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.

[Hemoperfusion in anesthesia and intensive care medicine: benefits, risks, and evidence for different systems]

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.

Extracorporeal adsorption of protective and toxic bile acids and bilirubin in patients with cholestatic liver dysfunction: a prospective study

BACKGROUND

The release of toxic bile acids (BAs) in the blood of critically ill patients with cholestatic liver dysfunction might lead to the damage of various organs. Their extracorporeal elimination using the cytokine adsorber Cytosorb® (CS) (adsorption of especially hydrophobic molecules < 60 kDa) might be promising, but data proving a potential adsorption are missing so far.

METHODS

The prospective Cyto-SOVLE study (NCT04913298) included 20 intensive care patients with cholestatic liver dysfunction, continuous kidney replacement therapy, total bilirubin concentration > 10 mg/dl and the application of CS into the dialysis circuit. Bilirubin and different BAs were measured pre- and post-CS at defined timepoints (10 min, 1, 3, 6, and 12 h after initiation). Relative reduction (RR, %) was calculated with: [Formula: see text].

RESULTS

The median RR for total and conjugated bilirubin after initiation was - 31.8% and - 30.3%, respectively, and decreased to - 4.5% and - 4.8% after 6 h. A high initial RR was observed for the toxic BAs GCA (- 97.4%), TCA (- 94.9%), GCDCA (- 82.5%), and TCDCA (- 86.0%), decreasing after 6 h to - 32.9%, - 32.7%, - 12.8%, and - 14.3%, respectively. The protective hydrophilic BAs showed a comparable RR after initiation (UDCA: - 77.7%, GUDCA: - 83.0%, TUDCA: - 91.3%) dropping after 6 h to - 7.4%, - 8.5%, and - 12.5%, respectively.

CONCLUSIONS

Cytosorb® can adsorb bilirubin and toxic as well as protective BAs. However, a fast saturation of the adsorber resulting in a rapid decrease of the RR was observed. Furthermore, no relevant difference between hydrophobic toxic and hydrophilic protective BAs was detected regarding the adsorption amount. The clinical benefit or harm of the BA adsorption needs to be evaluated in the future.

Pharmacokinetics of immunosuppressive agents during hemoperfusion in a sheep model

Introduction

Hemoadsorption shows promising signals in organ preservation and post lung transplantation. However, its potential impact on the pharmacokinetics of immunosuppressant drugs (ID) is still unknown.

Methods

In this interventional study, CytoSorb® hemoperfusion was tested in healthy sheep (n = 5) against a sham extracorporeal circuit (n = 3). Seven different ID (tacrolimus (TAC), cyclosporin A (CYA), mycophenolate mofetil (MMF), everolimus (EVER), basiliximab (BAS), methylprednisolone (MP) and prednisolone (PRED)) were administered in clinically relevant doses and combinations. Their levels were measured repeatedly in blood samples from the extracorporeal circulation over 6 h following administration. Population pharmacokinetic modeling analysis (NONMEM® 7.5) was performed.

Results

Negligible clearance was observed for PRED and BAS. For all other substances, a saturable adsorption sub-model with linear decrease of the adsorption effect over the adsorbed amount best described the measured concentrations. The maximum absolute adsorbed amounts (95% CI) for TAC, CYA, MMF, EVER, and MP were 0.040 (0.028-0.053), 1.15 (0.39-1.91), 4.17 (2.00-6.35), 0.0163 (0.007-0.026), and 53.4 mg (20.9-85.9), respectively, indicating an adsorption of less than 5% of the daily administered dosages for all investigated substances.

Discussion

In this large animal model, CytoSorb® hemoperfusion appears to have a limited effect on the clearance of tested ID.

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.

Towards model-informed precision dosing of piperacillin: multicenter systematic external evaluation of pharmacokinetic models in critically ill adults with a focus on Bayesian forecasting

PURPOSE

Inadequate piperacillin (PIP) exposure in intensive care unit (ICU) patients threatens therapeutic success. Model-informed precision dosing (MIPD) might be promising to individualize dosing; however, the transferability of published models to external populations is uncertain. This study aimed to externally evaluate the available PIP population pharmacokinetic (PopPK) models.

METHODS

A multicenter dataset of 561 ICU patients (11 centers/3654 concentrations) was used for the evaluation of 24 identified models. Model performance was investigated for a priori (A) predictions, i.e., considering dosing records and patient characteristics only, and for Bayesian forecasting, i.e., additionally including the first (B1) or first and second (B2) therapeutic drug monitoring (TDM) samples per patient. Median relative prediction error (MPE) [%] and median absolute relative prediction error (MAPE) [%] were calculated to quantify accuracy and precision.

