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Aims: Pregnancy after kidney transplantation is realistic but immunosuppressants should be continued to prevent rejection. Tacrolimus is safe during pregnancy and is routinely dosed based on whole-blood predose concentrations. However, maintaining these concentrations is complicated as physiological changes during pregnancy affect tacrolimus pharmacokinetics. The aim of this study was to describe tacrolimus pharmacokinetics throughout pregnancy and explain the changes by investigating covariates in a population pharmacokinetic model., Methods: Data of pregnant women using a twice-daily tacrolimus formulation following kidney transplantation were retrospectively collected from 6 months before conception, throughout gestation and up to 6 months postpartum. Pharmacokinetic analysis was performed using nonlinear mixed effects modelling. Demographic, clinical and genetic parameters were evaluated as covariates. The final model was evaluated using goodness-of-fit plots, visual predictive checks and a bootstrap analysis., Results: A total of 260 whole-blood tacrolimus predose concentrations from 14 pregnant kidney transplant recipients were included. Clearance increased during pregnancy from 34.5 to 41.7 L/h, by 15, 19 and 21% in the first, second and third trimester, respectively, compared to prior to pregnancy. This indicates a required increase in the tacrolimus dose by the same percentage to maintain the prepregnancy concentration. Haematocrit and gestational age were negatively correlated with tacrolimus clearance (P ≤ 0.01), explaining 18% of interindividual and 85% of interoccasion variability in oral clearance., Conclusions: Tacrolimus clearance increases during pregnancy, resulting in decreased exposure to tacrolimus, which is explained by gestational age and haematocrit. To maintain prepregnancy target whole-blood tacrolimus predose concentrations during pregnancy, increasing the dose is required., (© 2023 The Authors. British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

The Pharmacogene Variation Consortium (PharmVar) catalogs star (*) allele nomenclature for the polymorphic human CYP3A5 gene. Genetic variation within the CYP3A5 gene locus impacts the metabolism of several clinically important drugs, including the immunosuppressants tacrolimus, sirolimus, cyclosporine, and the benzodiazepine midazolam. Variable CYP3A5 activity is of clinical importance regarding tacrolimus metabolism. This GeneFocus provides a CYP3A5 gene summary with a focus on aspects regarding standardized nomenclature. In addition, this review also summarizes recent changes and updates, including the retirement of several allelic variants and provides an overview of how PharmVar CYP3A5 star allele nomenclature is utilized by the Pharmacogenomics Knowledgebase (PharmGKB) and the Clinical Pharmacogenetics Implementation Consortium (CPIC)., (© 2022 The Authors. Clinical Pharmacology & Therapeutics © 2022 American Society for Clinical Pharmacology and Therapeutics.)

Background and Objective: The tacrolimus concentration within peripheral blood mononuclear cells may correlate better with clinical outcomes after transplantation compared to concentrations measured in whole blood. However, intracellular tacrolimus measurements are not easily implemented in clinical practice. The prediction of intracellular concentrations based on whole-blood concentrations would be a solution for this. Therefore, the aim of this study was to describe the relationship between intracellular and whole-blood tacrolimus concentrations in a population pharmacokinetic (popPK) model., Methods: Pharmacokinetic analysis was performed using non-linear mixed effects modelling software (NONMEM). The final model was evaluated using goodness-of-fit plots, visual predictive checks, and a bootstrap analysis., Results: A total of 590 tacrolimus concentrations from 184 kidney transplant recipients were included in the study. All tacrolimus concentrations were measured in the first three months after transplantation. The intracellular tacrolimus concentrations (n  = 184) were best described with an effect compartment. The distribution into the effect compartment was described by the steady-state whole-blood to intracellular ratio (R WB:IC ) and the intracellular distribution rate constant between the whole-blood and intracellular compartments. Lean body weight was negatively correlated [delta objective function value (ΔOFV) -8.395] and haematocrit was positively correlated (ΔOFV = - 6.752) with R WB:IC , and both lean body weight and haematocrit were included in the final model., Conclusion: We were able to accurately describe intracellular tacrolimus concentrations using whole-blood concentrations, lean body weight, and haematocrit values in a popPK model. This model may be used in the future to more accurately predict clinical outcomes after transplantation and to identify patients at risk for under- and overexposure. Dutch National Trial Registry number NTR2226., (© 2022. The Author(s).)

A high intrapatient variability (IPV) in tacrolimus exposure is a risk factor for poor long-term outcomes after kidney transplantation. The main objective of this trial was to investigate whether tacrolimus IPV decreases after switching patients from immediate-release (IR)-tacrolimus to either extended-release (ER)-tacrolimus or LifeCyclePharma (LCP)-tacrolimus. In this randomized, prospective, open-label, cross-over trial, adult kidney transplant recipients on a stable immunosuppressive regimen, including IR-tacrolimus, were randomized for conversion to ER-tacrolimus or LCP-tacrolimus, and for the order in which IR-tacrolimus and the once-daily formulations were taken. Patients were followed 6 months for each formulation, with monthly tacrolimus predose concentration assessments to calculate the IPV. The IPV was defined as the coefficient of variation (%) of dose corrected predose concentrations. Ninety-two patients were included for analysis of the primary outcome. No significant differences between the IPV of IR-tacrolimus (16.6%) and the combined once-daily formulations (18.3%) were observed (% difference +1.7%, 95% confidence interval [CI] -1.1% to -4.5%, p = 0.24). The IPV of LCP-tacrolimus (20.1%) was not significantly different from the IPV of ER-tacrolimus (16.5%, % difference +3.6%, 95% CI -0.1% to 7.3%, p = 0.06). In conclusion, the IPV did not decrease after switching from IR-tacrolimus to either ER-tacrolimus or LCP-tacrolimus. These results provide no arguments to switch kidney transplant recipients from twice-daily (IR) tacrolimus formulations to once-daily (modified-release) tacrolimus formulations when the aim is to lower the IPV., (© 2021 The Authors. Clinical and Translational Science published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)

