AST, ALT, and LDH, and the lag time of the efficacy of each component is relatively long.

CONCLUSIONS

The plasma drug concentration of each component existed a good correlation with the three AST, ALT, and LDH, and the lag time of the efficacy of each component is relatively long in vivo.

Advanced delivery systems for peptide antibiotics

Antimicrobial peptides (AMPs) hold promise as alternatives to traditional antibiotics for preventing and treating multidrug-resistant infections. Although they have potent antimicrobial efficacy, AMPs are mainly limited by their susceptibility to proteases and potential off-site cytotoxicity. Designing the right delivery system for peptides can help to overcome such limitations, thus improving the pharmacokinetic and pharmacodynamic profiles of these drugs. The versatility of peptides and their genetically encodable structure make them suitable for both conventional and nucleoside-based formulations. In this review, we describe the main drug delivery procedures developed so far for peptide antibiotics: lipid nanoparticles, polymeric nanoparticles, hydrogels, functionalized surfaces, and DNA- and RNA-based delivery systems.

ADME, Pharmacokinetic Scaling, Pharmacodynamic and Prediction of Human Dose and Regimen of Novel Antiviral Drugs

The search for new drugs is an extremely time-consuming and expensive endeavour. Much of that time and money go into generating predictive human pharmacokinetic profiles from preclinical efficacy and safety animal data. These pharmacokinetic profiles are used to prioritize or minimize the attrition at later stages of the drug discovery process. In the area of antiviral drug research, these pharmacokinetic profiles are equally important for the optimization, estimation of half-life, determination of effective dose, and dosing regimen, in humans. In this article we have highlighted three important aspects of these profiles. First, the impact of plasma protein binding on two primary pharmacokinetic parameters-volume of distribution and clearance. Second, interdependence of primary parameters on unbound fraction of the drug. Third, the ability to extrapolate human pharmacokinetic parameters and concentration time profiles from animal profiles.

Pharmacokinetic/Pharmacodynamic Analysis of Oral Calcium Fosfomycin: Are Urine Levels Sufficient to Ensure Efficacy for Urinary Tract Infections?

Urinary tract infections (UTIs) are extremely common and a major driver for the use of antimicrobials. Calcium fosfomycin is an old antibiotic indicated for the treatment of UTIs; however, data about its urine pharmacokinetic profile are scarce. In this work, we have evaluated the pharmacokinetics of fosfomycin from urine concentrations after oral administration of calcium fosfomycin to healthy women. Moreover, we have assessed, by pharmacokinetic/pharmacodynamic (PK/PD) analysis and Monte Carlo simulations, its effectiveness considering the susceptibility profile of Escherichia coli, the main pathogen involved in UTIs. The accumulated fraction of fosfomycin excreted in urine was around 18%, consistent with its low oral bioavailability and its almost exclusively renal clearance by glomerular filtration as unchanged drug. PK/PD breakpoints resulted to be 8, 16, and 32 mg/L for a single dose of 500 mg, a single dose of 1000 mg, and 1000 mg q8h for 3 days, respectively. For empiric treatment, the estimated probability of treatment success was very high (>95%) with the three dose regimens, considering the susceptibility profile of E. coli reported by EUCAST. Our results show that oral calcium fosfomycin at a dose level of 1000 mg every 8 h provides urine concentrations sufficient to ensure efficacy for the treatment of UTIs in women.

Safety and Tolerability of Antimicrobial Agents in the Older Patient

Older patients are at high risk of infections, which often present atypically and are associated with high morbidity and mortality. Antimicrobial treatment in older individuals with infectious diseases represents a clinical challenge, causing an increasing burden on worldwide healthcare systems; immunosenescence and the coexistence of multiple comorbidities determine complex polypharmacy regimens with an increase in drug-drug interactions and spread of multidrug-resistance infections. Aging-induced pharmacokinetic and pharmacodynamic changes can additionally increase the risk of inappropriate drug dosing, with underexposure that is associated with antimicrobial resistance and overexposure that may lead to adverse effects and poor adherence because of low tolerability. These issues need to be considered when starting antimicrobial prescriptions. National and international efforts have been made towards the implementation of antimicrobial stewardship (AMS) interventions to help clinicians improve the appropriateness and safety of antimicrobial prescriptions in both acute and long-term care settings. AMS programs were shown to decrease consumption of antimicrobials and to improve safety in hospitalized patients and older nursing home residents. With the abundance of antimicrobial prescriptions and the recent emergence of multidrug resistant pathogens, an in-depth review of antimicrobial prescriptions in geriatric clinical practice is needed. This review will discuss the special considerations for older individuals needing antimicrobials, including risk factors that shape risk profiles in geriatric populations as well as an evidence-based description of antimicrobial-induced adverse events in this patient population. It will highlight agents of concern for this age group and discuss interventions to mitigate the effects of inappropriate antimicrobial prescribing.