RESULTS

The evaluation revealed a large inter-model variability (A: MPE - 135.6-78.3% and MAPE 35.7-135.6%). Integration of TDM data improved all model predictions (B1/B2 relative improvement vs. A: |MPE|median_all_models 45.1/67.5%; MAPEmedian_all_models 29/39%). The model by Kim et al. was identified to be most appropriate for the total dataset (A/B1/B2: MPE - 9.8/- 5.9/- 0.9%; MAPE 37/27.3/23.7%), Udy et al. performed best in patients receiving intermittent infusion, and Klastrup et al. best predicted patients receiving continuous infusion. Additional evaluations stratified by sex and renal replacement therapy revealed further promising models.

CONCLUSION

The predictive performance of published PIP models in ICU patients varied considerably, highlighting the relevance of appropriate model selection for MIPD. Our differentiated external evaluation identified specific models suitable for clinical use, especially in combination with TDM.

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).

Software- and TDM-Guided Dosing of Meropenem Promises High Rates of Target Attainment in Critically Ill Patients

Various studies have reported insufficient beta-lactam concentrations in critically ill patients. The optimal dosing strategy for beta-lactams in critically ill patients, particularly in septic patients, is an ongoing matter of discussion. This retrospective study aimed to evaluate the success of software-guided empiric meropenem dosing (CADDy, Calculator to Approximate Drug-Dosing in Dialysis) with subsequent routine meropenem measurements and expert clinical pharmacological interpretations. Adequate therapeutic drug exposure was defined as concentrations of 8-16 mg/L, whereas concentrations of 16-24 mg/L were defined as moderately high and concentrations >24 mg/L as potentially harmful. A total of 91 patients received meropenem as a continuous infusion (229 serum concentrations), of whom 60% achieved 8-16 mg/L, 23% achieved 16-24 mg/L, and 10% achieved unnecessarily high and potentially harmful meropenem concentrations >24 mg/L in the first 48 h using the dosing software. No patient showed concentrations <2 mg/L using the dosing software in the first 48 h. With a subsequent TDM-guided dose adjustment, therapeutic drug exposure was significantly (p ≤ 0.05) enhanced to 70%. No patient had meropenem concentrations >24 mg/L with TDM-guided dose adjustments. The combined use of dosing software and consecutive TDM promised a high rate of adequate therapeutic drug exposures of meropenem in patients with sepsis and septic shock.

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).

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.

Serum linezolid concentrations are reduced in critically ill patients with pulmonary infections: A prospective observational study

RATIONALE

The concentration-time profile of linezolid varies considerably in critically ill patients. Question of interest is, if the site of infection influences linezolid serum concentrations.

METHODS

68 critically ill patients, treated with linezolid, were included. The concentration-time-profile for linezolid was determined using maximum a-posteriori predictions. A trough concentration (C_min) between 2 and 10 mg/L was defined as the target. A generalized linear model (GLM) was established to evaluate potential covariates.

RESULTS

The indications for linezolid therapy were in descending order: peritonitis (38.2%), pneumonia (25.0%), infectious acute respiratory distress syndrome (ARDS) (19.1%), and other non-pulmonary infection (17.7%). 27.2 and 7.9% of C_min were subtherapeutic and toxic, respectively. In the GLM, ARDS (mean: -2.1 mg/L, CI: -3.0 to -1.2 mg/L) and pneumonia (mean: -2.2 mg/L, CI: -2.8 to -1.6 mg/L) were significant (p < 0.001) determinants of C_min. Patients with ARDS (mean: 2.3 mg/L, 51.2% subtherapeutic, 0.0% toxic) and pneumonia (mean: 3.5 mg/L, 41.5% subtherapeutic, 7.7% toxic) had significantly (p < 0.001) lower C_min than those with peritonitis (mean: 5.5 mg/L, 14.4% subtherapeutic, 9.3% toxic) and other non-pulmonary infection (mean: 5.2 mg/L, 3.3% subtherapeutic, 16.5% toxic).

CONCLUSION

Linezolid serum concentrations are reduced in patients with pulmonary infections. Future studies should investigate if other linezolid thresholds are needed in those patients due to linezolid pooling in patients´ lung.

