Impact of CYP3A5, POR, and CYP2C19 Polymorphisms on Trough Concentration to Dose Ratio of Tacrolimus in Allogeneic Hematopoietic Stem Cell Transplantation

Effect of CYP 3A4*1B and CYP3A5*3 Gene Polymorphisms in Antirejection of Tacrolimus in Liver Transplant Patients

BACKGROUND

Tacrolimus is a substrate of CYP 3A5; to reduce the rate of liver injury and rejection in liver transplant (LT) recipients, it is feasible to optimize the administration of tacrolimus by adding CYP gene polymorphism.

METHODS

We divided 151 LT recipients randomly into an optimization group and a control group. All were tested routinely for clinical indicators such as FK506 trough concentration and biochemistry, and their complications and survival were observed. The optimization group additionally detected single nucleotide polymorphisms in the CYP 3A4*1B and CYP 3A5*3 genes.

RESULTS

There were no significant differences in tacrolimus dosage, FK506 trough concentrations, and concentration/dose value between the 2 groups. In the optimization group, all patients tested CYP 3A4*1B as wild type. CYP 3A5*3 detection classification included 35 with the G/G mutation (45.5%) and 36 A/G wild-type individuals (46.8%). The concentration/dose values of G/G mutant patients were significantly higher than those of A/G wild-type and A/A mutant patients (G/G vs. A/G; P < .05), and no significant difference in FK506.

CONCLUSION

The CYP 3A4*1B genotype has less influence on tacrolimus metabolism. The genetic polymorphism of CYP 3A5*3 is obvious and largely affects tacrolimus metabolism, and the variant patients need lower doses of tacrolimus to reach the target concentration.

Pharmacokinetic Model of Drug Interaction of Tacrolimus with Combined Administration of CYP3A4 Inhibitors Voriconazole and Clarithromycin After Bone Marrow Transplantation

BACKGROUND AND OBJECTIVES

A pharmacokinetic model has been developed to quantify the drug-drug interactions of tacrolimus with concentration-dependent inhibition of cytochrome P450 (CYP) 3A4 from voriconazole and clarithromycin based on the CYP3A5 and CYP2C19 genotypes.

METHODS

This retrospective study recruited unrelated bone marrow transplant recipients receiving oral tacrolimus concomitantly with voriconazole and clarithromycin. The published population pharmacokinetic model that implemented genotypes of CYP3A5 (tacrolimus) and CYP2C19 (voriconazole) was integrated. The tested CYP3A4 inhibition models (Sigmoid efficacy maximum [Emax], Emax, log-linear, and linear) were a function of competitive inhibition of voriconazole and mechanism-based inhibition of clarithromycin in a virtual enzyme compartment.

RESULTS

The total tacrolimus trough concentrations were 119 points, with a median of 4.3 (range: 2.0-9.9) ng/mL (n = 3). The final model comprised the Sigmoid Emax model for voriconazole and clarithromycin, which depicted time-course alterations in tacrolimus concentration and clearance when given voriconazole and clarithromycin.

CONCLUSIONS

These findings could facilitate the model-informed precision dosing of tacrolimus after unrelated bone marrow transplant.

Individualized dosing parameters for tacrolimus in the presence of voriconazole: a real-world PopPK study

Objectives

Significant increase in tacrolimus exposure was observed during co-administration with voriconazole, and no population pharmacokinetic model exists for tacrolimus in renal transplant recipients receiving voriconazole. To achieve target tacrolimus concentrations, an optimal dosage regimen is required. This study aims to develop individualized dosing parameters through population pharmacokinetic analysis and simulate tacrolimus concentrations under different dosage regimens.

Methods

We conducted a retrospective study of renal transplant recipients who were hospitalized at the Second Xiangya Hospital of Central South University between January 2016 and March 2021. Subsequently, pharmacokinetic analysis and Monte Carlo simulation were employed for further analysis.

Results

Nineteen eligible patients receiving tacrolimus and voriconazole co-therapy were included in the study. We collected 167 blood samples and developed a one-compartment model with first-order absorption and elimination to describe the pharmacokinetic properties of tacrolimus. The final typical values for tacrolimus elimination rate constant (Ka), apparent volume of distribution (V/F), and apparent oral clearance (CL/F) were 8.39 h-1, 2690 L, and 42.87 L/h, respectively. Key covariates in the final model included voriconazole concentration and serum creatinine. Patients with higher voriconazole concentration had lower tacrolimus CL/F and V/F. In addition, higher serum creatinine levels were associated with lower tacrolimus CL/F.

