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Objectives Diagnostic samples are exposed to a spectrum of variables during transport to laboratories; therefore, the evaluation of a rather comprehensive stability profile of measurands is warranted. While appropriate testing standards have been established for pharmaceuticals and reagents, this is not the case for diagnostic samples. The aim of our work was to develop and evaluate a protocol applicable to diagnostic samples. Methods An isochronous approach with representation of temperature and exposure duration in a two-dimensional matrix was established. The deviations of the measurement results from the baseline associated with the exposure are evaluated with respect to the measurement uncertainty of the analytical measurement procedure applied. Variables of the experiment are documented in a standardized matrix. As a proof-of-concept, we profiled the stability patterns of a number of measurands at four temperature levels over up to 72 h in primary serum sample tubes. Results The protocol proved to be workable and allowed the description of a comprehensive stability profile of a considerable number of compounds based on 21 small-volume primary samples collected from each volunteer and exposed according to this protocol. Conclusions A straightforward and feasible isochronous protocol can be used to investigate in detail the effects of different pre-processing conditions on the stability of measurands in primary samples during transport to diagnostic laboratories. This is of significance as pre-analytical logistics become increasingly important with the centralization of analytical services.

Objectives Cystic fibrosis (CF) transmembrane conductance regulator (CFTR) modulators have revolutionized the therapeutic landscape in CF treatment. These vital drugs are extensively metabolized via CYP3A, so caution must be exercised in multimodal CF therapy because of the risk of adverse drug interactions. Our goal was to develop a highly sensitive assay for the purpose of therapeutic drug monitoring (TDM) in diagnostic laboratories. Methods After protein precipitation, the CFTR modulators ivacaftor, lumacaftor, tezacaftor, elexacaftor, and their metabolites ivacaftor-M1, ivacaftor-M6, and tezacaftor-M1 were separated with a two-dimensional chromatography setup within 5 min, and quantified with stable isotope-labeled internal standards. The method was validated according to the European Medicines Agency (EMA) guideline on bioanalytical method validation and applied to CF patient samples. Results Inaccuracy was ≤7.0% and the imprecision coefficient of variation (CV) was ≤8.3% for all quality controls (QCs). The method consistently compensated for matrix effects, recovery, and process efficiency were 105–115 and 96.5–103%, respectively. Analysis of CF serum samples provided concentrations comparable to the pharmacokinetic profile data reported in the EMA assessment report for the triple combination therapy Kaftrio. Conclusions We hereby present a robust and highly selective isotope dilution liquid chromatography tandem mass spectrometry (ID-LC-MS/MS) assay for the simultaneous quantification of the so far approved CFTR modulators and their metabolites in human serum. The assay is suitable for state-of-the-art pharmacovigilance of CFTR modulator therapy in CF patients, in order to maximize safety and efficacy, and also to establish dose-response relationships in clinical trials.

Introduction It is common for patients to switch between several healthcare providers. In this context, the long-term follow-up of medical conditions based on laboratory test results obtained from different laboratories is a challenge. The measurement uncertainty in an inter-laboratory context should also be considered in data mining research based on routine results from randomly selected laboratories. As a proof-of-concept study, we aimed at estimating the inter-laboratory reference change value (IL-RCV) for exemplary analytes from publicly available data on external quality assessment (EQA) and biological variation. Materials and methods External quality assessment data of the Reference Institute for Bioanalytics (RfB, Bonn, Germany) for serum creatinine, calcium, aldosterone, PSA, and of whole blood HbA1c from campaigns sent out in 2019 were analysed. The median CVs of all EQA participants were calculated based on 8 samples from 4 EQA campaigns per analyte. Using intra-individual biological variation data from the EFLM database, positive and negative IL-RCV were estimated with a formula based on log transformation under the assumption that the analytes under examination have a skewed distribution. Results We estimated IL-RCVs for all exemplary analytes, ranging from 13.3% to 203% for the positive IL-RCV and - 11.8% to - 67.0% for the negative IL-RCV (serum calcium - serum aldosterone), respectively. Conclusion External quality assessment data together with data on the biological variation - both freely available - allow the estimation of inter-laboratory RCVs. These differ substantially between different analytes and can help to assess the boundaries of interoperability in laboratory medicine.

