Systematic Evaluation of Pharmacokinetic Models for Model-Informed Precision Dosing of Meropenem in Critically Ill Patients Undergoing Continuous Renal Replacement Therapy.

The altered pharmacokinetics of renally cleared drugs such as meropenem in critically ill patients receiving continuous renal replacement therapy (CRRT) might impact target attainment. Model-informed precision dosing (MIPD) is applied to individualize meropenem dosing. However, most population pharmacokinetic (PopPK) models developed to date have not yet been evaluated for MIPD. Eight PopPK models based on adult CRRT patients were identified in a systematic literature research and encoded in NONMEM 7.4. A data set of 73 CRRT patients from two different study centers was used to evaluate the predictive performance of the models using simulation and prediction-based diagnostics for i) a priori dosing based on patient characteristics only and ii) Bayesian dosing by including the first measured trough concentration. Median prediction error (MPE) for accuracy within |20%| (95% confidence intervals including zero) and median absolute prediction error (MAPE) for precision ≤ 30% were considered clinically acceptable. For a priori dosing, most models (n = 5) showed accuracy and precision MPE within |20%| and MAPE <35%. The integration of the first measured meropenem concentration improved the predictive performance of all models (median MAPE decreased from 35.4 to 25.0%; median MPE decreased from 21.8 to 4.6%). The best predictive performance for intermittent infusion was observed for the O'Jeanson model, including residual diuresis as covariate (a priori and Bayesian dosing MPE within |2%|, MAPE <30%). Our study revealed the O'Jeanson model as the best-predicting model for intermittent infusion. However, most of the selected PopPK models are suitable for MIPD in CRRT patients when one therapeutic drug monitoring sample is available.

Cefepime Population Pharmacokinetics, Antibacterial Target Attainment, and Estimated Probability of Neurotoxicity in Critically Ill Patients.

Cefepime has been reported to cause concentration-related neurotoxicity, especially in critically ill patients with renal failure. This evaluation aimed to identify a dosing regimen providing a sufficient probability of target attainment (PTA) and the lowest justifiable risk of neurotoxicity in critically ill patients. A population pharmacokinetic model was developed based on plasma concentrations over four consecutive days obtained from 14 intensive care unit (ICU) patients. The patients received a median dose of 2,000 mg cefepime by 30-min intravenous infusions with dosing intervals of every 8 h (q8h) to q24h. A time that the free drug concentration exceeds the MIC over the dosing interval (fT>MIC) of 65% and an fT>2×MIC of 100% were defined as treatment targets. Monte Carlo simulations were carried out to identify a dosing regimen for a PTA of 90% and a probability of neurotoxicity not exceeding 20%. A two-compartment model with linear elimination best described the data. Estimated creatinine clearance was significantly related to the clearance of cefepime in nondialysis patients. Interoccasion variability on clearance improved the model, reflecting dynamic clearance changes. The evaluations suggested combining thrice-daily administration as an appropriate choice. In patients with normal renal function (creatinine clearance, 120 mL/min), for the pharmacodynamics target of 100% fT>2×MIC and a PTA of 90%, a dose of 1,333 mg q8h was found to be related to a probability of neurotoxicity of ≤20% and to cover MICs up to 2 mg/L. Continuous infusion appears to be superior to other dosing regimens by providing higher efficacy and a low risk of neurotoxicity. The model makes it possible to improve the predicted balance between cefepime efficacy and neurotoxicity in critically ill patients. (This study has been registered at ClinicalTrials.gov under registration no. NCT01793012).

Plasma and Cerebrospinal Fluid Population Pharmacokinetics of Vancomycin in Patients with External Ventricular Drain.

