Individualization of tacrolimus dosage basing on cytochrome P450 3A5 polymorphism – a prospective,randomized, controlled study

We investigated how cytochrome P450 (CYP) 3A5 polymorphism affects pharmacokinetics of tacrolimus and its interaction with diltiazem in Chinese kidney transplant recipients. Sixty‐two CYP3A5 expressers and 58 non‐expressers were, respectively, randomized to receive diltiazem supplement or not. Their pharmacokinetic profiles were acquired on 14th day, sixth month, and 18th month post‐transplant and compared among groups. A dosing equation was fit based on above data with CYP3A5 genotype and diltiazem co‐administration as variables. Then, necessary initial doses with or without diltiazem were calculated and used in 11 CYP3A5 expressers, respectively, when another 11 expressers received routine doses as control. Trough concentration was measured on the third‐day post‐transplant and patients failed to reach target range were presented in percentage. These two parameters were compared among three groups. Patients were followed up until June 2010, kidney function, biopsy‐proved acute rejection, and other adverse events were monitored. Results showed that CYP3A5 expressers needed more tacrolimus to reach therapeutic concentration window and were more susceptible to diltiazem‐induced concentration increase than CYP3A5 non‐expressers. CYP3A5 polymorphism‐guided dosing equation helped to determine appropriate initial doses of tacrolimus in individuals. In conclusion, CYP3A5 polymorphism profoundly influences pharmacokinetics of tacrolimus and helps to individualize tacrolimus dose.     

Long‐Term Clinical Impact of Adaptation of Initial Tacrolimus Dosing to CYP3A5 Genotype

Pretransplantation adaptation of the daily dose of tacrolimus to CYP3A5 genotype is associated with improved achievement of target trough concentration (C₀), but whether this improvement affects clinical outcomes is unknown. In the present study, we have evaluated the long‐term clinical impact of the adaptation of initial tacrolimus dosing according to CYP3A5 genotype: The transplantation outcomes of the 236 kidney transplant recipients included in the Tactique study were retrospectively investigated over a period of more than 5 years. In the Tactique study, patients were randomly assigned to receive tacrolimus at either a fixed dosage or a dosage determined by their genotype, and the primary efficacy end point was the proportion of patients for whom tacrolimus C₀ was within target range (10–15 ng/mL) at day 10. Our results indicate that the incidence of biopsy‐proven acute rejection and graft survival were similar between the control and the adapted tacrolimus dose groups, as well as between the patients who achieve the tacrolimus C₀ target ranges earlier. Patients' death, cancer, cardiovascular events, and infections were also similar, and renal function did not change. We conclude that optimization of initial tacrolimus dose using pharmacogenetic testing does not improve clinical outcomes.     

Genotypes associated with tacrolimus pharmacokinetics impact clinical outcomes in lung transplant recipients

Most lung transplantation immunosuppression regimens include tacrolimus. Single nucleotide polymorphisms (SNPs) in genes important to tacrolimus bioavailability and clearance (ABCB1, CYP3A4, and CYP3A5) are associated with differences in tacrolimus pharmacokinetics. We hypothesized that polymorphisms in these genes would impact immunosuppression‐related outcomes. We categorized ABCB1, CYP3A4, and CYP3A5 SNPs for 321 lung allograft recipients. Genotype effects on time to therapeutic tacrolimus level, interactions with antifungal medications, concentration to dose (C₀/D), acute kidney injury, and rejection were assessed using linear models adjusted for subject characteristics and repeat measures. Compared with CYP3A poor metabolizers (PM), time to therapeutic tacrolimus trough was increased by 5.1 ± 1.6 days for CYP3A extensive metabolizers (EM, P < 0.001). In the post‐operative period, CYP3A intermediate metabolizers spent 1.2 ± 0.5 days less (P = 0.01) and EM spent 2.1 ± 0.5 days less (P < 0.001) in goal tacrolimus range than CYP3A PM. Azole antifungals interacted with CYP3A genotype in predicting C₀/D (P < 0.001). Increased acute kidney injury rates were observed in subjects with high ABCB1 function (OR 3.0, 95% CI 1.1‐8.6, P = 0.01). Lower rates of acute cellular rejection were observed in subjects with low ABCB1 function (OR 0.36, 95% CI 0.07‐0.94, P = 0.02). Recipient genotyping may help inform tacrolimus dosing decisions and risk of adverse clinical outcomes.     

