Drug combinations and impact of experimental conditions on relative recovery in in vitro microdialysis investigations

Microdialysis as a safe and feasible method to study target-site piperacillin-tazobactam disposition in septic piglets and children

OBJECTIVES

Knowledge on the tissue penetration of piperacillin-tazobactam in children with sepsis is lacking. In this study, the feasibility and performance of microdialysis experiments were explored in septic piglets and children as part of a translational research project.

METHODS

Multiple-day microdialysis investigations were performed in muscle tissue of 22 piglets (of which 11 were septic) and 6 children with sepsis. An in vitro experiment preceded the (pre)clinical trials to derive optimal experimental settings and calibration technique. Linear mixed-effects models quantified the impact of sepsis on relative recovery (RR) and intercatheter, interindividual, interoccasion, and residual variability.

RESULTS

In vivo microdialysis was well tolerated in piglets and children, with no significant adverse events reported. Using identical experimental settings, lower RR values were recorded in healthy and septic piglets (range: piperacillin, 17.2-29.1% and tazobactam, 23.5-29.1%) compared with the in vitro experiment (piperacillin, 43.3% and tazobactam, 55.3%), and there were unacceptably low values in children with sepsis (<10%). As a result, methodological changes were made in the pediatric trial. Realistic tissue concentration-time curves were derived in piglets and children. In piglets, sepsis reduced the RR. The greatest contributors to RR variability were residual (>40%) and interoccasion (>30%) variability. The internal standard method was the preferred calibration technique in both piglets and children.

CONCLUSIONS

Microdialysis is a safe and applicable method for the measurement of tissue drug concentrations in piglets and children. This study demonstrated the impact of experimental settings, sepsis, and target population on individual RR.

Baicalin-berberine complex nanocrystals orally promote the co-absorption of two components

Baicalin (BA)-berberine (BBR) have been proposed as the couple in the prevention and treatment of numerous diseases due to their multiple functional attributes. However, with regard to certain factors involving unsatisfactory aqueous solubility and low bioavailability associated with its clinical application, there is need for continuous researches by scientist. In this study, after successfully preparing BA-BBR complex, BA-BBR complex nanocrystals were obtained through high-pressure homogenization and evaluated (in vitro and in vivo). The particle size, distribution, morphology, and crystalline properties for the optimal BA-BBR complex nanocrystals were characterized by the use of scanning electron microscope, dynamic light scattering, powder X-ray diffraction, and differential scanning calorimetry. The particle size and poly-dispersity index of BA-BBR complex nanocrystals were 318.40 ± 3.32 nm and 0.26 ± 0.03, respectively. In addition, evaluation of the in vitro dissolution extent indicated that BA and BBR in BA-BBR complex nanocrystals were 3.30- and 2.35-fold than BA-BBR complex. Subsequently, single-pass intestinal perfusion combined with microdialysis test and oral pharmacokinetics in SD rats was employed to evaluate the in vivo absorption improvement of BA-BBR complex nanocrystals. The pharmacokinetics results exhibited that the area under curve of BA and BBR in the BA-BBR complex nanocrystals group were 622.65 ± 456.95 h·ng/ml and 167.28 ± 78.87 h·ng/ml, respectively, which were separately 7.49- and 2.64-fold than the complex coarse suspension. In conclusion, the above results indicate that the developed and optimized BA-BBR complex nanocrystals could improve the dissolution rate and extent and oral bioavailability, as well as facilitate the co-absorption of the drug prescriptions BA and BBR.

Microdialysis of Drug and Drug Metabolite: a Comprehensive In Vitro Analysis for Voriconazole and Voriconazole N-oxide

Purpose

Voriconazole is a therapeutically challenging antifungal drug associated with high interindividual pharmacokinetic variability. As a prerequisite to performing clinical trials using the minimally-invasive sampling technique microdialysis, a comprehensive in vitro microdialysis characterization of voriconazole (VRC) and its potentially toxic N-oxide metabolite (NO) was performed.

Methods

The feasibility of simultaneous microdialysis of VRC and NO was explored in vitro by investigating the relative recovery (RR) of both compounds in the absence and presence of the other. The dependency of RR on compound combination, concentration, microdialysis catheter and study day was evaluated and quantified by linear mixed-effects modeling.