Vancomycin is a commonly used antibacterial agent in patients with primary central nervous system (CNS) infection. This study aims to examine predictors of vancomycin penetration into cerebrospinal fluid (CSF) in patients with external ventricular drainage and the feasibility of CSF sampling from the distal drainage port for therapeutic drug monitoring. Fourteen adult patients (9 with primary CNS infection) were treated with vancomycin intravenously. The vancomycin concentrations in blood and CSF (from proximal [CSF_P] and distal [CSF_D] drainage ports) were evaluated by population pharmacokinetics. Model-based simulations were conducted to compare various infusion modes. A three-compartment model with first-order elimination best described the vancomycin data. Estimated parameters included clearance (CL, 4.53 L/h), central compartment volume (Vc, 24.0 L), apparent CSF compartment volume (VCSF, 0.445 L), and clearance between central and CSF compartments (QCSF, 0.00322 L/h and 0.00135 L/h for patients with and without primary CNS infection, respectively). Creatinine clearance was a significant covariate on vancomycin CL. CSF protein was the primary covariate to explain the variability of QCSF. There was no detectable difference between the data for sampling from the proximal and the distal port. Intermittent infusion and continuous infusion with a loading dose reached the CSF target concentration faster than continuous infusion only. All infusion schedules reached similar CSF trough concentrations. Beyond adjusting doses according to renal function, starting treatment with a loading dose in patients with primary CSF infection is recommended. Occasionally, very high and possibly toxic doses would be required to achieve adequate CSF concentrations, which calls for more investigation of direct intraventricular administration of vancomycin. (This study has been registered at ClinicalTrials.gov under registration no. NCT04426383).

Correlation between Bilirubin Elimination with the Cytokine Adsorber CytoSorb® and Mortality in Critically Ill Patients with Hyperbilirubinemia.

INTRODUCTION: Hyperbilirubinemia is often the first evidence for any kind of liver disorder and over one-third of all patients in intensive care units (ICU) show elevated bilirubin concentrations. In critically ill patients, high concentrations of serum bilirubin are correlated with a poor outcome. Therapies to lower bilirubin concentrations are often just symptomatically and their effect on the patients' outcome is hardly evaluated. Therefore, this study investigates whether the extracorporeal elimination of bilirubin with the cytokine adsorber CytoSorb® (CS) reduces mortality in patients with hyperbilirubinemia. METHODS: Patients with bilirubin concentrations >10 mg/dL at the ICU were screened for evaluation from 2018 to 2020. Patients with kidney replacement therapy and older than 18 years were included. Patients with continuously decreasing bilirubin concentrations after liver transplantation or other liver support systems (i.e., Molecular Adsorbents Recirculating System [MARS®], Advanced Organ Support [ADVOS]) were excluded. CS therapy was used in clinical routine and was indicated by the treating physicians. Statistical analysis was performed with IBM SPSS statistics utilizing a multivariate model. Primary outcome measure was the effect of CS on the 30-day mortality. RESULTS: Data from 82 patients (mean Simplified Acute Physiology Score [SAPS] II: 74 points, mean bilirubin: 18 mg/dL, mean lactate: 3.7 mmol/L) were analyzed. There were no significant differences in patients with and without CS treatment. The multivariate model showed no significant effect of CS therapy (p = 0.402) on the 30-day mortality. In addition, a significant effect of bilirubin concentration (p = 0.274) or Model for End-Stage Liver Disease score (p = 0.928) on the 30-day mortality could not be shown. In contrast, lactate concentration (p = 0.001, b = 0.044) and SAPS II (p = 0.025, b = 0.008) had significant impact on 30-day mortality. CONCLUSION: The use of CS in patients with hyperbilirubinemia did not result in a significant reduction in 30-day mortality. Randomized and controlled studies with mortality as primary outcome measure are needed in the future to justify their use.

The effect of cytosorb® application on kidney recovery in critically ill patients with severe rhabdomyolysis: a propensity score matching analysis.

