CYP3A5*1-carrying graft liver reduces the concentration/oral dose ratio of tacrolimus in recipients of living-donor liver transplantation

A retrospective analysis of tacrolimus pharmacokinetic in Saudi paediatric patients in early post-liver transplantation period

BACKGROUND

Tacrolimus is an essential immunosuppressive medication in paediatric patients' post-liver transplantation. Achieving tacrolimus target concentration in early post-transplantation is crucial to minimise the risk of acute rejection; however, this is challenging due to inter- and intra-patient variability in tacrolimus metabolism and clearance. Therefore, our study aims to describe tacrolimus trough concentration variability and pharmacokinetics in paediatric post-liver transplantation during the first two weeks post-transplantation.

METHOD

This retrospective multicentre observational study included paediatric patients post-liver transplantation. Post-operative data was collected within the initial 14 days using electronic health records, including daily tacrolimus doses, measured trough concentrations, graft data, surgical data, and documented acute rejection. Pharmacokinetic analysis was completed using the Monolix software. We used the empirical Bayesian estimates of clearance and volume of distribution for covariate testing to assess possible correlations. We performed a stepwise regression analysis (alpha = 0.05).

RESULTS

Ninety-one paediatric patients were included in the study, with a mean age of 4.1 years (SD = 4.6). The mean graft-to-recipient weight ratio (GRWR) was 3% (SD = 6). The vast majority of the patients received the liver from living donors (n = 84, 92.3%). The average time needed to reach therapeutic concentration was 4.6 (SD = 2.8) days. The initial clearance (Clini) was very low at baseline (0.012 L/h), then increased dramatically to 9.84 L/h at 14 days post-transplantation. The clearance appeared to be time-dependent, and the time needed to reach 50% of maximum clearance was five days post-transplantation. The covariates that significantly affected clearance included bodyweight and aspartate transaminase, while the only significant covariate for volume of distribution was bodyweight.

CONCLUSION

Tacrolimus is a drug with high intra- and interindividual variability, making dosing challenging in the paediatric liver transplantation population. Prospective studies with more intensive sampling are needed to address the time-dependent changes in clearance, which will aid in establishing the optimal dosing regimens in this population.

A longitudinal study of long-term renal outcome after pediatric liver transplantation in relation to CNI exposure

BACKGROUND

Chronic kidney disease (CKD) is reported in 20%-30% of children after liver transplantation (LT). One of the proposed underlying causes is the long-term exposure to tacrolimus, a calcineurin inhibitor (CNI), which is the main immunosuppressive drug used after LT. Variation in tacrolimus absolute exposure and relative dose requirements are believed to be important risk factors for developing CNI-associated nephrotoxicity.

AIM

To describe the long-term renal outcome of pediatric LT recipients and determine the effects of tacrolimus exposure on renal outcome parameters.

METHODS

Retrospective single center study of renal function (GFR, proteinuria) and pharmacokinetic parameters (C0 , AUC0-12h ) obtained during annual follow-up in children after liver transplantation, between 1998 and 2019. Relevant pharmacogenetic variants for tacrolimus disposition (CYP3A5 and ABCB1) were determined in recipients and donors. The evolution of individual renal function and tacrolimus exposure was evaluated using linear mixed models for repeated measurements.

RESULTS

Twenty-six children were included (mean follow-up: 10.4 years (range 2-18.9)). Mean estimated GFR was 109.3 (SE: 7.4), vs. measured: 91.3 mL/min/1.73 m2 (SE: 6.3), which remained stable during follow-up. CKD stage ≥2 was observed in 32.8% of the visits based on eGFR versus 50.0% on mGFR. CKD stage ≥3 was uncommon (4.1% and 6.2% resp.). Mean tacrolimus C0 was 5.3 ng/mL (SE: 2.5) with a AUC0-12h of 72.7 ng*h/mL (SE: 30.3), which demonstrated a small decrease during follow-up. There was a negative correlation between C0 and mGFR (rS  = -0.3; p < .001). We found no correlation between GFR and tacrolimus dose requirements ((ng/mL)/(mg/kg)) or pharmacogenetic background.

CONCLUSION

Renal function during long-term follow-up after pediatric LT remained stable for the majority of our cohort. However, mild CKD was relatively common, warranting follow-up into adulthood. Although absolute tacrolimus exposure has a small depressing effect on concurrent GFR, there is no progressive deterioration of GFR due to long-term exposure, dose requirements or genetic background under the current target levels. These findings should be confirmed in a larger sample set, ideally including data from multiple centers.

CYP3A5 influences oral tacrolimus pharmacokinetics and timing of acute kidney injury following allogeneic hematopoietic stem cell transplantation

Introduction: Polymorphisms in genes responsible for the metabolism and transport of tacrolimus have been demonstrated to influence clinical outcomes for patients following allogeneic hematologic stem cell transplant (allo-HSCT). However, the clinical impact of germline polymorphisms specifically for oral formulations of tacrolimus is not fully described. Methods: To investigate the clinical impact of genetic polymorphisms in CYP3A4, CYP3A5, and ABCB1 on oral tacrolimus pharmacokinetics and clinical outcomes, we prospectively enrolled 103 adult patients receiving oral tacrolimus for the prevention of graft-versus-host disease (GVHD) following allo-HSCT. Patients were followed in the inpatient and outpatient phase of care for the first 100 days of tacrolimus therapy. Patients were genotyped for CYP3A5 *3 (rs776746), CYP3A4 *1B (rs2740574), ABCB1 exon 12 (rs1128503), ABCB1 exon 21 (rs2032582), ABCB1 exon 26 (rs1045642). Results: Expression of CYP3A5 *1 was highly correlated with tacrolimus pharmacokinetics in the inpatient phase of care (p < 0.001) and throughout the entirety of the study period (p < 0.001). Additionally, Expression of CYP3A5 *1 was associated with decreased risk of developing AKI as an inpatient (p = 0.06). Variants in ABCB1 were not associated with tacrolimus pharmacokinetics in this study. We were unable to discern an independent effect of CYP3A4 *1B or *22 in this population. Conclusion: Expression of CYP3A5 *1 is highly influential on the pharmacokinetics and clinical outcomes for patients receiving oral tacrolimus as GVHD prophylaxis following allo-HSCT.

The impact of CYP3A4 and CYP3A5 genetic variations on tacrolimus treatment of living-donor Egyptian kidney transplanted patients

BACKGROUND

Tacrolimus (TAC) is the mainstay of immunosuppressive regimen for kidney transplantations. Its clinical use is complex due to high inter-individual variations which can be partially attributed to genetic variations at the metabolizing enzymes CYP3A4 and CYP3A5. Two single nucleotide polymorphisms (SNPs), CYP3A4*22 and CYP3A5*3, have been reported as important causes of differences in pharmacokinetics that can affect efficacy and/or toxicity of TAC.

OBJECTIVE

Investigating the effect of CYP3A4*22 and CYP3A5*3 SNPs individually and in combination on the TAC concentration in Egyptian renal recipients.

METHODS

Overall, 72 Egyptian kidney transplant recipients were genotyped for CYP3A4*22 G>A and CYP3A5*3 T>C. According to the functional defect associated with CYP3A variants, patients were clustered into: poor (PM) and non-poor metabolizers (Non-PM). The impact on dose adjusted through TAC concentrations (C0) and daily doses at different time points after transplantation was evaluated.

RESULTS

Cyp3A4*1/*22 and PM groups require significantly lower dose of TAC (mg/kg) at different time points with significantly higher concentration/dose (C0/D) ratio at day 10 in comparison to Cyp3A4*1/*1 and Non-PM groups respectively. However, CyP3A5*3 heterozygous individuals did not show any significant difference in comparison to CyP3A5*1/*3 individuals. By comparing between PM and Non-PM, the PM group had a significantly lower rate of recipients not reaching target C0 at day 14.

CONCLUSION

This is the first study on Egyptian population to investigate the impact of CYP3A4*22 and CYP3A5*3 SNPs individually and in combination on the TAC concentration. This study and future multicenter studies can contribute to the individualization of TAC dosing in Egyptian patients.

Pharmacokinetic Evaluation of Tacrolimus in Chinese Adult Patients during the Early Stages Post-Lung Transplantation

BACKGROUND

Although tacrolimus has been widely used in patients undergoing lung transplantation, few studies have reported the pharmacokinetics of tacrolimus in Chinese patients after lung transplantation. Thus, we aimed to investigate the pharmacokinetics and influential factors in this patient cohort in the early stage after lung transplantation.

