Automation in Busulfan Therapeutic Drug Monitoring: Evaluation of an Immunoassay on two Routine Chemistry Analyzers.

BACKGROUND: Therapeutic drug monitoring (TDM) of busulfan is recommended for hematopoietic stem cell transplant recipients. Timely reporting of these TDM results is essential given the short administration period and the planned dose adjustments on day 2. The authors evaluated the performance of a new nanoparticle-based competitive immunoassay on two routine clinical chemistry analyzers and compared its performance to that of an in-house high-resolution mass spectrometry (HRMS) method. METHODS: The MyCare Oncology Busulfan Assay Kit (Saladax Biomedical) was applied on two routine clinical chemistry analyzers (Abbott Architect c8000 and Roche Cobas c502) with a linearity range of 187-2000 ng/mL. The study evaluation measured imprecision and accuracy, sample probe carry-over, and dilution integrity. Method comparison with liquid chromatography (LC)-HRMS was performed using samples from patients undergoing busulfan treatment. RESULTS: Within- and between-run coefficient of variations for both analyzers were ≤5.23% and ≤8.45%, respectively, across the busulfan concentration range. The obtained biases were ≤10.3%. Both analyzers met the acceptance criteria for sample probe carry-over and dilution integrity. Agreement between the immunoassay and LC-HRMS was high: 92% and 89% of the samples measured on Architect and Cobas, respectively, were within the ±15% limit compared to the corresponding LC-HRMS results. CONCLUSIONS: Overall, good analytical performance and high agreement with LC-HRMS results were obtained for the immunoassay installed on both routine clinical chemistry analyzers. Therefore, this assay could be implemented as a valid alternative for LC methods in clinical laboratories on different open-channel clinical chemistry analyzers, resulting in shorter turn-around times for reporting busulfan TDM results with subsequent faster dosage adjustments.

Analytical performance of eight enzymatic assays for ethanol in serum evaluated by data from the Belgian external quality assessment scheme.

OBJECTIVES: Fast and reliable ethanol assays analysis are used in a clinical context for patients suspected of ethanol intoxication. Mostly, automated systems using an enzymatic reaction based on ethanol dehydrogenase are used. The manuscript focusses on the evaluation of the performance of these assays. METHODS: Data included 30 serum samples used in the Belgian EQA scheme from 2019 to 2021 and concentrations ranged from 0.13 to 3.70 g/L. A regression line between target concentrations and reported values was calculated to evaluate outliers, bias, variability and measurement uncertainty. RESULTS: A total of 1,611 results were taken into account. Bias was the highest for Alinity c over the whole concentration range and the lowest for Vitros for low concentrations and Cobas 8000 using the c702 module for high concentrations. The Architect and Cobas c501/c502 systems showed the lowest variability over the whole concentration range. Highest variability was observed for Cobas 8000 using the 702 module, Thermo Scientific and Alinity c. Cobas 8000 using the c702 module showed the highest measurement uncertainty for lower concentrations. For higher concentrations, Alinity c, Thermo Scientific and Vitros were the methods with the highest measurement uncertainty. CONCLUSIONS: The bias of the enzymatic techniques is nearly negligible for all methods except Alinity c. Variability differs strongly between measurement procedures. This study shows that the Alinity c has a worse measurement uncertainty than other systems for concentrations above 0.5 g/L. Overall, we found the differences in measurement uncertainty to be mainly influenced by the differences in variability.

First identification, chemical analysis and pharmacological characterization of N-piperidinyl etonitazene (etonitazepipne), a recent addition to the 2-benzylbenzimidazole opioid subclass.