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.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 (CThe 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 CLinezolid 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.

BACKGROUND AND AIMS Previous data has shown a reduced immune response shortly after SARS-CoV-2 vaccinations in haemodialysis patients. We therefore investigated the long-term antibody response in patients from different outpatient dialysis centres at 4 weeks and 6 months after a complete vaccination against COVID-19. The results were compared with the humoral responses of non-dialysis subjects. METHODS We designed a retrospective multicentric cohort study, enrolling 106 haemodialysis patients and 50 non-dialysis patients after the SARS-CoV-2 vaccination. SARS-CoV-2 antibody testing was performed as part of routine clinical practice 4 weeks as well as 6 months after the immunization with chemiluminescence immunoassays designed to detect antibodies against the SARS-CoV-2 spike protein (Elecsys Anti-SARS-CoV-2 S, Roche Diagnostics, Mannheim, Germany). Testing was performed in the Institute of Laboratory Medicine of the University Hospital Munich. According to the manufacturer's specifications, anti-SARS-CoV-2 S titres >0.8 U/mL are considered reactive (sensitivity 98.8% and specificity 99.9%). Anti-SARS-CoV-2 S titres RESULTS A total of 106 haemodialysis patients with a median age of 73 years received a SARS-CoV-2 vaccination (n = 105 mRNA, n = 1 AstraZeneca). Of these, 50 non-dialysis patients with a median age of 56 years received a SARS-CoV-2 vaccination (n = 45 mRNA, n = 5 mRNA/AstraZeneca). During the observational period, 8 haemodialysis patients and 2 non-dialysis patients additionally contracted a SARS-CoV-2 infection. Between the two testings, an overall decrease in anti-SARS-CoV-2 S antibody titres was observed (haemodialysis patients from a median of 252 to 95 U/mL, non-dialysis patients from a median of 1621 to 441 U/mL). At 6 months after the complete vaccination, 99 (93%) haemodialysis patients still presented with a detectable anti-SARS-CoV-2 spike antibody response (>0.8 U/mL), comparable to 100% of the non-dialysis subjects. However, 60 (57%) haemodialysis patients showed low antibody response ( Patients with an additional infection showed an increased titre of antibodies during follow-up. CONCLUSIONS Our data suggest regular antibody testing as well as a need for booster vaccination in the vulnerable population of haemodialysis patients.

Background Appropriate monitoring of tobacco smoking is extremely important in several areas of medicine, e.g. management of chronic obstructive pulmonary disease (COPD), epidemiological surveys, and allocation of heart or lung transplants. The major metabolite of nicotine is cotinine that is increasingly used as a laboratory parameter for assessing tobacco smoke exposure. Methods Creatinine and cotinine were analyzed simultaneously in urine by ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) in one run within 3 min using a biphenyl column. For quantification, the respective stable-isotope-labeled standards were used. Results Detuning and measuring a natural isotope of creatinine as precursor and product ion allowed a simultaneous quantification of creatinine and cotinine. The method revealed robust validation results. For both analytes, inaccuracy and imprecision of the quality control and external quality assessment (EQA) samples were ≤−11.1%. Conclusions One essential novelty of the method presented here is the simultaneous quantification of creatinine and cotinine covered by one analytical method. Despite the very different natural concentrations of creatinine and cotinine, this allows the immediate reporting of the cotinine-to-creatinine ratio without the need for a separate creatinine analysis.

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 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.

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.).