METHODS

We enrolled 14 adult lung transplant recipients who were treated with tacrolimus and then intensively collected blood samples within a 12-h dosing interval. The pharmacokinetic parameters of tacrolimus were calculated using non-compartmental analysis, and the influence of pathophysiological characteristics and CYP3A5*3 and CYP3A4*1G genotypes on the pharmacokinetics of tacrolimus was assessed. Using linear regression analysis, we investigated the correlation between tacrolimus concentration at different sampling points and measured the area under the time-concentration curve (AUC0-12h).

RESULTS

Geometric mean of apparent clearance (CL/F) was 18.13 ± 1.65 L/h in non-CYP3A5*3/*3 carriers, five times higher than that in CYP3A5*3/*3 carriers (p < 0.001). Furthermore, the tacrolimus concentration 4 h after administration had the strongest correlation with AUC0-12h (R2 = 0.979).

CONCLUSION

The pharmacokinetics of tacrolimus varied largely between patients during the early stage post-transplantation, which could be partially explained by CYP3A5*3 genetic polymorphisms.

Impact of single-nucleotide polymorphisms on tacrolimus pharmacokinetics in liver transplant patients after switching to once-daily dosing

BACKGROUND

The effects of multidrug resistance-1 (MDR1), ABCC2, and P450 oxidoreductase (POR)*28 gene polymorphisms on tacrolimus metabolism following a switch to once-daily dosing have not been elucidated. We investigated the effects of recipient and donor CYP3A5, MDR1, ABCC2, and POR*28 polymorphisms on tacrolimus pharmacokinetics following a switch to once-daily tacrolimus dosing.

METHODS

Eighty-seven liver transplant recipients who were switched from twice- to once-daily tacrolimus dosing following living-donor liver transplantation and 81 matched donors were genotyped for CYP3A5, MDR1 (1236C>T, 2677G>T/A, and 3435C>T), ABCC2 (-24C>T, 1249G>A, and 3972C>T), and POR*28. Tacrolimus dose-adjusted trough levels (C0/dose) before and after the switch were determined and calculated based on past medical records. Recipients were divided into two groups, one group constituted of 38 patients with a C0/dose decrease of less than 30% following conversion (group 1) and the other constituted of 49 patients with a C0/dose decrease of ≥ 30% (group 2).

RESULTS

CYP3A5 *1/*3 and *3/*3 were more frequent in recipients in group 1 (60.5% vs. 36.8%), while CYP3A5 *1/*1 was more frequent in group 2 (59.2% vs. 32.7%) (p = 0.016). The proportions of donor ABCC2 1249G>A genotypes AA and AG were higher in group 2 than in group 1 (20.4% vs. 5.3%; p = 0.042).

CONCLUSION

Recipient CYP3A5 polymorphism and donor ABCC2 1249G>A polymorphism affected tacrolimus pharmacokinetics following the switch to once-daily dosing. Dose adjustment to maintain therapeutic tacrolimus levels following the switch to once-daily dosing should be considered based on polymorphisms in both the recipient and donor.

The Impact of ABCB1 SNPs on Tacrolimus Pharmacokinetics in Liver or Kidney Transplant Recipients: A Meta-analysis

PURPOSE

We aimed to investigate the association between ATP Binding Cassette Subfamily B Member 1 (ABCB1) single nucleotide polymorphisms (SNPs) and the pharmacokinetics of tacrolimus.

METHODS

A search was conducted in Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science (SCI), MEDLINE, and Embase from inception to November 2022. Outcomes included weightadjusted daily dose (DD) and dose-adjusted trough concentration (C0/Dose).

RESULTS

A total of 1059 liver or kidney transplant recipients from 14 publications were included. For adult liver transplantation recipients, DD of ABCB1 3435C>T CC carriers was 0.03 mg/kg/day (WMD = 0.03, 95% CI: 0.01 to 0.05, I2 = 0%) higher than ABCB1 3435C>T T carriers at post-transplantation ≤ 7 days; C0/dose of ABCB1 3435C>T CC carriers were 31.88 (WMD = -31.88, 95% CI: -62.32 to -1.45, I2 = 83.5%) or 34.61 (ng/ml)/(mg/kg/day) (WMD = -34.61, 95% CI: -65.26 to -3.97, I2 = 55.3%) lower than ABCB1 3435C>T T carriers at post-transplantation ≤ 7 or 14 days, respectively. No difference in C0/dose was observed for ABCB1 2677G>T/A or ABCB1 1236C>T SNPs in both liver and kidney transplant recipients.

CONCLUSION

ABCB1 3435C>T SNP might have a potential impact on tacrolimus pharmacokinetics in the early stage after liver transplantation, indicating the probability of individualized immunosuppressive therapy based on genetic polymorphism. Given some limitations, further well-designed prospective studies are warranted to validate these conclusions.

Influence of CYP3A4*22 and CYP3A5*3 combined genotypes on tacrolimus dose requirements in Egyptian renal transplant patients

BACKGROUND

Tacrolimus is a widely prescribed immunosuppressant agent for kidney transplantation. However, optimal dosing is challenging due to its narrow therapeutic index, potentially serious adverse effects, and wide inter-individual variability in pharmacokinetics. Cytochrome P450 3A (CPY3A) enzymes metabolize tacrolimus, so allelic variants such as CYP3A4*22 and CYP3A5*3 may contribute to individual differences in pharmacokinetics and therapeutic efficacy of tacrolimus. This study assessed the frequency and influences of CYP3A4*22 and CYP3A5*3 genotypes, alone and combined, on tacrolimus pharmacokinetics and dose requirements in Egyptian kidney transplant patients.

METHODS

This is a prospective multicenter observational cohort study. Patients were genotyped for the CYP3A4*22 (rs35599367), and CYP3A5*3 (rs776746). Tacrolimus dose (mg), through blood level (ng/ml), and dose-adjusted trough concentration (C0/D) (ng/ml per mg/kg) were recorded during the first and third months post-transplantation and compared among genotype groups.

RESULTS

The CYP3A4*22 allele was rare (3.2% of subjects) while the CYP3A5*3 allele was widespread (90.38%) in this cohort. At the third month post-transplantation, median C0/D was significantly higher among CYP3A4*22 carriers than CYP3A4*1/*1 (146.25 [100-380] versus 85.57 [27-370] ng/ml per mg/kg, p = 0.028). Patients harbouring the one copy of the CYP3A4*22 allele and the CYP3A5*3/*3 genotype (n = 5) were classified as poor tacrolimus metabolizers, the CYP3A5*3/*3 plus CYP3A4*1/*1 genotype as intermediate metabolizers (n = 60), and the CYP3A4*1/*1 plus CYP3A5*1/*1 genotype as normal metabolizers (n = 13). During the first month post-transplantation, C0/D was significantly greater in poor metabolizers (113.07 ng/ml per mg/kg) than intermediate and normal metabolizers (90.380 and 49.09 ng/ml per mg/kg) (p < 0.0005). This rank order was also observed during the third month. Acute rejection rate and renal function at discharge did not differ among genotypes.

CONCLUSION

Pharmacogenetics testing for CYP3A4*22 and CYP3A5*3 before renal transplantation may help in the adjustment of tacrolimus starting dose and identify patients at risk of tacrolimus overexposure or underexposure.

Association of P450 Oxidoreductase Gene Polymorphism with Tacrolimus Pharmacokinetics in Renal Transplant Recipients: A Systematic Review and Meta-Analysis

There are conflicting results regarding the effect of the P450 oxidoreductase (POR) *28 genotype on the tacrolimus (TAC) pharmacokinetics (PKs) during the early post-transplantation period in adult renal transplant recipients. Thus, we characterized the impact of POR*28 on TAC PKs. We conducted a systematic review on the association between POR*28 and PKs of TAC in adult renal transplant recipients. Structured searches were conducted using PubMed, Web of Science, and Embase. TAC standardized trough concentration (ng/mL per mg/kg) data were extracted. Mean differences (MD) and their corresponding 95% confidence intervals (CIs) were used to identify the differences between the POR*28 genotype and PKs of TAC. The subgroup analysis was conducted according to CYP3A5 expression status. Six studies (n = 1061) were included. TAC standardized trough concentrations were significantly lower in recipients with the POR*28 allele compared to recipients with POR*1/*1 (MD: 8.30 ng/mL per mg/kg; 95% CI: 1.93, 14.67; p = 0.01). In the subgroup analysis, TAC standardized trough concentrations were lower for subjects who were POR*28 carriers than those who were POR*1/*1 in CYP3A5 expressers (MD: 20.21 ng/mL per mg/kg; 95% CI: 16.85, 23.56; p < 0.00001). No significant difference between POR*28 carriers and POR*1/*1 was found in the CYP3A5 non-expressers. The results of our meta-analysis demonstrated a definite correlation between the POR*28 genotype and PKs of TAC. Patients carrying the POR*28 allele may require a higher dose of TAC to achieve target levels compared to those with POR*1/*1, especially in CYP3A5 expressers.