N-Piperidinyl etonitazene ('etonitazepipne') represents a recent addition to the rapidly expanding class of 2-benzylbenzimidazole 'nitazene' opioids. Following its first identification in an online-sourced powder and in biological samples from a patient seeking help for detoxification, this report details its in-depth chemical analysis and pharmacological characterization. Analysis of the powder via different techniques (LC-HRMS, GC-MS, UHPLC-DAD, FT-IR) led to the unequivocal identification of N-piperidinyl etonitazene. Furthermore, we report the first activity-based detection and analytical identification of N-piperidinyl etonitazene in authentic samples. LC-HRMS analysis revealed concentrations of 1.21 ng/mL in serum and 0.51 ng/mL in urine, whereas molecular networking enabled the tentative identification of various (potentially active) urinary metabolites. In addition, we determined that the extent of opioid activity present in the patient's serum was equivalent to the in vitro opioid activity exerted by 2.5-10 ng/mL fentanyl or 10-25 ng/mL hydromorphone in serum. Radioligand binding assays in rat brain tissue revealed that the drug binds with high affinity (Ki = 14.3 nM) to the µ-opioid receptor (MOR). Using a MOR-ß-arrestin2 activation assay, we found that N-piperidinyl etonitazene is highly potent (EC50 = 2.49 nM) and efficacious (Emax = 183% versus hydromorphone) in vitro. Pharmacodynamic evaluation in male Sprague Dawley rats showed that N-piperidinyl etonitazene induces opioid-like antinociceptive, cataleptic, and thermic effects, its potency in the hot plate assay (ED50 = 0.0205 mg/kg) being comparable to that of fentanyl (ED50 = 0.0209 mg/kg), and > 190 times higher than that of morphine (ED50 = 3.940 mg/kg). Taken together, our findings indicate that N-piperidinyl etonitazene is a potent opioid with the potential to cause harm in users.

Suboptimal Beta-Lactam Therapy in Critically Ill Children: Risk Factors and Outcome.

OBJECTIVES: In critically ill children, severely altered pharmacokinetics may result in subtherapeutic ß-lactam antibiotic concentrations when standard pediatric dosing regimens are applied. However, it remains unclear how to recognize patients most at risk for suboptimal exposure and their outcome. This study aimed to: 1) describe target attainment for ß-lactam antibiotics in critically ill children, 2) identify risk factors for suboptimal exposure, and 3) study the association between target nonattainment and clinical outcome. DESIGN: Post hoc analysis of the "Antibiotic Dosing in Pediatric Intensive Care" study (NCT02456974, 2012-2019). Steady-state trough plasma concentrations were classified as therapeutic if greater than or equal to the minimum inhibitory concentration of the (suspected) pathogen. Factors associated with subtherapeutic concentrations and clinical outcome were identified by logistic regression analysis. SETTING: The pediatric and cardiac surgery ICU of a Belgian tertiary-care hospital. PATIENTS: One hundred fifty-seven patients (aged 1 mo to 15 yr) treated intravenously with amoxicillin-clavulanic acid, piperacillin-tazobactam, or meropenem. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Three hundred eighty-two trough concentrations were obtained from 157 patients (median age, 1.25 yr; interquartile range, 0.4-4.2 yr). Subtherapeutic concentrations were measured in 39 of 60 (65%), 43 of 48 (90%), and 35 of 49 (71%) of patients treated with amoxicillin-clavulanic acid, piperacillin-tazobactam, and meropenem, respectively. Estimates of glomerular filtration rate (eGFR; 54% increase in odds for each sd increase in value, 95% CI, 0.287-0.736; p = 0.001) and the absence of vasopressor treatment (2.8-fold greater odds, 95% CI, 1.079-7.253; p = 0.034) were independently associated with target nonattainment. We failed to identify an association between antibiotic concentrations and clinical failure. CONCLUSIONS: Subtherapeutic ß-lactam concentrations are common in critically ill children and correlate with renal function. eGFR equations may be helpful in identifying patients who may require higher dosing. Future studies should focus on the impact of subtherapeutic concentrations on clinical outcome.

Development and evaluation of uncertainty quantifying machine learning models to predict piperacillin plasma concentrations in critically ill patients.