Bodyweight-based tacrolimus dosing followed by therapeutic drug monitoring is standard clinical care after renal transplantation. However, after transplantation, a meager 38% of patients are on target at first steady-state and it can take up to 3 weeks to reach the target tacrolimus predose concentration (C 0 ). Tacrolimus underexposure and overexposure is associated with an increased risk of rejection and drug-related toxicity, respectively. To minimize subtherapeutic and supratherapeutic tacrolimus exposure in the immediate post-transplant phase, a previously developed dosing algorithm to predict an individual's tacrolimus starting dose was tested prospectively. In this single-arm, prospective, therapeutic intervention trial, 60 de novo kidney transplant recipients received a tacrolimus starting dose based on a dosing algorithm instead of a standard, bodyweight-based dose. The algorithm included cytochrome P450 (CYP)3A4 and CYP3A5 genotype, body surface area, and age as covariates. The target tacrolimus C 0 , measured for the first time at day 3, was 7.5-12.5 ng/mL. Between February 23, 2019, and July 7, 2020, 60 patients were included. One patient was excluded because of a protocol violation. On day 3 post-transplantation, 34 of 59 patients (58%, 90% CI 47-68%) had a tacrolimus C 0 within the therapeutic range. Markedly subtherapeutic (< 5.0 ng/mL) and supratherapeutic (> 20 ng/mL) tacrolimus concentrations were observed in 7% and 3% of the patients, respectively. Biopsy-proven acute rejection occurred in three patients (5%). In conclusion, algorithm-based tacrolimus dosing leads to the achievement of the tacrolimus target C 0 in as many as 58% of the patients on day 3 after kidney transplantation., (© 2021 The Authors. Clinical Pharmacology & Therapeutics published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)

Aims: Tacrolimus is a critical dose drug and to avoid under- and overexposure, therapeutic drug monitoring is standard practice. However, rejection and drug-related toxicity occur despite whole-blood tacrolimus pre-dose concentrations ([Tac] blood ) being on target. Monitoring tacrolimus concentrations at the target site (within peripheral blood mononuclear cells; [Tac] cells ) may better correlate with drug-efficacy. The aim of this study was to (1) investigate the relationship between [Tac] blood and [Tac] cells , (2) identify factors affecting the tacrolimus distribution in cells and whole-blood, and (3) study the relationship between [Tac] cells and clinical outcomes after kidney transplantation., Methods: A total of 175 renal transplant recipients were prospectively followed. [Tac] blood and [Tac] cells were determined at Months 3, 6 and 12 post-transplantation. Patients were genotyped for ABCB1 1199G>A and 3435C>T, CYP3A4 15389C>T, and CYP3A5 6986G>A. Data on rejection and tacrolimus-related nephrotoxicity and post-transplant diabetes mellitus were collected., Results: Correlations between [Tac] blood and [Tac] cells were moderate to poor (Spearman's r = 0.31; r = 0.41; r = 0.61 at Months 3, 6 and 12, respectively). The [Tac] cells /[Tac] blood ratio was stable over time in most patients (median intra-patient variability 39.0%; range 3.5%-173.2%). Age, albumin and haematocrit correlated with the [Tac] cells /[Tac] blood ratio. CYP3A5 and CYP3A4 genotype combined affected both dose-corrected [Tac] blood and [Tac] cells . ABCB1 was not significantly related to tacrolimus distribution. Neither [Tac] blood nor [Tac] cells correlated with clinical outcomes., Conclusions: The correlation between [Tac] blood and [Tac] cells is poor. Age, albumin and haematocrit correlate with the [Tac] cells /[Tac] blood ratio, whereas genetic variation in ABCB1, CYP3A4 and CYP3A5 do not. Neither [Tac] blood nor [Tac] cells correlated with clinical outcomes., (© 2020 The Authors. British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

Ten years ago, a consensus report on the optimization of tacrolimus was published in this journal. In 2017, the Immunosuppressive Drugs Scientific Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicity (IATDMCT) decided to issue an updated consensus report considering the most relevant advances in tacrolimus pharmacokinetics (PK), pharmacogenetics (PG), pharmacodynamics, and immunologic biomarkers, with the aim to provide analytical and drug-exposure recommendations to assist TDM professionals and clinicians to individualize tacrolimus TDM and treatment. The consensus is based on in-depth literature searches regarding each topic that is addressed in this document. Thirty-seven international experts in the field of TDM of tacrolimus as well as its PG and biomarkers contributed to the drafting of sections most relevant for their expertise. Whenever applicable, the quality of evidence and the strength of recommendations were graded according to a published grading guide. After iterated editing, the final version of the complete document was approved by all authors. For each category of solid organ and stem cell transplantation, the current state of PK monitoring is discussed and the specific targets of tacrolimus trough concentrations (predose sample C0) are presented for subgroups of patients along with the grading of these recommendations. In addition, tacrolimus area under the concentration-time curve determination is proposed as the best TDM option early after transplantation, at the time of immunosuppression minimization, for special populations, and specific clinical situations. For indications other than transplantation, the potentially effective tacrolimus concentrations in systemic treatment are discussed without formal grading. The importance of consistency, calibration, proficiency testing, and the requirement for standardization and need for traceability and reference materials is highlighted. The status for alternative approaches for tacrolimus TDM is presented including dried blood spots, volumetric absorptive microsampling, and the development of intracellular measurements of tacrolimus. The association between CYP3A5 genotype and tacrolimus dose requirement is consistent (Grading A I). So far, pharmacodynamic and immunologic biomarkers have not entered routine monitoring, but determination of residual nuclear factor of activated T cells-regulated gene expression supports the identification of renal transplant recipients at risk of rejection, infections, and malignancy (B II). In addition, monitoring intracellular T-cell IFN-g production can help to identify kidney and liver transplant recipients at high risk of acute rejection (B II) and select good candidates for immunosuppression minimization (B II). Although cell-free DNA seems a promising biomarker of acute donor injury and to assess the minimally effective C0 of tacrolimus, multicenter prospective interventional studies are required to better evaluate its clinical utility in solid organ transplantation. Population PK models including CYP3A5 and CYP3A4 genotypes will be considered to guide initial tacrolimus dosing. Future studies should investigate the clinical benefit of time-to-event models to better evaluate biomarkers as predictive of personal response, the risk of rejection, and graft outcome. The Expert Committee concludes that considerable advances in the different fields of tacrolimus monitoring have been achieved during this last decade. Continued efforts should focus on the opportunities to implement in clinical routine the combination of new standardized PK approaches with PG, and valid biomarkers to further personalize tacrolimus therapy and to improve long-term outcomes for treated patients.