Systematic Evaluation of Voriconazole Pharmacokinetic Models without Pharmacogenetic Information for Bayesian Forecasting in Critically Ill Patients

Voriconazole (VRC) is used as first line antifungal agent against invasive aspergillosis. Model-based approaches might optimize VRC therapy. This study aimed to investigate the predictive performance of pharmacokinetic models of VRC without pharmacogenetic information for their suitability for model-informed precision dosing. Seven PopPK models were selected from a systematic literature review. A total of 66 measured VRC plasma concentrations from 33 critically ill patients was employed for analysis. The second measurement per patient was used to calculate relative Bias (rBias), mean error (ME), relative root mean squared error (rRMSE) and mean absolute error (MAE) (i) only based on patient characteristics and dosing history (a priori) and (ii) integrating the first measured concentration to predict the second concentration (Bayesian forecasting). The a priori rBias/ME and rRMSE/MAE varied substantially between the models, ranging from −15.4 to 124.6%/−0.70 to 8.01 mg/L and from 89.3 to 139.1%/1.45 to 8.11 mg/L, respectively. The integration of the first TDM sample improved the predictive performance of all models, with the model by Chen (85.0%) showing the best predictive performance (rRMSE: 85.0%; rBias: 4.0%). Our study revealed a certain degree of imprecision for all investigated models, so their sole use is not recommendable. Models with a higher performance would be necessary for clinical use.

Simultaneous LC-ESI-MS/MS Quantification of Levosimendan and Its Metabolites for Therapeutic Drug Monitoring of Cardiac Surgery Patients

Levosimendan is used in severe chronic cardiac insufficiency, also within the peri-operative setting. Real-life pharmacokinetic data in surgical patients is lacking, making therapeutic drug monitoring (TDM) of levosimendan, its pharmacologically active metabolite OR-1896, and its intermediate OR-1855 important. A simultaneous highly sensitive quantification of levosimendan and its metabolites in small-volume samples has not yet been described. Here, levosimendan (LLOQ 0.450 nM), OR-1896, and OR-1855 (LLOQ both 1.0 nM) were successfully quantified by LC-ESI-MS/MS after liquid-liquid extraction in 300 µL of blood. A short C8 column under reversed-phase conditions enabled simultaneous and fast quantification of levosimendan in the negative and the metabolites in the positive ionization mode in a single run within 2 min. Interestingly and unexpectedly, constitutional isomers of levosimendan metabolites with identical mass transitions and similar retention times were observed in surgical patients’ samples, which we identified as the metamizole metabolites 4-aminoantipyrine and 4-acetamidoantipyrine. A longer C8 column and a modified mobile phase enabled selective quantification of all analytes in a single run within 7 min. We developed, validated, and applied highly sensitive LC-ESI-MS/MS methods for simultaneous quantification of levosimendan and its metabolites, enabling efficient TDM of cardiac surgery patients even with additional metamizole administration.

[Therapeutic drug monitoring and pharmacokinetic models as a strategy for rational antibiotic therapy in intensive care patients]

BACKGROUND AND OBJECTIVE

Antibiotic dosing in intensive care patients is complex due to pharmacokinetic (PK) alterations. The aim of this article is to illustrate the role of therapeutic drug monitoring (TDM) and PK models to individualize antibiotic dosing.

MATERIAL AND METHODS

Guidelines and recommendations are discussed in the context of clinical practice and the prerequisites for routine TDM of different antibiotics are presented. In addition, the benefits and limitations of TDM are discussed. The advantages and disadvantages of TDM and PK models are described and the resulting future options are presented.

RESULTS

In the clinical routine, the peak or trough concentrations of antibiotics in blood are measured depending on the antibiotic class. Prerequisites for a purposeful TDM are a coordinated blood sampling and a prompt reporting of findings. As target ranges are not uniformly defined following rules, dosage adjustments are difficult. The PK models offer a valid possibility to individualize the antibiotic therapy of intensive care patients. Areas of application are the calculation of the loading dose and the combination with TDM for treatment control. For whom and how often TDM is necessary and how it can best be combined with PK models or even replace them should be investigated in the future, in addition to evaluation of the optimal target area.

CONCLUSION

The routine use of TDM for antibiotics in intensive care patients is only effective under the abovementioned conditions. By combination with PK models the treatment could be optimized in the future.

