Vancomycin Tissue Pharmacokinetics in Patients with Lower-Limb Infections via In Vivo Microdialysis

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

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

Predicting Antimicrobial Activity at the Target Site: Pharmacokinetic/Pharmacodynamic Indices versus Time-Kill Approaches

Antibiotic dosing strategies are generally based on systemic drug concentrations. However, drug concentrations at the infection site drive antimicrobial effect, and efficacy predictions and dosing strategies should be based on these concentrations. We set out to review different translational pharmacokinetic-pharmacodynamic (PK/PD) approaches from a target site perspective. The most common approach involves calculating the probability of attaining animal-derived PK/PD index targets, which link PK parameters to antimicrobial susceptibility measures. This approach is time efficient but ignores some aspects of the shape of the PK profile and inter-species differences in drug clearance and distribution, and provides no information on the PD time-course. Time–kill curves, in contrast, depict bacterial response over time. In vitro dynamic time–kill setups allow for the evaluation of bacterial response to clinical PK profiles, but are not representative of the infection site environment. The translational value of in vivo time–kill experiments, conversely, is limited from a PK perspective. Computational PK/PD models, especially when developed using both in vitro and in vivo data and coupled to target site PK models, can bridge translational gaps in both PK and PD. Ultimately, clinical PK and experimental and computational tools should be combined to tailor antibiotic treatment strategies to the site of infection.

Microdialysis sampling to monitor target-site vancomycin concentrations in septic infants: a feasible way to close the knowledge gap

This work is dedicated to the memory of Hartmut Derendorf (1953-2020), a pioneer of modern pharmacokinetics and valued mentor of this project.

OBJECTIVES

Septic infants/neonates need effective antibiotic exposure, but dosing recommendations are challenging as the pharmacokinetics in this age are highly variable. For vancomycin, which is used as a standard treatment, comprehensive pharmacokinetic knowledge especially at the infection site is lacking. Hence, an exploratory clinical study was conducted to assess the feasibility and safety of microdialysis sampling for vancomycin monitoring at the target site.

METHODS

Nine infants/neonates with therapeutic indications for vancomycin treatment were administered 15 mg/kg as 1-hour infusions every 8-24 hours. Microdialysis catheters were implanted in the subcutaneous interstitial space fluid of the lateral thigh. Samples were collected every 30 minutes over 24 hours, followed by retrodialysis for catheter calibration. Prior in vitro investigations have evaluated impact factors on relative recovery and retrodialysis.

RESULTS

In vitro investigations showed the applicability of microdialysis for vancomycin monitoring. Microdialysis sampling was well tolerated in all infants/neonates (23-255 days) without major bleeding or other adverse events. Pharmacokinetic profiles were obtained and showed plausible vancomycin concentration-time courses.

CONCLUSIONS

Microdialysis as a minimally invasive technique for continuous longer-term sampling is feasible and safe in infants/neonates. Interstitial space fluid profiles were plausible and showed substantial interpatient variation. Hence, a larger microdialysis trial is warranted to further characterise the pharmacokinetics and variability of vancomycin at the target site and ultimately improve vancomycin dosing in these vulnerable patients.

Clinical Pharmacokinetics and Pharmacodynamics of Telavancin Compared with the Other Glycopeptides

Telavancin was discovered by modifying the chemical structure of vancomycin and belongs to the group of lipoglycopeptides. It employs its antimicrobial potential through two distinct mechanisms of action: inhibition of bacterial cell wall synthesis and induction of bacterial membrane depolarization and permeabilization. In this article we review the clinically relevant pharmacokinetic and pharmacodynamic data of telavancin. For comparison, the pharmacokinetic and pharmacodynamic data of the other glycopeptides are presented. Although, in contrast to the newer lipoglycopeptides, telavancin demonstrates a relatively short half-life and rapid total clearance, its apparent volume of distribution (V_d) is almost identical to that of dalbavancin. The accumulation of telavancin after repeated dosing is only marginal, whereas the pharmacokinetic values of the other glycopeptides show much greater differences after administration of multiple doses. Despite its high plasma-protein binding of 90% and relatively low V_d of approximately 11 L, telavancin shows near complete equilibration of the free fraction in plasma with soft tissue. The ratio of the area under the plasma concentration-time curve from time zero to 24 h (AUC₂₄) of unbound plasma concentrations to the minimal inhibitory concentration (MIC) required to inhibit growth of 90% of organisms (MIC₉₀) of Staphylococcus aureus and S. epidermidis of telavancin are sufficiently high to achieve pharmacokinetic/pharmacodynamic targets indicative for optimal bacterial killing. Considering both the AUC₂₄/MIC ratios of telavancin and the near complete equilibration of the free fraction in plasma with soft tissue, telavancin is an appropriate antimicrobial agent to treat soft tissue infections caused by Gram-positive pathogens. Although the penetration of telavancin into epithelial lining fluid (ELF) requires further investigations, the AUC₂₄/MIC ratio for S. aureus indicates that bactericidal activity in the ELF could be expected.