Background: Multiple clinical, demographic, and genetic factors affect the pharmacokinetics of tacrolimus in children, yet in daily practice, a uniform body-weight based starting dose is used. It can take weeks to reach the target tacrolimus pre-dose concentration., Objectives: The objectives of this study were to determine the pharmacokinetics of tacrolimus immediately after kidney transplantation and to find relevant parameters for dose individualization using a population pharmacokinetic analysis., Methods: A total of 722 blood samples were collected from 46 children treated with tacrolimus over the first 6 weeks after renal transplantation. Non-linear mixed-effects modeling (NONMEM ® ) was used to develop a population pharmacokinetic model and perform a covariate analysis. Simulations were performed to determine the optimal starting dose and to develop dosing guidelines., Results: The data were accurately described by a two-compartment model with allometric scaling for bodyweight. Mean tacrolimus apparent clearance was 50.5 L/h, with an inter-patient variability of 25%. Higher bodyweight, lower estimated glomerular filtration rate, and higher hematocrit levels resulted in lower total tacrolimus clearance. Cytochrome P450 3A5 expressers and recipients who received a kidney from a deceased donor had a significantly higher tacrolimus clearance. The model was successfully externally validated. In total, these covariates explained 41% of the variability in clearance. From the significant covariates, the cytochrome P450 3A5 genotype, bodyweight, and donor type were useful to adjust the starting dose to reach the target pre-dose concentration. Dosing guidelines range from 0.27 to 1.33 mg/kg/day., Conclusion: During the first 6 weeks after transplantation, the tacrolimus weight-normalized starting dose should be higher in pediatric kidney transplant recipients with a lower bodyweight, those who express the cytochrome P450 3A5 genotype, and those who receive a kidney from a deceased donor.

A validated CYP3A genotype classification system allows clustering patients into poor, intermediate and extensive metabolizer phenotypes. However, substantial overlap exists between the clusters. A rare CYP3A4 allele, named CYP3A4*20 (rs67666821), has been specifically described in the Spanish population. The authors investigated the relevance of CYP3A4*20 testing to see if the above-mentioned metabolic CYP3A classification system can be improved. In a cohort of 204 kidney transplant recipients, one male patient carrying a CYP3A4*20 allele was detected. This patient was receiving very low doses of tacrolimus to maintain therapeutic levels from day 7 onward when compared with the majority of the patients. These data suggest that this patient should be regarded as a CYP3A-poor metabolizer.

Introduction: Tacrolimus (Tac) has a narrow therapeutic window and shows large between-patient pharmacokinetic variability. As a result, over-immunosuppression and under-immunosuppression are frequently encountered in daily clinical practice. Unraveling the impact of genetic polymorphisms on Tac pharmacokinetics may help to refine therapy. In this study, the associations of single-nucleotide polymorphisms (SNPs) in drug-metabolizing enzymes (CYP3A) with Tac pharmacokinetics were investigated in renal transplant recipients., Participants and Methods: In a cohort of 272 kidney transplant recipients, associations between functional genetic variants (CYP3A4*22 and CYP3A5*3) and dose-adjusted predose Tac concentrations (C0) and daily doses of Tac at days 5-7 and 15 and 1, 3, 6 and 12 months after renal transplantation were evaluated. Patients were genotyped and clustered according to both CYP3A4*22 and CYP3A5*3 allelic status: poor (PM) (CYP3A4*22 carriers with CYP3A5*3/*3), intermediate (IM) (CYP3A4*1/*1 with CYP3A5*3/*3 or CYP3A4*22 carriers with CYP3A5*1 carriers) and extensive CYP3A-metabolizers (EM) (CYP3A4*1/*1 and CYP3A5*1 carriers)., Results: EM had an 88% lower dose-adjusted C0 compared with IM. PM had a 26% higher dose-adjusted C0 compared with IM. The percentage of patients with supratherapeutic Tac exposure (C0>15 ng/ml) was significantly higher in PM (43.5%) compared with EM (0%) at days 5-7 after transplantation (P=0.01). About 30% of EM had subtherapeutic exposure (C0<5 ng/ml) at days 5-7 after transplantation (P=0.001)., Conclusion: The combined CYP3A4 and CYP3A5 genotype of renal transplant recipients has a major influence on the Tac dose required to reach the target exposure.

Background: The aim of this study was to develop a population pharmacokinetic model of tacrolimus in paediatric patients at least 1 year after renal transplantation and simulate individualised dosage regimens., Patients and Methods: We included 54 children with median age of 11.1 years (range 3.8-18.4 years) with 120 pharmacokinetic profiles performed over 2 to 4 h. The pharmacokinetic analysis was performed using the non-linear mixed-effects modelling software (NONMEM(®)). The impact of covariates including concomitant medications, age, the cytochrome P450 (CYP) CYP3A5*3 gene and the adenosine triphosphate binding cassette protein B1 (ABCB1) 3435 C→T gene polymorphism on tacrolimus pharmacokinetics was analysed. The final model was externally validated on an independent dataset and dosing regimens were simulated., Results: A two-compartment model adequately described tacrolimus pharmacokinetics. Apparent oral clearance (CL/F) was associated with weight (allometric scaling) but not age. Children with lower weight and CYP3A5 expressers required higher weight-normalised tacrolimus doses. CL/F was inversely associated with haematocrit (P < 0.05) and γ-glutamyl transpeptidase (γGT) (P < 0.001) and was increased by 45 % in carriers of the CYP3A5*1 allele (P < 0.001). CL/F was not associated with concomitant medications. Dose simulations show that a daily tacrolimus dose of 0.2 mg/kg generates a pre-dose concentration (C 0) ranging from 5 to 10 µg/L depending on the weight and CYP3A5 polymorphism. The median area under the plasma concentration-time curve (AUC) corresponding with a tacrolimus C 0 of 4-8 µg/L was 97 h·µg/L (interquartile range 80-120)., Conclusions: In patients beyond the first year after transplantation, there is a cumulative effect of CYP3A5*1 polymorphism and weight on the tacrolimus C 0. Children with lower weight and carriers of the CYP3A5*1 allele have higher weight-normalised tacrolimus dose requirements.