BACKGROUND: Beta-lactam antimicrobial concentrations are frequently suboptimal in critically ill patients. Population pharmacokinetic (PopPK) modeling is the golden standard to predict drug concentrations. However, currently available PopPK models often lack predictive accuracy, making them less suited to guide dosing regimen adaptations. Furthermore, many currently developed models for clinical applications often lack uncertainty quantification. We, therefore, aimed to develop machine learning (ML) models for the prediction of piperacillin plasma concentrations while also providing uncertainty quantification with the aim of clinical practice. METHODS: Blood samples for piperacillin analysis were prospectively collected from critically ill patients receiving continuous infusion of piperacillin/tazobactam. Interpretable ML models for the prediction of piperacillin concentrations were designed using CatBoost and Gaussian processes. Distribution-based Uncertainty Quantification was added to the CatBoost model using a proposed Quantile Ensemble method, useable for any model optimizing a quantile function. These models are subsequently evaluated using the distribution coverage error, a proposed interpretable uncertainty quantification calibration metric. Development and internal evaluation of the ML models were performed on the Ghent University Hospital database (752 piperacillin concentrations from 282 patients). Ensuing, ML models were compared with a published PopPK model on a database from the University Medical Centre of Groningen where a different dosing regimen is used (46 piperacillin concentrations from 15 patients.). RESULTS: The best performing model was the Catboost model with an RMSE and [Formula: see text] of 31.94-0.64 and 33.53-0.60 for internal evaluation with and without previous concentration. Furthermore, the results prove the added value of the proposed Quantile Ensemble model in providing clinically useful individualized uncertainty predictions and show the limits of homoscedastic methods like Gaussian Processes in clinical applications. CONCLUSIONS: Our results show that ML models can consistently estimate piperacillin concentrations with acceptable and high predictive accuracy when identical dosing regimens as in the training data are used while providing highly relevant uncertainty predictions. However, generalization capabilities to other dosing schemes are limited. Notwithstanding, incorporating ML models in therapeutic drug monitoring programs seems definitely promising and the current work provides a basis for validating the model in clinical practice.

Long-term chemogenetic suppression of seizures in a multifocal rat model of temporal lobe epilepsy.

OBJECTIVE: One third of epilepsy patients do not become seizure-free using conventional medication. Therefore, there is a need for alternative treatments. Preclinical research using designer receptors exclusively activated by designer drugs (DREADDs) has demonstrated initial success in suppressing epileptic activity. Here, we evaluated whether long-term chemogenetic seizure suppression could be obtained in the intraperitoneal kainic acid rat model of temporal lobe epilepsy, when DREADDs were selectively expressed in excitatory hippocampal neurons. METHODS: Epileptic male Sprague Dawley rats received unilateral hippocampal injections of adeno-associated viral vector encoding the inhibitory DREADD hM4D(Gi), preceded by a cell-specific promotor targeting excitatory neurons. The effect of clozapine-mediated DREADD activation on dentate gyrus evoked potentials and spontaneous electrographic seizures was evaluated. Animals were systemically treated with single (.1 mg/kg/24 h) or repeated (.1 mg/kg/6 h) injections of clozapine. In addition, long-term continuous release of clozapine and olanzapine (2.8 mg/kg/7 days) using implantable minipumps was evaluated. All treatments were administered during the chronic epileptic phase and between 1.5 and 13.5 months after viral transduction. RESULTS: In the DREADD group, dentate gyrus evoked potentials were inhibited after clozapine treatment. Only in DREADD-expressing animals, clozapine reduced seizure frequency during the first 6 h postinjection. When administered repeatedly, seizures were suppressed during the entire day. Long-term treatment with clozapine and olanzapine both resulted in significant seizure-suppressing effects for multiple days. Histological analysis revealed DREADD expression in both hippocampi and some cortical regions. However, lesions were also detected at the site of vector injection. SIGNIFICANCE: This study shows that inhibition of the hippocampus using chemogenetics results in potent seizure-suppressing effects in the intraperitoneal kainic acid rat model, even 1 year after viral transduction. Despite a need for further optimization, chemogenetic neuromodulation represents a promising treatment prospect for temporal lobe epilepsy.

A sensitive and high-throughput quantitative liquid chromatography high-resolution mass spectrometry method for therapeutic drug monitoring of 10 ß-lactam antibiotics, linezolid and two ß-lactamase inhibitors in human plasma.