Conclusion

Our findings suggest that clinicians can predict tacrolimus concentration and estimate optimal tacrolimus dosage based on voriconazole concentration and serum creatinine. The effect of voriconazole concentration on tacrolimus concentration was more significant than serum creatinine. These findings may inform clinical decision-making in the management of tacrolimus and voriconazole therapy in solid organ transplant recipients.

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.

Association between CYP3A4, CYP3A5 and ABCB1 genotype and tacrolimus treatment outcomes among allogeneic HSCT patients

Aim: Successful treatment with tacrolimus to prevent graft versus host disease (GVHD) and minimize tacrolimus-related toxicities among allogeneic hematopoietic cell transplantation (alloHCT) recipients is contingent upon quickly achieving and maintaining concentrations within a narrow therapeutic range. The primary objective was to investigate associations between CYP3A4, CYP3A5 or ABCB1 genotype and the proportion of patients that attained an initial tacrolimus goal concentration following initiation of intravenous (iv.) and conversion to oral administration. Materials & methods: We retrospectively evaluated 86 patients who underwent HLA-matched (8/8) related donor alloHCT and were prescribed a tacrolimus-based regimen for GVHD prophylaxis. Results & conclusion: The findings of the present study suggests that CYP3A5 genotype may impact attainment of initial therapeutic tacrolimus concentrations with oral administration in alloHCT recipients.

Nirmatrelvir/ritonavir-induced elevation of blood tacrolimus levels in a patient in the maintenance phase post liver transplantation

Nirmatrelvir is an orally administered anti-SARS-CoV-2 drug used in combination with ritonavir, the drug-metabolizing cytochrome P450 (CYP) 3A inhibitor, to evade metabolism and extend bioavailability. Meanwhile, the immunosuppressant tacrolimus is a CYP3A4/5 substrate, and CYP3A inhibition results in drug-drug interactions. Herein, we report the case of a coronavirus disease 19 (COVID-19) patient in the maintenance phase post liver transplantation, receiving tacrolimus treatment, with a marked increase of blood tacrolimus levels after the initiation of concomitant nirmatrelvir/ritonavir treatment. A 61-year-old Japanese woman underwent a living donor liver transplant for Caroli disease 25 years ago and received tacrolimus 2 mg/day for immunosuppressive treatment. Three days before the observed high tacrolimus blood concentration, she presented to our emergency department with a fever and was diagnosed with COVID-19. She was prescribed an adjusted dose of nirmatrelvir/ritonavir (150 mg/100 mg, twice daily) for 5 days as a high-risk case with immunosuppressive treatment and reduced renal function (estimated glomerular filtration rate, eGFR: 46.6 mL/min/1.73 m2). At the return visit on day 1, blood tacrolimus level was >60 ng/mL on trough sampling, above the upper limit of measurement, with nausea and vomiting as side effects. Tacrolimus treatment was discontinued on the same day. Drug-drug interactions resulting from CYP3A inhibition by nirmatrelvir/ritonavir were deemed responsible for elevated blood tacrolimus levels. Therefore, in liver transplant recipients, tacrolimus dose reduction or discontinuation is required during COVID-19 treatment with nirmatrelvir/ritonavir.

The Effect of Voriconazole on Tacrolimus in Kidney Transplantation Recipients: A Real-World Study

Tacrolimus is an immunosuppressant with a narrow therapeutic window. Tacrolimus exposure increased significantly during voriconazole co-therapy. The magnitude of this interaction is highly variable, but it is hard to predict quantitatively. We conducted a study on 91 kidney transplantation recipients with voriconazole co-therapy. Furthermore, 1701 tacrolimus concentration data were collected. Standard concentration adjusted by tacrolimus daily dose (C/D) and weight-adjusted standard concentration (CDW) increased to 6 times higher during voriconazole co-therapy. C/D and CDW increased with voriconazole concentration. Patients with the genotype of CYP3A5 *3/*3 and CYP2C19 *2/*2 or *2/*3 were more variable at the same voriconazole concentration level. The final prediction model could explain 54.27% of the variation in C/D and 51.11% of the variation in CDW. In conclusion, voriconazole was the main factor causing C/D and CDW variation, and the effect intensity should be quantitative by its concentration. Kidney transplant recipients with CYP3A5 genotype of *3/*3 and CYP2C19 genotype of *2/*2 and *2/*3 should be given more attention during voriconazole co-therapy. The prediction model established in this study may help to reduce the occurrence of rejection.