Results

Median RR of VRC and NO during individual microdialysis were high (87.6% and 91.1%). During simultaneous microdialysis of VRC and NO, median RR did not change (87.9% and 91.1%). The linear mixed-effects model confirmed the absence of significant differences between RR of VRC and NO during individual and simultaneous microdialysis as well as between the two compounds (p > 0.05). No concentration dependency of RR was found (p = 0.284). The study day was the main source of variability (46.3%) while the microdialysis catheter only had a minor effect (4.33%). VRC retrodialysis proved feasible as catheter calibration for both compounds.

Conclusion

These in vitro microdialysis results encourage the application of microdialysis in clinical trials to assess target-site concentrations of VRC and NO. This can support the generation of a coherent understanding of VRC pharmacokinetics and its sources of variability. Ultimately, a better understanding of human VRC pharmacokinetics might contribute to the development of personalized dosing strategies.

Comparative Plasma and Interstitial Tissue Fluid Pharmacokinetics of Meropenem Demonstrate the Need for Increasing Dose and Infusion Duration in Obese and Non-obese Patients

BACKGROUND AND OBJECTIVES

A quantitative evaluation of the PK of meropenem, a broad-spectrum β-lactam antibiotic, in plasma and interstitial space fluid (ISF) of subcutaneous adipose tissue of obese patients is lacking as of date. The objective of this study was the characterisation of meropenem population pharmacokinetics in plasma and ISF in obese and non-obese patients for identification of adequate dosing regimens via Monte-Carlo simulations.

METHODS

We obtained plasma and microdialysate concentrations after administration of meropenem 1000 mg to 15 obese and 15 non-obese surgery patients from a prospective clinical trial. After characterizing plasma- and microdialysis-derived ISF pharmacokinetics via population pharmacokinetic analysis, we simulated thrice-daily (TID) meropenem short-term (0.5 h), prolonged (3.0 h), and continuous infusions. Adequacy of therapy was assessed by the probability of pharmacokinetic/pharmacodynamic (PK/PD) target attainment (PTA) analysis based on time unbound concentrations exceeded minimum inhibitory concentrations (MIC) on treatment day 1 (%fT _{> MIC}) and the sum of PTA weighted by relative frequency of MIC values for infections by pathogens commonly treated with meropenem. To avoid interstitial tissue fluid concentrations below MIC for the entire dosing interval during continuous infusions, a more conservative PK/PD index was selected (%fT _{> 4 × MIC}).

RESULTS

Adjusted body weight (ABW) and calculated creatinine clearance (CLCR_{CG_ABW}) of all patients (body mass index [BMI] = 20.5-81.5 kg/m²) explained a considerable proportion of the between-patient pharmacokinetic variability (15.1-31.0% relative reduction). The ISF:plasma ratio of %fT _{> MIC} was relatively similar for MIC ≤ 2 mg/L but decreased for MIC = 8 mg/L over ABW = 60-120 kg (0.50-0.20). Steady-state concentrations were 2.68 times (95% confidence interval [CI] = 2.11-3.37) higher in plasma than in ISF, supporting PK/PD targets related to four times the MIC during continuous infusions to avoid suspected ISF concentrations constantly below the MIC. A 3000 mg/24 h continuous infusion was sufficient at MIC = 2 mg/L for patients with CLCR_{CG_ABW} ≤ 100 mL/min and ABW < 90 kg, whereas 2000 mg TID prolonged infusions were adequate for those with CLCR_{CG_ABW} ≤ 100 mL/min and ABW > 90 kg. For MIC = 2 mg/L and %fT_{> MIC} = 95, PTA was adequate in patients over the entire investigated range of body mass and renal function using a 6000 mg continuous infusion. A prolonged infusion of meropenem 2000 mg TID was sufficient for MIC ≤ 8 mg/L and all investigated ABW and CLCR_{CG_ABW} when employing the PK/PD target %fT _{> MIC} = 40. Short-term infusions of 1000 mg TID were sufficient for CLCR_{CG_ABW} ≤ 130 mL/min and distributions of MIC values for Escherichia coli, Citrobacter freundii, and Klebsiella pneumoniae but not for Pseudomonas aeruginosa.

CONCLUSIONS

This analysis indicated a need for higher doses (≥ 2000 mg) and prolonged infusions (≥ 3 h) for obese and non-obese patients at MIC ≥ 2 mg/L. Higher PTA was achieved with prolonged infusions in obese patients and with continuous infusions in non-obese patients.

TRIAL REGISTRATION

EudraCT: 2012-004383-22.