Introduction: Chronic kidney disease (CKD) after liver transplantation (LT) is a major clinical problem that appears to be associated with nongenetic as well as genetic determinants. Calcineurin inhibitor (CNI) use is considered to play a major role in the development of CKD after LT. We studied the influence of single-nucleotide polymorphisms (SNPs) in the genes of the donor and recipient CNI-metabolizing enzyme CYP3A5 and the CNI-transporting ABCB1 on the development of CKD after LT., Materials and Methods: Tacrolimus (Tac) predose concentrations at different time-points after transplantation and the CYP3A5 6986A>G and ABCB1 3435C>T SNPs were determined in 125 LT recipients and their respective donors to study the influence of Tac predose levels and genetics on the development of CKD., Results: After a median follow-up of 5.7±2.9 years, CKD developed in 47 patients (36%). The Tac predose levels were not correlated with the development of CKD. Neither did we find a correlation between the investigated SNPs in either donor or recipient ABCB1 and CYP3A5 genes (or combinations thereof) and the development of CKD. These genetic variations did not relate to Tac predose blood concentrations in our study., Conclusion: An individual's risk of developing CKD after LT is not associated with genetic variation in either recipient or donor CYP3A5 or ABCB1 genotype status.

Background: Both age and CYP3A5 genotype are important determinants of tacrolimus disposition in pediatric kidney transplant recipients. In a recent study in adults, POR*28 was associated with increased dosing requirements early after transplant of CYP3A5-expressing kidney transplant recipients. The authors aimed to evaluate the additional contribution of POR*28 to early tacrolimus disposition in pediatric kidney transplant recipients., Methods: Retrospective data of 43 pediatric kidney transplant recipients up to 14 days posttransplant were evaluated on tacrolimus dose and tacrolimus predose blood concentrations. Recipient POR*28 and CYP3A5 genotype were determined., Results: CYP3A5 expressers carrying at least 1 POR*28 allele had on average 18.3% lower tacrolimus predose concentrations and 20.2% lower concentration/dose ratios compared with CYP3A5 expressers with POR*1/*1 genotype (P = 0.002 and P = 0.001, respectively). In CYP3A5 nonexpressers, tacrolimus disposition did not significantly differ between POR genotypes., Conclusions: In this small cohort of pediatric kidney transplant recipients, POR*28 genotype seems to explain part of the variability found in tacrolimus disposition, in addition to age and CYP3A5 genotype. This finding should be validated in a larger population, and it would be worthwhile to evaluate the clinical impact of this genotype.

The calcineurin inhibitor tacrolimus is the backbone of immunosuppressive drug therapy after solid organ transplantation. Tacrolimus is effective in preventing acute rejection but has considerable toxicity and displays marked inter-individual variability in its pharmacokinetics and pharmacodynamics. The genetic basis of these phenomena is reviewed here. With regard to its pharmacokinetic variability, a single nucleotide polymorphism (SNP) in cytochrome P450 (CYP) 3A5 (6986A>G) has been consistently associated with tacrolimus dose requirement. Patients expressing CYP3A5 (those carrying the A nucleotide, defined as the *1 allele) have a dose requirement that is around 50 % higher than non-expressers (those homozygous for the G nucleotide, defined as the *3 allele). A randomised controlled study in kidney transplant recipients has demonstrated that a CYP3A5 genotype-based approach to tacrolimus dosing leads to more patients reaching the target concentration early after transplantation. However, no improvement of clinical outcomes (rejection incidence, toxicity) was observed, which may have been the result of the design of this particular study. In addition to CYP3A5 genotype, other genetic variants may also contribute to the variability in tacrolimus pharmacokinetics. Among these, the CYP3A4*22 and POR*28 SNPs are the most promising. Individuals carrying the CYP3A4*22 T-variant allele have a lower tacrolimus dose requirement than individuals with the CYP3A4*22 CC genotype and this effect appears to be independent of CYP3A5 genotype status. Individuals carrying the POR*28 T-variant allele have a higher tacrolimus dose requirement than POR*28 CC homozygotes but this association was only found in CYP3A5-expressing individuals. Other, less well-defined SNPs have been inconsistently associated with tacrolimus dose requirement. It is envisaged that in the future, algorithms incorporating clinical, demographic and genetic variables will be developed that will aid clinicians with the determination of the tacrolimus starting dose for an individual transplant recipient. Such an approach may limit early tacrolimus under-exposure and toxicity. With regard to tacrolimus pharmacodynamics, no strong genotype-phenotype relationships have been identified. Certain SNPs associate with rejection risk but these observations await replication. Likewise, the genetic basis of tacrolimus-induced toxicity remains unclarified. SNPs in the genes encoding for the drug transporter ABCB1 and the CYP3A enzymes may relate to chronic nephrotoxicity but findings have been inconsistent. No genetic markers reliably predict new-onset diabetes mellitus after transplantation, hypertension or neurotoxicity. The CYP3A5*1 SNP is currently the most promising biomarker for tailoring tacrolimus treatment. However, before CYP3A5 genotyping is incorporated into the routine clinical care of transplant recipients, prospective clinical trials are needed to determine whether such a strategy improves patient outcomes. The role of pharmacogenetics in tacrolimus pharmacodynamics should be explored further by the study of intra-lymphocyte and tissue tacrolimus concentrations.