Population Pharmacokinetics and Dosing Optimization of Vancomycin in Pediatric Liver Transplant Recipients

Methicillin-resistant Staphylococcus aureus infections are a significant cause of morbidity and mortality in pediatric liver transplant (LT) recipients. Physiological changes following LT may affect vancomycin pharmacokinetics; however, appropriate dosing to achieve sufficient drug exposure (i.e., 24-h area under the concentration-time curve [AUC₂₄]/MIC ≥ 400) in pediatric LT recipients has not been reported. This retrospective pharmacokinetics study of LT recipients aged <18 years utilized data on patient characteristics with vancomycin concentrations and dosing information obtained from electronic medical records. Population pharmacokinetics analysis was conducted by nonlinear mixed-effects modeling with the Phoenix NLME software. Potential covariates were screened with univariate and multivariate analysis. Monte Carlo simulations were performed using the final model to explore appropriate dosing. The study included 270 pharmacokinetics profiles encompassing 1,158 concentrations measured in 161 patients. The median age was 13.3 (interquartile range, 7.6 to 53.5) months, serum creatinine (sCr) was 0.16 (0.12 to 0.23) mg/dl, and days from LT (DFLT) was 17 (6 to 31). Multivariate analysis demonstrated that lower sCr and shorter DFLT were associated with higher clearance. By post hoc estimation, the average clearance and volume of distribution were 0.18 liters/h/kg and 1.01 liters/kg, respectively. The Monte Carlo simulations revealed that only 16% of patients achieved an AUC₂₄/MIC of ≥400 with the assumed vancomycin MIC of 1 μg/ml. DFLT and sCr were significant covariates for vancomycin clearance in pediatric LT recipients. Standard vancomycin dosing may be insufficient, and higher or more frequent dosing may be required to achieve an AUC₂₄/MIC of ≥400 in pediatric LT recipients with normal renal function.

IMPORTANCE We evaluated vancomycin pharmacokinetics in pediatric LT recipients and developed a population pharmacokinetics model by considering various factors that might account for alterations in vancomycin pharmacokinetics. Our analyses revealed that lower serum creatinine levels and a shorter duration from the day of LT were associated with higher vancomycin clearance and led to subtherapeutic drug exposure. We also performed Monte Carlo simulations to determine the appropriate dosing strategy in pediatric LT recipients, which revealed that a standard vancomycin dosing might be insufficient and that higher or more frequent dosing might be necessary to achieve an AUC₂₄/MIC of ≥400 in pediatric LT recipients with normal renal function. To the best of our knowledge, this is the first study to assess vancomycin pharmacokinetics in pediatric LT recipients by population pharmacokinetics analysis.

Association of CYP3A5 polymorphisms and parathyroid hormone with blood level of tacrolimus in patients with end-stage renal disease

Because tacrolimus is predominantly metabolized by CYP3A, the blood concentration/dose (C/D) ratio is affected by CYP3A5 polymorphism. Parathyroid hormone (PTH) expression increases in secondary hyperparathyroidism, which is frequently associated with end‐stage renal disease. Recently, PTH has been shown to downregulate CYP3A expression at mRNA level. In this study, we examined the influence of CYP3A5 polymorphism on and association of serum intact‐PTH (iPTH) level with blood tacrolimus concentration in patients with end‐stage renal disease just before kidney transplantation. Forty‐eight patients who satisfied the selection criteria were analyzed. Subjects were classified into two phenotype subgroups: CYP3A5 expressor (CYP3A5*1/*1 and *1/*3; n = 15) and CYP3A5 nonexpressor (CYP3A5*3/*3; n = 33). The blood tacrolimus C/D (per body weight) ratio was significantly lower in CYP3A5 expressors than that in CYP3A5 nonexpressors. A significant positive correlation was found between tacrolimus C/D and iPTH concentrations (r = 0.305, p = 0.035), and the correlation coefficient was higher after excluding 20 patients co‐administered CYP3A inhibitor or inducer (r = 0.428, p = 0.023). A multiple logistic regression analysis by stepwise selection identified CYP3A5 polymorphism and serum iPTH level as significant factors associated with tacrolimus C/D. These results may suggest the importance of dose design considering not only the CYP3A5 phenotype but also serum iPTH level when using tacrolimus in patients who undergo renal transplantation.

Significance of Ethnic Factors in Immunosuppressive Therapy Management After Organ Transplantation

Clinical outcomes after organ transplantation have greatly improved in the past 2 decades with the discovery and development of immunosuppressive drugs such as calcineurin inhibitors, antiproliferative agents, and mammalian target of rapamycin inhibitors. However, individualized dosage regimens have not yet been fully established for these drugs except for therapeutic drug monitoring-based dosage modification because of extensive interindividual variations in immunosuppressive drug pharmacokinetics. The variations in immunosuppressive drug pharmacokinetics are attributed to interindividual variations in the functional activity of cytochrome P450 enzymes, UDP-glucuronosyltransferases, and ATP-binding cassette subfamily B member 1 (known as P-glycoprotein or multidrug resistance 1) in the liver and small intestine. Some genetic variations have been found to be involved to at least some degree in pharmacokinetic variations in post-transplant immunosuppressive therapy. It is well known that the frequencies and effect size of minor alleles vary greatly between different races. Thus, ethnic considerations might provide useful information for optimizing individualized immunosuppressive therapy after organ transplantation. Here, we review ethnic factors affecting the pharmacokinetics of immunosuppressive drugs requiring therapeutic drug monitoring, including tacrolimus, cyclosporine, mycophenolate mofetil, sirolimus, and everolimus.

The impact of cytochrome P450 3A genetic polymorphisms on tacrolimus pharmacokinetics in ulcerative colitis patients

Tacrolimus (Tac) is an effective remission inducer of refractory ulcerative colitis (UC). Gene polymorphisms result in interindividual variability in Tac pharmacokinetics. In this study, we aimed to examine the relationships between gene polymorphisms and the metabolism, pharmacokinetics, and therapeutic effects of Tac in patients with UC. Forty-five patients with moderate-to-severe refractory UC treated with Tac were retrospectively enrolled. Genotyping for cytochrome P450 (CYP) 3A4*1G, CYP3A5*3, CYP2C19*2, CYP2C19*3, nuclear receptor subfamily 1 group I member 2 (NR1I2)–25385C>T, ATP-binding cassette subfamily C member 2 (ABCC2)–24C>T, ABCC2 1249G>A, and ABCC2 3972C>T was performed. Concentration/dose (C/D) ratio, clinical therapeutic effects, and adverse events were evaluated. The C/D ratio of Tac in UC patients with the CYP3A4*1G allele was statistically lower than in those with the CYP3A4*1/*1 allele (P = 0.005) and significantly lower in patients with CYP3A5*3/*3 than in those with CYP3A5*1 (P < 0.001). Among patients with the CYP3A4*1G allele, the C/D ratio was significantly lower in patients with CYP3A5*1 than in those with CYP3A5*3/*3 (P = 0.001). Patients with the NR1I2–25385C/C genotype presented significantly more overall adverse events than those with the C/T or T/T genotype (P = 0.03). Although CYP3A4*1G and CYP3A5*3 polymorphisms were related to Tac pharmacokinetics, CYP3A5 presented a stronger effect than CYP3A4. The NR1I2–25385C/C genotype was related to the overall adverse events. The evaluation of these polymorphisms could be useful in the treatment of UC with Tac.