Investigation of pharmacologic interactions between omeprazole and tacrolimus in a membranous nephropathy patient with CYP3A5 nonexpresser: a case report

Tacrolimus has been widely used in membranous nephropathy in recent years. The drug interactions of the coadministration of tacrolimus with omeprazole in CYP3A5 nonexpresser membranous nephropathy patients have not been demonstrated. Here, we report an idiopathic membranous nephropathy patient who was with CYP2C19*2/*2, CYP3A5*3/*3 (nonexpresser) and ABCB1 (3435 TT, 1236 computed tomography, 2677 TT) genotype requiring treatment with tacrolimus and omeprazole and found to have fluctuating metabolism of tacrolimus. This study shows that tacrolimus and omeprazole have pharmacologic drug interactions in CYP3A5 nonexpressers, implying that the CYP3A and ABCB1 gene mutations linked to tacrolimus metabolism may alter tacrolimus levels in the blood. The observed concentrations of tacrolimus were decreased after the discontinuation of omeprazole therapy. It demonstrates that, in addition to genotype, clinical covariates, such as omeprazole are important when it comes to better understanding and prediction of tacrolimus dosage. It is deemed necessary to monitor tacrolimus blood concentrations and make dose adjustments when patients were coadministered with omeprazole.

Cytochrome P450 oxidoreductase variant A503V contributes to the increased CYP3A5 activity with tacrolimus in vitro

BACKGROUND

Tacrolimus is a calcineurin inhibitor with a strong efficacy in prevention of graft rejection after transplantation. It is well known that cytochrome P450 3A5 (CYP3A5) has a high metabolic capacity for tacrolimus, and mutations in human cytochrome P450 oxidoreductase (POR) cause altered CYP3A5 activity. Recently, clinical studies have revealed that POR*28 contributes enhanced tacrolimus clearance in CYP3A5 expressers. A503V is an amino acid sequence variant encoded by POR*28. In this study, we first evaluated the impact of A503V on CYP3A5 activity with tacrolimus as the substrate in vitro.

RESEARCH DESIGN & METHODS

Wild-type (WT) and A503V POR, with WT CYP3A5 were expressed in recombinant HepG2 cells and reconstituted proteins. Michaelis constant (K_m) and maximum velocity (V_max) of CYP3A5 with tacrolimus as substrates were determined, and catalytic efficiency is expressed as V_max/K_m.

RESULTS

WT and A503V POR both down-regulated the CYP3A5 mRNA expression, and WT POR rather than A503V down-regulated the protein expression of CYP3A5 in recombinant HepG2 cells. Compared with WT POR, A503V increased metabolism of tacrolimus by CYP3A5 in both cellular and protein level.

CONCLUSION

A503V can affect CYP3A5-catalyzed tacrolimus metabolism in vitro, which suggests that A503V has the potential to serve as a biomarker for tacrolimus treatment in transplantation recipients.

Why We Need to Take a Closer Look at Genetic Contributions to CYP3A Activity

Cytochrome P450 3A (CYP3A) subfamily enzymes are involved in the metabolism of 40% of drugs in clinical use. Twin studies have indicated that 66% of the variability in CYP3A4 activity is hereditary. Yet, the complexity of the CYP3A locus and the lack of distinct drug metabolizer phenotypes has limited the identification and clinical application of CYP3A genetic variants compared to other Cytochrome P450 enzymes. In recent years evidence has emerged indicating that a substantial part of the missing heritability is caused by low frequency genetic variation. In this review, we outline the current pharmacogenomics knowledge of CYP3A activity and discuss potential future directions to improve our genetic knowledge and ability to explain CYP3A variability.

Impact of POR*28 Variant on Tacrolimus Pharmacokinetics in Kidney Transplant Patients with Different CYP3A5 Genotypes

BACKGROUND

The introduction of tacrolimus (TAC) in clinical practice was essential to the establishment of transplantation as therapy for patients with chronic renal disease. However, the higher interindividual variation of TAC metabolism has been an important limiting factor for its clinical use. Although the relationship between CYP3A5 polymorphisms and TAC pharmacokinetics (PK) is well established, the effects of other genetic variants on TAC metabolism, such as POR*28, still remain uncertain.

OBJECTIVE

To evaluate the impact of POR variants on TAC PK in renal transplant patients with different CYP3A5 genotypes (expressers and non-expressers).

