Franck Saint-Marcoux

Falsely elevated whole-blood tacrolimus concentrations in a kidney-transplant patient: potential hazards.

Tacrolimus‐based immunosuppression is the most frequently prescribed immunosuppression for kidney‐transplant (KT) patients. Because tacrolimus has a narrow therapeutic window, drug monitoring is mandatory. Of the many methods used to assess whole‐blood trough levels, antibody‐conjugated magnetic immunoassay (ACMIA) is popular because, compared with microparticle enzyme‐linked immunoassays (MEIA), there is no need to pretreat samples, thus reducing time taken by the laboratory technician. Herein, we report on a KT tacrolimus‐treated patient who experienced falsely elevated whole‐blood tacrolimus concentrations after using the ACMIA method. ACMIA gave trough levels of 24 ng/ml, whereas the actual trough level, when measured by enzyme‐multiplied immunoassay technique (EMIT) and high‐performance liquid chromatography coupled with mass spectrometry (LC‐MS/MS), was nil. After a workup we only found one factor that might have caused the elevated concentration: positive anti‐double stranded DNA autoantibodies. We conclude that, when ACMIA produces surprisingly high tacrolimus concentrations in organ‐transplant patients, these should be reassessed immediately using either LC‐MS/MS or another immunoassay in order to eliminate falsely elevated results.

Development of a Bayesian estimator for the therapeutic drug monitoring of mycophenolate mofetil in children with idiopathic nephrotic syndrome.

The use of mycophenolate mofetil (MMF) in children with idiopathic nephrotic syndrome (INS) is increasing. However, the clinical benefit of its monitoring has been scarcely studied, and little is known about its pharmacokinetics in this context. The objectives of the present study were: (i) to study and model the pharmacokinetics of mycophenolic acid (MPA; the active moiety of MMF) in paediatric patients with INS given MMF, at all stages of the disease; (ii) to develop a Bayesian estimator (MAP-BE) for individual inter-dose area under the concentration-time curve (AUC) prediction in this population, using a limited blood sampling strategy (LSS). Full-pharmacokinetic (PK) profiles of MPA collected in paediatric inpatients with INS already treated with a maintenance immunosuppressive therapy based on MMF (with no calcineurin inhibitors; CNI) were studied. A classical iterative two-stage (ITS) method was applied to model the data and develop MAP-BEs using a one-compartment open model where the absorption is described by a double gamma law allowing the description of a potential enterohepatic recirculation. The performance of the MAP-BE developed for individual exposure assessment was evaluated by the bias and precision of predicted AUCs with respect to measured, trapezoidal AUCs (reference value), and by the proportion of predicted AUCs with absolute error >20%. These PK tools were tested in an independent group of patients. Sixty PK profiles of MPA from children receiving MMF in association to corticosteroids or given alone were included in the study. Forty-five of these PK profiles were used to develop a PK model and a MAP-BE, and 15 for their validation. In the building group, the PK model fitted accurately the PK profiles of MPA: mean residual error of modelled vs. reference AUC was m±SD=-0.015±0.092 (range: -0.153 to 0.204). The MAP-BE which allowed the estimation of MPA AUC on the basis of a 20 min-60 min-180 min LSS was then developed. In the independent group of patients, its mean residual error vs. reference AUCs was m±SD=-0.036±0.145 (range: -0.205 to 0.189). Thus, a PK model and its derived MAP-BE for MMF (without any associated CNI) when given to children with INS have been developed. Clinical trials using these PK tools could test the potential impact of the therapeutic drug monitoring of MMF based on the AUC on the clinical evolution of INS.

Towards therapeutic drug monitoring of everolimus in cancer? Results of an exploratory study of exposure-effect relationship

Introduction: Therapeutic drug monitoring (TDM) of everolimus is not performed in oncology and no trough level (C0) target has been yet defined. The aim of this study was to determine everolimus C0 target for toxicity and efficacy. Materials and methods: Clinical, biological and radiologic data from 54 patients were collected. Toxicity event was defined by termination, temporary interruption and/or dose reduction of everolimus while efficacy was defined as progression‐free survival. C0 values were dichotomized by ROC curve analysis and the association between exposure and outcome was determined using Cox models for repeated events (toxicity) or Cox model censured at the first event (progression free survival). Results: Among the 42 patients (77.8%) with breast cancer, 10 (18.5%) kidney cancer and 2 (3.7%) neuroendocrine cancer, adverse events were reported in 75.9% of the patients (everolimus termination in 25.9% patients). C0 everolimus higher than 26.3 ng/mL (Sen = 0.38,Spe = 0.88) were associated with a 4‐fold increased risk of toxicity (HR = 4.12, IC95% = [1.48–11.5], p = 0.0067) whereas C0 lower than 11.9 ng/mL were associated with a 3‐fold increased risk of progression (HR = 3.2, IC95% = [1.33–7.81],p = 0.001). Discussion: Further studies are required to evaluate the everolimus C0 threshold proposed for toxicity (26.3 ng/mL) and for progression (11.9 ng/mL) especially with a large number of patients and more homogeneous types of cancer. However, these results are in favour of TDM for everolimus in oncology.