An ultra-high pressure liquid chromatography high-resolution mass spectrometric (UHPLC-HRMS) method was developed for the simultaneous and sensitive quantification of 10 ß-lactam antibiotics (cefepime, meropenem, amoxicillin, cefazolin, benzylpenicillin, ceftazidime, piperacillin, flucloxacillin, cefuroxime and aztreonam), linezolid and ß-lactamase inhibitors tazobactam and clavulanic acid in human plasma. Validation according to the EMA guidelines showed excellent within- and between-run accuracy and precision (i.e. between 1.1 and 8.5%) and high sensitivity (i.e. lower limit of quantification between 0.25 and 1 mg/L). The UHPLC-HRMS method enables a short turnaround time and high sensitivity and needs only a small amount of plasma, allowing appropriate routine therapeutic drug monitoring. The short turnaround time is obtained by speeding up the protocol on multiple levels, i.e. fast and workload-efficient sample preparation (i.e. protein precipitation and dilution), short (4 min) instrument run time, simultaneous measurement of all relevant ß-lactam antibiotics used in the intensive care unit and the use of the same instrument, column and mobile phases as for the other routine methods in our laboratory.

Population pharmacokinetics and evaluation of the predictive performance of pharmacokinetic models in critically ill patients receiving continuous infusion meropenem: a comparison of eight pharmacokinetic models.

Background: Several population pharmacokinetic (PopPK) models for meropenem dosing in ICU patients are available. It is not known to what extent these models can predict meropenem concentrations in an independent validation dataset when meropenem is infused continuously. Patients and methods: A PopPK model was developed with concentration-time data collected from routine care of 21 ICU patients (38 samples) receiving continuous infusion meropenem. The predictability of this model and seven other published PopPK models was studied using an independent dataset that consisted of 47 ICU patients (161 samples) receiving continuous infusion meropenem. A statistical comparison of imprecision (mean square prediction error) and bias (mean prediction error) was conducted. Results: A one-compartment model with linear elimination and creatinine clearance as a covariate of clearance best described our data. The mean ± SD parameter estimate for CL was 9.89 ±âŸ3.71 L/h. The estimated volume of distribution was 48.1 L. The different PopPK models showed a bias in predicting serum concentrations from the validation dataset that ranged from -8.76 to 7.06 mg/L. Imprecision ranged from 9.90 to 42.1 mg/L. Conclusions: Published PopPK models for meropenem vary considerably in their predictive performance when validated in an external dataset of ICU patients receiving continuous infusion meropenem. It is necessary to validate PopPK models in a target population before implementing them in a therapeutic drug monitoring program aimed at optimizing meropenem dosing.

Measuring Unbound Versus Total Piperacillin Concentrations in Plasma of Critically Ill Patients: Methodological Issues and Relevance.

BACKGROUND: Piperacillin is considered a moderately protein-bound antibiotic (20%-40%), with albumin being an important binding protein. Although infrequently used in practice, different methods to measure the fraction unbound (fu) are available, but uncertainty remains as to what the most appropriate method is. The main goal of this study was to estimate the impact of the methodology used to measure unbound piperacillin in plasma on the fu of piperacillin; we compared ultrafiltration (UF) at 4°C and 37°C with the reference method, equilibrium dialysis. In addition, we analyzed the impact of other proteins on the fu. METHODS: Anonymized left-over Li-heparin plasma samples (n = 41) from 30 critically ill patients who were treated with piperacillin were used for the analyses. RESULTS: We found that the piperacillin fu, determined by UF, is on average 8% higher at 37°C (91%) than at 4°C (83%). There were no systematic or proportional differences between UF at 4°C and equilibrium dialysis at 4°C. This emphasizes the importance of the temperature during UF, which should therefore be clearly stated in publications that report on the methodology of UF. No significant impact of the albumin-, IgA-, total protein-, or α1-acid glycoprotein concentration on the fu was found. The fu found in this study was higher than the generally assumed fu value of 60%-80%. A possible explanation lies in the studied population or in the temperature used. Based on our results, routine monitoring of unbound piperacillin in intensive care unit patients is not recommended. CONCLUSIONS: Based on the prediction model, we can state that in intensive care patients the fu of piperacillin is 91% (SD 7%), determined with UF at 37°C.

