Towards a better detection of patients at-risk of linezolid toxicity in clinical practice: a prospective study in three Belgian hospital centers.

Introduction: Linezolid is a last-resort antibiotic for infections caused by multidrug-resistant microorganisms. It is widely used for off-label indications and for longer than recommended treatment durations, exposing patients at higher risk of adverse drug reactions (ADRs), notably thrombocytopenia. This study aimed to investigate ADR incidence and risk factors, identify thrombocytopenia-related trough levels based on treatment duration, and evaluate the performance of predictive scores for ADR development. Methods: Adult in- and outpatients undergoing linezolid therapy were enrolled in three hospitals and ADRs and linezolid trough levels prospectively monitored over time. A population pharmacokinetic (pop-PK model) was used to estimate trough levels for blood samples collected at varying times. Results: A multivariate analysis based on 63 treatments identified treatment duration ≥10 days and trough levels >8 mg/L as independent risk factors of developing thrombocytopenia, with high trough values correlated with impaired renal function. Five patients treated for >28 days did not develop thrombocytopenia but maintained trough values in the target range (<8 mg/L). The Buzelé predictive score, which combines an age-adjusted Charlson comorbidity index with treatment duration, demonstrated 77% specificity and 67% sensitivity to predict the risk of ADR. Conclusion: Our work supports the necessity of establishing guidelines for dose adjustment in patients with renal insufficiency and the systematic use of TDM in patients at-risk in order to keep trough values ≤8 mg/L. The Buzelé predictive score (if ≥7) may help to detect these at-risk patients, and pop-PK models can estimate trough levels based on plasma samples collected at varying times, reducing the logistical burden of TDM in clinical practice.

The free cortisol calculated: correlation with the free cortisol concentrations measured with liquid chromatography-tandem mass spectrometry after equilibrium dialysis and establishment of reference intervals.

BACKGROUND: Changes in cortisol binding globulin (CBG) impact the total serum cortisol concentration and affect the accurate assessment of adrenal function. Free biologically cortisol can be calculated using different equations or directly measured after complicated procedures. METHODS: The free cortisol index (FCI) obtained using the Bonte formula as well as the free cortisol concentration calculated (Coolens equation) were first estimated for 45 healthy workers. The CBG level was determined by a competitive radioimmunoassay and the total cortisol concentration, was measured with an electrochemiluminescent assay. The correlations between FCI, the free cortisol concentrations calculated and the free cortisol levels measured with liquid chromatography-tandem mass spectrometry after equilibrium dialysis were studied for those 45 samples. Reference limits were established on 158 healthy hospital workers and patients with serum samples collected between 7:30 am and 10 am. RESULTS: The FCI as well as the free cortisol concentrations calculated obtained for the 45 samples correlated significantly with the free cortisol levels measured. Although the cortisol and CBG levels were statistically higher in women using contraceptives compared with women not taking them as well as men, the calculated FCI and free cortisol concentrations did not differ between these groups. The medians (P2.5-P97.5) obtained for the 158 healthy workers were respectively 26.4% (12.3-51.6%) and 10.6 nmol/L (4.3-26.7 nmol/L). CONCLUSIONS: This study highlighted a significant correlation between the FCI, the free cortisol concentrations calculated and the free cortisol levels measured with LC-MS/MS, it has also allowed the establishment of reference intervals for calculated FCI and free cortisol.

Cascadion™ SM Clinical Analyzer: Evaluation of the whole blood immunosuppressants quantification and routine usability.

BACKGROUND: Liquid chromatography coupled with tandem mass spectrometry (LC- MS/MS) tends to overcome other methods for therapeutic drugs monitoring (TDM) due to its very good analytical performances. Nevertheless, the lack of automation still limits its use in laboratory medicine. The Cascadion SM Clinical Analyzer (Thermo Fisher Scientific) is the first fully automated LC-MS/MS instrument available. We evaluated its immunosuppressant drugs (ISD) assay and the incorporation of such instrument into a core-laboratory. METHODS: An extended analytical verification of the Cascadion ISD panel including cyclosporin A, tacrolimus, everolimus and sirolimus was performed. It was compared to the MassTox ISD assay (Chromsystems). Different preanalytical and analytical conditions were tested. Finally, a turnaround-time evaluation and a satisfaction survey of users after 11 months of use in a core-laboratory were performed. RESULTS: Precision and linearity results were within the analytical goals fixed. The comparison with the MassTox ISD assay showed results in agreement except for cyclosporin A where a bias of -11.6% was observed, probably due to a greater trueness of the Cascadion method. Additional experiments showed good performances. The random accessibility and the ease of use by non-specialized staff members allowed a wider working time range and a reduction of the turnaround-time of 55%. CONCLUSION: The Cascadion ISD Panel held its promises in term of analytical performances, workflow aspects and ease of use by non-specialized staff.

Development, validation and clinical use of a LC-MS/MS method for the simultaneous determination of the nine main antituberculosis drugs in human plasma.