Hemadsorption of cytokines is used in critically ill patients with sepsis or septic shock. Concerns have been raised that the cytokine adsorber CytoSorbCritically ill patients with sepsis or septic shock receiving continuous renal replacement therapy and CytoSorb20 CytoSorbWe recommend the infusion of 500 mg vancomycin over 2 h during CytoSorb

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

Several studies have addressed the poor stability of meropenem in aqueous solutions, though not considering the main degradation product, the open-ring metabolite (ORM) form. In the present work, we elucidate the metabolic fate of meropenem and ORM from continuous infusion to the human bloodstream. We performed in vitro infusate stability tests at ambient temperature with 2% meropenem reconstituted in 0.9% normal saline, and body temperature warmed buffered human serum with 2, 10, and 50 mg/L meropenem, covering the therapeutic range. We also examined meropenem and ORM levels over several days in six critically ill patients receiving continuous infusions. Meropenem exhibited a constant degradation rate of 0.006/h and 0.025/h in normal saline at 22 °C and serum at 37 °C, respectively. Given that 2% meropenem remains stable for 17.5 h in normal saline (≥90% of the initial concentration), we recommend replacement of the infusate every 12 h. Our patients showed inter-individually highly variable, but intra-individually constant molar ORM/(meropenem + ORM) ratios of 0.21–0.52. Applying a population pharmacokinetic approach using the degradation rate in serum, spontaneous degradation accounted for only 6% of the total clearance.

BackgroundSome studies have shown an attenuated immune response in haemodialysis patients after vaccination. The present study examines the humoral response after mRNA vaccination against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a large population of haemodialysis patients from different outpatient dialysis centres.MethodsWe retrospectively assessed antibodies against SARS-CoV-2 spike protein and nucleocapsid protein (chemiluminescence immunoassays, Roche diagnostics) 3–6 weeks after the second mRNA vaccine dose in 179 maintenance haemodialysis and 70 non-dialysis patients (control cohort). Differences in anti-SARS-CoV-2 spike protein titers were statistically analysed with respect to patient-relevant factors, including age, gender, previous coronavirus disease 2019 (COVID-19) infection, systemic immunosuppressive therapy and time on dialysis.ResultsWe found a favourable, but profoundly lower SARS-CoV-2 spike protein antibody response in comparison with a non-dialysis cohort (median 253.5 versus 1756 U/mL, P ConclusionWe strongly argue in favour of regular antibody testing after COVID-19 vaccination in haemodialysis patients. Further studies should elucidate the utility of booster vaccinations to foster a stronger and persistent antibody response.

Severe intravascular hemolysis leads to the simultaneous presence of free heme pigments (oxyhemoglobin, methemoglobin, and methemalbumin) and bilirubin in human plasma. Standard spectrophotometric methods used to assess in vivo hemolysis inadequately address this complex analytical situation. Thus, we propose a novel quantification algorithm to ensure the highest analytical specificity. A corresponding second-derivative fitting algorithm was validated according to the guideline of bioanalytical method validation from the European Medicines Agency using plasma specimens (n = 1759) spiked with different concentrations of oxyhemoglobin and methemoglobin. The results were compared to standard spectrophotometric quantification methods described by Harboe, Noe, and Fairbanks. Based on the second-derivative method, simultaneous quantification of oxyhemoglobin and methemoglobin/methemalbumin in samples with total bilirubin concentrations ≤4.9 mg/dL (83.8 μmol/L) provided robust results (inaccuracy ≤20%, imprecision ≤16%). Analyzing UV/VIS spectra of plasma from patients with confirmed severe intravascular hemolysis evidenced an underestimation of up to 33% for the combined free heme pigment content. The employed second-derivative algorithm allows for automated and highly specific quantification of the free heme pigment content in diluted human plasma, which cannot be realized with standard spectrophotometric evaluation methods. An Excel-based tool readily applicable to clinical datasets accompanies this manuscript.