Development and validation of an LC tandem MS assay for the quantification of ß-lactam antibiotics in the sputum of cystic fibrosis patients.

OBJECTIVES: Antibiotic therapy is of vital importance for the control of infectious exacerbations in cystic fibrosis (CF) patients. However, very little is known regarding the fraction of systemically administered antibiotics reaching the lower respiratory tract secretions. We developed and validated a method to measure the concentrations of piperacillin, ceftazidime, meropenem and aztreonam in CF sputum, and present the validation data. METHODS: Ultra-performance LC coupled to tandem MS was used. A single sample can be measured in 2.5 min with multiple reaction monitoring in positive electrospray ionization mode. Deuterated internal standards were used and a concentration range of 0.7-160 mg/L was covered. The method was validated according to the EMA guideline on analytical method validation. RESULTS: The boundaries within which a reliable measurement in CF sputum can be performed were determined. A few constraints are linked to the instability of the antibiotics in sputum. Piperacillin showed limited stability at room temperature and during freeze-thaw cycles. Autosampler instability was observed after 15 h for aztreonam at low concentrations. CONCLUSIONS: The method allows a reliable measurement of the selected antibiotics, if precautions are taken regarding the limited stability of piperacillin at room temperature. Due to freeze-thaw instability, piperacillin should always be analysed on the day of sampling. Quick review of the analytical data and reanalysis are needed as low concentrations of aztreonam are not stable in the autosampler.

Multicenter Evaluation of a New Electrochemiluminescence Immunoassay for Everolimus Concentrations in Whole Blood.

BACKGROUND: The precise monitoring of everolimus, an immunosuppressant drug, is vital for transplant recipients due to its narrow therapeutic range. This study evaluated the analytical performance of a new electrochemiluminescence immunoassay (ECLIA) for everolimus concentrations in whole blood. METHODS: Accuracy, imprecision, and sensitivity studies for the Roche Elecsys everolimus ECLIA were performed at 5 European laboratories. The ECLIA was compared with liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods, as well as the Quantitative Microsphere System everolimus assay. RESULTS: Everolimus ECLIA accuracies were within the range 100% ± 9%. Coefficients of variation (CVs) across the target range were ≤4.8% for repeatability and ≤8.4% for intermediate imprecision, whereas multisite reproducibility at lower (2.71 mcg/L) and higher everolimus concentrations (3.0-30.0 mcg/L) resulted in CVs of ≤13.7% and ≤12.4%, respectively. The CV at the assay's lower limit of quantification without considering bias was excellent, estimated as ≤9.3% at 0.5 mcg/L. The weighted Deming regression analysis, used for comparison of the results obtained by everolimus ECLIA and by LC-MS/MS methods, yielded a slope of 1.21 [95% confidence interval (CI): 1.15-1.26], intercept of 0.478 mcg/L (95% CI: 0.241-0.716), and a Pearson correlation coefficient (r) of 0.91. A single-site comparison between the ECLIA and the Quantitative Microsphere System assay revealed a slope of 1.05 (95% CI: 0.917-1.17), intercept of 1.03 mcg/L (95% CI: 0.351-1.70), and r of 0.91. CONCLUSIONS: Based on these results, the Roche Elecsys everolimus ECLIA can be considered suitable for routine therapeutic drug monitoring. A positive bias was observed with respect to LC-MS/MS methods, suggesting that it may be necessary to rebaseline individual patients when switching from LC-MS/MS to the ECLIA; however, this must also be considered for any change of method for everolimus measurement.

A pragmatic bottom-up approach to harmonize the units of clinical chemistry tests among Belgian clinical laboratories, focusing on immunoassays.