Severe rhabdomyolysis frequently results in acute kidney injury (AKI) due to myoglobin accumulation with the need of kidney replacement therapy (KRT). The present study investigated whether the application of Cytosorb® (CS) led to an increased rate of kidney recovery in patients with KRT due to severe rhabdomyolysis. Adult patients with a myoglobin-concentration >10,000 ng/ml and KRT were included from 2014 to 2021. Exclusion criteria were chronic kidney disease and CS-treatment before study inclusion. Groups 1 and 2 were defined as KRT with and without CS, respectively. The primary outcome parameter was independence from KRT after 30 days. Propensity score (PS) matching was performed (predictors: myoglobin, SAPS-II, and age), and the chi2-test was used. 35 pairings could be matched (mean age: 57 vs. 56 years; mean myoglobin: 27,218 vs. 26,872 ng/ml; mean SAPS-II: 77 vs. 76). The probability of kidney recovery was significantly (p = .04) higher in group 1 (31.4 vs. 11.4%, mean difference: 20.0%, odds ratio (OR): 3.6). Considering patients who survived 30 days, kidney recovery was also significantly (p = .03) higher in patients treated with CS (61.1 vs. 23.5%, mean difference: 37.6%, OR: 5.1). In conclusion, the use of CS might positively affect renal recovery in patients with severe rhabdomyolysis. A prospective randomized controlled trial is needed to confirm this hypothesis.

Combination of Pharmacokinetic and Pathogen Susceptibility Information To Optimize Meropenem Treatment of Gram-Negative Infections in Critically Ill Patients.

Meropenem is one of the most frequently used antibiotics to treat life-threatening infections in critically ill patients. This study aimed to develop a meropenem dosing algorithm for the treatment of Gram-negative infections based on intensive care unit (ICU)-specific resistance data. Antimicrobial susceptibility testing of Gram-negative bacteria obtained from critically ill patients was carried out from 2016 to 2020 at a tertiary care hospital. Based on the observed MIC distribution, stochastic simulations (n = 1,000) of an evaluated pharmacokinetic meropenem model, and a defined pharmacokinetic/pharmacodynamic target (100%T>4×MIC while minimum concentrations were <44.5 mg/L), dosing recommendations for patients with varying renal function were derived. Pathogen-specific MIC distributions were used to calculate the cumulative fraction of response (CFR), and the overall MIC distribution was used to calculate the local pathogen-independent mean fraction of response (LPIFR) for the investigated dosing regimens. A CFR/LPIFR of >90% was considered adequate. The observed MIC distribution significantly differed from the EUCAST database. Based on the 6,520 MIC values included, a three-level dosing algorithm was developed. If the pathogen causing the infection is unknown (level 1), known (level 2), known to be neither Pseudomonas aeruginosa nor Acinetobacter baumannii, or classified as susceptible (level 3), a continuous infusion of 1.5 g daily reached sufficient target attainment independent of renal function. In all other cases, dosing needs to be adjusted based on renal function. ICU-specific susceptibility data should be assessed regularly and integrated into dosing decisions. The presented workflow may serve as a blueprint for other antimicrobial settings.

Target Site Pharmacokinetics of Meropenem: Measurement in Human Explanted Lung Tissue by Bronchoalveolar Lavage, Microdialysis, and Homogenized Lung Tissue.

Pneumonia is one of the most common infections in intensive care patients, and it is often treated with beta-lactam antibiotics. Even if therapeutic drug monitoring in blood is available, it is unclear whether sufficient concentrations are reached at the target site: the lung. The present study was initiated to fill this knowledge gap. Various compartments from 10 patients' explanted lungs were subjected to laboratory analysis. Meropenem was quantified in serum, bronchoalveolar lavage (BAL) fluid, microdialysate, and homogenized lung tissue with isotope dilution liquid chromatography tandem mass spectrometry (ID-LC-MS/MS). BAL fluid represents diluted epithelial lining fluid (ELF), and microdialysate represents interstitial fluid (IF). Differences between target site and blood concentrations were investigated. The median meropenem concentration in blood, ELF, IF, and tissue were 26.8, 18.0, 12.1, and 9.1 mg/liter, respectively. A total of 37.5% of the target site ELF and IF meropenem concentrations were below the clinical EUCAST breakpoint of 8 mg/liter. The median ELF/serum quotient was 61.8% (interquartile range [IQR], 24.8% to 87.6%), the median IF/serum quotient was 35.4% (IQR, 23.8% to 54.3%), and the median tissue/serum quotient was 34.2% (IQR, 28.3% to 38.2%). We observed a substantial interindividual variability between the blood and the compartments (ELF and IF), whereas the intraindividual variability was relatively low. Target site measurement in different lung compartments was feasible and successfully applied in a clinical setting. A relevant amount of 37.5% of the target site concentrations were below the clinical EUCAST breakpoint, indicating subtherapeutic dosing in high-risk patients receiving perioperative antibiotic prophylaxis in lung transplantation. (This study has been registered at ClinicalTrials.gov under identifier NCT03970265.).