A Randomized Controlled Trial Comparing the Efficacy of Cyp3a5 Genotype‐Based With Body‐Weight‐Based Tacrolimus Dosing After Living Donor Kidney Transplantation

Patients expressing the cytochrome P450 (CYP) 3A5 gene require a higher tacrolimus dose to achieve therapeutic exposure compared with nonexpressers. This randomized‐controlled study investigated whether adaptation of the tacrolimus starting dose according to CYP3A5 genotype increases the proportion of kidney transplant recipients being within the target tacrolimus predose concentration range (10–15 ng/mL) at first steady‐state. Two hundred forty living‐donor, renal transplant recipients were assigned to either receive a standard, body‐weight‐based or a CYP3A5 genotype‐based tacrolimus starting dose. At day 3, no difference in the proportion of patients having a tacrolimus exposure within the target range was observed between the standard‐dose and genotype‐based groups: 37.4% versus 35.6%, respectively; p = 0.79. The proportion of patients with a subtherapeutic (i.e. <10 ng/mL) or a supratherapeutic (i.e. >15 ng/mL) Tac predose concentration in the two groups was also not significantly different. The incidence of acute rejection was comparable between both groups (p = 0.82). Pharmacogenetic adaptation of the tacrolimus starting dose does not increase the number of patients having therapeutic tacrolimus exposure early after transplantation and does not lead to improved clinical outcome in a low immunological risk population.     

The role of CYP3A5 genotypes in dose requirements of tacrolimus and everolimus after heart transplantation

Kniepeiss D, Renner W, Trummer O, Wagner D, Wasler A, Khoschsorur GAli, Truschnig‐Wilders M, Tscheliessnigg K‐H. The role of CYP3A5 genotypes in dose requirements of tacrolimus and everolimus after heart transplantation.
Clin Transplant 2011: 25: 146–150. © 2009 John Wiley & Sons A/S. Abstract: Background: tacrolimus and everolimus are immunosuppressive drugs metabolized by enzymes of the CYP3A subfamily. A common variant of the CYP3A5 gene, CYP3A5*3, results in strongly decreased CYP3A5 activity and has been shown to influence Tacrolimus blood concentrations, but its role for the pharmacogenetics of Everolimus remains unclear. Aim of the study was to examine the role of CYP3A5*3 variant in tacrolimus and everolimus dose and drug levels after heart transplantation. Methods: The present study comprised 15 patients with Tacrolimus and 30 patients with Everolimus‐based maintenance therapy after heart transplantation. CYP3A5 genotypes were determined and correlated with clinical data. Results: In the Tacrolimus group, 13 subjects were CYP3A5 non‐expressors (*3/*3 genotype) and two were heterozygous expressors (*1/*3 genotype). Average Tacrolimus dose was significantly higher in subjects expressing CYP3A5 compared to non‐expressors. Tacrolimus levels were not significantly different at any point of time. In the Everolimus group, 27 subjects were CYP3A5 non‐expressors (*3/*3 genotype) and three were heterozygous expressors (*1/*3). Neither Everolimus dose nor levels were significantly different between CYP3A5 expressors and non‐expressors at any point of time. Discussion: We conclude that in adult patients after heart transplantation, CYP3A5 genotypes have a strong influence on Tacrolimus, but not Everolimus dose requirement.     

The Influence of Pharmacogenetics on the Time to Achieve Target Tacrolimus Concentrations after Kidney Transplantation

Previously, we reported that, at 3 months after renal transplantation, individuals with CYP3AP1 genotype CYP3AP1*1 (linked to CYP3A5*1 and strongly associated with expression of CYP3A5) required twofold higher doses of tacrolimus to achieve target blood concentrations than individuals with the genotype CYP3AP1*3/*3 (CYP3A5 nonexpressors). This study assesses the relationship between concentration-controlled dosing during the early period after transplantation, the time to achieve target concentrations and genotype in 178 renal transplant recipients (CYP3AP1*1/*3 or *1/*1: n = 53, CYP3AP1*3/*3: n = 125). Patients with CYP3AP1*1/*3 or *1/*1 had lower mean tacrolimus concentrations during the first week (Median 13.5 vs. 18.5 microg/L, p < 0.0001) with significant delay in achieving target concentrations (15-20 microg/L during week 1, then 10-15 microg/L). More CYP3AP1*3/*3 patients had tacrolimus concentrations above target during the first week (73.6% vs. 35.8%, p = 0.003). There was no difference in the rate of biopsy-confirmed acute rejection, but rejection occurred earlier in the CYP3AP1*1/*3 or *1/*1 group (median 7 d vs. 13 d, p = 0.005). In conclusion, an initial dosing regimen for tacrolimus based on knowledge of the CYP3AP1 genotype and subsequently guided by concentration measurements has the potential to increase the proportion of patients achieving target blood concentrations early after transplantation.     