Hexadecylphosphocholine (HePC, Miltefosine) is a drug from the class of alkylphosphocholines with an antineoplastic and antiprotozoal activity. We previously reported that HePC uptake from thermosensitive liposomes (TSL) containing 1,2-dipalmitoyl-sn-glycero-3-phosphodiglycerol (DPPG2) into cancer cells is accelerated at mild hyperthermia (HT) resulting in increased cytotoxicity. In this study, we compared HePC release of different TSL formulations in serum. HePC showed rapid but incomplete release below the transition temperature (Tm) of investigated TSL formulations in serum. Short heating (5 min) to 42 °C increased HePC release from DPPG2-TSL (Tm = 41 °C) by a factor of two in comparison to body temperature (37 °C). Bovine serum albumin (BSA) induced HePC release from DPPG2-TSL comparable to serum. Furthermore, multilamellar vesicles (MLV) were capable to extract HePC from DPPG2-TSL in a concentration- and temperature-dependent manner. Repetitive exposure of DPPG2-TSL to MLV at 37 °C led to a fast initial release of HePC which slowed down after subsequent extraction cycles finally reaching approx. 50% HePC release. A pharmacokinetic study in rats revealed a biphasic pattern with an immediate clearance of approx. 50% HePC whereas the remaining 50% HePC showed a prolonged circulation time. We speculate that HePC located in the external leaflet of DPPG2-TSL is rapidly released upon contact with suitable biological acceptors. As demonstrated by MLV transfer experiments, asymmetric incorporation of HePC into the internal leaflet of DPPG2-TSL might improve HePC retention in presence of complex biological media and still give rise to HT-induced HePC release.

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

Background Therapeutic drug monitoring (TDM) of beta-lactam antibiotics and, among them, especially meropenem gains importance in the field of laboratory medicine. Meropenem is known to be unstable, resulting in a degradation product with an open beta-lactam ring. For a more comprehensive TDM of meropenem, the aim was to develop a LC–MS/MS method for the simultaneous quantification of meropenem and its main degradation product, the open-ring metabolite (ORM). Methods The method involves a protein precipitation followed by chromatographic separation using a formic acid-ammonium formate methanol gradient on a pentafluorophenyl column. Multiple reaction monitoring in the positive ion mode and stable isotope labeled internal standards were used for quantification. Validation was performed according to the European Medicines Agency guideline. Results Validation was successful performed within the linear drug concentration range of 1.0–100.0 mg/l for meropenem and 0.62–62.30 mg/l for the ORM. Investigation of selectivity, accuracy and precision showed good results and potential matrix effects were successfully compensated by the internal standards. The suitability of the method was shown by the comparison of 35 anonymized leftover serum samples from intensive care patients with routine analyses. Conclusion For the first time, we herein describe a liquid chromatography tandem mass spectrometry (LC–MS/MS) method for the simultaneous quantification of meropenem and its ORM in human serum. The ratio of active to inactive compound provides valuable pharmaceutical and pharmacokinetic information, which may contribute to therapeutic efficacy.

Background In tandem mass spectrometry, analyte detection is based on collision-induced fragmentation, which is modulated by the collision energy (CE) setting. Variation in CE leads to differential ion yield, and optimization is usually performed empirically as “tuning” during method development. Our aim was to build a method to objectify the impact of collision energy settings on ion yield for individual compounds. Methods Collision energy (CE)-breakdown curves were generated based on acquisition files in which a large number of quasi-identical mass transitions were recorded simultaneously, with variation of CE over a defined range within a single injection. Ion yield (normalized to an internal standard recorded with a locked collision energy) was plotted as a curve versus CE settings. Piperacillin and testosterone were studied as exemplary analytes in matrix-free and serum matrix-based liquid chromatography tandem mass spectrometry (LC-MS/MS) measurements. More detailed testosterone CE-breakdown curves were investigated with regard to sample preparation techniques and the isotope labeling pattern of corresponding internal standards. Results CE-breakdown curves were found characteristically for the piperacillin quantifier transition with respect to CE-related maximum ion yield, as well as curve width and shape. A diverging curve profile was observed for the piperacillin qualifier transition. For testosterone analyses, no impact from different sample preparation techniques or the isotope labeling patterns on the selected CE was shown. Conclusion CE-breakdown curves are a convenient and valuable tool to verify LC-MS/MS methods regarding consistent fragmentation characteristics between sample sources or native analytes and isotope-labeled counterparts.