Background: The P450 oxidoreductase (POR)*28 variant allele has been associated with altered cytochrome P450 3A enzyme activities. Both CYP3A5 and CYP3A4 are involved in the metabolism of calcineurin inhibitors and recent data show that POR*28 may explain part of the variability observed in tacrolimus (Tac) pharmacokinetics. The aim of this study was to investigate the impact of the POR*28 allele on Tac and cyclosporine A (CsA) immunosuppressive therapies., Methods: Kidney transplant recipients receiving either Tac (n = 184) or CsA (n = 174), participating in a prospective multicenter trial, were genotyped for POR*28, CYP3A4*22, and CYP3A5*3., Results: CYP3A5 expressers that were carriers of at least 1 POR*28 allele had a 16.9% decrease in dose-adjusted predose concentrations when compared CYP3A5 expressers that carried the POR*1/*1 genotype (P = 0.03), indicating an increased CYP3A5 activity for POR*28 carriers. In CYP3A5, nonexpressers carrying 2 POR*28 alleles, a 24.1% (confidence interval95% = -39.4% to -4.9%; P = 0.02) decrease in dose-adjusted predose concentrations was observed for Tac, suggesting higher CYP3A4 activity. For CsA, POR*28/*28 patients not expressing CYP3A5 and not carrying the CYP3A4*22 decrease-of-function allele showed 15% lower CsA dose-adjusted predose concentrations (P = 0.01), indicating also increased CYP3A4 activity. In both cohorts (ie, Tac and CsA), the POR*28 allele was neither associated with the incidence of delayed graft function nor with biopsy-proven acute rejection. These results were further confirmed in 2 independent cohorts., Conclusions: Our results show that the POR*28 allele is associated with increased in vivo CYP3A5 activity for Tac in CYP3A5 expressers, whereas POR*28 homozygosity was associated with a significant higher CYP3A4 activity in CYP3A5 nonexpressers for both Tac and CsA.

Background: New-onset diabetes after transplantation (NODAT) is an important complication after kidney transplantation. The etiology of the malady is multifactorial and includes both environmental and genetic factors. NODAT is a polygenic disease and many single-nucleotide polymorphisms could constitute potential risk factors. Peroxisome proliferator-activated receptor α (PPARα) and P450 oxidoreductase (POR) play a central role in the control of energy metabolism in humans. Some recent data highlighted a possible functional impact of two single-nucleotide polymorphisms in PPARα (rs4253728 G>A and rs4823613 A>G) and one coding variant in POR (rs1057868; POR*28; A503V) on the activity of their respective encoded proteins. In the present study, we assessed the association between these variants and the risk of developing NODAT after kidney transplantation., Methods: Development of NODAT was investigated in 101 renal transplant recipients receiving tacrolimus-based immunosuppressive therapy. Patients were genotyped for PPARα and POR. The incidence of NODAT was compared between different genotypes. Kaplan-Meier and Cox's proportional-hazard analysis were used to evaluate the association of NODAT with potential risk factors. Potential nongenetic risk factors were also considered., Results: The PPARα rs4253728A>G and POR*28 variant alleles were both independently associated with an increased risk for NODAT with respective odds ratios of 8.6 [95% confidence interval (CI)=1.4-54.2; P=0.02] and 8.1 (95% CI=1.1-58.3; P=0.04). Other risk predictors included sex and body weight., Conclusion: This candidate-gene study shows that polymorphisms in PPARα and POR might predispose patients being treated with tacrolimus to the development of NODAT after kidney transplantation. Patient management after organ transplantation might benefit from genotype data.

Background: Tacrolimus (Tac) metabolism is mainly mediated by the cytochrome P450 3A (CYP3A) subfamily. Recently, it has been reported that kidney transplant recipients carrying the CYP3A4*22 decrease-of-function allele require lower Tac doses and are more at risk of Tac overexposure than CYP3A4*1/*1 patients. This effect was shown to be independent of the CYP3A5*3 allelic status. However, the pharmacokinetic (PK) parameters assessed in previous studies were limited on single time point whole blood trough concentrations (C0) during routine follow-up of the patient after transplantation., Methods: Our study investigates the impact of the CYP3A4*22 allele on Tac PK [C0, area under the time vs concentration curve (AUC0-12h), apparent clearance (Cl/F), Cmax, and dose requirement], time to achieve target C0, and creatinine clearance (CrCl) in 96 kidney transplant recipients considering the 2 first weeks after the graft. All patients were genotyped for both the CYP3A4*22 and the CYP3A5*3 polymorphisms., Results: CYP3A4*22 carriers had higher Tac C0 during the first week with significant longer exposures to C0 > 15 ng/mL. These patients showed reduced Tac Cl/F but higher dose-adjusted AUC0-12h and Cmax and were at increased risk of C0 > 20 ng/mL. These effects were independent from CYP3A5*3 genotype: clustering patients according to both CYP3A4*22 and CYP3A5*3 allelic status did increase the predictive value of the genotype to explain interindividual differences in Tac PK. During the second week after transplantation, CrCl was on average 9.5 mL/min higher for CYP3A4*22 carriers compared with CYP3A4*1/*1 patients (P = 0.007), suggesting that Tac overexposure in CYP3A4*22 carriers might provide a renal function benefit., Conclusions: Our study confirms the decreased CYP3A4 activity toward Tac for CYP3A4*22 carriers early after transplantation and provides evidence for refining genotype-based dosage by adding the CYP3A4*22 genotype information to the CYP3A5*3 allelic status.

Introduction: Tacrolimus has a large interindividual pharmacokinetic variability, and quantification of its effect is difficult. It is a substrate of ABCB1, an efflux pump expressed more on CD8 T cells than on CD4 T cells. The ABCB1 3435C>T single-nucleotide polymorphism (SNP) has been associated with interindividual differences in ABCB1 activity and may influence drug efficacy. Here the influence of this SNP on the biological effect of tacrolimus was studied., Methods: Rhodamine (Rh123) efflux was used to study ABCB1 activity, with or without the addition of the ABCB1 inhibitor verapamil. Intracellular interleukin (IL) 2 production in T cells was used to measure the pharmacodynamic effect of tacrolimus after phorbol-12-myristate-13-acetate/ionomycin stimulation of whole blood. In addition, the ABCB1 genotype of 36 tacrolimus-treated renal transplant patients was related to ABCB1 activity and tacrolimus efficacy., Results: The mean Rh123 efflux was higher in CD8 T cells compared with CD4 T cells: 40% versus 19% of cells, respectively (P < 0.001). Verapamil almost completely blocked Rh123 efflux (to 1.8% of CD4 T cells and 0.5% of CD8 T cells), whereas tacrolimus did not change Rh123 efflux. Tacrolimus 10 ng/mL reduced the production of IL-2 in CD4 and CD8 T cells by 28.9% and 45.4% (P < 0.05). Tacrolimus-mediated inhibition of IL-2 was enhanced by verapamil (P < 0.05). This effect on tacrolimus pharmacodynamics was associated with ABCB1 3435C>T SNP in renal transplant patients: verapamil reduced the percentage of IL-2-producing CD4 and CD8 T cells by 14% and 22% in patients with the CC genotype (P < 0.05) but not in patients with the TT genotype. Moreover, the ratio of tacrolimus C0 over the percent of IL-2-producing CD8 T cells in CC genotype patients was significantly higher compared with TT genotype patients (P < 0.05), showing a smaller pharmacodynamic effect in CC genotype patients., Conclusion: The ABCB1 3435C>T SNP influences ABCB1 activity of T cells and the pharmacodynamic effect of tacrolimus in kidney transplant patients.