Similar Piperacillin/Tazobactam Target Attainment in Obese versus Nonobese Patients despite Differences in Interstitial Tissue Fluid Pharmacokinetics

Precision dosing of piperacillin/tazobactam in obese patients is compromised by sparse information on target-site exposure. We aimed to evaluate the appropriateness of current and alternative piperacillin/tazobactam dosages in obese and nonobese patients. Based on a prospective, controlled clinical trial in 30 surgery patients (15 obese/15 nonobese; 0.5-h infusion of 4 g/0.5 g piperacillin/tazobactam), piperacillin pharmacokinetics were characterized in plasma and at target-site (interstitial fluid of subcutaneous adipose tissue) via population analysis. Thereafter, multiple 3-4-times daily piperacillin/tazobactam short-term/prolonged (recommended by EUCAST) and continuous infusions were evaluated by simulation. Adequacy of therapy was assessed by probability of pharmacokinetic/pharmacodynamic target-attainment (PTA ≥ 90%) based on time unbound piperacillin concentrations exceed the minimum inhibitory concentration (MIC) during 24 h (%fT>MIC). Lower piperacillin target-site maximum concentrations in obese versus nonobese patients were explained by the impact of lean (approximately two thirds) and fat body mass (approximately one third) on volume of distribution. Simulated steady-state concentrations were 1.43-times, 95%CI = (1.27; 1.61), higher in plasma versus target-site, supporting targets of %fT>2×MIC instead of %fT>4×MIC during continuous infusion to avoid target-site concentrations constantly below MIC. In all obesity and renally impairment/hyperfiltration stages, at MIC = 16 mg/L, adequate PTA required prolonged (thrice-daily 4 g/0.5 g over 3.0 h at %fT>MIC = 50) or continuous infusions (24 g/3 g over 24 h following loading dose at %fT>MIC = 98) of piperacillin/tazobactam.

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.

Evaluation of Benzylpenicillin as an Internal Standard for Measurement of Piperacillin Bone Concentrations Via Microdialysis

Microdialysis is a pharmacokinetic tool that can be advantageous when obtaining tissues' pharmacokinetic information. Since absolute extracellular tissue concentrations are needed in pharmacokinetic studies, calibrating the microdialysis system is necessary. The internal standard method is superior when compared to other calibration methods. However, thorough evaluation of the internal standard is required before it can be used. In vitro experiments and an in vivo study on pigs (n = 8) were conducted to assess the relative recoveries by gain and by loss for piperacillin, both with and without a benzylpenicillin concentration of 5 µg/mL. Furthermore, the in vivo setup allowed for an evaluation of piperacillin cancellous bone and subcutaneous tissue concentrations in a single 8 h dosing interval. Ultra-high performance liquid chromatography (UHPLC) was used to determine piperacillin and benzylpenicillin concentrations. Relative recovery by loss for benzylpenicillin and relative recovery by gain for piperacillin were similar in in vitro and in vivo. Presence of benzylpenicillin did not affect the relative recovery for piperacillin. Relative recovery, pharmacokinetic parameters and fT>MIC were similar when comparing the retrodialysis by drug and the internal standard calibration methods (p > 0.31). Mean fT>MIC (16 µg/mL) for plasma, cancellous bone and subcutaneous tissue were 232 min, 255 min and 295 min, respectively. Our findings suggest that benzylpenicillin is suitable as an internal standard for piperacillin in microdialysis studies. Mean fT>MIC (16 µg/mL) for plasma, cancellous bone, and subcutaneous tissue reached a target of 50% fT>MIC under the investigated conditions (mean range: 52%-66%); however, the target was not obtained in all pigs in all compartments. Moreover, 100% fT>MIC was not obtained in any case, suggesting that different strategies must be taken into consideration if higher targets are employed.

Quantification of microdialysis related variability in humans: Clinical trial design recommendations

OBJECTIVE

Target-site concentrations obtained via the catheter-based minimally invasive microdialysis technique often exhibit high variability. Catheter calibration is commonly performed via retrodialysis, in which a transformation factor, termed relative recovery (RR), is determined. Leveraging RR values from a rich data set of a very large clinical microdialysis study, promised to contribute critical insight into the origin of the reportedly high target-site variability. The present work aimed (i) to quantify and explain variability in RR associated with the patient (including non-obese vs. obese) and the catheter, and (ii) to derive recommendations on the design of future clinical microdialysis studies.

METHODS

A prospective, age- and sex-matched parallel group, single-centre trial in non-obese and obese patients (BMI=18.7-86.9 kg/m²) was performed. 1-3 RR values were obtained in the interstitial fluid of the subcutaneous fat tissue in one catheter per upper arm of 120 patients via the retrodialysis method (n_RR=1008) for a panel of drugs (linezolid, meropenem, tigecycline, cefazolin, fosfomycin, piperacillin and acetaminophen). A linear mixed-effects model was developed to quantify the different types of variability in RR and to explore the association between RR and patient body size descriptors.