METHODS

A total of 115 patients were included in this study. Genomic DNA was isolated from peripheral blood, and the real-time PCR technique was used to analyze the polymorphism POR rs1057868; C>T.

RESULTS

During the initial post-transplant period, variant allele carriers (*1/*28 and *28/*28) showed a lower TAC dose requirement than POR wild homozygotes (*1/*1). Regarding the influence of the different polymorphisms of POR within the CYP3A5 expresser and non-expresser groups, no differences were observed in any of the PK parameters analyzed during 12 months after transplantation.

CONCLUSION

In the studied population, the variant allelic POR*28 was significantly associated with lower TAC dose requirements and higher Co/D ratio in the first-month post-transplant. However, the effects of this polymorphism on the CYP3A5 enzyme activity were not observed.

Prediction of Tacrolimus Dose/Weight-Adjusted Trough Concentration in Pediatric Refractory Nephrotic Syndrome: A Machine Learning Approach

Purpose

Tacrolimus (TAC) is a first-line immunosuppressant for patients with refractory nephrotic syndrome (NS). However, there is a high inter-patient variability of TAC pharmacokinetics, thus therapeutic drug monitoring (TDM) is required. In this study, we aimed to employ machine learning algorithms to investigate the impact of clinical and genetic variables on the TAC dose/weight-adjusted trough concentration (C₀/D) in Chinese children with refractory NS, and then develop and validate the TAC C₀/D prediction models.

Patients and Methods

The association of 82 clinical variables and 244 single nucleotide polymorphisms (SNPs) with TAC C₀/D in the third month since TAC treatment was examined in 171 children with refractory NS. Extremely randomized trees (ET), gradient boosting decision tree (GBDT), random forest (RF), extreme gradient boosting (XGBoost), and Lasso regression were carried out to establish and validate prediction models, respectively. The best prediction models were validated on a cohort of 30 refractory NS patients.

Results

GBDT algorithm performed best in the whole group (R²=0.444, MSE=591.032, MAE=20.782, MedAE=18.980) and CYP3A5 nonexpresser group (R²=0.264, MSE=477.948, MAE=18.119, MedAE=18.771), while ET algorithm performed best in the CYP3A5 expresser group (R²=0.380, MSE=1839.459, MAE=31.257, MedAE=19.399). These prediction models included 3 clinical variables (ALB0, AGE0, and gender) and 10 SNPs (ACTN4 rs3745859, ACTN4 rs56113315, ACTN4 rs62121818, CTLA4 rs4553808, CYP3A5 rs776746, IL2RA rs12722489, INF2 rs1128880, MAP3K11 rs7946115, MYH9 rs2239781, and MYH9 rs4821478).

Conclusion

The association between the clinical and genetic variables and TAC C₀/D was described, and three TAC C₀/D prediction models integrating clinical and genetic variables were developed and validated using machine learning, which may support individualized TAC dosing.

Impact of Pharmacogenetics on Intravenous Tacrolimus Exposure and Conversions to Oral Therapy

CYP3A5 and CYP3A4 are the predominant enzymes responsible for tacrolimus metabolism; however only a proportion of the population expresses CYP3A5 secondary to genetic variation. CYP3A5 is expressed in both the intestine and the liver and has been shown to impact both the bioavailability and metabolism of orally administered tacrolimus. Increasing the initial tacrolimus dose by 50% to 100% is recommended in patients who are known CYP3A5 expressers; however, whether this dose adjustment is appropriate for i.v. tacrolimus administration is unclear. The objective of this study was to evaluate the impact of CYP3A5 genotype as well as other pharmacogenes on i.v. tacrolimus exposure to determine whether the current genotype-guided dosing recommendations are appropriate for this formulation. In addition, this study aimed to investigate dose conversion requirements among CYP3A5 genotypes when converting from i.v. to p.o. tacrolimus. This study is a retrospective chart review of all patients who underwent allogeneic stem cell transplantation at Michigan Medicine between June 1, 2014, and March 1, 2018, who received i.v. tacrolimus at the time of their transplantation. Secondary use samples were obtained for genotyping CYP3A5, CYP3A4, and ABCB1. Patient demographic information, tacrolimus dosing and trough levels, and concomitant medications received at the time of tacrolimus trough were collected retrospectively from the patients' medical records. The i.v. dose-controlled concentration (C/D) and the i.v.:p.o. exposure ratio was calculated for all tacrolimus doses and patients, respectively. The impact of CYP3A5, CYP3A4, and ABCB1 genotypes on the i.v. C/D were evaluated with linear mixed modeling. The impact of CYP3A5 genotype on the i.v.:p.o. ratio was evaluated while controlling for age and concomitant use of an azole inhibitor. CYP3A5 and CYP3A4 genotypes were significantly associated with the i.v. C/D, with CYP3A5 expressers and CYP3A4 rapid metabolizers having 20% lower tacrolimus exposure. Neither genotype remained significant in the multivariable model, although age, hematocrit, and concomitant use of strong azole inhibitors were associated with increased i.v. C/D. When controlling for patient age and sex, CYP3A5 expressers had significantly higher i.v.:p.o. ratios than CYP3A5 nonexpressers (3.42 versus 2.78; P = .04). Post hoc analysis showed that the i.v.:p.o. ratio may differ among different CYP3A5 genotypes and azole inhibitor combinations. This study demonstrates that the current genotype-guided tacrolimus dose adjustment recommendations are inappropriate for CYP3A5 expressers receiving i.v. tacrolimus. Although CYP3A5 genotype is likely a minor contributor to i.v. tacrolimus exposure, genotype, in addition to capturing concomitant CYP3A inhibitors, would likely improve i.v.:p.o. dose conversion selection. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Effects and safety evaluation of Wuzhi Capsules combined with tacrolimus for the treatment of kidney transplantation recipients