The treatment of tuberculosis, in particular the multi-drug resistant tuberculosis, remains a challenge mainly because of the therapy duration and the pharmacokinetic variability of the drugs included in the regimen. The monitoring of antituberculosis drugs is a recent tool that could improve the outcome of patients. We developed a LC-MS/MS method allowing the simultaneous quantification of the four first-line drugs (isoniazid, rifampicin, pyrazinamide and ethambutol), a metabolite of isoniazid (acetylisoniazid) and the five main second-line drugs (rifabutin, levofloxacin, moxifloxacin, linezolid and bedaquiline). An isotopologue standard was used for each drug. The protein precipitation was performed with acetonitrile and the separation was carried out using an EC-18 column and a gradient elution. The validated ranges for each drug were adapted to monitor the plasma concentration at 2 h (peak) and 6 h to evaluate their enteric absorption. The intermediate precision (CV) and the trueness at the limit of quantification were ≤ 10.1% and ≤ 10.7%, respectively. Preliminary data were obtained for 12 patients. The results showed that 38% of the patients had infra-therapeutic levels for both rifampicin and isoniazid, that the leading cause of an impaired oral absorption seemed to be malabsorption and that the effective concentrations for rifampicin were in the lower range of the therapeutic interval.

Development and validation of a simple correction method for the measurement of neuron-specific enolase in hemolyzed serum samples.

The Neuron-specific enolase (NSE), a biomarker of neuroendocrine tumors or ischemic brain damage, has limited clinical applicability since its measurement is overestimated by hemolysis. In this study, an NSE correction method was developed for hemolyzed samples. The NSE concentration and the hemolysis index (HI) of serum were measured before and after spiking a hemolysate prepared with red blood cells from the serum-separating tube and extrapolating the NSE value corresponding to a HI of zero. To validate the approach (n = 46), NSE concentrations and HI were measured before (NSE0 and HI0) and after spiking the samples with 50 µL (HIA, NSEA) and 100 µL (HIB, NSEB) of hemolysate. A linear regression analysis was performed between (HIA, NSEA) and (HIB, NSEB). The y-intercept was taken as the corrected NSE concentration (NSEintercept) and compared with NSE0. On the same samples, the equation of Tolan et al. was applied and the corrected values of NSE (NSEcorr) were compared to NSE0. The average bias (±SD) between the NSE0 and the NSEintercept was equal to -3.2% (± 14.3) versus 34.6% (± 19.8) against the NSEcorr. Applying the allowable total error proposed by the European Federation of Laboratory Medicine, 72% of the NSE results were adequately corrected while the reference method corrected only 8.7% of the results. The individualized hemolysis correction method developed is simple, fast, requires one serum-separating tube, provides increased accuracy compared to the method described by Tolan et al. and should improve the quality of patient care.

Pharmacokinetics and target attainment of intravenous posaconazole in critically ill patients during extracorporeal membrane oxygenation.

BACKGROUND: Posaconazole is an antifungal drug used for prophylaxis and treatment of invasive fungal infections. Severe influenza has been identified as a risk factor for invasive pulmonary aspergillosis in critically ill patients. In this population, extracorporeal membrane oxygenation (ECMO) is used as rescue therapy, although little is known about the pharmacokinetics (PK) of posaconazole during ECMO. OBJECTIVES: To determine the PK and target attainment of six patients treated with IV posaconazole under ECMO and to develop a population PK model that can be used to simulate the PTA. METHODS: Critically ill patients treated with posaconazole and ECMO were included in this study. Plasma samples were collected at several timepoints within one dosing interval on two occasions: an early (Day 2-3) and a late (Day 4-7) sampling day. Daily trough concentrations were measured. RESULTS: The median (IQR) AUC0-24, CL and Vd were 34.3 (28.3-37.7) mg·h/L, 8.7 (8.0-10.6) L/h and 389 (314-740) L, if calculated with non-compartmental analysis based on the observed concentrations. All measured trough concentrations were ≥0.7 mg/L and 11/16 were ≥1 mg/L, which are the haematological thresholds for prophylaxis and treatment of invasive aspergillosis, respectively. The targeted PTA (>90%) was attained for prophylaxis but not for treatment. CONCLUSIONS: ECMO does not appear to influence posaconazole exposure compared with haematology patients. However, some trough levels were below the lower limit for treatment. An a priori dose adjustment does not appear to be necessary but drug monitoring is recommended.

Cefepime therapeutic drug monitoring: Evaluation of agreement between peripheral and central venous blood sampling.

BACKGROUND: Therapeutic drug monitoring for cefepime is increasingly being performed because of the potential relation between exposure and neurotoxicity. An in vitro pilot study suggested significant carryover of cefepime from central venous catheters when blood sampling is carried out via the same catheter used for administration of cefepime. Therefore, the aim of this study was to evaluate carryover of cefepime in a real-life clinical setting. METHODS: A prospective single-center study was conducted at the hematology department of the University Hospitals Leuven. Patients treated with cefepime, and having a central venous catheter, were included. Cefepime trough samples were taken simultaneously via the central venous catheter and peripheral venepuncture. RESULTS: Twenty-four patients were included in this study, resulting in 28, 11 and 5 paired samples for tunnelled catheters, implantable port catheters and peripherally inserted central catheters, respectively. No statistically nor clinically significant difference was found between cefepime concentrations measured in centrally versus peripherally obtained blood samples, overall and for all three types of central venous catheters separately. Of note, four paired samples showed a difference larger than 10%, with lower central concentrations probably reflecting a dilution error. CONCLUSION: There was no significant carryover of cefepime from long-term central venous catheters. Cefepime samples can be drawn reliably via the central venous catheter, after flushing and discarding the first blood sample. Although, flushing and discard volumes should be standardized to avoid potential dilution errors.