RESULTS

Estimated RR was highest for acetaminophen (69.7%, 95%CI=65.0% to 74.3%) and lowest for piperacillin (40.4%, 95%CI=34.6% to 46.0%). The linear mixed-effects modelling analysis showed that variability associated with the patient (σ=15.9%) was the largest contributor (46.7%) to overall variability, whereas the contribution of variability linked to the catheter (σ=5.55%) was ~1/6 (16.8%). The relative contribution of residual unexplained variability (σ=12.0%, including intracatheter variability) was ~1/3 (36.4%). The limits of agreement of repeated RR determinations in a single catheter ranged from 0.694-1.64-fold (linezolid) to 0.510-3.02-fold (cefazolin). Calculated fat mass affected RR, explaining the observed lower RR in obese (ΔRR_mean= -29.7% relative reduction) versus non-obese patients (p<0.001); yet only 15.8% of interindividual variability was explained by this effect. No difference in RR was found between catheters implanted into the left or right arm (p=0.732).

CONCLUSIONS

Three recommendations for clinical microdialysis trial design were derived: 1) High interindividual variability underscored the necessity of measuring individual RR per patient. 2) The low relative contribution of intercatheter variability to overall variability indicated that measuring RR with a single catheter per patient is sufficient for reliable catheter calibration. 3) The wide limits of agreement from multiple RR in the same catheter implied an uncertainty of a factor of two in target-site drug concentration estimation necessitating to perform catheter calibration (retrodialysis sampling) multiple times per patient. To allow routine clinical use of microdialysis, research efforts should aim at further understanding and minimising the method-related variability. Optimised study designs in clinical trials will ultimately yield more informative microdialysis data and increase our understanding of this valuable sampling technique to derive target-site drug exposure.

[Anti-infective treatment in obesity-"just double it?"]

Adaequate antibiotic therapy is crucial for successful anti-infective therapy. In addition to the choice of the right antibiotic and the duration of therapy, the dose also plays a decisive role. Obesity has an influence on the pharmacokinetics of antibiotics, which can lead to underdosing if previous weight-independent dosing regimes are used. It is therefore necessary to carry out systematic measurements of concentrations in obese patients. Since pharmacokinetic differences between plasma and the interstitial fluid of different target tissues have been observed for different antibiotics, the measurement is also necessary in the target tissue. The technique of microdialysis is best suited for this purpose as it allows concentrations to be measured continuously in the target tissue.

Linezolid Concentrations in Plasma and Subcutaneous Tissue are Reduced in Obese Patients, Resulting in a Higher Risk of Underdosing in Critically Ill Patients: A Controlled Clinical Pharmacokinetic Study

Background: Linezolid is used for the treatment of soft tissue infections in critically ill patients. However, data for characterizing the pharmacokinetics (PK) and assessing whether effective concentrations are reached at the target site are lacking. We hypothesized that current dosing regimens do not lead to effective concentrations in the plasma and interstitial fluid (ISF) of subcutaneous tissue in obese patients. Methods: As a controlled clinical model, critically ill obese and non-obese patients undergoing intra-abdominal surgery received 600 mg linezolid as a single infusion. Concentrations in the plasma and microdialysate from the ISF of subcutaneous tissue were determined up to 8 h after dosing. Pharmacokinetic analysis was performed by non-compartmental methods. As a therapeutic target, we used fAUC/MIC > 80. Results: Fifteen obese (BMI: 48.7 ± 11.2 kg/m²) and 15 non-obese (23.9 ± 2.1 kg/m²) patients were analyzed. AUC_0–8 in ISF decreased by −1.69 mg*h/L (95% CI: −2.59 to −0.79, p < 0.001) for every 10 kg increase in weight. PK in obese patients were characterized by lower maximal plasma concentrations (median 3.8 vs. 8.3 mg/L, p < 0.001) and a higher volume of distribution (41.0 vs. 30.8 L, p < 0.001), and the therapeutic target was not reached for MIC ≥ 1 mg/L in ISF and ≥ 2 mg/L in plasma. Conclusions: Increasing the weight led to a decrease of linezolid concentrations in the plasma and subcutaneous tissue. The current dosing regimen does not seem to produce sufficient concentrations to kill bacteria with MIC ≥ 2 mg/L, especially as empirical antimicrobial therapy in critically ill obese patients.