WHAT IS KNOWN AND OBJECTIVE

Tacrolimus (FK506), an effective and potent calcineurin inhibitor, is the cornerstone of immunosuppression after kidney transplantation. Wuzhi capsule (WZC), a prescribed ethanol extract of Nan-Wuweizi (Schisandra sphenanthera), is widely prescribed for kidney transplant recipients for the maintenance of tacrolimus concentration in clinical settings. Previous studies have demonstrated that WZC can increase the blood concentration of tacrolimus. However, it remains controversial whether to use WZC can be used to increase tacrolimus concentration in clinical practice. Our study aimed to evaluate the efficacy and safety of WZC combined with tacrolimus in the treatment of kidney transplant recipients.

METHODS

One hundred and ninety four Chinese kidney transplant recipients were included in this retrospective study. The recipients were divided into two groups (non-WZC group and WZC group). We investigated the effects of WZC on tacrolimus in terms of tacrolimus metabolism, laboratory tests, pharmacogenomics, renal function and adverse reactions.

RESULTS AND DISCUSSION

The concentration/dose (C₀ /D) of tacrolimus was significantly higher in the WZC group than the non-WZC group. The laboratory findings of blood routine tests, liver and kidney function were not significantly different between the two groups. The CYP3A5 genotype showed clearly associated with tacrolimus C₀ /D, whereas no significant difference was observed in patients with CYP3A4*1B, CYP3A4*22, ABCB1, ABCC2, POR*28 or PXR alleles. The improvement of C₀ /D by administration of WZC was significant in CYP3A5 expressers compared to non-expressers. Furthermore, the WZC group had a remarkably higher proportion of subjects who reached the target tacrolimus concentration than the non-WZC group. No significant differences in renal function and adverse reactions were observed between the groups.

WHAT IS NEW AND CONCLUSION

Wuzhi capsule can increase tacrolimus concentration without negative effects on renal function and adverse reactions, especially in CYP3A5 expressers. Efficient and economical synergistic effects can be achieved by the combined administration of WZC in kidney transplant recipients.

The impact of IL-10 and CYP3A5 gene polymorphisms on dose-adjusted trough blood tacrolimus concentrations in early post-renal transplant recipients

BACKGROUND

The strong inter-individual pharmacokinetic variability and the narrow therapeutic window of tacrolimus (TAC) have hampered the clinical application. Gene polymorphisms play an important role in TAC pharmacokinetics. Here, we investigate the influence of genotypes of IL-10, CYP3A5, CYP2C8, and ABCB1 on dose-adjusted trough blood concentrations (the C₀/D ratio) of TAC to reveal unclear genetic factors that may affect TAC dose requirements for renal transplant recipients.

METHODS

Genetic polymorphisms of IL-10, CYP3A5, CYP2C8, and ABCB1 in 188 renal transplant recipients were determined using Kompetitive Allele Specific PCR (KASP). Statistical analysis was applied to examine the effect of genetic variation on the TAC C₀/D at 5, 10, 15, and 30 days after transplantation.