Early impact of donor CYP3A5 genotype and Graft-to-Recipient Weight Ratio on tacrolimus pharmacokinetics in pediatric liver transplant patients

Tacrolimus (TAC) pharmacokinetics is influenced by the donor CYP3A5 genotype and the age of pediatric liver recipients. However, an optimization of a genotype-based algorithm for determining TAC starting is needed to earlier achieve stable target levels. As the graft itself is responsible for its metabolism, the Graft-to-Recipient Weight Ratio (GRWR) might play a role in TAC dose requirements. A single-center study was carried out in a cohort of 49 pediatric recipients to analyse the impact of patient and graft characteristics on TAC pharmacokinetics during the first 15 post-transplant days. Children < 2 years received grafts with a significantly higher GRWR (4.2%) than children between 2–8 (2.6%) and over 8 (2.7%). TAC concentration/weight-adjusted dose ratio was significantly lower in recipients from CYP3A5*1/*3 donors or with extra-large (GRWR > 5%) or large (GRWR 3–5%) grafts. The donor CYP3A5 genotype and GRWR were the only significant predictors of the TAC weight adjusted doses. Patients with a GRWR > 4% had a higher risk of acute rejection, observed in 20/49 (41%) patients. In conclusion, TAC starting dose could be guided according to the donor CYP3A5 genotype and GRWR, allowing for a quicker achievement of target concentrations and eventually reducing the risk of rejection.

ABCB1 c.2677G>T/c.3435C>T diplotype increases the early-phase oral absorption of losartan

Losartan has been shown to be a substrate of the drug-efflux transporter MDR1, encoded by the ABCB1 gene. ABCB1 c.2677G>T and c.3435C>T variants are known to be associated with reduced expression and function of P-glycoprotein (P-gp). We investigated the effects of ABCB1 diplotype on the pharmacokinetics of losartan. Thirty-eight healthy Korean volunteers with different ABCB1 diplotypes [c.2677G> T and c.3435C>T; carriers of GG/CC (n = 13), GT/CT (n = 12) and TT/TT (n = 13) diplotype] were recruited and administered a single 50 mg oral dose of losartan potassium. Losartan and its active metabolite E-3174 samples in plasma and urine were collected up to 10 and 8 h after drug administration, respectively, and the concentrations of both samples were determined by HPLC method. Significant differences were observed in C_max of losartan and losartan plus E-3174 (Lo + E) among the three diplotype groups (both P < 0.01). However, the power of the performed test is less than the desired power (0.800). The t_max of losartan and E-3174 in three diplotype groups were also significantly different (both P < 0.01). The AUC values of Lo + E were significantly different among the three diplotype groups until 6 h after losartan administration (P < 0.01). On the contrary, AUC at the periods of 8-10 h and 10 h-infinity of Lo + E were significantly lower in the TT/TT group than in the GG/CC group. Urinary excretion of losartan until 4 h after losartan administration in the TT/TT group was higher than that of the GG/CC group. These results suggest that c.2677G>T/c.3435C>T diplotypes of ABCB1 may significantly increase the early-phase absorption of losartan, but not the total absorption.

Impacts of High Intra- and Inter-Individual Variability in Tacrolimus Pharmacokinetics and Fast Tacrolimus Metabolism on Outcomes of Solid Organ Transplant Recipients

Tacrolimus is a first-line calcineurin inhibitor (CNI) and an integral part of the immunosuppressive strategy in solid organ transplantation. Being a dose-critical drug, tacrolimus has a narrow therapeutic index that necessitates periodic monitoring to maintain the drug’s efficacy and reduce the consequences of overexposure. Tacrolimus is characterized by substantial intra- and inter-individual pharmacokinetic variability. At steady state, the tacrolimus blood concentration to daily dose ratio (C/D ratio) has been described as a surrogate for the estimation of the individual metabolism rate, where a low C/D ratio reflects a higher rate of metabolism. Fast tacrolimus metabolism (low C/D ratio) is associated with the risk of poor outcomes after transplantation, including reduced allograft function and survival, higher allograft rejection, CNI nephrotoxicity, a faster decline in kidney function, reduced death-censored graft survival (DCGS), post-transplant lymphoproliferative disorders, dyslipidemia, hypertension, and cardiovascular events. In this article, we discuss the potential role of the C/D ratio in a noninvasive monitoring strategy for identifying patients at risk for potential adverse events post-transplant.

CYP3A5 Genotype as a Potential Pharmacodynamic Biomarker for Tacrolimus Therapy in Ulcerative Colitis in Japanese Patients

Tacrolimus has been used to induce remission in patients with steroid-refractory ulcerative colitis. It poses a problem of large individual differences in dosage necessary to attain target blood concentration and, often, this leads to drug inefficacy. We examined the difference in mRNA expression levels of ATP binding cassette transporter B1 (ABCB1) between inflamed and non-inflamed tissues, and the influence of CYP3A5 genotype on tacrolimus therapy. The mRNA expression of CYP3A4 in colonic mucosa and that of cytochrome p450 3A5 (CYP3A5) and ABCB1 in inflamed and non-inflamed areas were examined in 14 subjects. The mRNA expression levels of CYP3A5 were higher than that of CYP3A4. The mRNA expression of ABCB1 was lower in the inflamed than in the non-inflamed mucosa, despite that of CYP3A5 mRNA level being not significantly changed. Hence, the deterioration of the disease is related to the reduction of the barrier in the inflamed mucosa. The relationship between CYP3A5 genotype and blood concentration, dose, and concentration/dose (C/D) ratio of tacrolimus in 15 subjects was studied. The tacrolimus dose to maintain equivalent blood concentrations was lower in CYP3A5*3/*3 than in CYP3A5*1 carriers, and the C/D ratio was significantly higher in the latter. Thus, CYP3A5 polymorphism information played a role in determining the initial dose of tacrolimus. Furthermore, since the effect of tacrolimus appears earlier in CYP3A5*3/*3 than in CYP3A5*1/*1 and *1/*3, it seems necessary to change the evaluation time of therapeutic effect by CYP3A5 genotype. Additionally, the relationship between CYP3A5 genotype and C/D ratio of tacrolimus in colonic mucosa was investigated in 10 subjects. Tacrolimus concentration in the mucosa was two-fold higher in CYP3A5*3/*3 than in CYP3A5*1 carriers, although no significant difference in tacrolimus-blood levels was observed. Therefore, the local concentration of tacrolimus affected by CYP3A5 polymorphism might be related to its therapeutic effect.

Donor CYP3A5 Gene Polymorphism Alone Cannot Predict Tacrolimus Intrarenal Concentration in Renal Transplant Recipients

CYP3A5 gene polymorphism in recipients plays an important role in tacrolimus blood pharmacokinetics after renal transplantation. Even though CYP3A5 protein is expressed in renal tubular cells, little is known about the influence on the tacrolimus intrarenal exposure and hence graft outcome. The aim of our study was to investigate how the tacrolimus intrarenal concentration (C_tissue) could be predicted based on donor CYP3A5 gene polymorphism in renal transplant recipients. A total of 52 Japanese renal transplant patients receiving tacrolimus were enrolled in this study. Seventy-four renal biopsy specimens were obtained at 3 months and 1 year after transplantation to determine the donor CYP3A5 polymorphism and measure the C_tissue by liquid chromatography-tandem mass spectrometry (LC-MS-MS). The tacrolimus C_tissue ranged from 52 to 399 pg/mg tissue (n = 74) and was weak but significantly correlated with tacrolimus trough concentration (C₀) at 3 months after transplantation (Spearman, r = 0.3560, p = 0.0096). No significant relationship was observed between the donor CYP3A5 gene polymorphism and C_tissue or C_tissue/C₀. These data showed that the tacrolimus systemic level has an impact on tacrolimus renal accumulation after renal transplantation. However, donor CYP3A5 gene polymorphism alone cannot be used to predict tacrolimus intrarenal exposure_. This study may be valuable for exploring tacrolimus renal metabolism and toxicology mechanism in renal transplant recipients.