Background: Tacrolimus metabolism depends on CYP3A4 and CYP3A5. We aimed to determine the relationship between the CYP3A4*22 polymorphism and combined CYP3A genotypes with tacrolimus disposition in pediatric heart transplant recipients., Methods: Sixty pediatric heart transplant recipients were included. Tacrolimus doses and trough concentrations were collected in the first 14 days post-transplantation. CYP3A phenotypes were defined as extensive (CYP3A5*1 + CYP3A4*1/*1 carriers), intermediate (CYP3A5*3/*3 + CYP3A4*1/*1 carriers) or poor (CYP3A5*3/*3 + CYP3A4*22 carriers) metabolizers., Results: CYP3A4*22 carriers needed 30% less tacrolimus (p = 0.016) to reach similar target concentrations compared with CYP3A4*1/*1 (n = 56) carriers. Poor CYP3A metabolizers required 17% (p = 0.023) less tacrolimus than intermediate and 48% less (p < 0.0001) than extensive metabolizers. Poor metabolizers showed 18% higher dose-adjusted concentrations than intermediate (p = 0.35) and 193% higher than extensive metabolizers (p < 0.0001)., Conclusion: Analysis of CYP3A4*22, either alone or in combination with CYP3A5*3, may help towards individualization of tacrolimus therapy in pediatric heart transplant patients.

Purpose: In children, data on the combined impact of age, genotype, and disease severity on tacrolimus (TAC) disposition are scarce. The aim of this study was to evaluate the effect of these covariates on tacrolimus dose requirements in the immediate post-transplant period in pediatric kidney and liver recipients., Methods: Data were retrospectively collected describing tacrolimus disposition, age, CYP3A5 and ABCB1 genotype, and pediatric risk of mortality (PRISM) scores for up to 14 days post-transplant in children receiving liver and renal transplants. Initial TAC dosing was equal in all patients and adjusted using therapeutic drug monitoring. We determined the relationship between covariates and tacrolimus disposition., Results: Forty-eight kidney and 42 liver transplant recipients (median ages 11.5 and 1.5 years, ranges 1.5-17.7 and 0.05-14.8 years, respectively) received TAC post-transplant. In both transplant groups, younger children (<5 years) needed higher TAC doses than older children [kidney: 0.15 (0.07-0.35) vs. 0.09 (0.02-0.20) mg/kg/12h, p = 0.046, liver: 0.12 (0.04-0.32) vs. 0.09 (0.01-0.18) mg/kg/12h, p = 0.038]. In kidney but not liver transplants, CYP3A5 expressors needed significantly higher TAC doses than nonexpressors [0.15 (0.07-0.20) vs. 0.09 (0.02-0.35) mg/kg/12h, P = 0.001]. In these patients, age and CYP3A5 genotype were independently associated with TAC dosing requirement. In liver, but not kidney transplant patients, homozygous ABCB1 T-T-T haplotype carriers needed higher TAC doses than noncarriers [0.26 (0.15-0.32) vs. 0.11 (0.01-0.25) mg/kg/12h, p = 0.013]., Conclusion: CYP3A5 genotype may explain variation in tacrolimus disposition early after transplant in pediatric kidney recipients, independent of age-related variation. In contrast, in pediatric liver recipients, variation in tacrolimus disposition appears related to age and ABCB1 genotype. These findings illustrate the importance of the interplay among age, genotype, and transplant organ on tacrolimus disposition.

Background: Tacrolimus is one of the commonly used immunosuppressive drugs for pediatric heart transplants. Large variation exists in pharmacokinetics during the direct post-transplant period, resulting in an increased risk of adverse events. Limited data are available on the interaction of age, CYP3A5 and ABCB1 genotype, and disease severity on the variation in disposition and outcome in pediatric heart transplant recipients., Method: We studied the relationship between age and CYP3A5 and ABCB1 genotype and the Pediatric Risk of Mortality (PRISM) score on tacrolimus dose (mg/kg), steady-state trough concentrations, and concentration/dose ratio, as well as rejection and renal function for 14 days after heart transplant in children., Results: Tacrolimus was administered to 39 children (median age, 6.0 years) after transplant. A correlation was found between the age at the time of transplant and the tacrolimus dosing requirements (r(s) = -0.447, p = 0.004) and the concentration/dose ratio (r(s) = 0.351, p = 0.029). CYP3A5 expressors required median (interquartile range) higher doses of tacrolimus (0.14 [0.09] vs 0.06 [0.04] mg/kg/12 hours, p = 0.001), and had lower concentration/dose ratios (45.34 [44.54] vs 177.78 [145.38] ng/ml per mg/kg/12 hours, p < 0.0001). This relationship was not seen with the ABCB1 genotype. Age and CYP3A5 genotype predicted the tacrolimus dosing requirements as well as the concentration/dose ratio (R(2) = 0.351, p = 0.001 and R(2) = 0.521, p < 0.001). No relationship was found between any of the CYP3A5 or ABCB1 genotypes and the estimated glomerular filtration rate., Conclusion: Younger age and CYP3A5 expressor genotype were independently associated with higher dosing requirements and lower tacrolimus concentration/dose ratios., (Copyright © 2011 International Society for Heart and Lung Transplantation. All rights reserved.)