Bone and Joint Tissue Penetration of the Staphylococcus-Selective Antibiotic Afabicin in Patients Undergoing Elective Hip Replacement Surgery

Afabicin (formerly Debio 1450, AFN-1720) is a prodrug of afabicin desphosphono (Debio 1452, AFN-1252), a novel antibiotic in development which targets the staphylococcal enoyl-acyl carrier protein reductase (FabI) and exhibits selective potent antibacterial activity against staphylococcal species, including methicillin-resistant Staphylococcus aureus. As part of clinical development in bone and joint infections, a distribution study in bone was performed in 17 patients who underwent elective hip replacement surgery.

Afabicin (formerly Debio 1450, AFN-1720) is a prodrug of afabicin desphosphono (Debio 1452, AFN-1252), a novel antibiotic in development which targets the staphylococcal enoyl-acyl carrier protein reductase (FabI) and exhibits selective potent antibacterial activity against staphylococcal species, including methicillin-resistant Staphylococcus aureus. As part of clinical development in bone and joint infections, a distribution study in bone was performed in 17 patients who underwent elective hip replacement surgery. Patients received 3 doses of 240 mg afabicin orally (every 12 h) at various time points before surgery. Afabicin desphosphono concentrations were measured by liquid chromatography-tandem mass spectrometry in plasma, cortical bone, cancellous bone, bone marrow, soft tissue, and synovial fluid collected during surgery at 2, 4, 6, or 12 h after the third afabicin dose. The study showed good penetration of afabicin desphosphono into bone tissues, with mean area under the curve ratios for cortical bone-, cancellous bone-, bone marrow-, soft tissue-, and synovial fluid-to-total plasma concentrations of 0.21, 0.40, 0.32, 0.35, and 0.61, respectively. When accounting for the free fraction in plasma (2%) and synovial fluid (9.4%), the mean ratio was 2.88, which is indicative of excellent penetration and which showed that the afabicin desphosphono concentration was beyond the MIC₉₀ of S. aureus over the complete dosing interval. These findings, along with preclinical efficacy data, clinical efficacy data for skin and soft tissue staphylococcal infection, the availability of both intravenous and oral formulations, and potential advantages over broad-spectrum antibiotics for the treatment of staphylococcal bone or joint infections, support the clinical development of afabicin for bone and joint infections. (This study has been registered at ClinicalTrials.gov under identifier NCT02726438.)

Monitoring drug pharmacokinetics and immunologic biomarkers in dermal interstitial fluid using a microneedle patch

Minimally invasive point-of-care diagnostic devices are of great interest for rapid detection of biomarkers in diverse settings. Although blood is the most common source of biomarkers, interstitial fluid (ISF) is an alternate body fluid that does not clot or contain red blood cells that often complicate analysis. However, ISF is difficult to collect. In this study, we assessed the utility of a microneedle patch to sample microliter volumes of ISF in a simple and minimally invasive manner. We demonstrated the use of ISF collected in this way for therapeutic drug monitoring by showing similar vancomycin pharmacokinetic profiles in ISF and serum from rats. We also measured polio-specific neutralizing antibodies and anti-polio IgG in ISF similar to serum in rats immunized with polio vaccine. These studies demonstrate the potential utility of ISF collected by microneedle patch in therapeutic drug monitoring and immunodiagnostic applications.

A Novel Method for the Determination of Vancomycin in Serum by High-Performance Liquid Chromatography-Tandem Mass Spectrometry and Its Application in Patients with Diabetic Foot Infections

A novel, precise, and accurate high-performance liquid chromatography-tandem mass spectrometry (Q-trap-MS) method was developed, optimized, and validated for determination of vancomycin in human serum using norvancomycin as an internal standard. Effect of different parameters on the analysis was evaluated. ZORBAX SB-C18 column (150 × 4.6 mm, 5 μm) using water (containing 0.1% formic acid, v/v)⁻acetonitrile (containing 0.1% formic acid, v/v) as a mobile phase was chosen. The calibration curve was linear over the concentration ranges of 1 to 2000 ng/mL for vancomycin. The limit of detection (LOD) and limit of quantification (LOQ) for vancomycin were 0.3 and 1.0 ng/mL. Recoveries were between 87.2 and 102.3%, which gave satisfactory precision. A total of 100 serum samples (from 50 patients with diabetic foot proven Gram-positive infection and 50 nondiabetic patients with pneumonia requiring hospitalization and antibiotic therapy) were analyzed by this method. The trough vancomycin concentrations of diabetic foot infection (DFI) patients and nondiabetic patients were 8.20 ± 2.83 μg/mL (range: 4.80⁻14.2 μg/mL) and 15.80 ± 5.43 μg/mL (range: 8.60⁻19.5 μg/mL), respectively. The method is sensitive, precise, and reproducible, it could be applied for routine laboratory analysis of vancomycin in serum samples.