Influence of POR*28 Polymorphisms on CYP3A5*3-Associated Variations in Tacrolimus Blood Levels at an Early Stage after Liver Transplantation

It is well known that the CYP3A5*3 polymorphism is an important marker that correlates with the tacrolimus dose requirement after organ transplantation. Recently, it has been revealed that the POR*28 polymorphism affects the pharmacokinetics of tacrolimus in renal transplant patients. In this study, we examined whether POR*28 as well as CYP3A5*3 polymorphism in Japanese recipients and donors would be another biomarker for the variation of tacrolimus blood levels in the recipients during the first month after living-donor liver transplantation. We enrolled 65 patients treated with tacrolimus, who underwent liver transplantation between July 2016 and January 2019. Genomic DNA was extracted from whole-blood samples, and genotyping was performed to examine the presence of CYP3A5*3 and POR*28 polymorphisms in the recipients and donors. The CYP3A5*3/*3 genotype (defective CYP3A5) of the recipient (standard partial regression coefficient [median C/D ratio of CYP3A5 expressor vs. CYP3A5 non-expressor, p value]: Pod 1–7, β= −0.389 [1.76 vs. 2.73, p < 0.001]; Pod 8–14, β = −0.345 [2.03 vs. 2.83, p < 0.001]; Pod 15–21, β= −0.417 [1.75 vs. 2.94, p < 0.001]; Pod 22–28, β = −0.627 [1.55 vs. 2.90, p < 0.001]) rather than donor (Pod 1–7, β = n/a [1.88 vs. 2.76]; Pod 8–14, β = n/a [1.99 vs. 2.93]; Pod 15–21, β = −0.175 [1.91 vs. 2.94, p = 0.004]; Pod 22–28, β = n/a [1.61 vs. 2.67]) significantly contributed to the increase in the concentration/dose (C/D) ratio of tacrolimus for at least one month after surgery. We found that the tacrolimus C/D ratio significantly decreased from the third week after transplantation when the recipient carried both CYP3A5*1 (functional CYP3A5) and POR*28 (n = 19 [29.2%], median C/D ratio [inter quartile range] = 1.58 [1.39–2.17]), compared with that in the recipients carrying CYP3A5*1 and POR*1/*1 (n = 8 [12.3%], median C/D ratio [inter quartile range] = 2.23 [2.05–3.06]) (p < 0.001). In conclusion, to our knowledge, this is the first report suggesting that the POR*28 polymorphism is another biomarker for the tacrolimus oral dosage after liver transplantation in patients carrying CYP3A5*1 rather than CYP3A5*3/*3.

Effects of donor-recipient combinational CYP3A5 genotypes on tacrolimus dosing in Chinese DDLT adult recipients

BACKGROUND

For liver transplant (LT) recipients, the liver CYP3A5 metabolic enzymes are determined by the donor's genes, whereas the intestinal enzymes are encoded by the recipient's genes. This combinational form confuses the metabolism of tacrolimus (Tac) in vivo. This retrospective study was conducted to investigate the combined effects of donor-recipient CYP3A5 genotype on tacrolimus pharmacokinetics in Chinese LT adult patients.

METHODS

Three hundred seventy-three LT patients from two Chinese organ transplant centers were enrolled, and both recipients and donors were genotyped for CYP3A5. Patients were divided into four groups (R_ND_N, R_ED_N, R_ND_E, R_ED_E) according to CYP3A5*3 allele expressers (E) and non-expressers (N) in recipients (R) and donors (D). The dose-adjusted trough levels (C/D ratio) of tacrolimus were assessed for six months among the four groups. Multiple linear regression analysis was performed to assess the effects of the CYP3A5 genotype and several clinical variables on the C/D ratio.

RESULTS

The R_ND_N group consistently had the largest C/D ratio throughout the entire study period, whereas the R_ED_E group had the smallest C/D ratio, and the R_ED_N/R_ND_E group had an intermediate (R_ND_N > R_ED_N/R_ND_E > R_ED_E) ratio. The C/D ratio in the R_ND_N and R_ND_E groups was higher than that in the R_ED_N and R_ED_E groups within three months, respectively; the ratio in the R_ND_N group was higher than that in the R_ND_E group, and the ratio in the R_ED_N group was higher than that in the R_ED_E group at six months. The effect of the donor CYP3A5 genotype on C/D values was observed throughout the timeline, and the recipient's genetics correlated only in the first three months. Among non-genetic factors, hemoglobin (HGB) and albumin (ALB) were correlated with Tac C/D values at a few time points.

CONCLUSIONS

To predict the initial dose of tacrolimus in LT patients, both donor and recipient CYP3A5 genotypes must be taken into account; during the maintenance phase of targeted blood concentration, the donor's CYP3A5 genotype may be of prime importance, especially at three months after transplantation.

A Low Tacrolimus Concentration/Dose Ratio Increases the Risk for the Development of Acute Calcineurin Inhibitor-Induced Nephrotoxicity

Fast tacrolimus metabolism is linked to inferior outcomes such as rejection and lower renal function after kidney transplantation. Renal calcineurin-inhibitor toxicity is a common adverse effect of tacrolimus therapy. The present contribution hypothesized that tacrolimus-induced nephrotoxicity is related to a low concentration/dose (C/D) ratio. We analyzed renal tubular epithelial cell cultures and 55 consecutive kidney transplant biopsy samples with tacrolimus-induced toxicity, the C/D ratio, C0, C2, and C4 Tac levels, pulse wave velocity analyses, and sublingual endothelial glycocalyx dimensions in the selected kidney transplant patients. A low C/D ratio (C/D ratio < 1.05 ng/mL×1/mg) was linked with higher C2 tacrolimus blood concentrations (19.2 ± 8.7 µg/L vs. 12.2 ± 5.2 µg/L respectively; p = 0.001) and higher degrees of nephrotoxicity despite comparable trough levels (6.3 ± 2.4 µg/L vs. 6.6 ± 2.2 µg/L respectively; p = 0.669). However, the tacrolimus metabolism rate did not affect the pulse wave velocity or glycocalyx in patients. In renal tubular epithelial cells exposed to tacrolimus according to a fast metabolism pharmacokinetic profile it led to reduced viability and increased Fn14 expression. We conclude from our data that the C/D ratio may be an appropriate tool for identifying patients at risk of developing calcineurin-inhibitor toxicity.

Identification of Factors Affecting Tacrolimus Trough Levels in Latin American Pediatric Liver Transplant Patients

Tacrolimus is the cornerstone in pediatric liver transplant immunosuppression. Despite close monitoring, fluctuations in tacrolimus blood levels affect safety and efficacy of immunosuppressive treatments. Identifying the factors related to the variability in tacrolimus exposure may be helpful in tailoring the dose. The aim of the present study was to characterize the clinical, pharmacological, and genetic variables associated with systemic tacrolimus exposure in pediatric liver transplant patients. De novo transplant patients with a survival of more than 1 month were considered for inclusion and were genotyped for cytochrome P450 3A5 (CYP3A5). Peritransplant clinical factors and laboratory covariates were recorded retrospectively between 1 month and 2 years after transplant, including alanine aminotransferase (ALT), aspartate aminotransferase, hematocrit, and tacrolimus predose steady-state blood concentrations collected 12 hours after tacrolimus dosing. A linear mixed effect (LME) model was used to assess the association of these factors and the log-transformed tacrolimus dose-normalized trough concentration (logC0/D) levels. Bootstrapping was used to internally validate the final model. External validation was performed in an independent group of patients who matched the original population. The developed LME model described that logC0/D increases with increases in time after transplant (β = 0.019, 95% confidence interval [CI], 0.010-0.028) and ALT values (β = 0.00030, 95% CI, 0.00002-0.00056), whereas logC0/D is significantly lower in graft CYP3A5 expressers compared with nonexpressers (β = -0.349, 95% CI, -0.631 to -0.062). In conclusion, donor CYP3A5 genotype, time after transplant, and ALT values are associated with tacrolimus disposition between 1 month and 2 years after transplant. A better understanding of tacrolimus exposure is essential to minimize the occurrence of an out-of-range therapeutic window that may lead to adverse drug reactions or acute rejection.

The impact of liver transplant recipient and donor genetic variability on tacrolimus exposure and transplant outcome

This study investigated the effect of recipient and donor genetic variability on dose-adjusted steady-state tacrolimus concentrations (C_ss ) and clinical outcomes 3 and 6 months after liver transplant. Twenty-nine recipients and matched donor blood samples were genotyped for 27 single nucleotide polymorphisms including CYP3A5*3 (rs776746), ABCB1 haplotype and immune genes. Associations between genetic variability and clinical parameters and C_ss and the occurrence of rejection and nephrotoxicity were analysed by multivariate and multinomial logistic regression modelling and Jonckheere-Terpstra tests examined the impact of combined donor/recipient CYP3A5 expression on C_ss . At 3 months post-transplant modelling revealed an association between tacrolimus C_ss and recipient CASP1 rs580523 genotype (P = 0.005), accounting for 52% C_ss variance. Jonckheere-Terpstra tests revealed that as combined donor/recipient CYP3A5 expression increased, C_ss decreased (P = 0.010 [3 months], 0.018 [6 months]). As this is the first report of CASP1 genetic variability influencing tacrolimus C_ss , further validation in larger cohorts is required.