Digestive enzymes of fungal origin as a relevant cause of false positive Aspergillus antigen testing in intensive care unit patients.

BACKGROUND: Galactomannan antigen (GM) testing is widely used in the diagnosis of invasive aspergillosis (IA). Digestive enzymes play an important role in enzyme substitution therapy in exocrine pancreatic insufficiency. As digestive enzymes of fungal origin like Nortase contain enzymes from Aspergillus, a false-positive result of the test might be possible because of cross-reacting antigens of the cell wall of the producing fungi. We, therefore, asked whether the administration of fungal enzymes is a relevant cause of false-positive GM antigen test results. METHODS: Patients with a positive GM antigen test between January 2016 and April 2020 were included in the evaluation and divided into two groups: group 1-Nortase-therapy, group 2-no Nortase-therapy. In addition, dissolved Nortase samples were analyzed in vitro for GM and ß-1,3-D-glucan. For statistical analysis, the chi-squared and Mann‒Whitney U tests were used. RESULTS: Sixty-five patients were included in this evaluation (30 patients receiving Nortase and 35 patients not receiving Nortase). The overall false positivity rate of GM testing was 43.1%. Notably, false-positive results were detected significantly more often in the Nortase group (73.3%) than in the control group (17.1%, p < 0.001). While the positive predictive value of GM testing was 0.83 in the control group, there was a dramatic decline to 0.27 in the Nortase group. In vitro analysis proved that the Nortase enzyme preparation was highly positive for the fungal antigens GM and ß-1,3-D-glucan. CONCLUSIONS: Our data demonstrate that the administration of digestive enzymes of fungal origin like Nortase leads to a significantly higher rate of false-positive GM test results compared to that in patients without digestive enzyme treatment.

Comparing posaconazole and itraconazole for antifungal prophylaxis in critically ill lung transplant recipients: Efficacy and plasma concentrations.

BACKGROUND: Posaconazole and itraconazole are commonly used for systemic antifungal prophylaxis after lung transplantation. The aim of this study on critically ill lung transplant recipients was to assess the rate of adequate plasma concentrations and the frequency of fungal-induced transitions from antifungal prophylaxis to therapy after the administration of either posaconazole or itraconazole for systemic prophylaxis. METHODS: Critically ill lung transplant recipients with postoperative posaconazole or itraconazole prophylaxis and therapeutic drug monitoring from February 2016 to November 2019 were retrospectively included in the study. Positive fungal cultures or Aspergillus antigen tests resulting in a transition from antifungal prophylaxis to therapy were analyzed from the first day of prophylaxis until 7 days after the last sample for each patient. Adequate plasma concentrations were defined as ≥500 µg/L for itraconazole and ≥700 µg/L for posaconazole. RESULTS: Two hundred seventy-five samples from 73 patients were included in the analysis. Overall, 60% of the posaconazole and 55% of the itraconazole concentrations were subtherapeutic. Administration of posaconazole suspension resulted significantly (P < .01) more often in subtherapeutic concentrations than tablets (68% vs 10%). Patients treated with posaconazole showed less positive fungal records resulting in a transition from prophylaxis to therapy than patients treated with itraconazole (10% vs 33%, P-value: .029). The detection of a fungal pathogen was not associated with the measured plasma concentrations or the achievement of the target concentrations. CONCLUSION: Our findings suggest that posaconazole should be used instead of itraconazole for systemic prophylaxis in critically ill lung transplant recipients.