Background: Tacrolimus (Tac) is a potent immunosuppressant with considerable toxicity. Tac pharmacokinetics varies between individuals and thus complicates its use in preventing rejection after kidney transplantation. This variability might be caused by genetic polymorphisms in metabolizing enzymes., Methods: We used TaqMan analyses to evaluate the impact of a newly discovered CYP3A4 (cytochrome P450, family 3, subfamily A, polypeptide 4) single-nucleotide polymorphism (SNP) (rs35599367C>T; CYP3A4*22) on Tac pharmacokinetics in 185 renal transplant recipients who participated in an international randomized controlled clinical trial (fixed-dose, concentration-controlled study)., Results: The overall mean daily-dose requirement to reach the same predose Tac blood concentration was 33% lower for carriers of the T variant allele than for rs35599367CC patients (95% CI, -46% to -20%; P = 0.018). When combined with the *3 genotype of the CYP3A5 (cytochrome P450, family 3, subfamily A, polypeptide 5) gene, the rs35599367C>T SNP was also associated with a risk of supratherapeutic Tac concentrations (>15 μg/L) during the first 3 days after surgery, with an odds ratio of 8.7 for carriers of the CYP3A4 T allele plus CYP3A5*3/*3 (P = 0.027) and 4.2 for the CYP3A4 CC homozygotes plus CYP3A5*3/*3 (P = 0.002), compared with CYP3A4 CC homozygotes having 1 or 2 CYP3A5*1 alleles. The overall increase in the Tac dose-adjusted trough blood concentration was +179% for carriers of the CYP3A4 T allele with CYP3A5*3/*3 (P < 0.001), +101% for CYP3A4 CC homozygotes with CYP3A5*3/*3 (P < 0.001), and +64% for CYP3A4 T allele carriers with CYP3A5*1 (P = 0.020),compared with CYP3A4 CC homozygotes with CYP3A5*1., Conclusions: The CYP3A4 rs35599367C>T polymorphism is associated with a significantly altered Tac metabolism and therefore increases the risk of supratherapeutic Tac concentrations early after transplantation. Analysis of this CYP3A4*22 SNP may help in identifying patients at risk of Tac overexposure.

Aims: CYP3A4 is involved in the oxidative metabolism of many drugs and xenobiotics including the immunosuppressants tacrolimus (Tac) and cyclosporine (CsA). The objective of the study was to assess the potential influence of a new functional SNP in CYP3A4 on the pharmacokinetic parameters assessed by dose requirements and trough blood levels of both calcineurin inhibitors (CNI) in stable renal transplant patients., Patients & Methods: A total of 99 stable renal transplant patients receiving either Tac (n = 49) or CsA (n = 50) were genotyped for the CYP3A4 intron 6 C>T (rs35599367) and CYP3A5*3 SNPs. Trough blood levels ([Tac](0) or [CsA](0) in ng/ml), dose-adjusted [Tac](0) or [CsA](0) (ng/ml per mg/kg bodyweight) as well as doses (mg/kg bodyweight) required to achieve target concentrations were compared among patients according to allelic status for CYP3A4 and CYP3A5., Results: Dose-adjusted concentrations were 2.0- and 1.6-fold higher in T-variant allele carriers for the CYP3A4 intron 6 C>T SNP compared with homozygous CC for Tac and CsA, respectively. When CYP3A4/CYP3A5 genotypes were combined, the difference was even more striking as the so-defined CYP3A poor metabolizer group presented dose-adjusted concentration 1.6- and 4.1-fold higher for Tac, and 1.5- and 2.2-fold higher for CsA than the intermediate metabolizer and extensive metabolizer groups, respectively. Multiple linear regression analysis revealed that, taken together, both CYP3A4 intron 6 and CYP3A5*3 SNPs explained more than 60 and 20% of the variability observed in dose-adjusted [Tac](0) and [CsA](0), respectively., Conclusion: The CYP3A4 intron 6 C>T polymorphism is associated with altered Tac and CsA metabolism. CYP3A4 intron 6 C>T along with CYP3A5*3 (especially for Tac) pharmacogenetic testing performed just before transplantation may help identifying patients at risk of CNI overexposure and contribute to limit CNI-related nephrotoxicity by refining the starting dose according to their genotype. Original submitted 5 May 2011; Revision submitted 29 June 2011.

Background: The risk of long-term chronic allograft nephropathy and graft loss after kidney transplantation is increased in patients with a high intrapatient variability of tacrolimus (Tac) clearance., Methods: To test whether this intrapatient variability is associated with an individual's CYP3A5 genotype, we measured the intrapatient variability in Tac clearance in a cohort of 208 kidney transplant recipients treated with Tac and mycophenolate mofetil., Results: Tac dose requirement was significantly higher in patients expressing CYP3A5. However, intraindividual variability of Tac clearance was not related to CYP3A5 genotype., Conclusions: Intraindividual variability in Tac clearance is not related to CYP3A5 genotype. Other factors, including patient adherence, may explain the variability in Tac clearance within an individual patient over time.

Objective: Patients expressing the tacrolimus-metabolizing enzyme, cytochrome P450 (CYP) 3A5, require more tacrolimus to reach target concentrations. We studied the influence of the CYP3A5(*)3 allele, which results in the absence of CYP3A5 protein, on tacrolimus dose and exposure, as well as the incidence of biopsy-proven acute rejection (BPAR) after renal transplantation., Methods: A total of 136 patients participating in a prospective, randomized-controlled clinical trial with the primary aim of comparing the efficacy of a fixed-dose versus a concentration-controlled mycophenolate mofetil immunosuppressive regimen, were genotyped for CYP3A5(*)3. The patients described herein, participated in a pharmacogenetic substudy and were all treated with mycophenolate mofetil, corticosteroids and tacrolimus. Tacrolimus predose concentrations (C(0)) were measured on day 3 and 10, and month 1, 3, 6 and 12., Results: Compared with CYP3A5(*)3/(*)3 individuals (n=110), patients carrying at least one CYP3A5(*)1 (wild-type) allele (CYP3A5 expressers; n=26) had a lower tacrolimus C(0) on day 3 only (16.6 versus 12.3 ng/ml, respectively), whereas dose-corrected tacrolimus C(0) were significantly lower in the latter group at all time points. After day 3, the overall daily tacrolimus dose was 68% higher in CYP3A5 expressers (P<0.001). The incidence of BPAR was comparable between CYP3A5 expressers and nonexpressers (8 versus 16%, respectively; P=0.36)., Conclusion: We conclude that patients expressing CYP3A5 need more tacrolimus to reach target concentrations and have a lower tacrolimus exposure shortly after transplantation. This delay in reaching target concentrations, however, did not result in an increased incidence of early BPAR and therefore, genotyping for CYP3A5 is unlikely to improve short-term transplantation outcome.

