Marie-Clémence Verdier

Opportunity to monitor immunosuppressive drugs in peripheral blood mononuclear cells: where are we and where are we going?

Immunosuppressive (IS) drugs are now widely used as preventive treatments of allograft rejection in transplantation. Therapeutic drug monitoring (TDM) using trough whole blood concentrations is usually warranted and therapeutic range is recommended to ensure efficacy and prevent toxicity from these drugs. This intensive TDM reduces acute graft rejection but despite this management, the acute rejection rate still remains high in the first two years post-transplantation and few improvements have been made recently to reduce this rate. Moreover, in some patients, acute rejections occur despite adequate trough whole blood IS concentrations. Thus, other ways to monitor immunosuppressive drug effects have to be investigated. As lymphocyte cells are the site of action of IS drugs and so the effect compartment of the drug, monitoring IS drugs in lymphocytes, or for practical reasons in peripheral blood mononuclear cells (PBMC), could be more relevant than standard TDM. The aim of this paper is to review the recent work conducted on the advantages of monitoring IS drugs in PBMC, particularly for calcineurin inhibitors and mammalian target of rapamycin (m-TOR) inhibitors, from an analytical point of view as well as a clinical point of view.

Pharmacokinetics and pharmacodynamics of tacrolimus in liver transplant recipients: inside the white blood cells

OBJECTIVESnDespite improvements in patient management and extensive use of therapeutic drug monitoring (TDM), the rate of acute cellular rejection (ACR) remains high in patients treated with tacrolimus (TAC). Moreover, some patients experienced ACR while their whole-blood (WB) concentrations were maintained within the therapeutic range meaning that TDM in WB misrepresents the drug effect. Thus, monitoring TAC directly inside of its effect compartment (intracellular concentrations) or monitoring directly the inhibitory effect on the target protein (calcineurin activity) could be more relevant. The aim of the present study was to explore, in 10 de novo liver transplant recipients, the relationship between TAC whole-blood concentrations, TAC intracellular concentrations and TAC-induced intracellular calcineurin inhibition at day 1 and day 7 after treatment initiation.nnnDESIGN AND METHODSnProspective monocentric observational pharmacokinetic (WB and intracellular concentrations)-pharmacodynamic (calcineurin activity) study.nnnRESULTSnFull intracellular TAC pharmacokinetic as well as calcineurin activity steady-state profiles is presented in the study. The main result of this study is the lack of relationship between TAC pharmacokinetics (WB and leukocytes) and calcineurin activity in leukocytes at day 1 and day 7 after the graft implantation.nnnCONCLUSIONSnDrug monitoring of TAC intracellular concentrations and determination of the calcineurin activity are among future potential biomarkers of acute rejection in transplant recipients. A better knowledge of the relationship between TAC whole blood and intracellular concentrations and calcineurin activity appears necessary before planning clinical trials to evaluate their potential interest as predictive biomarkers.

Increased inhibition of cytochrome P450 3A4 with the tablet formulation of posaconazole.

Being a substrate of the cytochrome P450 3A4 (CYP3A4) isoenzyme, sirolimus metabolism is decreased when posaconazole is administered concomitantly. However, because of the poor bioavailability of the oral suspension of posaconazole with which low plasma concentrations are obtained, CYP3A4 inhibition is weak and a 50-75% dose reduction of sirolimus is sufficient to avoid sirolimus overdosage. The new tablet formulation allows reaching posaconazole concentrations 3-4 fold higher than those obtained with the oral suspension. Based on a case of sirolimus overdosage following posaconazole tablets administration, we modelled the inhibition of sirolimus clearance by posaconazole, and then simulated several dosage regimens of sirolimus taken together with posaconazole tablets. We were able to describe well the interaction, and found a value of IC50 of posaconazole towards sirolimus clearance of 0.68xa0μg/mL. The simulations showed that even a 80% decrease of the daily dose of sirolimus is unsuitable in many cases with trough concentrations of posaconazole of 2xa0μg/mL. A decrease of 40% of the dose with spacing administrations of 3 days may be considered. The clinicians and pharmacologists must be warned that the use of posaconazole tablets may result in an inhibition of CYP3A4 of greater magnitude than with the oral suspension.