Plasma and interstitial fluid population pharmacokinetics of vancomycin in critically ill patients with sepsis

Vancomycin is a commonly prescribed antibiotic in the intensive care unit. However, there are limited data describing its distribution into the interstitial fluid (ISF) of tissues. The aim of this study was to describe the plasma and tissue ISF population pharmacokinetics of vancomycin in critically ill patients with sepsis. Serial vancomycin blood and ISF samples were collected at pre-specified time intervals in critically ill patients with sepsis. ISF sampling occurred using a subcutaneously inserted microdialysis catheter. Bioanalysis was undertaken using a validated spectrometric assay method. Population pharmacokinetic analysis was performed using Pmetrics^®. Seven patients were recruited and pharmacokinetic data were available for six of them. The median (interquartile range) age, weight, Acute Physiology and Chronic Health Evaluation (APACHE) II score, Sequential Organ Failure Assessment (SOFA) score and measured creatinine clearance (CL_Cr) were 55 (44-67) years, 85 (81-102) kg, 20 (16-29), 5 (4-8) and 90 (83-98) mL/min, respectively. Vancomycin pharmacokinetics was best described by a three-compartment linear model. Measured CL_Cr (on vancomycin clearance) and weight (on volume of distribution of the central compartment) were the only patient covariates that improved the model fit. Coefficients of variation for the vancomycin rate constants into and out of the peripheral and tissue ISF compartments were also high, ranging from 47% to 134%. There is significant variability of vancomycin distribution into tissue ISF, which it was not possible to explain with patient characteristics.

Recovery rates of combination antibiotic therapy using in vitro microdialysis simulating in vivo conditions

Microdialysis is a technique used to measure the unbound antibiotic concentration in the interstitial spaces, the target site of action. In vitro recovery studies are essential to calibrating the microdialysis system for in vivo studies. The effect of a combination of antibiotics on recovery into microdialysate requires investigation. In vitro microdialysis recovery studies were conducted on a combination of vancomycin and tobramycin, in a simulated in vivo model. Comparison was made between recoveries for three different concentrations and three different perfusate flow rates. The overall relative recovery for vancomycin was lower than that of tobramycin. For tobramycin, a concentration of 20μg/mL and flow rate of 1.0μL/min had the best recovery. A concentration of 5.0μg/mL and flow rate of 1.0μL/min yielded maximal recovery for vancomycin. Large molecular size and higher protein binding resulted in lower relative recoveries for vancomycin. Perfusate flow rates and drug concentrations affected the relative recovery when a combination of vancomycin and tobramycin was tested. Low perfusate flow rates were associated with higher recovery rates. For combination antibiotic measurement which includes agents that are highly protein bound, in vitro studies performed prior to in vivo studies may ensure the reliable measurement of unbound concentrations.

Revolutionizing Therapeutic Drug Monitoring with the Use of Interstitial Fluid and Microneedles Technology

While therapeutic drug monitoring (TDM) that uses blood as the biological matrix is the traditional gold standard, this practice may be impossible, impractical, or unethical for some patient populations (e.g., elderly, pediatric, anemic) and those with fragile veins. In the context of finding an alternative biological matrix for TDM, this manuscript will provide a qualitative review on: (1) the principles of TDM; (2) alternative matrices for TDM; (3) current evidence supporting the use of interstitial fluid (ISF) for TDM in clinical models; (4) the use of microneedle technologies, which is potentially minimally invasive and pain-free, for the collection of ISF; and (5) future directions. The current state of knowledge on the use of ISF for TDM in humans is still limited. A thorough literature review indicates that only a few drug classes have been investigated (i.e., anti-infectives, anticonvulsants, and miscellaneous other agents). Studies have successfully demonstrated techniques for ISF extraction from the skin but have failed to demonstrate commercial feasibility of ISF extraction followed by analysis of its content outside the ISF-collecting microneedle device. In contrast, microneedle-integrated biosensors built to extract ISF and perform the biomolecule analysis on-device, with a key feature of not needing to transfer ISF to a separate instrument, have yielded promising results that need to be validated in pre-clinical and clinical studies. The most promising applications for microneedle-integrated biosensors is continuous monitoring of biomolecules from the skin's ISF. Conducting TDM using ISF is at the stage where its clinical utility should be investigated. Based on the advancements described in the current review, the immediate future direction for this area of research is to establish the suitability of using ISF for TDM in human models for drugs that have been found suitable in pre-clinical experiments.