Does the cytokine adsorber CytoSorb® reduce vancomycin exposure in critically ill patients with sepsis or septic shock? a prospective observational study

BACKGROUND

Hemadsorption of cytokines is used in critically ill patients with sepsis or septic shock. Concerns have been raised that the cytokine adsorber CytoSorb^® unintentionally adsorbs vancomycin. This study aimed to quantify vancomycin elimination by CytoSorb^®.

METHODS

Critically ill patients with sepsis or septic shock receiving continuous renal replacement therapy and CytoSorb^® treatment during a prospective observational study were included in the analysis. Vancomycin pharmacokinetics was characterized using population pharmacokinetic modeling. Adsorption of vancomycin by the CytoSorb^® was investigated as linear or saturable process. The final model was used to derive dosing recommendations based on stochastic simulations.

RESULTS

20 CytoSorb^® treatments in 7 patients (160 serum samples/24 during CytoSorb^®-treatment, all continuous infusion) were included in the study. A classical one-compartment model, including effluent flow rate of the continuous hemodialysis as linear covariate on clearance, best described the measured concentrations (without CytoSorb^®). Significant adsorption with a linear decrease during CytoSorb^® treatment was identified (p < 0.0001) and revealed a maximum increase in vancomycin clearance of 291% (initially after CytoSorb^® installation) and a maximum adsorption capacity of 572 mg. For a representative patient of our cohort a reduction of the area under the curve (AUC) by 93 mg/L*24 h during CytoSorb^® treatment was observed. The additional administration of 500 mg vancomycin over 2 h during CytoSorb^® attenuated the effect and revealed a negligible reduction of the AUC by 4 mg/L*24 h.

CONCLUSION

We recommend the infusion of 500 mg vancomycin over 2 h during CytoSorb^® treatment to avoid subtherapeutic concentrations. Trial registration NCT03985605. Registered 14 June 2019, https://clinicaltrials.gov/ct2/show/NCT03985605.

Trough concentrations of meropenem and piperacillin during slow extended dialysis in critically ill patients with intermittent and continuous infusion: A prospective observational study

Beta-lactam dosing is challenging in critically ill patients with slow extended daily dialysis (SLEDD). This prospective observational study aimed to investigate meropenem and piperacillin concentrations and half-lives during SLEDD and in SLEDD-free intervals. Critically ill patients with SLEDD-therapy and meropenem or piperacillin therapy were included. Breakpoints of target attainment were defined as 2 and 20.8 mg/L for meropenem and piperacillin, respectively. Daily TDM was performed and therapies were adapted based on the measured concentrations. Elimination rate constants were determined by using nonlinear regression analysis. Seventeen patients were included (48 SLEDD intervals; median SLEDD-duration: 7.25 h). The median antibiotic trough concentrations and half-lives were significantly (p < 0.001) lower during and after the SLEDD-therapy compared to SLEDD-free intervals (median meropenem: 22.3 (IQR: 12.8, 25.6) vs. 28.3 mg/L (IQR: 16.9, 37.4); median piperacillin: 55.8 (IQR: 45.1, 84.9) vs. 130 mg/L (IQR: 91.5, 154.5); relative change: -48.0% each, IQR meropenem: -33.3, -58.5%; IQR piperacillin: -36.3, -52.1%). However, none of the measured trough concentrations were subtherapeutic during SLEDD. SLEDD leads to a reduction in meropenem and piperacillin concentrations of approximately 50% independently of the initial concentration. If the concentration is twice as high as the breakpoint of target attainment before SLEDD-therapy, subtherapeutic levels can be avoided.

Can the cytokine adsorber CytoSorb® help to mitigate cytokine storm and reduce mortality in critically ill patients? A propensity score matching analysis

Background

A cytokine storm is life threatening for critically ill patients and is mainly caused by sepsis or severe trauma. In combination with supportive therapy, the cytokine adsorber Cytosorb^® (CS) is increasingly used for the treatment of cytokine storm. However, it is questionable whether its use is actually beneficial in these patients.

Methods

Patients with an interleukin-6 (IL-6) > 10,000 pg/ml were retrospectively included between October 2014 and May 2020 and were divided into two groups (group 1: CS therapy; group 2: no CS therapy). Inclusion criteria were a regularly measured IL-6 and, for patients allocated to group 1, CS therapy for at least 90 min. A propensity score (PS) matching analysis with significant baseline differences as predictors (Simplified Acute Physiology Score (SAPS) II, extracorporeal membrane oxygenation, renal replacement therapy, IL-6, lactate and norepinephrine demand) was performed to compare both groups (adjustment tolerance: < 0.05; standardization tolerance: < 10%). U-test and Fisher’s-test were used for independent variables and the Wilcoxon test was used for dependent variables.