Blood purification with a cytokine adsorber for the elimination of myoglobin in critically ill patients with severe rhabdomyolysis.

BACKGROUND: Rhabdomyolysis is frequently occurring in critically ill patients, resulting in a high risk of acute kidney injury (AKI) and potentially permanent kidney damage due to increased myoglobin levels. The extracorporeal elimination of myoglobin might be an approach to prevent AKI, but its molecular weight of 17 kDa complicates an elimination with conventional dialysis membranes. Question of interest is, if myoglobin can be successfully eliminated with the cytokine adsorber Cytosorb® (CS) integrated in a high-flux dialysis system. METHODS: Patients were included between 10/2014 and 05/2020 in the study population if they had an anuric renal failure with the need of renal replacement therapy, if CS therapy was longer than 90 min and if myoglobin level was > 5.000 ng/ml before treatment. The measurement times of the laboratory values were: d-1 = 24-36 h before CS, d0 = shortly before starting CS and d1 = 12-24 h after starting CS treatment. Statistical analysis were performed with Spearman's correlation coefficient, Wilcoxon test with associated samples and linear regression analysis. RESULTS: Forty-three patients were included in the evaluation (median age: 56 years, 77% male patients, 32.6% ECMO therapy, median SAPS II: 80 points and in-hospital mortality: 67%). There was a significant equilateral correlation between creatine kinase (CK) and myoglobin at all measurement points. Furthermore, there was a significant reduction of myoglobin (p = 0.03, 95% confidence interval (CI): - 9030, - 908 ng/ml) during CS treatment, with a median relative reduction of 29%. A higher median reduction of 38% was seen in patients without ongoing rhabdomyolysis (CK decreased during CS treatment, n = 21). In contrast, myoglobin levels did not relevantly change in patients with increasing CK and therefore ongoing rhabdomyolysis (n = 22, median relative reduction 4%). Moreover, there was no significant difference in myoglobin elimination in patients with and without ECMO therapy. CONCLUSION: Blood purification with Cytosorb® during high-flux dialysis led to a significant reduction of myoglobin in patients with severe rhabdomyolysis. The effect might be obscured by sustained rhabdomyolysis, which was seen in patients with rising CK during treatment. Prospective clinical trials would be useful in investigating its benefits in avoiding permanent kidney damage.

Comparative LC-MS/MS and HPLC-UV Analyses of Meropenem and Piperacillin in Critically Ill Patients.

BACKGROUND: Therapeutic drug monitoring (TDM) of beta-lactam antibiotics has become a valuable tool to guide dosing in critically ill patients. The main goal of the study was to compare two routinely used techniques for beta-lactam TDM in intensive care unit (ICU) patient samples, namely isotope dilution liquid chromatography tandem mass spectrometry (ID-LC-MS/MS) and high-performance liquid chromatography combined with ultra-violet detection (HPLC-UV). METHODS: A set of 80 sera/plasma samples from ICU patients receiving therapeutic meropenem or piperacillin dosage was investigated. Sample duplicates and quality assessment samples were assayed in parallel with an in-house LC-MS/MS and a commercially available IVD HPLC-UV kit. A pharmacokinetic and pharmacodynamic (PK/PD) target with ≥ 22.5 mg/L for piperacillin and ≥ 8.0 mg/L for meropenem was used for medical assessment of trough sample (n = 40) antibiotic concentrations. RESULTS: There was no difference between serum and Li-heparin plasmas. Concentration deviations were found for 4% of meropenem and 17% of piperacillin samples. Eliminating the influence of the systemic bias of approximately 10% for piperacillin, measurement discrepancies ≥ 25% between LC-MS/MS and HPLC-UV analyses were only observed for ≈ 4 - 6% of all samples. In the same way, identical PK/PD target attainment rates of 50 - 60% could be obtained. CONCLUSIONS: After correction of the analytical bias for piperacillin measurements, both methods showed comparable results, also with respect to clinical decision limits. HPLC-UV analysis is an adequate TDM methodology for testing of beta-lactam antibiotics in centers where no special knowledge in LC-MS/MS based TDM is present. However, potential matrix effects, interferences, and calibration issues for both methods must be taken into account.