RESULTS

Recipients carrying the IL-10 -819C > T TT genotype showed a significantly higher TAC C₀/D than those with the TC/CC genotype (p < 0.05). Additionally, the TAC C₀/D values of recipients with the capacity for low IL-10 activity (-819 TT) engrafted with CYP3A5 non-expressers were higher compared to the intermediate/high activity of IL-10 -819C > T TC or CC carrying CYP3A5 expressers, and the difference was statistically significant at different time points (p < 0.05).

CONCLUSIONS

Genetic polymorphisms of IL-10 -819C > T and CYP3A5 6986A > G influence the TAC C₀/D, which may contribute to variation in TAC dose requirements during the early post-transplantation period. Detecting IL-10 -819C > T and CYP3A5 6986A > G polymorphisms may allow determination of individualized tacrolimus dosage regimens for renal transplant recipients during the early post-transplantation period.

Relationship between CYP3A5 Polymorphism and Tacrolimus Blood Concentration Changes in Allogeneic Hematopoietic Stem Cell Transplant Recipients during Continuous Infusion

A polymorphism in the gene encoding the metabolic enzyme cytochrome P450 family 3 subfamily A member 5 (CYP3A5) is a particularly influential factor in the use of tacrolimus in Japanese patients. Those who are homozygotic for the *3 mutation lack CYP3A5 activity, which results in substantial individual differences in tacrolimus metabolism. The aim of this study was to analyze the relationship between individual differences in tacrolimus blood concentration changes and CYP3A5 polymorphisms in allogeneic hematopoietic stem cell transplantation recipients during the period of increasing blood concentration of the drug following treatment onset. This was a prospective observational cohort study, involving 20 patients administered tacrolimus by continuous infusion. The subjects were divided into the *1/*3 and *3/*3 groups based on CYP3A5 polymorphism analysis. The tacrolimus blood concentration/dose (C/D) ratio increased from day 1 and was largely stable on day 5, and a significant difference was observed between the *1/*3 and *3/*3 groups in the time course of the C/D ratio during this period (p < 0.05). This study reveals the effects of CYP3A5 polymorphism on continuous changes in tacrolimus blood concentration.

CYP3A5 and PPARA genetic variants are associated with low trough concentration to dose ratio of tacrolimus in kidney transplant recipients

PURPOSE

Genetic polymorphisms have been associated with variation in the metabolism of tacrolimus (TAC) in kidney transplant patients. This study is aimed at assessing the impact of allelic variants of CYP3A5 and PPARA genes on the pharmacokinetics (PK) of TAC in Brazilian kidney transplant recipients in the first-year post-transplant.

METHODS

A total of 127 patients were included for genetic evaluation. Genomic DNA was isolated from peripheral blood and real-time PCR was used to analyze the main polymorphisms described for the genes CYP3A5 (rs776746; C > G) and PPARA (rs4823613; A > G and rs4253728; G > A).

RESULTS

CYP3A5 expressors showed a lower Co/dose ratio than non-expressors, with the median values of this parameter <1.01 ng/mL/mg in the first group at all evaluated times. Additionally, PPARA variant homozygotes had a lower Co/D ratio than wild allele carriers in the 12-month post-transplant period, with a median value of 0.65 ng/mL/mg. In the CYP3A5 expressers, the presence of the variant homozygous genotype PPARA was associated with a lower value of Co/D compared with the other genotypic groups at month 12.

CONCLUSION

In the population under study, polymorphisms on CYP3A5 and PPARA were identified as determining and independent factors associated with the reduction of Co/D of TAC. Thus, the genotyping of these genetic variants may be a useful tool for the individualized prescription of TAC in kidney transplant patients.

Donor UNC-93 Homolog B1 genetic polymorphism predicts survival outcomes after unrelated bone marrow transplantation

UNC-93 homolog B1 (UNC93B1) is a key regulator of toll-like receptors (TLRs), pattern recognition receptors that sense invading pathogens and manage the innate immune response and deliver them from the endoplasmic reticulum to their respective endosomal signaling compartments. Several types of TLRs are known to contribute to the inflammatory process after allogeneic hematopoietic stem cell transplantation (SCT), so UNC93B1 might play integral roles there. We investigated the influence of the UNC93B1 single-nucleotide polymorphism (SNP) rs308328 (T>C) on transplant outcomes in a cohort of 237 patients undergoing unrelated HLA-matched bone marrow transplantation (BMT) for hematologic malignancies through the Japan Marrow Donor Program. The donor UNC93B1 C/C genotype was associated with a better 3-year overall survival than the donor UNC93B1 C/T or T/T genotype. An analysis of the UNC93B1 rs308328 genotype may therefore be useful for selecting the donor, estimating the prognosis, and creating therapeutic strategies after allogeneic SCT.