Population Pharmacokinetics of Posaconazole Tablets and Monte Carlo Simulations To Determine whether All Patients Should Receive the Same Dose

ABSTRACT Posaconazole is extensively used for prophylaxis for invasive fungal infections. The gastro-resistant tablet formulation has allowed the bioavailability issues encountered with the oral suspension to be overcome. However, overexposure is now frequent. This study aimed to (i) describe the pharmacokinetics of posaconazole tablets in a real-life cohort of patients with hematological malignancies and (ii) perform Monte Carlo simulations to assess the possibility that the daily dose can be reduced while keeping a sufficient exposure. Forty-nine consecutive inpatients were prospectively included in the study. Posaconazole trough concentrations (TC) were measured once a week, and biological and demographic data were collected. The concentrations were analyzed by compartmental modeling, and Monte Carlo simulations were performed using estimated parameters to assess the rate of attainment of the target TC after dose reduction. The pharmacokinetics of posaconazole were well described using a one-compartment model with first-order absorption and elimination. The values of the parameters (interindividual variabilities) were as follows: the absorption constant (ka) was 0.588 h−1 (fixed), the volume of distribution (V/F) was 420 liters (28.2%), and clearance (CL/F) was 7.3 liters/h (24.2%) with 31.9% interoccasion variability. Forty-nine percent of the simulated patients had TC at steady state of ≥1.5 μg/ml and maintained a TC above 1 μg/ml after a reduction of the dose to 200 mg daily. A third of these patients eligible for a dose reduction had TC of ≥1.5 μg/ml as soon as 48 h of treatment. Though posaconazole tablets were less impacted by bioavailability issues than the oral suspension, the pharmacokinetics of posaconazole tablets remain highly variable. Simulations showed that approximately half of the patients would benefit from a reduction of the dose from 300 mg to 200 mg while keeping the TC above the minimal recommended target of 0.7 μg/ml, resulting in a 33% savings in the cost of this very expensive drug.

Safety study and therapeutic drug monitoring of the oral tablet formulation of posaconazole in patients with haematological malignancies

PurposePosaconazole is a triazole antifungal widely used for prophylaxis of invasive fungal disease (IFI). Posaconazole tablets allow reaching higher plasma levels than the oral suspension, but safety data with this formulation in real life are scarce. This study aimed at evaluating the safety profile, the pharmacokinetic variability, and the concentration–toxicity relationship of posaconazole tablets in patients with haematological malignancies.MethodsSixty neutropenic patients treated with posaconazole tablets for prophylaxis of IFI were prospectively included in the study. Adverse drug reactions (ADR) were recorded and analyzed by the Regional Pharmacovigilance Centre to assess posaconazole implication. Blood samples were drawn once a week and plasma trough concentrations (Cmin) were assayed by LC–MS/MS. The rates of ADR by quartile of Cmin were compared.ResultsEighteen patients (30%) experienced at least one ADR attributed to posaconazole. Liver function test (LFT) abnormalities were encountered in 20% of patients and resulted in four (6.7%) treatment discontinuations. Posaconazole median (range) Cmin was 1.36 (<xa00.1–3.44) µg/mL (inter-patient CVxa0=xa043.9%). During follow-up, 28.6% of patients had at least one concentration <xa00.7xa0µg/mL, and 35.7% had at least one concentration >xa02xa0µg/mL. Rates of ADR by quartile of Cmin were not different.ConclusionsPosaconazole was well tolerated; however, LFT abnormalities were frequent. ADR occurrence was not linked to posaconazole exposure. Because posaconazole concentrations were highly variable, TDM can be helpful to avoid underexposure to the drug and increase its efficacy in preventing IFI. Conversely, a large proportion of patients was overexposed and might have benefited of a dose reduction.

A high performance liquid chromatography tandem mass spectrometry for the quantification of tacrolimus in human bile in liver transplant recipients

Tacrolimus whole-blood concentrations imperfectly reflect concentrations at the effect site. Tacrolimus concentrations in the transplanted organ could be more relevant to predict rejection events. Because liver biopsy cannot be repeatedly performed after liver transplantation, we suggested measuring tacrolimus in the bile to have a cost-effective and clinically implementable surrogate marker of intra-hepatic tacrolimus concentration. We developed and fully validated a liquid chromatography-tandem mass spectrometry method for the determination of tacrolimus in human bile. Sample purification was achieved using protein precipitation and liquid-liquid extraction with ethyl-acetate. Gradient elution was performed using a C18 analytical column with a 5min run-time. The method was linear from 0.5ng/mL to 20ng/mL. In this concentration range, within-day and between-day precisions as well as overall bias were within ±15%. Matrix effect was fully corrected by the internal standard (ascomycin). The assay was optimized to achieve good selectivity in this complex biological matrix. Tacrolimus was found to be stable in bile stored 6 months at -80°C, after 3 freeze and thaw cycles, 20h at room temperature and 24h in extracts kept at 15°C in the auto-sampler. The method was applied to quantify tacrolimus in bile from liver transplant recipients. It allowed getting preliminary data about tacrolimus excretion profile in bile and showed the lack of correlation between tacrolimus whole blood concentration and tacrolimus liver exposition. This alternative and innovative analytical approach of tacrolimus bio-analysis appears suitable for further studies evaluating relevance of biliary tacrolimus concentration as a new pharmacological marker of immunosuppressive activity.