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

BACKGROUND: Standard doses of linezolid may not be suitable for all patient groups. Intensive care unit (ICU) patients in particular may be at risk of inadequate concentrations. This study investigated variability of drug exposure and its potential sources in this population. METHODS: Plasma concentrations of linezolid were determined by high-performance liquid chromatography in a convenience sample of 20 ICU patients treated with intravenous linezolid 600 mg twice daily. Ultrafiltration applying physiological conditions (pH 7.4/37°C) was used to determine the unbound fraction. Individual pharmacokinetic (PK) parameters were estimated by population PK modeling. As measures of exposure to linezolid, area under the concentration-time curve (AUC) and trough concentrations (Cmin) were calculated and compared with published therapeutic ranges (AUC 200-400 mg*h/L, Cmin 2-10 mg/L). Coadministered inhibitors or inducers of cytochrome P450 and/or P-glycoprotein were noted. RESULTS: Data from 18 patients were included into the PK evaluation. Drug exposure was highly variable (median, range: AUC 185, 48-618 mg*h/L, calculated Cmin 2.92, 0.0062-18.9 mg/L), and only a minority of patients had values within the target ranges (6 and 7, respectively). AUC and Cmin were linearly correlated (R = 0.98), and classification of patients (underexposed/within therapeutic range/overexposed) according to AUC or Cmin was concordant in 15 cases. Coadministration of inhibitors was associated with a trend to higher drug exposure, whereas 3 patients treated with levothyroxine showed exceedingly low drug exposure (AUC ∼60 mg*h/L, Cmin <0.4 mg/L). The median unbound fraction in all 20 patients was 90.9%. CONCLUSIONS: Drug exposure after standard doses of linezolid is highly variable and difficult to predict in ICU patients, and therapeutic drug monitoring seems advisable. PK drug-drug interactions might partly be responsible and should be further investigated; protein binding appears to be stable and irrelevant.

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

AIMS: The aim of the present study was to assess the pharmacokinetics of total and unbound ceftriaxone in intensive care unit (ICU) patients and its protein binding characteristics. METHODS: Twenty patients (m/f 15/5, age 25-86 years, body weight 60-121 kg, APACHE II 7-40, estimated glomerular filtration rate 19-157 ml min(-1) , albumin 11.7-30.1 g l(-1) , total bilirubin <0.1-36.1 mg dl(-1) ) treated with intravenous ceftriaxone were recruited from two ICUs. Timed plasma samples were obtained using an opportunistic study protocol. Ceftriaxone concentrations were determined by high-performance liquid chromatography; unbound concentrations were determined after ultrafiltration using a new method which maintains physiological pH and temperature. The pharmacokinetics was described by a one-compartment model, the protein-binding characteristics by Michaelis-Menten kinetics. RESULTS: For total drug, the volume of distribution was 20.2 l (median; interquartile range 15.6-24.5 l), the half-life 14.5 h (10.0-25.5 h) and the clearance 0.96 l h(-1) (0.55-1.28 l h(-1) ). The clearance of unbound drug was 1.91 l h(-1) (1.46-6.20 l h(-1) ) and linearly correlated with estimated glomerular filtration rate (slope 0.85, y-intercept 0.24 l h(-1) , r(2) = 0.70). The unbound fraction was higher in ICU patients (33.0%; 20.2-44.5%) than reported in healthy volunteers, particularly when renal impairment or severe hyperbilirubinaemia was present. In all patients, unbound concentrations during treatment with ceftriaxone 2 g once daily remained above the EUCAST susceptibility breakpoint (≤1 mg l(-1) ) throughout the whole dosing interval. CONCLUSIONS: Protein binding of ceftriaxone is reduced and variable in ICU patients due to hypoalbuminaemia, but also to altered binding characteristics. Despite these changes, the pharmacokinetics of unbound ceftriaxone is governed by renal function. For patients with normal or reduced renal function, standard doses are sufficient.