Results

In total, 143 patients were included in the initial evaluation (group 1: 38; group 2: 105). Nineteen comparable pairings could be formed (mean initial IL-6: 58,385 vs. 59,812 pg/ml; mean SAPS II: 77 vs. 75). There was a significant reduction in IL-6 in patients with (p < 0.001) and without CS treatment (p = 0.005). However, there was no significant difference (p = 0.708) in the median relative reduction in both groups (89% vs. 80%). Furthermore, there was no significant difference in the relative change in C-reactive protein, lactate, or norepinephrine demand in either group and the in-hospital mortality was similar between groups (73.7%).

Conclusion

Our study showed no difference in IL-6 reduction, hemodynamic stabilization, or mortality in patients with Cytosorb^® treatment compared to a matched patient population.

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.

Successful elimination of bilirubin in critically ill patients with acute liver dysfunction using a cytokine adsorber and albumin dialysis: a pilot study

There are different methods of artificial liver support for patients with acute liver dysfunction (ALD). However, CytoSorb (CS) might be a new approved option for those patients. Question of interest is whether the elimination performance of CS was comparable to that of advanced organ support (ADVOS). Patients, treated with CS (integrated into high-flux dialysis) or ADVOS and a total bilirubin > 10 mg/dl were included. Laboratory parameters were evaluated before starting therapy (d0) and 12–24 h thereafter (d1). The Wilcoxon-test with associated samples was used for statistical analysis. Thirty-nine patients (33 CS, 6 ADVOS) were included. The median bilirubin at d0 was 16.9 and 17.7 mg/dl and at d1 was 13.2 and 15.9 mg/dl, in the CS and ADVOS group, respectively. There was a significant bilirubin reduction as well in the CS group (p < 0.001, median relative reduction: 22.5%) as in the ADVOS group (p = 0.028, median relative reduction: 22.8%). There was no significant difference in the relative bilirubin reduction between CS and ADVOS therapies. The use of CytoSorb and ADVOS in patients with ALD led to a significant and comparable decrease in total bilirubin. The easy use of CS might be an advantage compared to other procedures.

Simultaneous quantification of seven repurposed COVID-19 drugs remdesivir (plus metabolite GS-441524), chloroquine, hydroxychloroquine, lopinavir, ritonavir, favipiravir and azithromycin by a two-dimensional isotope dilution LC-MS/MS method in human serum

BACKGROUND

The present COVID-19 pandemic has prompted worldwide repurposing of drugs. The aim of the present work was to develop and validate a two-dimensional isotope-dilution liquid chromatrography tandem mass spectrometry (ID-LC-MS/MS) method for accurate quantification of remdesivir and its active metabolite GS-441524, chloroquine, hydroxychloroquine, lopinavir, ritonavir, favipiravir and azithromycin in serum; drugs that have gained attention for repurposing in the treatment of COVID-19.

METHODS

Following protein precipitation, samples were separated with a two-dimensional ultra-high performance liquid chromatography (2D-UHPLC) setup, consisting of an online solid phase extraction (SPE) coupled to an analytical column. For quantification, stable isotope-labelled analogues were used as internal standards for all analytes. The method was validated on the basis of the European Medicines Agency bioanalytical method validation protocol.

RESULTS

Detuning of lopinavir and ritonavir allowed simultaneous quantification of all analytes with different concentration ranges and sensitivity with a uniform injection volume of 5 μL. The method provided robust validation results with inaccuracy and imprecision values of ≤ 9.59 % and ≤ 11.1 % for all quality controls.

CONCLUSION

The presented method is suitable for accurate and simultaneous quantification of remdesivir, its metabolite GS-441525, chloroquine, hydroxychloroquine, lopinavir, ritonavir, favipiravir and azithromycin in human serum. The quantitative assay may be an efficient tool for the therapeutic drug monitoring of these potential drug candidates in COVID-19 patients in order to increase treatment efficacy and safety.

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.

The higher the better? Defining the optimal beta-lactam target for critically ill patients to reach infection resolution and improve outcome

OBJECTIVES

Beta-lactam antibiotics are often subject to therapeutic drug monitoring, but breakpoints of target attainment are mostly based on expert opinions. Studies that show a correlation between target attainment and infection resolution are missing. This analysis investigated whether there is a difference in infection resolution based on two breakpoints of target attainment.