Should we fear tubing adsorption of antibacterial drugs in extracorporeal membrane oxygenation? An answer for cephalosporins and carbapenems

Extracorporeal membrane oxygenation (ECMO) procedure used in the management of patients with cardiac and/or respiratory failure could modify drugs pharmacokinetics (PK) properties. Studying the impact of ECMO devices on drugs PK is warranted to optimize dosage and ensure clinical outcomes. We aimed to characterize the behavior of four cephalosporins and three carbapenems commonly used in an ECMO circuit with an in-vitro approach focusing on the coated tubing, support of the extracorporeal circulation. Results suggest that these antibiotics are not sequestrated by ECMO tubing. This pilot mechanistic study provides original data that will contribute to improve our understanding of the impact of ECMO on the PK of drugs commonly used in intensive care unit patients.

Modeling Immunization To Infliximab in Children With Crohn’s Disease Using Population Pharmacokinetics: A Pilot Study

BackgroundnAntidrug antibodies (ADAs) dramatically increase infliximab clearance and are responsible for underexposure to the drug, leading to treatment failure. This pilot study aimed at developing a population pharmacokinetic model to detect and describe an early increase in infliximab clearance due to ADA.nnnMethodsnTwenty children with Crohns disease (CD) were followed for 1 year or until treatment failure. Infliximab trough concentration, ADA, C-reactive protein (CRP), and Paediatric Crohns Disease Activity Index (PCDAI) were recorded at each visit. A time-varying clearance population pharmacokinetic model was built to detect and describe an increase in infliximab clearance, independent from ADA testing. Factors associated with clearance variation and the relationships between infliximab concentrations, clearance variation, and clinical response were investigated.nnnResultsnThe model detected important increases in clearance in 4 patients. These patients had suboptimal early response, with higher mean PCDAI (P = 0.0086) and CRP (P = 0.028) compared with other patients. Two of them had detectable ADA. Clearance increase as described by the model and lower infliximab trough concentration at week 2 were associated with poorer outcomes in a multivariate Cox model (P = 0.001 and P = 0.0048, respectively).nnnConclusionsnBeing able to detect an increase in infliximab clearance, this model could allow the early detection of immunization to infliximab and therefore could help with dose adjustment in patients with CD. Moreover, the results suggest that clearance variations could be used as a predictive marker of clinical response. These findings need to be confirmed in a larger cohort, however, and predictive factors of clearance increase have to be investigated.

Tacrolimus diffusion across the peripheral mononuclear blood cell membrane: impact of drug transporters

Measuring tacrolimus (TAC) concentration in peripheral blood mononuclear cells (PBMCs) could better reflect the drug effect on its target (calcineurin (CaN) in lymphocytes) than whole blood concentrations. Mechanisms influencing TAC diffusion into PBMC are not well characterized. This work aimed at describing, ex vivo, TAC diffusion kinetics into PBMC and investigating the contribution of membrane transporters to regulate TAC intracellular concentration as well as the impact on CaN activity. PBMCs were incubated with TAC for 5 min to 4 h and under several experimental conditions: 37 °C (physiological conditions), 4 °C (inhibition of influx and efflux active transport), 37 °C + transporter inhibitors (verapamil, carvedilol, and probenecid and bromosulfophthalein, respectively, inhibitors of P‐gp, OAT, and OATP). TAC concentration and CaN activity were measured in PBMC using liquid chromatography coupled with mass spectrometry. TAC intra‐PBMC concentration was maximal after 1 h of incubation. Mean TAC PMBC concentrations were significantly lower in samples incubated at 4 °C compared to the 37 °C groups. Addition of verapamil slightly increased TAC accumulation in PBMC while other inhibitors had no effect. A significant correlation was found between TAC intra‐PBMC concentration and the level of inhibition of CaN. Using an ex vivo cellular model, these results suggest that P‐gp is involved in the drug efflux from PBMC while influx active transporters likely to regulate TAC intra‐PBMC disposition remain to be identified. TAC concentration in PBMC is correlated with its pharmacodynamic effect. Then, TAC intra‐PBMC concentration appears to be a promising biomarker to refine TAC therapeutic drug monitoring.

Intra‐patient variability in solid organ transplantation: should we make the first move earlier?

We read with great interest the article of Gueta and colleagues and we wanted to congratulate the authors for this first observation of intra-patient variability (IPV) impact on clinical outcomes in heart transplant (HTx) recipients (1). Indeed, in their retrospective study conducted in 72 HTx patients, the authors found that the coefficient of variation (CV) of tacrolimus (TAC) whole-blood trough concentrations measured between 3 and 12 months is associated with worst mid- to long-term (total rejection score after the first year post-transplantation that is the sum of all biopsies grades divided by the number of biopsies; 0.33 vs. 0, p=0.035) outcome. Despite this relatively small cohort, Gueta etxa0al. found that high TAC CV was a tremendous risk factor for the onset of rejection (OR=8.52 [1.63-44.53], p=0.011) but not for mortality (probably due to a lack of statistical power). This article is protected by copyright. All rights reserved.