Transitions of care in the management of acute bacterial skin and skin structure infections: a paradigm shift

Acute bacterial skin and skin structure infections (ABSSSI) have evolved over a relatively short period of time to become one of the most challenging medical problems encountered in clinical practice. Notably the high incidence of methicillin-resistant S. aureus (MRSA) across the continuum of care has coincided with increased outpatient failures and higher rates of hospital admissions for parental antibiotic therapy. Consequently the management of ABSSSI constitutes a tremendous burden to the healthcare system in terms of cost of care and consumption of institutional and clinical resources. This perspective piece discusses current and new approaches to the management of ABSSSI in a hospital setting and the need for a multifaceted approach. Treatment strategies for the management through the utilization of observation units (OU), Outpatient Parental Antibiotic Therapy (OPAT), and newly developed antibiotics for the use against skin infections caused by Gram-positive bacteria will be discussed in the context of ABSSSI.

In Vitro Pharmacodynamics of Vancomycin against Methicillin-Susceptible and -Resistant Staphylococcus aureus: Considering the Variability in Observed Tissue Exposure

Vancomycin is considered a first-line antibiotic for complicated skin and skin structure infections (cSSSI) because of the risk of methicillin-resistant Staphylococcus aureus (MRSA). The vancomycin exposure of tissue can vary widely in patients with cSSSI, yet most models test only the average exposure. The in vitro pharmacodynamic model was used to simulate three tissue exposure levels attained by administering vancomycin at 1 g every 12 h (q12h), based on the median (50th), 25th, and 10th percentile tissue area under the concentration-time curve (AUC) values observed during an in vivo microdialysis study of diabetic patients. Four clinical isolates (two of MRSA [vancomycin MIC, 1 and 2 μg/ml] and two of methicillin-susceptible S. aureus [MSSA] [MIC, 1 and 2 μg/ml]) were evaluated. Experiments were performed over 72 h in duplicate. Time-kill curves were constructed, and the area under the bacterial killing and regrowth curve (AUBC) during the final 24-h dosing interval (48 to 72 h) (AUBC48-72) was calculated. Reductions in the 72-h number of CFU/ml and AUBC48-72 at the different exposure levels were compared. Target tissue vancomycin exposure levels for the 50th (AUC0-12, 102.0 ± 9.1 μg · h/ml), 25th (AUC0-12, 44.3 ± 1.8 μg · h/ml), and 10th (AUC0-12, 25.3 ± 3.1 μg · h/ml) percentiles were obtained in all studies. No differences in the 72-h number of CFU or AUBC were observed between exposure levels when all of the isolates were analyzed together. However, for the two MRSA isolates, the 10th percentile exposure level achieved a lower 72-h number of CFU/ml (-1.4 ± 0.4 log10 CFU/ml, P = 0.007) and a greater AUBC48-72 (97.1 ± 20.0 log10 CFU · h/ml, P = 0.011) than the higher exposure levels. The majority of the tissue exposure levels achieved with a vancomycin dosing regimen of 1 g q12h resulted in substantial killing of MSSA and MRSA; however, the lowest exposure levels observed in a minority of the population may explain the poor vancomycin response.

Antibiotic Tissue Penetration in Diabetic Foot Infections A Review of the Microdialysis Literature and Needs for Future Research

Although many antimicrobial agents display good in vitro activity against the pathogens frequently implicated in diabetic foot infections, effective treatment can be complicated by reduced tissue penetration in this population secondary to peripheral arterial disease and emerging antimicrobial resistance, which can result in clinical failure. Improved characterization of antibiotic tissue pharmacokinetics and penetration ratios in diabetic foot infections is needed. Microdialysis offers advantages over the skin blister and tissue homogenate studies historically used to define antibiotic penetration in skin and soft-tissue infections by defining antibiotic penetration into the interstitial fluid over the entire concentration versus time profile. However, only a select number of agents currently recommended for treating diabetic foot infections have been evaluated using these methods, which are described herein. Better characterization of the tissue penetration of antibiotic agents is needed for the development of methods for maximizing the pharmacodynamic profile of these agents to ultimately improve treatment outcomes for patients with diabetic foot infections.