Impact of direct-acting antivirals for hepatitis C virus therapy on tacrolimus dosing in liver transplant recipients

INTRODUCTION

Direct-acting antivirals (DAAs) have transformed hepatitis C virus (HCV) management post-liver transplant. As HCV clears during DAA treatment, hepatic metabolism improves, resulting in decreased tacrolimus concentrations that may require dose adjustment. The purpose of this study was to determine appropriate management of immunosuppression in liver transplant recipients during and following treatment of HCV.

METHODS

This study was a single-center retrospective analysis of 71 liver transplant recipients who were treated for HCV with DAAs. The primary outcome was change in dose-normalized tacrolimus concentrations from the start of DAA treatment to 12 weeks following therapy.

RESULTS

The mean change in log-transformed dose-normalized tacrolimus concentrations was a reduction of 0.43 ng/mL/mg (95% CI; 0.26-0.60, P < 0.0001). The greatest decrease occurred in the first 4 weeks of treatment, after which levels stabilized. The overall mean tacrolimus concentration was 4.8 ng/mL (±2.5). Two patients (3%) developed acute cellular rejection and two patients (3%) had graft loss and died.

CONCLUSION

From the start of treatment to 12 weeks post-DAA therapy, liver transplant recipients experienced a significant decrease in dose-normalized tacrolimus concentrations. In conclusion, close monitoring of tacrolimus concentrations is warranted during and following treatment with DAAs, as dose increases may be indicated in order to maintain therapeutic concentrations to prevent graft rejection.

Gene Polymorphism of Tacrolimus-Metabolizing Enzymes Associated With Impaired Absorption of Tacrolimus Following Allogeneic Hematopoietic Stem Cell Transplantation: A Case Report

OBJECTIVE

To elucidate the mechanisms by which orally administered tacrolimus was not absorbed in a patient following allogeneic hematopoietic stem cell transplantation.

CLINICAL COURSE

A 17-year-old girl with acute myeloid leukemia underwent HLA-haploidentical peripheral blood stem cell transplantation following fludarabine, busulfan, and total-body irradiation. Graft-vs-host disease prophylaxis was post-transplant cyclophosphamide, followed by intravenous tacrolimus and mycophenolate mofetil. When tacrolimus was switched to oral administration, its blood level declined rapidly, resulting in development of acute graft-vs-host disease, which was ameliorated by switching back to intravenous administration.

METHODS/RESULTS

To elucidate if impaired tacrolimus absorption could be related to genetic polymorphism of tacrolimus-metabolizing enzymes, we analyzed gene polymorphisms of cytochrome P450 3A4, cytochrome P450 3A5, and multidrug resistance 1 (MDR1). The patient had wild-type cytochrome P450 3A4 (*1/*1) and variant-type cytochrome P450 3A5 (*3/*3), while MDR1 genes (2677A/G, 3435C/C) were wild-type.

CONCLUSION

Wild-type MDR1 gene product P-glycoprotein expressed in the intestine reduces drug absorption from the gastrointestinal tract and may have contributed to low blood levels of tacrolimus in this patient when tacrolimus was orally administered.

Graft-to-Recipient Weight Ratio Associated With Tacrolimus Metabolism Following Pediatric Living Donor Liver Transplantations

OBJECTIVES

Tacrolimus (TAC) is an important immunosuppressant in liver transplantation. Since TAC is mainly metabolized by the liver enzymes CYP3A4 and 5, liver function is crucial for its pharmacokinetics (PK). Liver function is dynamic after liver transplantation; hence the PK of TAC metabolism after pediatric liver transplantation is not well understood. We aimed to investigate the time-dependent changes in TAC metabolism and to find factors influencing TAC PK after pediatric liver transplantation.

METHODS

We retrospectively reviewed the characteristics of the donors and recipients in pediatric living donor liver transplantation and used the TAC concentration-dose (CD) ratio as a surrogate marker of TAC metabolism.

RESULTS

Included were 326 patients with a median age of 13 months. After the liver transplantation, the CD ratio gradually decreased, then plateaued around day 21 to 28. A linear regression analysis demonstrated that a lower graft-to-recipient weight ratio (GRWR) and higher prothrombin time-international normalized ratio (PT-INR) were independently associated with a higher CD ratio in the early period after liver transplantation. However, association between GRWR and TAC CD ratio disappeared around 6 to 12 months after a liver transplantation possibly owing to graft regeneration.

CONCLUSIONS

Tacrolimus metabolism improved within the first month after liver transplantation, and the small graft size was associated with lower TAC metabolism in the early period after pediatric living donor liver transplantation.

Biomarkers for individualized dosage adjustments in immunosuppressive therapy using calcineurin inhibitors after organ transplantation

Calcineurin inhibitors (CNIs), such as cyclosporine A and tacrolimus, are widely used immunosuppressive agents for the prevention of post-transplantation rejection and have improved 1-year graft survival rates by up to 90%. However, CNIs can induce severe reactions, such as acute or chronic allograft nephropathy, hypertension, and neurotoxicity. Because CNIs have varied bioavailabilities, narrow therapeutic ranges, and individual propensities for toxic effects, therapeutic drug monitoring is necessary for all CNIs. Identifying the genetic polymorphisms in drug-metabolizing enzymes will help to determine personalized dosage regimens for CNIs, as CNIs are substrates for CYP3A5 and P-glycoprotein (P-gp, MDR1). CNIs are often concomitantly administered with voriconazole or proton pump inhibitors (PPIs), giving rise to drug interaction problems. Voriconazole and PPIs can increase the blood concentrations of CNIs, and both are primarily metabolized by CYP2C19. Thus, it is expected that interactions between CNIs and voriconazole or PPI would be affected by CYP2C19 and CYP3A5 polymorphisms. CNI-induced acute kidney injury (AKI) is a serious complication of transplantations. Neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule 1 (KIM-1) are noninvasive urinary biomarkers that are believed to be highly sensitive to CNI-induced AKI. In this article, we review the adverse events and pharmacokinetics of CNIs and the biomarkers related to CNIs, including CYP3A5, CYP2C19, MDR1, NGAL, and KIM-1. We hope that these data will help to identify the optimal biomarkers for monitoring CNI-based immunosuppressive therapy after organ transplantation.

Factors involved in phenoconversion of CYP3A using 4β-hydroxycholesterol in stable kidney transplant recipients

BACKGROUND

Phenoconversion is a phenomenon whereby some genotypic extensive metabolizers transiently exhibit drug metabolizing enzyme activity at similar level as that of poor metabolizers. Renal failure is known to decrease CYP3A activity in humans. Indoxyl sulfate, parathyroid hormone (PTH), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α) have been reported to cause CYP3A downregulation in renal failure. We measured plasma concentrations of the above compounds in stable kidney transplant recipients, and evaluated their relations with phenoconversion of CYP3A evaluated by plasma concentration of 4β-hydroxycholesterol, a biomarker of CYP3A activity. Phenoconversion was defined as a genotypic extensive/intermediate metabolizer exhibiting CYP3A activity below the cutoff value that discriminates extensive/intermediate from poor metabolizers.

METHODS

Sixty-three Japanese kidney transplant recipients who underwent transplantation more than 180 days prior to the study were included. Morning blood samples were collected, and CYP3A5 polymorphism as well as plasma concentrations of 4β-hydroxycholesterol, indoxyl sulfate, intact-PTH, IL-6 and TNF-α were determined.

RESULTS

Significantly higher plasma 4β-hydroxycholesterol concentration was observed in recipients with CYP3A5*1 allele (n = 23) compared to those without the allele (n = 40), and the cut-off value was 40.0 ng/mL. Ten recipients with CYP3A5*1 allele exhibited CYP3A activity below 40.0 ng/mL (phenoconversion). Only plasma indoxyl sulfate concentration was significantly higher in recipients with CYP3A phenoconversion compared to those without phenoconversion.