Predictors of Adverse Events and Determinants of the Voriconazole Trough Concentration in Kidney Transplantation Recipients

Voriconazole is the mainstay for the treatment of invasive fungal infections in patients who underwent a kidney transplant. Variant CYP2C19 alleles, hepatic function, and concomitant medications are directly involved in the metabolism of voriconazole. However, the drug is also associated with numerous adverse events. The purpose of this study was to identify predictors of adverse events using binary logistic regression and to measure its trough concentration using multiple linear modeling. We conducted a prospective analysis of 93 kidney recipients cotreated with voriconazole and recorded 213 trough concentrations of it. Predictors of the adverse events were voriconazole trough concentration with the odds ratios (OR) of 2.614 (P = 0.016), cytochrome P450 2C19 (CYP2C19), and hemoglobin (OR 0.181, P = 0.005). The predictive power of these three factors was 91.30%. We also found that CYP2C19 phenotypes, hemoglobin, platelet count, and concomitant use of ilaprazole had quantitative relationships with voriconazole trough concentration. The fit coefficient of this regression equation was R²  = 0.336, demonstrating that the model explained 33.60% of interindividual variability in the disposition of voriconazole. In conclusion, predictors of adverse events are CYP2C19 phenotypes, hemoglobin, and voriconazole trough concentration. Determinants of the voriconazole trough concentration were CYP2C19 phenotypes, platelet count, hemoglobin, concomitant use of ilaprazole. If we consider these factors during voriconazole use, we are likely to maximize the treatment effect and minimize adverse events.

Population pharmacokinetics of tacrolimus in umbilical cord blood transplant patients focusing on the variation in red blood cell counts

WHAT IS KNOWN AND OBJECTIVE

The distribution of tacrolimus (TAC), an immunosuppressant used during cord blood transplantation (CBT)-one of the haematopoietic stem cell transplantations, to red blood cell (RBC) is approximately 90% in whole blood. In CBT patients, the total RBC count shows dramatic fluctuation due to conditioning before transplantation, including anticancer agents and total body irradiation, as well as RBC transfusions during the treatment period. Therefore, the amount of TAC in whole blood may show wide variation. However, therapeutic drug monitoring (TDM) of TAC has been performed based on the whole blood concentration. In this study, to contribute to TDM of TAC in CBT, we performed the population pharmacokinetic (PPK) analysis of TAC in 56 CBT patients and investigated the factors that affected the concentration of TAC, focusing the variation of RBC count.

METHOD

A one-compartment model was applied to the observed whole blood TAC concentrations, and a PPK analysis was conducted with a non-linear mixed effect model.

RESULTS AND DISCUSSION

Our final PPK model indicated good robustness and accuracy. In addition, haemoglobin (Hb) level was an influential covariate on Vd, which was expressed as Vd(L) = 91.4 × (Hb/8.2)^(-1.07) .

WHAT IS NEW AND CONCLUSION

In this study, our results showed the necessity for the Hb level monitoring during TDM of TAC in CBT patients and provided useful information for improving TDM strategy of TAC.

The stability of initial tacrolimus concentration following allogeneic hematopoietic stem cell transplantation reduces the risk of acute GVHD

BACKGROUND

Early tacrolimus (TAC) concentrations correlate with the risk of acute graft-versus-host disease (aGVHD); however, whether the variability of early TAC concentrations after allo-HSCT governs the occurrence of aGVHD remains unknown. Here, we evaluate the correlation between the intrapatient variability (IPV) of initial TAC concentrations and the development of aGVHD.

METHODS

We retrospectively assessed 202 patients who underwent allo-HSCT and received standard GVHD prophylaxis by continuous intravenous (iv) infusion of TAC and iv methotrexate. IPV was calculated by using the % coefficient of variation in the initial 4 weeks.

RESULTS

With median follow-up duration of 20.7 months, 24 patients were diagnosed with grades II-IV aGVHD. Overall survival (OS) and relapse at 12 months after allo-HSCT were 70.6% (95% confidence interval [CI], 63.7%-76.4%) and 18.9% (95% CI, 13.0%-24.4%), respectively. When IPV was categorized into two groups (high: ≥9.5%; low: <9.5%), the cumulative incidence of grades II-IV aGVHD was greater in the IPV-high group at week 3 (odds ratio: 4.15; 95% CI, 1.37%-12.6%, P = .01). No significant differences were observed in OS and relapse between the two groups.