Studies of blood-brain barrier permeability of gastrodigenin in vitro and in vivo

According to the basic theories of traditional Chinese medicine, Gastrodia elata (GE) is clinically utilized for the treatment of cephalalgia and migraine. The gastrodigenin (p-hydroxybenzyl alcohol, HBA), one of the effective components of GE, may pass through the blood-brain barrier (BBB) to exert its pharmacological effects. This study aimed to investigate BBB permeability of HBA via in vitro hCMEC/D3 BBB model and in vivo microdialysis in rats. For the establishment of in vitro BBB model, hCMEC/D3 cells were used to construct the monolayer. The integrity of the monolayer was evaluated by TEER measurements, expression analysis of tight junction proteins (claudin-5, zo-1 and occludin) and apparent permeability coefficients (P_app) of fluorescein disodium. During the 6-day incubation of hCMEC/D3 cells, the values of TEER gradually increased and maintained above 100 Ω·cm². Besides, the expression levels of claudin-5 and zo-1 in hCMEC/D3 cells increased over time, and tended to be stable, suggesting that integrity of the monolayer has been completely established. Moreover, the P_app of fluorescein disodium was 3.94 × 10^-7 cm·s^-1 after administration for 180 min, indicating that the monolayer retains the characteristics of BBB and can restrict the diffusion of hydrophilic small-molecule compounds. A sensitive HPLC method was established for HBA detection, and the transport rate of HBA was assessed by a transwell system. HBA crossed the hCMEC/D3 BBB model rapidly, but a plateau was observed when HBA concentrations were relatively similar between the two sides of transwell. Permeability assay revealed that 32.91% of HBA could penetrate the in vitro BBB model after 240 min of administration. In vivo BBB permeability was evaluated by determining the concentrations of HBA in blood and brain simultaneously. Following HBA administration, the samples of microdialysis were collected at 20, 40 and 60 min, and then every 30 min until the procedure ended. Pharmacokinetic parameters of HBA showed that HBA could pass through BBB and reach its maximum concentration at 40 min in blood and brain tissue. Furthermore, AUC_0-t and AUC_0-inf for the brain-to-blood distribution ratio of HBA were 0.1925 and 0.2083, respectively, indicating that approximately 20% of HBA in blood could pass through the BBB and subsequently transported into the brain. Both in vitro and in vivo experiments confirmed that HBA could penetrate the BBB. In summary, the findings of this study highlight that a promising amount of HBA in blood can pass through the BBB and exerts its pharmacological effects on central nervous system (CNS) diseases.

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

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

Measurement of soft tissue drug concentrations in morbidly obese and non-obese patients - A prospective, parallel group, open-labeled, controlled, phase IV, single center clinical trial

Background

Pharmacokinetic (PK) and pharmacodynamic (PD) data on perioperative antibiotic prophylaxis or antibiotic therapy are rare in patients suffering from morbid obesity. Furthermore, dosing regimens should be based on PK/PD models that ensure effective antibiotic exposure not in plasma, but primarily at the site of infection, mostly in the interstitial fluid (ISF). The aim of this trial is to investigate whether current dosing regimens of various antibiotics lead to effective concentrations in the ISF of morbidly obese patients.

Methods

We designed a prospective, parallel group, open-labeled, controlled single center trial to investigate the plasma and tissue pharmacokinetics of the antibiotics linezolid, meropenem, tigecycline, piperacillin/tazobactam, fosfomcyine, cefazolin, metronidazole and as secondary aim the analgesics metamizole and acetaminophen. Inclusion criteria comprise body mass index ≥35 kg/m² for obese or between 18.5 and 30 kg/m² for non-obese patients scheduled for elective abdominal surgery. For PK analysis, blood and microdialysate samples of subcutaneous tissue were collected 0–8 h after study drug administration. The primary endpoint is to investigate a possible dependency of the area-under-the-curve (AUC_0-8) in the interstitial fluid on body weight and obesity with population based pharmacokinetic analysis.

Discussion

Inadequate dosing regimes of antibiotics may be a relevant factor for morbidity and mortality of patients, as well as for the development of bacterial antibiotic resistance. The measurement of plasma and tissue concentrations will provide information necessary for PK/PD-modelling. These data about antibiotic PK/PDcharacteristics in soft tissue and their dependence on weight should help to develop weight-dependent models for calculation of patient's individual doses of different antibiotics.

Trial registration

EU clinical trials register (EudraCT-No. 2012-004383-22) and German Clinical trials Register (DRKS00004776);