CONCLUSIONS

These findings suggest that higher plasma indoxyl sulfate concentration may be involved in CYP3A phenoconversion. Dose adjustment of drugs metabolized by CYP3A may be needed in patients with CYP3A5*1 allele and high blood indoxyl sulfate.

Intravenous Administration of Tacrolimus Stabilizes Control of Blood Concentration Regardless of CYP3A5 Polymorphism in Living Donor Liver Transplantation: Comparison of Intravenous Infusion and Oral Administration in Early Postoperative Period

BACKGROUND

We compared achievement rate of sufficient tacrolimus blood concentration in the early postoperative period and incidence of acute cellular rejection within 1 month after living donor liver transplantation (LDLT) between tacrolimus intravenous (IV) and oral administration groups.

METHODS

From October 2005 to November 2016, 61 LDLT patients administered tacrolimus, who could be genotyped for CYP3A5*3 and *1, were chosen from the electronic record database. The patients were then divided into the 2 groups (an IV group [n = 38] and an oral group [n = 23]). We defined patients with 1*1 or *1*3 as expressors and those with *3*3 as nonexpressors. Sufficient trough level tacrolimus blood concentration on postoperative day (POD) 3 was defined as 10-20 ng/mL.

RESULTS

Comparable concentrations were seen between the 2 groups, with mean blood concentration 13.7 ± 8.5 ng/mL in the oral group and 15.2 ± 4.3 ng/mL in the IV group. Achievement rate of sufficient tacrolimus concentration on POD 3 was significantly higher in the IV group than in oral group: 97% (37 of 38) vs 65% (15 of 23), respectively (P = .001). When we focused on achievement rate in the oral group according to CYP3A5 polymorphism, the frequency of expressors (17%) was significantly lower than that of nonexpressors (82%) (P = .016). However, in the IV group this negative influence was totally eliminated, resulting in high achievement rates regardless of CYP3A5 polymorphism. In terms of incidence of acute cellular rejection, there was no significant difference between the 2 groups (IV 32% vs oral 17%, P = .250).

CONCLUSION

IV administration of tacrolimus allowed us to obtain more stable control of blood concentration regardless of CYP3A5 genotype.

A randomized clinical trial of age and genotype-guided tacrolimus dosing after pediatric solid organ transplantation

BACKGROUND

Tacrolimus pharmacokinetics are influenced by age and CYP3A5 genotype with CYP3A5 expressors (CYP3A5*1/*1 or *1/*3) being fast metabolizers. However, the benefit of genotype-guided dosing in pediatric solid organ transplantation has been understudied.

OBJECTIVE

To determine whether age and CYP3A5 genotype-guided starting dose of tacrolimus result in earlier attainment of therapeutic drug concentrations.

SETTING

Single hospital-based transplant center.

METHODS

This was a randomized, semi-blinded, 30-day pilot trial. Between 2012 and 2016, pediatric patients listed for solid organ transplant were consented and enrolled into the study. Participants were categorized as expressors, CYP3A5*1/*1 or CYP3A5*1/*3, and nonexpressors, CYP3A5*3/*3. Patients were stratified by age (≤ or > 6 years) and randomized (2:1) after transplant to receive genotype-guided (n = 35) or standard (n = 18) starting dose of tacrolimus for 36-48 hours and were followed for 30 days.

RESULTS

Median age at transplant in the randomized cohort was 2.1 (0.75-8.0) years; 24 (45%) were male. Participants in the genotype-guided arm achieved therapeutic concentrations earlier at a median (IQR) of 3.4 (2.5-6.6) days compared to those in the standard dosing arm of 4.7 (3.5-8.6) days (P = 0.049), and had fewer out-of-range concentrations [OR (95% CI) = 0.60 (0.44, 0.83), P = 0.002] compared to standard dosing, with no difference in frequency of adverse events between the two groups.

CONCLUSIONS

CYP3A5 genotype-guided dosing stratified by age resulted in earlier attainment of therapeutic tacrolimus concentrations and fewer out-of-range concentrations.

Tacrolimus Dose Optimization Strategy for Refractory Ulcerative Colitis Based on the Cytochrome P450 3A5 Polymorphism Prediction Using Trough Concentration after 24 Hours

BACKGROUND

In the tacrolimus treatment for refractory ulcerative colitis (UC), dose adjustment is necessary because the required doses to keep appropriate drug concentrations are significantly different among individuals. Cytochrome P450 (CYP) 3A5 polymorphism affects tacrolimus blood concentrations. However, it is difficult to obtain genetic information in real clinical practice. In the present study, we investigated possible factors that may predict CYP3A5 polymorphism and proposed a dose optimization strategy based on the obtained predicting factors.

SUMMARY

We retrospectively analyzed 41 patients who underwent remission induction therapy with tacrolimus for UC in our hospital. First, we performed a correlation analysis of CYP3A5 polymorphism and pharmacokinetics. In the CYP3A5 non-expressers, the dose of tacrolimus (mg/kg) was lower and dose-adjusted trough levels (ng/mL per mg/kg) were higher compared with those in expressers. Next, we investigated factors that could predict CYP3A5 polymorphism. Trough concentration 24 h following tacrolimus administration was extracted as a significant factor. When the trough cutoff value at 24 h was set to 2.6 ng/mL, sensitivity and specificity for estimation of CYP3A5 polymorphism were 63 and 96% respectively. Therefore, when the trough concentration 24 h after administration is ≤2.6 ng/mL, the patient can be estimated as a CYP3A5 expresser and an increase in dose should be proposed. Key Message: The trough concentration 24 h after the first tacrolimus administration appears to be a useful predictor of -CYP3A5 polymorphism. Performing dose optimization strategy based on the prediction of CYP3A5 polymorphism can lead to earlier and safer remission induction.

Artificial neural network model for predicting the bioavailability of tacrolimus in patients with renal transplantation

The objective of the current study was to explore the role of ABCB1 and CYP3A5 genetic polymorphisms in predicting the bioavailability of tacrolimus and the risk for post-transplant diabetes. Artificial neural network (ANN) and logistic regression (LR) models were used to predict the bioavailability of tacrolimus and risk for post-transplant diabetes, respectively. The five-fold cross-validation of ANN model showed good correlation with the experimental data of bioavailability (r2 = 0.93-0.96). Younger age, male gender, optimal body mass index were shown to exhibit lower bioavailability of tacrolimus. ABCB1 1236 C>T and 2677G>T/A showed inverse association while CYP3A5*3 showed a positive association with the bioavailability of tacrolimus. Gender bias was observed in the association with ABCB1 3435 C>T polymorphism. CYP3A5*3 was shown to interact synergistically in increasing the bioavailability in combination with ABCB1 1236 TT or 2677GG genotypes. LR model showed an independent association of ABCB1 2677 G>T/A with post transplant diabetes (OR: 4.83, 95% CI: 1.22-19.03). Multifactor dimensionality reduction analysis (MDR) revealed that synergistic interactions between CYP3A5*3 and ABCB1 2677 G>T/A as the determinants of risk for post-transplant diabetes. To conclude, the ANN and MDR models explore both individual and synergistic effects of variables in modulating the bioavailability of tacrolimus and risk for post-transplant diabetes.

Donor CYP3A5 genotype influences tacrolimus disposition on the first day after paediatric liver transplantation

AIM

The aim of the present study was to investigate the influence of the cytochrome P450 (CYP) 3A4/5 genotype in paediatric liver transplant recipients and donors, and the contribution of age and gender to tacrolimus disposition on the first day after transplantation.

METHODS

The contribution of the CYP3A4/5 genotype in paediatric liver transplant recipients and donors to the tacrolimus blood trough concentrations (C0 ) and the tacrolimus concentration/weight-adjusted dose ratio on day 1 was evaluated in 67 liver-transplanted children: 33 boys and 34 girls, mean age 4.5 years.

RESULTS

Donor CYP3A5 genotype appears to be significantly associated with tacrolimus disposition on the first day after liver transplantation (P < 0.0002). Other physiological factors, such as recipient age and donor gender may also play a role and lead to significant differences in tacrolimus C0 and tacrolimus concentration/weight-adjusted dose ratio on day 1. However, according to the general linear model, only recipient age appears to be independently associated with tacrolimus disposition on the first day after liver transplantation (P < 0.03). Indeed, there was a faster tacrolimus metabolism in children under 6 years of age (P < 0.02).