CONCLUSION

We concluded that adjusting early TAC concentration stable may reduce aGVHD after allo-HSCT without affecting the relapse rate.

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.

Pharmacogenetics and tacrolimus administration in stem cell transplantation

Tacrolimus is the gold standard immunosuppressant administered in solid organ and stem cell transplantation to avoid graft rejection post-transplant. Despite its widespread use, there is a large variation in response to therapy, likely due to high inter-individual pharmacokinetic variability. Therapeutic drug monitoring is employed to improve clinical response and reduce toxicity. There is substantial evidence that pharmacogenetics influences drug exposure and response. CYP3A5 genotype significantly impacts oral tacrolimus concentrations and response after solid organ transplantation. There are fewer studies in stem cell transplantation and with intravenous tacrolimus dosing. This report highlights recent evidence suggesting genes such as CYP3A4 and ABCB1 play a larger role after intravenous dosing compared with CYP3A5, and the role for novel genes on tacrolimus outcomes.

Tacrolimus treatment in childhood refractory nephrotic syndrome: A retrospective study on efficacy, therapeutic drug monitoring, and contributing factors to variable blood tacrolimus levels

Tacrolimus, an immunosuppressive drug, was recommended by the 2012 KDIGO guidelines to treat nephrotic syndrome (NS) in children and adults. However, it has high interpatient pharmacokinetic variability and exposure levels should be monitored, although there are no specified target concentrations. This retrospective study aimed to review efficacy and safety after concomitant treatment with tacrolimus and prednisone, and to identify factors that contribute to the variable blood-trough-concentration-to-dose (C₀/Dose) ratio in children with refractory NS (RNS). A 6-month therapy induced complete or partial remission in 95% of patients. One-year follow-up indicated a high remission rate and low nephrotoxicity. Under maintenance dosages, approximately 95% of the C₀ values were 2-7 ng/mL. Body weight (BW), age, CYP3A5 polymorphisms were the factors affecting the C₀/Dose ratio. The C₀/Dose ratio in patients with a BW of <20 kg was 1.5-fold than that in patients with BW of ≥40 kg. Moreover, the C₀/Dose ratio in patients aged 1-≤6 and 6-≤12 years was significantly lower than that in patients aged 12-≤18 years, by 25% and 48%, respectively. There were no significant association between CYP3A5 genotyping and C₀/Dose ratio in younger children (1-≤6 years), rather than older children (6-≤18 years). In conclusion, routine CYP3A5 genotyping should be considered in children aged over 6 years and exposure levels (C₀) of 2-7 ng/mL may be feasible when tacrolimus is combined with low-dose prednisone to treat childhood RNS.

Influence of Germline Genetics on Tacrolimus Pharmacokinetics and Pharmacodynamics in Allogeneic Hematopoietic Stem Cell Transplant Patients

Tacrolimus exhibits high inter-patient pharmacokinetics (PK) variability, as well as a narrow therapeutic index, and therefore requires therapeutic drug monitoring. Germline mutations in cytochrome P450 isoforms 4 and 5 genes (CYP3A4/5) and the ATP-binding cassette B1 gene (ABCB1) may contribute to interindividual tacrolimus PK variability, which may impact clinical outcomes among allogeneic hematopoietic stem cell transplantation (HSCT) patients. In this study, 252 adult patients who received tacrolimus for acute graft versus host disease (aGVHD) prophylaxis after allogeneic HSCT were genotyped to evaluate if germline genetic variants associated with tacrolimus PK and pharmacodynamic (PD) variability. Significant associations were detected between germline variants in CYP3A4/5 and ABCB1 and PK endpoints (e.g., median steady-state tacrolimus concentrations and time to goal tacrolimus concentration). However, significant associations were not observed between CYP3A4/5 or ABCB1 germline variants and PD endpoints (e.g., aGVHD and treatment-emergent nephrotoxicity). Decreased age and CYP3A5*1/*1 genotype were independently associated with subtherapeutic tacrolimus trough concentrations while CYP3A5*1*3 or CYP3A5*3/*3 genotypes, myeloablative allogeneic HSCT conditioning regimen (MAC) and increased weight were independently associated with supratherapeutic tacrolimus trough concentrations. Future lines of prospective research inquiry are warranted to use both germline genetic and clinical data to develop precision dosing tools that will optimize both tacrolimus dosing and clinical outcomes among adult HSCT patients.