Purpose Optimization of antibiotic therapy is still urgently needed in critically ill patients. The aim of the ONTAI survey (online survey on the use of Therapeutic Drug Monitoring of antibiotics in intensive care units) was to evaluate which strategies intensive care physicians in Germany use to improve the quality of antibiotic therapy and what role a Therapeutic Drug Monitoring (TDM) plays. Methods Among the members of the German Society for Anaesthesiology and the German Society for Medical Intensive Care Medicine and Emergency Medicine, a national cross-sectional survey was conducted using an online questionnaire. Results The questionnaire was completely answered by 398 respondents. Without TDM, prolonged infusion was judged to be the most appropriate dosing regimen for beta lactams. A TDM for piperacillin, meropenem and vancomycin was performed in 17, 22 and 75% of respondents, respectively. For all beta lactams, a TDM was requested more often than it was available. There was great uncertainty as to the optimal pharmacokinetic/pharmacodynamic index for beta-lactams. 86% of the respondents who received minimal inhibitory concentrations adapted the therapy accordingly. Conclusion German intensive care physicians are convinced of TDM for dose optimization. However, practical implementation, the determination of MICs and defined target values are still lacking.

Objectives The risk of sample confusion continues to be a challenge for the pre-analytical part of the overall testing process. We here describe a novel system to track samples based on a chemical code labeling of test tubes with unique combinations of indicator compounds, which are naturally not present in specimens of human origin. As part of the sample vessel filling, the liquid specimens are permanently labeled with the compound code that can be tracked back to the primary tube. Methods As a proof of concept we used 10 stable-isotope-labeled derivates of medical drugs as indicator substances to create a combinatory 10-digit binary number ID for individual test tubes, i.e. presence/absence of the respective compound. For this purpose, combinations of indicator compounds were provided in evaporated form in polypropylene tubes prior to filling with anonymized patient whole blood and corresponding plasmas subjected to liquid chromatography tandem-mass spectrometry designed to detect the 10 indicator compounds. Results In the blind analysis, we correctly identified 307 different whole blood samples by readout of a 10-digit binary number ID based on the detection of indicator compounds with respect to their presence and number. Conclusions We have demonstrated the feasibility of an internal labeling procedure for diagnostic samples with mass spectrometry-based readout of dissolved indicator compound combinations as a binary number ID. With an increasing number of coding compounds (≫10) a vast number of combinations for sample labeling can be realized beyond the proof of concept setting studied herein.

Background Therapeutic drug monitoring (TDM) of the immunosuppressant mycophenolic acid (MPA) is especially recommended for the control of personalized immunosuppressive therapy. Various test systems are available for MPA monitoring, including high performance liquid chromatography combined with UV detection (HPLC-UV) and isotope dilution liquid chromatography tandem mass spectrometry (ID-LC-MS/MS). Methods In the present work, commercially available kits for MPA monitoring with HPLC-UV and ID-LC-MS/ MS were subjected to routine use TDM. Following method verification according to the Clinical and Laboratory Standards Institute (CLSI) guidelines, 105 native sample duplicates from patients under therapy with mycophenolate mofetil were assayed with both procedures for comparative testing. Results Using bi-level quality controls, the estimate of repeatability, within-laboratory imprecision and inaccuracy were ≤ 5.18%, ≤ 5.95% and ≤ 3.86% for all MPA measurements. Weighted Deming regression analysis yielded a slope of 0.93, an intercept of 0.04, and Pearson's correlation coefficient (r) of 0.99, while Bland-Altman analysis showed a combined relative bias of 4.93% (± 1.96 SD: -16.68 - 26.54%). Plasma samples taken from a patient re-peatedly showed the presence of an interferent only in HPLC-UV analysis. Conclusions Based on these results, HPLC-UV testing can be considered suitable for routine TDM of MPA in the clinical setting with high precision. Due to the risk of unforeseen analytical interference in ever-increasing multimorbidity and polypharmacy, highly selective ID-LC-MS/MS methodology should be given preference over HPLC-UV analysis whenever feasible.

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 &lt, 70 mL/min had high rates of target attainment with the standard dosing regimens. There was a low number of patients with a CrCl &gt, 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.