BACKGROUND: Harmonization of units is an important step to improve the comparability of clinical chemistry results, but few examples exist of successful harmonization efforts. We present the results of a pragmatic approach that was implemented in Belgium from 2012. METHODS: After a large consultation and information of stakeholders, preferred units were proposed for 140 assays, including the 23 immunoassays discussed in more detail here. The change occurred in two phases, first involving assays for which there was no change in the numerical result, then changes involving a change in numerical results. Laboratories were invited to participate in this harmonization on a voluntary basis. The project was based on a bottom-up approach, large consultation and the pragmatic choice of the proposed units, including conventional and SI units. RESULTS: The large heterogeneity of units was drastically reduced; adoption of the preferred units increased from 3% (insulin) - 45% (HCG) to 70% (insulin) - 96% (LH and FSH). Adoption of the preferred units was higher if it involved no change in numerical values (90%) than when there was a change (76%). CONCLUSIONS: We believe that the harmonization effort has reached its goals. Without aiming at implementing SI units for all parameters, our strategy was successful with a large majority of the laboratories switching to the proposed units. Moreover, the harmonization program is still progressing, with additional laboratories converting to the consensus units.

Dose optimization of piperacillin/tazobactam in critically ill children.

Objectives: To characterize the population pharmacokinetics of piperacillin and tazobactam in critically ill infants and children, in order to develop an evidence-based dosing regimen. Patients and methods: This pharmacokinetic study enrolled patients admitted to the paediatric ICU for whom intravenous piperacillin/tazobactam (8:1 ratio) was indicated (75 mg/kg every 6 h based on piperacillin). Piperacillin/tazobactam concentrations were measured by an LC-MS/MS method. Pharmacokinetic data were analysed using non-linear mixed effects modelling. Results: Piperacillin and tazobactam blood samples were collected from 47 patients (median age 2.83 years; range 2 months to 15 years). Piperacillin and tazobactam disposition was best described by a two-compartment model that included allometric scaling and a maturation function to account for the effect of growth and age. Mean clearance estimates for piperacillin and tazobactam were 4.00 and 3.01 L/h for a child of 14 kg. Monte Carlo simulations showed that an intermittent infusion of 75 mg/kg (based on piperacillin) every 4 h over 2 h, 100 mg/kg every 4 h given over 1 h or a loading dose of 75 mg/kg followed by a continuous infusion of 300 mg/kg/24 h were the minimal requirements to achieve the therapeutic targets for piperacillin (60% f T >MIC >16 mg/L). Conclusions: Standard intermittent dosing regimens do not ensure optimal piperacillin/tazobactam exposure in critically ill patients, thereby risking treatment failure. The use of a loading dose followed by a continuous infusion is recommended for treatment of severe infections in children >2 months of age.

A comparative study of screening instruments and biomarkers for the detection of cannabis use.

BACKGROUND: The aim of this study was to compare the usefulness of 3 different screening instruments (questionnaires) for the detection of cannabis use (CU) with biological markers in blood and hair. METHODS: Ninety-four students were recruited in October 2013. Participants filled out the Severity of Dependence Scale (SDS), the CAGE-AID ("Cut down Annoyed Guilty Eye-opener"-Adapted to Include Drugs), and ProbCannabis-DT questionnaires concerning their possible CU. Blood and hair samples were taken and analyzed by gas chromatography-mass spectrometry. Logistic regression (Nagelkerke R(2)) and receiver operating characteristic (ROC) curve analyses were performed. THCCOOH (Δ(9)-tetrahydrocannabinoic acid) plasma of ≥5 ng/mL and THC (Δ(9)-tetrahydrocannabinol) hair concentrations of ≥0.1 and ≥0.02 ng/mg were used as the gold standard for CU. The questionnaire results were compared with different concentration ranges for THCCOOH in plasma (<5, 5-75, and >75 ng/mL, indicating the intensity of use) and THC in hair (≥0.02 ng/mg, ≥0.1 ng/mg). RESULTS: The Nagelkerke R(2) for comparing the SDS, CAGE-AID, and ProbCannabis-DT with THCCOOH in plasma was 0.350, 0.489, and 0.335, respectively. The area under the ROC curve (95% confidence interval) was 0.772 (0.662-0.882), 0.797 (0.710-0.884), and 0.769 (0.669-0.870), respectively. Corresponding sensitivity/specificity were 70%/84%, 100%/59%, and 87%/67%, respectively. These values were similar to those compared to a 0.02 ng/mg THC cutoff in hair. CONCLUSIONS: Moderate agreement was found between all questionnaires and biomarkers of CU. The CAGE-AID and probCannabis-DT questionnaires were very sensitive, but less specific. SDS was less sensitive, but more specific.