Background: The calcineurin inhibitors cyclosporine (INN, cyclosporin) and tacrolimus have a narrow therapeutic index and show considerable interindividual variability in their pharmacokinetics. The low oral bioavailability of calcineurin inhibitors is thought to result from the actions of the metabolizing enzymes cytochrome P450 (CYP) 3A4 and CYP3A5 and the multidrug efflux pump P-glycoprotein, encoded by MDR-1., Objective: Our objective was to determine the role of genetic polymorphisms in CYP3A4, CYP3A5, and MDR-1 with respect to interindividual variability in cyclosporine and tacrolimus pharmacokinetics., Methods: Kidney transplant recipients receiving cyclosporine (n = 110) or tacrolimus (n = 64) were genotyped for CYP3A4*1B and *3, CYP3A5*3 and *6, and MDR-1 C3435T. Dose-adjusted trough levels were determined and correlated with the corresponding genotype., Results: Tacrolimus dose-adjusted trough levels were higher in CYP3A5*3/*3 patients (n = 45) than in *1/*3 plus *1/*1 patients (n = 17), as follows: median and range, 94 (34-398) ng/mL per mg/kg versus 61 (37-163) ng/mL per mg/kg (P <.0001, Mann-Whitney test). CYP3A4*1B allele carriers (n = 10) had lower tacrolimus dose-adjusted trough levels compared with those in patients with the wild-type (*1/*1) genotype (n = 54): median and range, 57 (40-163) ng/mL per mg/kg versus 89 (34-398) ng/mL per mg/kg) (P =.003, Mann-Whitney test). No evidence was found supporting a role for the MDR-1 C3435T polymorphism in tacrolimus dose requirement. None of the polymorphisms studied correlated with cyclosporine dose-adjusted predose concentrations., Conclusion: As a group, patients with the CYP3A5*3/*3 genotype require less tacrolimus to reach target predose concentrations compared with CYP3A5*1 allele carriers, whereas CYP3A4*1B carriers require more tacrolimus to reach target trough concentrations compared with CYP3A4*1 homozygotes.

A high intrapatient variability (IPV) in tacrolimus exposure is a risk factor for poor long‐term outcomes after kidney transplantation. The main objective of this trial was to investigate whether tacrolimus IPV decreases after switching patients from immediate‐release (IR)‐tacrolimus to either extended‐release (ER)‐tacrolimus or LifeCyclePharma (LCP)‐tacrolimus. In this randomized, prospective, open‐label, cross‐over trial, adult kidney transplant recipients on a stable immunosuppressive regimen, including IR‐tacrolimus, were randomized for conversion to ER‐tacrolimus or LCP‐tacrolimus, and for the order in which IR‐tacrolimus and the once‐daily formulations were taken. Patients were followed 6 months for each formulation, with monthly tacrolimus predose concentration assessments to calculate the IPV. The IPV was defined as the coefficient of variation (%) of dose corrected predose concentrations. Ninety‐two patients were included for analysis of the primary outcome. No significant differences between the IPV of IR‐tacrolimus (16.6%) and the combined once‐daily formulations (18.3%) were observed (% difference +1.7%, 95% confidence interval [CI] −1.1% to ‒4.5%, p = 0.24). The IPV of LCP‐tacrolimus (20.1%) was not significantly different from the IPV of ER‐tacrolimus (16.5%, % difference +3.6%, 95% CI −0.1% to 7.3%, p = 0.06). In conclusion, the IPV did not decrease after switching from IR‐tacrolimus to either ER‐tacrolimus or LCP‐tacrolimus. These results provide no arguments to switch kidney transplant recipients from twice‐daily (IR) tacrolimus formulations to once‐daily (modified‐release) tacrolimus formulations when the aim is to lower the IPV. [ABSTRACT FROM AUTHOR]

Tacrolimus (Tac) is a profoundly effective immunosuppressant that reduces the risk of rejection after solid organ transplantation. However, its use is hampered by its narrow therapeutic window along with its highly variable pharmacological (pharmacokinetic [PK] and pharmacodynamic [PD]) profile. Part of this variability is explained by genetic polymorphisms affecting the metabolic pathway. The integration of CYP3A4 and CY3A5 genotype in tacrolimus population-based PK (PopPK) modeling approaches has been proven to accurately predict the dose requirement to reach the therapeutic window. The objective of the present study was to develop an accurate PopPK model in a cohort of 59 kidney transplant patients to deliver this information to clinicians in a clear and actionable manner. We conducted a non-parametric non-linear effects PopPK modeling analysis in PmetricsR. Patients were genotyped for the CYP3A4*22 and CYP3A5*3 alleles and were classified into 3 different categories [poor-metabolizers (PM), Intermediate-metabolizers (IM) or extensive-metabolizers (EM)]. A one-compartment model with double gamma absorption route described very accurately the tacrolimus PK. In covariate analysis, only CYP3A genotype was retained in the final model (Δ-2LL = -73). Our model estimated that tacrolimus concentrations were 33% IC95%[20-26%], 41% IC95%[36-45%] lower in CYP3A IM and EM when compared to PM, respectively. Virtually, we proved that defining different starting doses for PM, IM and EM would be beneficial by ensuring better probability of target concentrations attainment allowing us to define new dosage recommendations according to patient CYP3A genetic profile. [ABSTRACT FROM AUTHOR]