Optimization of Therapy and the Risk of Probiotic Use during Antibiotherapy in Septic Critically Ill Patients: A Narrative Review

Optimizing the entire therapeutic regimen in septic critically ill patients should be based not only on improving antibiotic use but also on optimizing the entire therapeutic regimen by considering possible drug–drug or drug–nutrient interactions. The aim of this narrative review is to provide a comprehensive overview on recent advances to optimize the therapeutic regimen in septic critically ill patients based on a pharmacokinetics and pharmacodynamic approach. Studies on recent advances on TDM-guided drug therapy optimization based on PK and/or PD results were included. Studies on patients <18 years old or with classical TDM-guided therapy were excluded. New approaches in TDM-guided therapy in septic critically ill patients based on PK and/or PD parameters are presented for cefiderocol, carbapenems, combinations beta-lactams/beta-lactamase inhibitors (piperacillin/tazobactam, ceftolozane/tazobactam, ceftazidime/avibactam), plazomicin, oxazolidinones and polymyxins. Increased midazolam toxicity in combination with fluconazole, nephrotoxic synergism between furosemide and aminoglycosides, life-threatening hypoglycemia after fluoroquinolone and insulin, prolonged muscle weakness and/or paralysis after neuromuscular blocking agents and high-dose corticosteroids combinations are of interest in critically ill patients. In the real-world practice, the use of probiotics with antibiotics is common; even data about the risk and benefits of probiotics are currently spares and inconclusive. According to current legislation, probiotic use does not require safety monitoring, but there are reports of endocarditis, meningitis, peritonitis, or pneumonia associated with probiotics in critically ill patients. In addition, probiotics are associated with risk of the spread of antimicrobial resistance. The TDM-guided method ensures a true optimization of antibiotic therapy, and particular efforts should be applied globally. In addition, multidrug and drug–nutrient interactions in critically ill patients may increase the likelihood of adverse events and risk of death; therefore, the PK and PD particularities of the critically ill patient require a multidisciplinary approach in which knowledge of clinical pharmacology is essential.

Population pharmacokinetics of levornidazole in healthy subjects and patients, and sequential dosing regimen proposal using pharmacokinetic/pharmacodynamic analysis

Although sequential treatment with levornidazole has been used for anaerobic infection in clinical practice, there is no evidence-based dosing regimen. This study aimed to evaluate the pharmacokinetics (PK) of levornidazole in healthy subjects and patients, and to propose an evidence-based sequential dosing regimen by pharmacokinetic/pharmacodynamic (PK/PD) analysis. A population PK model was built using the data of 116 Chinese subjects, including 88 healthy young subjects, 12 healthy elderly subjects, and 16 patients with intra-abdominal anaerobic infection. PK/PD analysis was performed combining the minimum inhibitory concentration (MIC) values of levornidazole against 375 anaerobic strains. Four sequential dosing regimens (500 mg q12h, 1000 mg loading dose followed by 500 mg q12h, 750 mg q24h, and 1000 mg q24h) were evaluated in terms of cumulative fraction of response (CFR) and probability of target attainment (PTA) by Monte Carlo simulation. The concentration data of levornidazole and its active metabolites were described adequately by two- and one-compartment models, respectively. Body weight was identified as a significant covariate of levornidazole clearance. Simulations showed that satisfactory PTA (>90%) was achieved for the four dosing regimens when MIC ≤1 mg/L. Considering the simulation results, patients' safety and compliance, levornidazole 750 mg intravenous infusion q24h for 2 days followed by 750 mg oral dose q24h for 5 days was optimal for Bacteroides spp. with an identified MIC ≤1 mg/L.

A rapid, simple, high-performance liquid chromatography method for the clinical measurement of beta-lactam antibiotics in serum and interstitial fluid

Background: enhanced methods of therapeutic drug monitoring are required to support the individualisation of antibiotic dosing based on pharmacokinetics (PK) parameters. PK studies can be hampered by limited total serum volume, especially in neonates, or by sensitivity in the case of critically ill patients. We aimed to develop a liquid chromatography-mass spectrometry (LC/MS) analysis of benzylpenicillin, phenoxymethylpenicillin and amoxicillin in single low volumes of human serum and interstitial fluid (ISF) samples, with an improved limit of detection (LOD) and limit of quantification (LOQ), compared with previously published assays. Methods: sample clean-up was performed by protein precipitation using acetonitrile. Reverse phase chromatography was performed using triple quadrupole LC/MS. The mobile phase consisted of 55% methanol in water + 0.1% formic acid, with a flow rate of 0.4 mL min^-1. Antibiotics stability was assessed at different temperatures. Results: chromatographic separation was achieved within 3 minutes for all analytes. Three common penicillins can now be measured in a single low-volume blood and ISF sample (15 μL) for the first time. Validation has demonstrated the method to be linear over the range 0.0015-10 mg L^-1, with an accuracy of 93-104% and high sensitivity, with LOD ≈ 0.003 mg L^-1 and LOQ ≈ 0.01 mg L^-1 for all three analytes, which is critical for use in dose optimisation/individualisation. All evaluated penicillins indicated good stability at room temperature over 4 h, at (4 °C) over 24 h and at -80 °C for 6 months. Conclusion: the developed method is simple, rapid, accurate and clinically applicable for the quantification of three penicillin classes.