A Simulation Study Reveals Lack of Pharmacokinetic/Pharmacodynamic Target Attainment in De-escalated Antibiotic Therapy in Critically Ill Patients.

De-escalation of empirical antibiotic therapy is often included in antimicrobial stewardship programs in critically ill patients, but differences in target attainment when antibiotics are switched are rarely considered. The primary objective of this study was to compare the fractional target attainments of contemporary dosing of empirical broad-spectrum ß-lactam antibiotics and narrower-spectrum antibiotics for a number pathogens for which de-escalation may be considered. The secondary objective was to determine whether alternative dosing strategies improve target attainment. We performed a simulation study using published population pharmacokinetic (PK) studies in critically ill patients for a number of broad-spectrum ß-lactam antibiotics and narrower-spectrum antibiotics. Simulations were undertaken using a data set obtained from critically ill patients with sepsis without absolute renal failure (n = 49). The probability of target attainment of antibiotic therapy for different microorganisms for which de-escalation was applied was analyzed. EUCAST MIC distribution data were used to calculate fractional target attainment. The probability that therapeutic exposure will be achieved was lower for the narrower-spectrum antibiotics with conventional dosing than for the broad-spectrum alternatives and could drastically be improved with higher dosages and different modes of administrations. For a selection of microorganisms, the probability that therapeutic exposure will be achieved was overall lower for the narrower-spectrum antibiotics using conventional dosing than for the broad-spectrum antibiotics.

Augmented renal clearance implies a need for increased amoxicillin-clavulanic acid dosing in critically ill children.

There is little data available to guide amoxicillin-clavulanic acid dosing in critically ill children. The primary objective of this study was to investigate the pharmacokinetics of both compounds in this pediatric subpopulation. Patients admitted to the pediatric intensive care unit (ICU) in whom intravenous amoxicillin-clavulanic acid was indicated (25 to 35 mg/kg of body weight every 6 h) were enrolled. Population pharmacokinetic analysis was conducted, and the clinical outcome was documented. A total of 325 and 151 blood samples were collected from 50 patients (median age, 2.58 years; age range, 1 month to 15 years) treated with amoxicillin and clavulanic acid, respectively. A three-compartment model for amoxicillin and a two-compartment model for clavulanic acid best described the data, in which allometric weight scaling and maturation functions were added a priori to scale for size and age. In addition, plasma cystatin C and concomitant treatment with vasopressors were identified to have a significant influence on amoxicillin clearance. The typical population values of clearance for amoxicillin and clavulanic acid were 17.97 liters/h/70 kg and 12.20 liters/h/70 kg, respectively. In 32% of the treated patients, amoxicillin-clavulanic acid therapy was stopped prematurely due to clinical failure, and the patient was switched to broader-spectrum antibiotic treatment. Monte Carlo simulations demonstrated that four-hourly dosing of 25 mg/kg was required to achieve the therapeutic target for both amoxicillin and clavulanic acid. For patients with augmented renal function, a 1-h infusion was preferable to bolus dosing. Current published dosing regimens result in subtherapeutic concentrations in the early period of sepsis due to augmented renal clearance, which risks clinical failure in critically ill children, and therefore need to be updated. (This study has been registered at Clinicaltrials.gov as an observational study [NCT02456974].).

Application of the characteristic function to evaluate and compare analytical variability in an external quality assessment scheme for serum ethanol.