Unbound fraction of ertapenem in intensive care unit patients.

OBJECTIVES: To determine unbound ertapenem concentrations in plasma and to describe the pharmacokinetics of unbound ertapenem in intensive care unit (ICU) patients. PATIENTS AND METHODS: For assessing the influence of experimental conditions and for development of the ultrafiltration protocol, plasma from healthy volunteers was used. Concentrations of total and unbound ertapenem were determined by HPLC in 29 plasma samples from six ICU patients treated with 1 g of ertapenem once daily. The concentration-time courses were described by a one-compartment model. Ertapenem binding to albumin was assessed by Michaelis-Menten kinetics in solutions of human serum albumin, in plasma from healthy volunteers and in plasma from ICU patients. RESULTS: The unbound fraction (fu) of ertapenem was highly susceptible to pH and temperature during ultrafiltration and was ∼20% in plasma from healthy volunteers at clinically relevant concentrations. In ICU patients, fu was substantially higher (range 30.9%-53.6%). The unbound concentrations of ertapenem exceeded 2 mg/L for 72% (median; range 39%-100%) of the 24 h dosing interval and 0.25 mg/L for 100% (range 79%-100%). The number of binding sites per albumin molecule was 1.22 (95% CI 1.07-1.38) in plasma from healthy volunteers and 0.404 (95% CI 0.158-0.650) in samples from ICU patients. CONCLUSIONS: Determination of unbound ertapenem by ultrafiltration is susceptible to experimental conditions. When determined at physiological pH and temperature, fu of ertapenem is 2- to 4-fold higher than previously reported and even higher in ICU patients. Binding studies indicate that hypoalbuminaemia alone does not explain these differences. This issue should be further investigated for its clinical relevance.

Does Sample Size, Sampling Strategy, or Handling of Concentrations Below the Lower Limit of Quantification Matter When Externally Evaluating Population Pharmacokinetic Models?

BACKGROUND AND OBJECTIVES: Precision dosing requires selecting the appropriate population pharmacokinetic model, which can be assessed through external evaluations (EEs). The lack of understanding of how different study design factors influence EE study outcomes makes it challenging to select the most suitable model for clinical use. This study aimed to evaluate the impact of sample size, sampling strategy, and handling of concentrations below the lower limit of quantification (BLQ) on the outcomes of EE for four population pharmacokinetic models using vancomycin and tobramycin as examples. METHODS: Three virtual patient populations undergoing vancomycin or tobramycin therapy were simulated with varying sample size and sampling scenarios. The three approaches used to handle BLQ data were to (1) discard them, (2) impute them as LLOQ/2, or (3) use a likelihood-based approach. EEs were performed with NONMEM and R. RESULTS: Sample size did not have an important impact on the EE results for a given scenario. Increasing the number of samples per patient did not improve predictive performance for two out of the three evaluated models. Evaluating a model developed with rich sampling did not result in better performance than those developed with regular therapeutic drug monitoring. A likelihood-based method to handle BLQ samples impacted the outcomes of the EE with lower bias for predicted troughs. CONCLUSIONS: This study suggests that a large sample size may not be necessary for an EE study, and models selected based on TDM may be more generalizable. The study highlights the need for guidelines for EE of population pharmacokinetic models for clinical use.

Can linezolid be validly measured in endotracheal aspiration in critically ill patients? A proof-of-concept trial.