Quelques considérations sur la LC-MS/MS et le suivi thérapeutique pharmacologique

Therapeutic drug monitoring can be defined as a multiple step activity involving: (i) the measurement of a drug; (ii) the interpretation of the concentration by taking into account the concentration-effect relationship; (iii) the individual dose adjustment. For over 15 years pharmacology-toxicology departments have implemented liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) on a daily basis. This article discusses the current position of this technology in TDM routine activity.

High-Throughput Monitoring of Cocaine and Its Metabolites in Hair Using Microarrays for Mass Spectrometry and Matrix-Assisted Laser Desorption/Ionization-Tandem Mass Spectrometry

Because of inhomogeneous matrix-assisted laser desorption/ionization (MALDI) matrix crystallization and laser shot-to-shot variability, quantitation is not generally performed by MALDI mass spectrometry. Here we introduce a high-throughput MALDI method using an innovative high-density microarray for mass spectrometry (MAMS) technology, which allows semiquantitative measurement of cocaine and its metabolites, benzoylecgonine, cocaethylene, and ecgonine methyl ester. A MAMS slide containing lanes of hydrophilic spots and an automated slider to drag a sample droplet over several small spots can accomplish automatic sample aliquoting and lead to homogeneous crystallization of the matrix-analyte mixture and, thus, to a reproducible signal (average RSD 6%). Four hair samples of self-reported drug users were analyzed in parallel by MALDI-MS/MS and by a validated LC-MS/MS method. The consumption profiles as well as the metabolite-parent drug ratios obtained correlated well, confirming the effectiveness of the MALDI-MS/MS method to establish a calendar of consumption in only 1 mg of hair. The analysis time for 10 hair samples is below 40 min, with 12 replicates per sample. Since only 3 μL of a 20 μL extract is analyzed, complementary assays are possible, such as the detection of additional drugs. The semiquantitative MALDI method worked well with only a small amount of hair and gave results in less than 4 min per sample, including replicates. This was made possible by the use of MAMS slides for sample preparation, which thus present significant advantages over traditional methods in cases where results are required urgently or if samples are scarce.

Mycophenolic mofetil optimized pharmacokinetic modelling, and exposure-effect associations in adult heart transplant recipients.

UNLABELLED Mycophenolic acid (MPA) area under the curve (AUC) has been associated with graft outcome. THE AIMS OF OUR STUDY WERE (1) to develop pharmacokinetic tools to optimize MPA inter-dose AUC estimation in heart transplant patients; and (2) to investigate the relationships between acute allograft rejection and MPA AUC, trough level (C0) or mycophenolate mofetil (MMF) dose. Two independent modeling approaches (parametric and non parametric) were used to fit 56 rich MPA pharmacokinetic (PK) profiles collected from 40 adult heart transplant recipients enrolled in the PIGREC study, receiving MMF and a calcineurin inhibitor (CNI), in the first year post-transplantation. In addition, associations between drug exposure (MPA C0, AUC and MMF dose) and acute rejection or MMF adverse events were investigated using time-dependent Cox models with stratification on the type of calcineurin inhibitor. Exposure threshold values were investigated using ROC curve analysis. The 2 models developed fit adequately the data and the use of their combination yielded 100% consistency with the measured AUC in terms of strategy of dose adjustment (maintain, increase or decrease). MPA measured AUC adjusted on CNI exposure was significantly associated with rejection (per unit increase: HR [95% CI]=0.97 [0.95-0.99], p=0.0122), while no effect was shown for adverse events attributable to MMF. An AUC threshold of 50 mg×h/L was proposed (sensitivity=77%, specificity=25%) beyond which the risk of rejection was significantly increased (low vs. high: HR=3.48 [1.21-10.0], p=0.0204). The tools developed have already been made available to the heart transplant community on our ISBA website (https://pharmaco.chu-limoges.fr).

Cyclosporine therapeutic window evaluation by Chebyshev's inequality method in kidney recipients

OBJECTIVE The aim of this study was to identify a cyclosporine therapeutic range for kidney recipients. MATERIALS AND METHODS The cyclosporine exposure level was based on the calculation of the mean area under the concentration-time curve AUC(0-12). The AUC(0-12) was estimated using a Bayesian estimator and a 3-point limited sampling strategy. Cyclosporine exposure levels were obtained from 3 blood samples: 0, 1, and 3h postdose; and analyses were performed using a liquid chromatography-tandem mass spectrometry method. The therapeutic window of cyclosporine was calculated by the Chebyshevs inequality method with a 99% guarantee (α=0.01) using the IBM SPSS Statistics 20 software. RESULTS It was found that the therapeutic window of cyclosporine estimated by the Chebyshevs inequality method and put on the AUC(0-12) exposure lies in the ranges from 2.84-3.13 mg h/L with the 99% confidence for the patients with the target AUC(0-12) exposure of 3.8 mg h/L (posttransplantation time >1 year). The therapeutic window of cyclosporine differs in different posttransplantation time groups: the estimated AUC exposure range in the group of patients who have a graft longer than 5 years is 2.70-2.98 mg h/L, and the estimated AUC exposure range in the group of patients who have a graft for 1-5 years is 3.05-3.75 mg h/L. CONCLUSIONS Chebyshevs inequality could be an appropriate and more precise method to determine the therapeutic window for cyclosporine in kidney recipients than the target AUC(0-12) value and further studies should be conducted to evaluate patients with postoperative time <1 year.