Katrine Agergaard (1,2), Helle C. Thiesson (2), Jan Carstens (2), Christine E. Staatz (3), Erkka Järvinen (4), Flemming Nielsen (4), Heidi Dahl Christensen (5), Rikke Juhl-Sandberg (6), Kim Brøsen (4), Tore Bjerregaard Stage (4), Dorte Terp Andersen (8), Maria C. Kjellsson (9), Troels K. Bergmann (1,7)
(1) Department of Regional Health Research, University of Southern Denmark, Esbjerg, Denmark, (2) Department of Nephrology, Odense University Hospital, Odense, Denmark, (3) School of Pharmacy, University of Queensland, Brisbane, Australia, 4102, (4) Department of Public Health, University of Southern Denmark, Odense, Denmark, (5) Department of Nephrology, University Hospital of Southern Denmark, Esbjerg, Denmark, (6) Medicinsk Afdeling, Sygehus Lillebælt, Kolding, Denmark, (7) Department of Clinical Pharmacology, Odense University Hospital, Odense, Denmark, (8) Department of Clinical Molecular Biology, University Hospital of Southern Denmark, Esbjerg, Denmark, (9) Pharmacometrics Research Group, Department of Pharmacy, Uppsala University, Uppsala, Sweden
Introduction: Tacrolimus is an immunosuppressive drug used to prevent organ rejection in kidney transplanted patients. It has a narrow therapeutic index and displays a large inter- and intraindividual pharmacokinetic variability [1, 2]. Despite, whole blood therapeutic drug monitoring tacrolimus still gives erratic results. One possible explanation for this is that whole blood concentrations correlate poorly to intracellular concentrations in lymphocytes [3], the pharmacological target site of tacrolimus [4]. Therapeutic monitoring of tacrolimus in human peripheral blood mononuclear cells (PBMCs) has been suggested as an alternative [5]. This study is the first to describe the correlation between tacrolimus whole blood and PBMC concentrations in stable kidney transplanted patients using the population approach. One other study examined the relationship similarly, but in newly transplanted patients [6].
Objectives: With this study, we aimed 1) to describe the relationship between whole blood and intracellular PBMC concentration of tacrolimus in kidney transplanted adults using population pharmacokinetic modelling, and 2) to identify patient characteristics influencing this relationship.
Methods: We prospectively enrolled 63 stable adult kidney transplanted patients and collected dense (predose, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10, and 12 h post-dose) or sparse (predose, 0.5, 1.5, and 4 h post-dose) pharmacokinetic profiles of tacrolimus. PBMCs were isolated from whole blood using Ficoll density gradient centrifugation, and drug concentrations were analyzed using LC-MS/MS in whole blood and in PBMCs. Genotype variants in CYP3A4/5, ABCB1, and NR1I2 were assessed with TaqMan assays and PCR. Patient demographics and clinical biochemistry were collected from medical charts. Pharmacokinetic data were analyzed with non-linear mixed effects modelling in NONMEM. Covariates were selected based on their known or suspected relationship with tacrolimus pharmacokinetics. The stepwise covariate model approach with forward inclusion and backward elimination was used to systematically search for important covariates. The covariate model is currently under development, and the performance and uncertainty of the final model will be evaluated with e.g. prediction corrected visual predictive checks (pcVPCs), bootstrapping, and sampling importance resampling methods.
Results: The population pharmacokinetic model was based on 691 samples (whole blood=348, PBMC=325) from 63 stabile kidney transplanted patients (sparse group=45, dense group=18). Linear regression showed a poor correlation between whole blood and PBMC concentrations (r2=0.239, p<0.001). A two-compartment model with three transit-compartments and first-order absorption and elimination best described the whole blood tacrolimus concentrations. The PBMC concentrations were mirroring the central concentrations of tacrolimus with a scaling factor Rcentral:PBMC, which had a skewed η-distribution and was boxcox transformed. Typical values in the base model for apparent oral whole blood clearance (CL/F), central volume of distribution (V/F), intercompartmental clearance (Q/F), and peripheral volume of distribution (VP/F) were 19.6 L/h, 285.5 L, 134.9 L/h, and 1,600 L, respectively. Interim results from the forward inclusion of the stepwise covariate model approach identified the following relations: CL/F was associated with genotype variant CYP3A5*3 and with comedication with calcium channel blockers, bioavailability (F) with age, VP/F with sex, and Rcentral:PBMC with the plasma albumin and with genotype variants CYP3A5*3 and NR1I2 -25385C>T.
Conclusions: The distribution of tacrolimus from whole blood to the target site in PBPMCs can be described as mirroring the central compartment with a scaling factor Rcentral:PBMC. Interim covariate analyses identified plasma albumin, and genotype variants CYP3A5*3 and NR1I2 -25385C>T as potential modulators of the Rcentral:PBMC. The model could be used in the future to estimate the tacrolimus concentration at the target site based on whole blood concentration and to identify kidney transplanted patients at risk of intracellular under- or overexposure.
References:
[1] Brunet M, van Gelder T, Åsberg A, Haufroid V, Hesselink DA, Langman L, et al. Therapeutic drug monitoring of tacrolimus-personalized therapy: Second consensus report. Therapeutic Drug Monitoring. 2019.
[2] Staatz CE, Tett SE. Clinical pharmacokinetics and pharmacodynamics of tacrolimus in solid organ transplantation. Clinical Pharmacokinetics. 2004;43(10):623-53.
[3] Francke MI, Andrews LM, Lan Le H, van de Velde D, Dieterich M, Udomkarnjananun S, et al. Monitoring Intracellular Tacrolimus Concentrations And Its Relationship With Rejection In The Early Phase After Renal Transplantation. Clin Biochem. 2021.
[4] Thomson AW, Bonham CA, Zeevi A. Mode of Action of Tacrolimus (FK506): Molecular and Cellular Mechanisms. Therapeutic Drug Monitoring. 1995;17(6):584-91.
[5] Capron A, Musuamba F, Latinne D, Mourad M, Lerut J, Haufroid V, et al. Validation of a Liquid Chromatography-Mass Spectrometric Assay for Tacrolimus in Peripheral Blood Mononuclear Cells. Therapeutic Drug Monitoring. 2009;31(2):178-86.
[6] Franken LG, Francke MI, Andrews LM, van Schaik RHN, Li Y, de Wit LEA, et al. A Population Pharmacokinetic Model of Whole-Blood and Intracellular Tacrolimus in Kidney Transplant Recipients. Eur J Drug Metab Pharmacokinet. 2022.
Reference: PAGE 32 (2024) Abstr 11177 [www.page-meeting.org/?abstract=11177]
Poster: Drug/Disease Modelling - Other Topics