Investigations on In Vivo Pharmacokinetic/Pharmacodynamic Determinants of Fosfomycin in Murine Thigh and Kidney Infection Models

Background: Amidst the era of widespread resistance, there has been a renewed interest in older antibiotics such as fosfomycin, owing to its activity against certain resistant Gram-negative pathogens, including multidrug-resistant variants expressing extended spectrum β-lactamases or carbapenemases. The goal of the study was to investigate pharmacokinetic/pharmacodynamic (PK/PD) index and PK/PD targets of fosfomycin in murine thigh and kidney infection models, employing clinical isolates of Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae). Methods: Seven isolates of E. coli (one wild-type and six clinical isolates) and five isolates of K. pneumoniae (one wild-type and four clinical isolates) were utilized for in vivo PK/PD studies. Single-dose plasma PK studies were conducted in infected mice by subcutaneous route. PD index was determined from exposure-response analysis employing 24-hr dose fractionation studies in neutropenic murine thigh infection model, while pharmacodynamic targets (PDTs) were derived from both thigh and kidney infection models. Results: Dose fractionation studies demonstrated that in vivo efficacy of fosfomycin best correlated with AUC/MIC for E. coli (R² = 0.9227) and K. pneumoniae (R² = 0.8693). The median AUC/MIC linked to 1 log10 kill effects were 346.2 and 745.2 in thigh infection model and 244.1 and 425.4 in kidney infection model for E. coli and K. pneumoniae, respectively. The mice plasma protein binding of fosfomycin was estimated to be 5.4%. Conclusions: The in vivo efficacy of fosfomycin against Enterobacterales was best described by AUC/MIC. The PDTs derived from this study may help define the coverage potential of fosfomycin at the clinical doses approved.

Pharmacokinetics of Antimicrobials in Children with Emphasis on Challenges Faced by Low and Middle Income Countries, a Clinical Review

Effective antimicrobial exposure is essential to treat infections and prevent antimicrobial resistance, both being major public health problems in low and middle income countries (LMIC). Delivery of drug concentrations to the target site is governed by dose and pharmacokinetic processes (absorption, distribution, metabolism and excretion). However, specific data on the pharmacokinetics of antimicrobials in children living in LMIC settings are scarce. Additionally, there are significant logistical constraints to therapeutic drug monitoring that further emphasize the importance of understanding pharmacokinetics and dosing in LMIC. Both malnutrition and diarrheal disease reduce the extent of enteral absorption. Multiple antiretrovirals and antimycobacterial agents, commonly used by children in low resource settings, have potential interactions with other antimicrobials. Hypoalbuminemia, which may be the result of malnutrition, nephrotic syndrome or liver failure, increases the unbound concentrations of protein bound drugs that may therefore be eliminated faster. Kidney function develops rapidly during the first years of life and different inflammatory processes commonly augment renal clearance in febrile children, potentially resulting in subtherapeutic drug concentrations if doses are not adapted. Using a narrative review approach, we outline the effects of growth, maturation and comorbidities on maturational and disease specific effects on pharmacokinetics in children in LMIC.

Linezolid@MOF-74 as a host-guest system with antimicrobial activity

Linezolid (LNZ) is a new-generation synthetic molecule for the antibacterial treatment of severe infections, particularly in infective cases where the bacterial resistance to first-choice drugs is caused by Gram-positive pathogens. In this context, since 2009, some strains resistant to LNZ in patients with long-term treatments have been reported. Therefore, there is a need to use not only new drug molecules with antibacterial activities in the dosage form but also a different approach to pharmacotherapeutic strategies for skin infections, which lead to a reduction in the concentration of biocides. This work explores LNZ hosted at two isostructural MOFs, MOF-74(Zn) and MOF-74(Cu), as promising antimicrobial systems for gradual biocide release within 6 h. These systems reach a lower minimum inhibitory concentration (MIC) in comparison to free LNZ. Even a decreased MIC value is also observed, which is an encouraging result regarding the efficiency of the systems to control concentration-dependent antimicrobial resistance.

Optimizing Clinical Outcomes Through Rational Dosing Strategies: Roles of Pharmacokinetic/Pharmacodynamic Modeling Tools

Significant progress in previous decades has led to several methodologies developed to facilitate the design of optimal antimicrobial dosing. In this review, we highlight common pharmacokinetic/pharmacodynamic (PKPD) modeling techniques and their roles in guiding rational dosing regimen design. In the early drug development phases, dose fractionation studies identify the PKPD index most closely associated with bacterial killing. Once discerned, this index is linked to clinical efficacy end points, and classification and regression tree analysis can be used to define the PKPD target goal. Monte Carlo simulations integrate PKPD and microbiological data to identify dosing strategies with a high probability of achieving the established PKPD target. Results then determine dosing regimens to investigate and/or validate the findings of randomized controlled trials. Further improvements in PKPD modeling could lead to an era of precision dosing and personalized therapeutics.