CONCLUSIONS

Donor CYP3A5 genotype, recipient age and, to a lesser extent, donor gender appear to be associated with tacrolimus disposition on day 1 after transplant. This suggests that increasing the starting tacrolimus doses in paediatric patients under 6 years of age who receive a graft from a male extensive metabolizer may enhance the possibility of their tacrolimus levels reaching the therapeutic range sooner.

Pharmacogenetics of immunosuppressants: State of the art and clinical implementation - recommendations from the French National Network of Pharmacogenetics (RNPGx)

Therapeutic drug monitoring is already widely used for immunosuppressive drugs due to their narrow therapeutic index. This article summarizes evidence reported in the literature regarding the pharmacogenetics of (i) immunosuppressive drugs used in transplantation and (ii) azathioprine used in chronic inflammatory bowel disease. The conditions of use of currently available major pharmacogenetic tests are detailed and recommendations are provided based on a scale established by the RNPGx scoring tests as "essential", "advisable" and "potentially useful". Other applications for which the level of evidence is still debated are also discussed.

Long-Term Influence of CYP3A5 Gene Polymorphism on Pharmacokinetics of Tacrolimus and Patient Outcome After Living Donor Liver Transplantation

BACKGROUND

We investigated a long-term association between donor/recipient CYP3A5 polymorphisms, pharmacokinetics of tacrolimus, and recipient outcomes in settings of living donor liver transplantation (LDLT).

METHODS

From February 2002 to November 2009, 67 couples of donor/recipients with tacrolimus administration, who could be genotyped for CYP3A5*3 and *1, were eligible in this study. We compared the dose-adjusted trough levels (C/D ratio) and dose/weight ratio of tacrolimus at 1 to 36 months postoperatively and recipient prognosis according to donor/recipient CYP3A5 polymorphisms; *1*1 in 7, *1*3 in 15, and *3*3 in 45, based on recipient genotype, and *1*1 in 1, *1*3 in 28, and *3*3 in 38, based on donor genotype.

RESULTS

On the basis of the data from C/D ratio and dose/weight ratio of tacrolimus, the recipients who had *1 allele and/or whose donor had *1allele required significantly high doses of tacrolimus with, compared with those without, all through 3 years after transplantation. These data allowed us to show the importance of not only recipient CYP3A5 polymorphisms but also donor polymorphisms to obtain the target tacrolimus blood concentration. The overall survival rates of the recipients with *1*1 (5-year survival rate: 28.6%) were significantly unfavorable, which might have been caused by over-immunosuppression, compared with those with *1*3 (5-year survival rate: 78.8%) and *3*3 genotype (5-year survival rate: 84.3%).

CONCLUSIONS

Immune suppressive therapy with the use of tacrolimus should be tailored on the basis of CYP3A5 genotype, which may reduce the adverse effects and improve graft outcome.

Impact of Genetic Polymorphisms of ABCB1 (MDR1, P-Glycoprotein) on Drug Disposition and Potential Clinical Implications: Update of the Literature

ATP-binding cassette transporter B1 (ABCB1; P-glycoprotein; multidrug resistance protein 1) is an adenosine triphosphate (ATP)-dependent efflux transporter located in the plasma membrane of many different cell types. Numerous structurally unrelated compounds, including drugs and environmental toxins, have been identified as substrates. ABCB1 limits the absorption of xenobiotics from the gut lumen, protects sensitive tissues (e.g. the brain, fetus and testes) from xenobiotics and is involved in biliary and renal secretion of its substrates. In recent years, a large number of polymorphisms of the ABCB1 [ATP-binding cassette, sub-family B (MDR/TAP), member 1] gene have been described. The variants 1236C>T (rs1128503, p.G412G), 2677G>T/A (rs2032582, p.A893S/T) and 3435C>T (rs1045642, p.I1145I) occur at high allele frequencies and create a common haplotype; therefore, they have been most widely studied. This review provides an overview of clinical studies published between 2002 and March 2015. In summary, the effect of ABCB1 variation on P-glycoprotein expression (messenger RNA and protein expression) and/or activity in various tissues (e.g. the liver, gut and heart) appears to be small. Although polymorphisms and haplotypes of ABCB1 have been associated with alterations in drug disposition and drug response, including adverse events with various ABCB1 substrates in different ethnic populations, the results have been majorly conflicting, with limited clinical relevance. Future research activities are warranted, considering a deep-sequencing approach, as well as well-designed clinical studies with appropriate sample sizes to elucidate the impact of rare ABCB1 variants and their potential consequences for effect sizes.

Significant effect of age on docetaxel pharmacokinetics in Japanese female breast cancer patients by using the population modeling approach

PURPOSE

Docetaxel is frequently used in the treatment of a wide variety of solid tumors, including breast cancer. The aim of this study is to obtain the population pharmacokinetic parameters of docetaxel in Japanese female patients with breast cancer.

METHODS

Blood samples from 24 patients were collected sequentially before and after docetaxel infusion. Genomic DNA was isolated from the peripheral blood and genotyped for the selected polymorphisms in the candidate genes of drug transporters and metabolizing enzymes. The influence of patient characteristics on the pharmacokinetics of docetaxel was evaluated using the nonlinear-mixed-effect modeling program, NONMEM. As a basis for comparison, the pharmacokinetics of another taxane paclitaxel in 41 separate female patients with breast cancer was calculated.

RESULTS

A two-compartment model adequately described the pharmacokinetic profiles of docetaxel. The population mean estimates of the total body clearance for patients aged 58 years or less and the central volume of distribution for docetaxel were 32.6 L/h and 5.77 L, respectively. In patients over 58 years, the clearance was 24 % higher than that in the younger patients. No influences of the genotypes examined were noted on the clearance of docetaxel. The clearance of paclitaxel was not affected by patient age.

CONCLUSIONS

Patients over the age of 58 years showed significantly higher clearance of docetaxel than that in patients aged 58 years or less. Since the clearance of paclitaxel was not affected by the age, it is possible that the pharmacokinetic mechanisms of docetaxel might be specifically affected by age in females.

Impact of CYP3A5 and MDR-1 gene polymorphisms on the dose and level of tacrolimus among living-donor liver transplanted patients: single center experience

AIM OF WORK

To assess the impact of Cytochrome P450 3A5 (CYP3A5) and multidrug resistance-1 gene (MDR-1) single nucleotide polymorphisms on the dose and blood level of tacrolimus among liver transplanted patients.

PATIENTS AND METHODS

We enrolled a prospective study of 41 liver transplanted patients. Dose-adjusted trough blood concentration (C/D ratio) was calculated. Polymerase chain reaction-restriction fragment length polymorphism followed by sequencing was done for genotyping of CYP3A5*3 (6986A > G).

RESULTS

At 1 week, 1 and 3 months C/D ratio were significantly lower in CYP3A5 expressers *1/*1 patients compared to non-expressers *3/*3.

CONCLUSION

CYP3A5 (6986A > G) genotype, rather than MDR-1 (2677G > A/T) variant, has an impact on tacrolimus pharmacokinetics.

Pharmacokinetics of drugs in adult living donor liver transplant patients: regulatory factors and observations based on studies in animals and humans

INTRODUCTION

Limited information is available on the pharmacokinetics of drugs in the donors and recipients following adult living donor liver transplantation (LDLT). Given that both the donors and recipients receive multiple drug therapies, it is important to assess the pharmacokinetics of drugs used in these patients.

AREAS COVERED

Pathophysiological changes that occur post-surgery and regulatory factors that may influence pharmacokinetics of drugs, especially hepatic drug metabolism and transport in both LDLT donors and the recipients are discussed. Pharmacokinetic data in animals with partial hepatectomy are presented. Clinical pharmacokinetic data of certain drugs in LDLT recipients are further reviewed.

EXPERT OPINION

It takes up to six months for the liver volume to return to normal after LDLT surgery. In the LDLT recipients, drug exposure generally is higher with lower clearance during early period post-transplant; lower initial dosages of immunosuppressants are used than deceased donor liver transplant recipients during the first six months post-transplantation. In animals, the activities of hepatic drug metabolizing enzymes and transporters are known to be altered differentially during liver regeneration. Future studies on the actual hepatic function with reference to drug metabolism, drug transport, and biliary secretion in both LDLT donors and recipients are required.