METHODS

An outcome group out of 1392 critically ill patients treated with meropenem or piperacillin-tazobactam was formed due to different selection criteria. Afterwards, three groups were created: group 1=free drug concentration (f) was < 100% of the time (T) above the minimal inhibitory concentration (MIC) (< 100% fT > MIC), group 2=100% fT > MIC < 4xMIC, and group 3=100% fT > 4xMIC. Parameters for infection control, renal and liver function, and estimated and observed in-hospital mortality were compared between those groups. Statistical analysis was performed with one-way analysis of variance, Tukey post hoc test, U test, and bivariate logistic regression.

RESULTS

The outcome group consisted of 55 patients (groups 1-3, 17, 24, and 14 patients, respectively). Patients allocated to group 2 or 3 had a significantly faster reduction of the C-reactive protein in contrast to patients allocated to group 1 (p = 0.033 and p = 0.026). Patients allocated to group 3 had a worse renal function, a higher Acute Physiology and Chronic Health Evaluation (APACHE II) score, were older, and had a significantly higher in-hospital mortality compared to group 1 (p = 0.017) and group 2 (p = 0.001). The higher mortality was significantly influenced by worse liver function, higher APACHE II, and higher Sequential Organ Failure Assessment (SOFA) score and norepinephrine therapy.

CONCLUSION

Achieving the target 100% fT > MIC leads to faster infection resolution in the critically ill. However, there was no benefit for patients who reached the highest target of 100% fT > 4xMIC, although the mortality rate was higher possibly due to confounding effects. In conclusion, we recommend the target 100% fT > MIC < 4xMIC for critically ill patients.

TRIAL REGISTRATION

NCT03985605.

Therapeutic Drug Monitoring of Meropenem and Piperacillin in Critical Illness-Experience and Recommendations from One Year in Routine Clinical Practice

Various studies have reported insufficient beta-lactam concentrations in critically ill patients. The extent to which therapeutic drug monitoring (TDM) in clinical practice can reduce insufficient antibiotic concentrations is an ongoing matter of investigation. We retrospectively evaluated routine meropenem and piperacillin measurements in critically ill patients who received antibiotics as short infusions in the first year after initiating a beta-lactam TDM program. Total trough concentrations above 8.0 mg/L for meropenem and above 22.5 mg/L for piperacillin were defined as the breakpoints for target attainment. We included 1832 meropenem samples and 636 piperacillin samples. We found that 39.3% of meropenem and 33.6% of piperacillin samples did not reach the target concentrations. We observed a clear correlation between renal function and antibiotic concentration (meropenem, r = 0.53; piperacillin, r = 0.63). Patients with renal replacement therapy or creatinine clearance (CrCl) of <70 mL/min had high rates of target attainment with the standard dosing regimens. There was a low number of patients with a CrCl >100 mL/min that achieved the target concentrations with the maximum recommended dosage. Patients with impaired renal function only required TDM if toxic side effects were noted. In contrast, patients with normal renal function required different dosage regimens and TDM-guided therapy to reach the breakpoints of target attainment.

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.

Impact of Experimental Variables on the Protein Binding of Tigecycline in Human Plasma as Determined by Ultrafiltration

Tigecycline, a tetracycline derivative, shows atypical plasma protein binding behavior. The unbound fraction decreases with increasing concentration at therapeutic concentrations. Moreover, uncertainty exists about the magnitude of tigecyline's protein binding in man. Unbound fractions between 2.5% and 35% have been reported in plasma from healthy volunteers, and between 25% and 100% in patients, respectively. In the present study, the protein binding of tigecycline has been investigated by ultrafiltration using different experimental conditions. Whereas temperature had only a marginal influence, the unbound fraction at 0.3/3.0 mg/L was low at pH 8.2 (9.4%/1.9%) or in unbuffered pooled plasma (6.3%/1.2%), compared with plasma buffered with HEPES to pH 7.4 (65.9%/39.7%). In experiments with phosphate buffer and EDTA, the concentration dependency was markedly attenuated or abolished, which is compatible with a cooperative binding mechanism involving divalent cations such as calcium. The unbound fraction in clinical plasma samples from patients treated with tigecycline was determined to 66.3 ± 13.7% at concentrations <0.3 mg/L compared with 41.3 ± 16.0% at >1 to <5 mg/L. To summarize, tigecycline appears to be only moderately bound to plasma proteins as determined by ultrafiltration, when a physiological pH is maintained.

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.