BACKGROUND: As a cornerstone of quality management in the laboratory, External Quality Assessment (EQA) schemes are used to assess laboratory and analytical method performance. The characteristic function is used to describe the relation between the target concentration and the EQA standard deviation, which is an essential part of the evaluation process. The characteristic function is also used to compare the variability of different analytical methods. METHODS: We fitted the characteristic function to data from the Belgian External Quality Assessment program for serum ethanol. Data included results from headspace gas chromatography and the enzymatic methods of Abbott, Roche, Siemens, and Ortho-Clinical Diagnostics. We estimated the characteristic function with weighted nonlinear regression. By introducing dummy variables, we rewrote the original formula of the characteristic function to assess statistical inference for comparing the variability of the different analytical methods. RESULTS: The characteristic function fitted the data precisely. Comparison between methods showed that there was little difference between the estimated variability for low concentrations, and that the increase in SD with increasing target concentration was slower for Abbott and Roche than for the other methods. CONCLUSIONS: The characteristic function can successfully be introduced in clinical schemes, although its applicability to fit the data should always be assessed. Because of its easy parameterization, it can be used to assess differences in performance between analytical methods and to assess laboratory performance. The characteristic function also offers an alternative framework for coefficients of variation to describe variability of analytical methods.

Measuring unbound versus total vancomycin concentrations in serum and plasma: methodological issues and relevance.

BACKGROUND: Studies on the unbound fraction (fu) of vancomycin report highly variable results. Great controversy also exists about the correlation between unbound and total vancomycin concentrations. As differences in (pre-)analytic techniques may explain these findings, we investigated the impact of the procedure used to isolate unbound vancomycin in serum/plasma on fu and the correlation between total and unbound concentrations. METHODS: Patient samples (n = 39) were analyzed for total and unbound vancomycin concentrations after ultrafiltration (UF, Centrifree at 4°C and 37°C) or equilibrium dialysis (ED, using a Fast Micro-Equilibrium Dialyzer at 37°C) on an Architect i2000SR. To investigate correlations with potential binding proteins, total protein, albumin, alpha-1-acid glycoprotein, and IgA concentrations were also measured. RESULTS: The median fu after ED was 72.5% [interquartile range (IQR), 68.7%-75.0%]. Ultrafiltration at 4°C and 37°C resulted in a median fu of 51.6% (IQR, 48.6%-54.8%) and 75.2% (IQR, 69.3%-78.6%), respectively, with no significant difference between unbound vancomycin concentrations after ED and UF at 37°C (P = 0.13). Unbound concentrations obtained through ED and UF correlated linearly (4°C: r = 0.9457; 37°C: r = 0.9478; both P < 0.0001). Linear mixed-model regression showed that total vancomycin as such was the predominant determinant for the unbound concentration, allowing a reliable prediction (mean bias ± SD, 5.0% ± 7.6%). The studied protein concentrations were of no added value in predicting the unbound concentration. CONCLUSIONS: Vancomycin fu after UF at 4°C was on average 30.6% lower than that after UF at 37°C, demonstrating the importance of temperature during UF. Ultrafiltration at 37°C resulted in unbound vancomycin concentrations equivalent with ED. As the unbound concentration could be reliably predicted based on total vancomycin concentrations as such, measurement of unbound vancomycin concentrations has little added value over measurements of total vancomycin concentrations.

What are the most important tasks of tutors during the tutorials in hybrid problem-based learning curricula?

BACKGROUND: In problem-based learning, a tutor, the quality of the problems and group functioning play a central role in stimulating student learning. This study is conducted in a hybrid medical curriculum where problem-based learning is one of the pedagogical approaches. The aim of this study was to examine which tutor tasks are the most important during the tutorial sessions and thus should be promoted in hybrid (and in maybe all) problem-based learning curricula in higher education. METHODS: A student (N = 333) questionnaire was used to obtain data about the problem-based learning process, combined with the achievement score of the students on a multiple-choice exam. Structural equation modeling was used to test the fit of different models (two existing models and a new simplified model) representing the factors of interest and their relationships, in order to determine which tutor characteristics are the most important in the present study. RESULTS: A new simplified model is presented, which demonstrates that stimulation of active and self-directed learning by tutors enhances the perceived case quality and the perceived group functioning. There was no significant effect between the stimulation of collaborative learning and perceived group functioning. In addition, group functioning was not a significant predictor for achievement. CONCLUSIONS: We found that stimulating active and self-directed learning are perceived as tutors' most important tasks with regard to perceived case quality and group functioning. It is necessary to train and teach tutors how they can stimulate active and self-directed learning by students.