BACKGROUND: Therapeutic drug monitoring (TDM) of anti-infectives such as linezolid is routinely performed in blood of intensive care unit (ICU) patients to optimize target attainment. However, the concentration at the site of infection is considered more important for a successful therapy. Until now, bronchoalveolar lavage (BAL) is the gold standard to measure intrapulmonary concentrations of anti-infective agents. However, it is an invasive method and unsuitable for regular TDM. The aim of this proof-of-concept study was to investigate whether it is possible to reliably determine the intrapulmonary concentration of linezolid from endotracheal aspiration (ENTA). METHODS: Intubated ICU patients receiving 600 mg intravenous linezolid twice daily were examined in steady state. First, preliminary experiments were performed in six patients to investigate which patients are suitable for linezolid measurement in ENTA. In a second step, trough and peak linezolid concentrations of plasma and ENTA were determined in nine suitable patients. RESULTS: Linezolid can validly be detected in ENTA with viscous texture and > 0.5 mL volume. The mean (SD) linezolid trough concentration was 2.02 (1.27) mg/L in plasma and 1.60 (1.36) mg/L in ENTA, resulting in a median lung penetration rate of 104%. The mean (SD) peak concentration in plasma and ENTA was 10.77 (5.93) and 4.74 (2.66) mg/L. CONCLUSIONS: Linezolid can validly be determined in ENTA with an adequate texture and volume. The penetration rate is comparable to already published BAL concentrations. This method might offer a simple and non-invasive method for TDM at the site of infection "lung". Due to promising results of the feasibility study, comparison of ENTA and BAL in the same patient should be investigated in a further trial.

[Hemoperfusion in anesthesia and intensive care medicine: benefits, risks, and evidence for different systems]. / Hämoperfusion in Anästhesie und Intensivmedizin: Chancen, Risiken und Evidenz verschiedener Systeme.

BACKGROUND: Hemoperfusion is a technique for the extracorporeal elimination of endogenous and exogenous toxins and harmful mediators by adsorption. It can be used as a stand-alone device, as part of a heart-lung machine or extracorporeal membrane oxygenation (ECMO) or, as is currently the case, integrated into a kidney replacement procedure. In the meantime, various suppliers offer devices with different technologies. OBJECTIVE: The aim of this work was to evaluate the benefits, risks and evidence of the different systems, how they work and for which indications they are approved in Germany. METHOD: To achieve this goal, a narrative assessment of the existing literature and guidelines for different indications was performed. The focus was on in vivo studies. RESULTS: In principle, a distinction must be made in adsorption techniques between pure adsorption and the combination as adsorption and kidney replacement therapy. The adsorbers available in Germany include Cytosorb®, HA-330, Seraph®-100 and Toraymyxin. Combined procedures (adsorption and kidney replacement) are offered with coupled plasma filtration and adsorption (CPFA) and oXiris®. Most adsorbers have been developed for cytokine and endotoxin removal in patients with sepsis; however, to date, no randomized controlled trial (RCT) has demonstrated a survival benefit when using hemoperfusion. Therefore, the S3 guidelines for treatment of sepsis and the surviving sepsis campaign guidelines advise against its routine use. When the corona pandemic began, hemoperfusion was considered as a promising therapeutic approach. Cytosorb®, Seraph®-100, and oXiris® received emergency approval by the FDA to be used in critically ill patients with COVID-19, so questions arose about the appropriateness and importance of its use; however, the data generated did not show positive results, so its use cannot be recommended routinely either. In addition, they are not mentioned as a treatment option in the current guidelines. The use of adsorption procedures in patients with liver failure and rhabdomyolysis has only been rudimentarily studied, so any evidence is currently lacking. The only adsorber that has CE approval in Germany for both applications is Cytosorb®. In the next few years, studies will have to follow that investigate the efficacy and thus either justify or refute the use in clinical routine. Hemoperfusion procedures are used in the heart-lung machine as part of cardiac surgery for either cytokine or anticoagulant adsorption. No congruent data are available to support the use for the elimination of cytokines. If emergency cardiac surgery is required in a patient with pre-existing anticoagulation, hemoperfusion procedures can be used to prevent bleeding complications. Cytosorb® has CE approval for this indication. All available techniques are nonselective adsorption processes, so that adsorption of known and unknown substances can occur. Unintentional adsorption of drugs, such as various anti-infective agents is a relevant risk, especially when used in patients with sepsis. DISCUSSION: Various adsorption systems can eliminate different known and unknown substances. Currently, there is a lack of evidence for all indications and systems to justify their routine use except in clinical trials. Future clinical trials should evaluate the potential benefits but also dangers, so that in the meantime the routine use can be justified or a recommendation against the use can be given.