Determinants of the Magnitude of Interaction Between Tacrolimus and Voriconazole/Posaconazole in Solid Organ Recipients

Administration of azole antifungals to tacrolimus‐treated solid organ recipients results in a major drug–drug interaction characterized by increased exposure to tacrolimus. The magnitude of this interaction is highly variable but cannot currently be predicted. We performed a retrospective analysis of 126 solid organ recipients (95 lung, 31 kidney) co‐treated with tacrolimus and voriconazole (n = 100) or posaconazole (n = 26). Predictors of the change in tacrolimus dose‐corrected trough concentrations (C/D) between baseline and tacrolimus–azole co‐therapy were assessed using linear mixed modeling. Patients were genotyped for relevant polymorphisms in CYP3A4, CYP3A5, MDR1, CYP2C19, POR, and UGT1A4. Tacrolimus C/D increased by a factor 5.0 ± 2.7 (range 1.0–20.2) for voriconazole and 4.4 ± 2.6 (range 0.9–18.0) for posaconazole, suggesting that a 66% dose reduction is insufficient for the majority of patients. Change in C/D was blunted in CYP3A5 expressors (estimated effect: ‐43%, p = 0.017) and affected by hematocrit (+8% per %, p = 0.004), baseline C/D (‐14% per 100% increase, p < 0.001), and age (+1%, p = 0.008). However, the final model explained only 22% of interindividual variability in C/D change. In conclusion, CYP3A5 genotype and several clinical variables were identified as modulators of the tacrolimus–azole interaction, but these did not permit accurate predictions in individual patients.     

Impact of CYP3A5 genomic variances on clinical outcomes among African American kidney transplant recipients

Little is known about the impact of CYP3A5 polymorphisms on transplantation outcomes among African American (AA) kidney transplant recipients (KTRs). To assess this issue, clinical outcomes were compared between AA CYP3A5*1 expressers and nonexpressers. This retrospective cohort study analyzed AA KTRs. Biopsy‐proven acute rejection (BPAR), delayed graft function (DGF), glomerular filtration rate (GFR), infections, and tacrolimus dosing requirements were examined in 106 immunologically high‐risk AA kidney transplant patients over a 2‐year follow‐up period. In CYP3A5*1 expressers compared to nonexpressers, the incidence of BPAR was significantly higher in the first 6 months (13% vs 0%; P = .016) compared to 24 months (13% vs 7%; P = .521). Tacrolimus total daily dose at first therapeutic level was significantly higher in CYP3A5*1 expressers (12 mg/day) compared to nonexpressers (8 mg/day; P < .001). Compared to CYP3A5*1 nonexpressers, DGF incidence was significantly higher among CYP3A5*1 expressers (27.6% vs 6.7%; P = .006). By contrast, median GFR was significantly higher in CYP3A5*1 expressers compared to nonexpressers (54.5 mL/min vs 50.0 mL/min; P = .003) at 24 months. The findings from this retrospective study suggest that AAs with CYP3A5*1 expression require 50% more tacrolimus and have an increased incidence of DGF and acute rejection.     

Influence of CYP3A5 and ABCB1 gene polymorphisms on calcineurin inhibitor‐related neurotoxicity after hematopoietic stem cell transplantation

Yanagimachi M, Naruto T, Tanoshima R, Kato H, Yokosuka T, Kajiwara R, Fujii H, Tanaka F, Goto H, Yagihashi T, Kosaki K, Yokota S. Influence of CYP3A5 and ABCB1 gene polymorphisms on calcineurin inhibitor‐related neurotoxicity after hematopoietic stem cell transplantation.
Clin Transplant 2010: 24: 855–861. © 2009 John Wiley & Sons A/S. Abstract: Background: One severe side effect of calcineurin inhibitors (CNIs: such as cyclosporine [CsA] and tacrolimus [FK506]) is neurotoxicity. CNIs are substrates for CYP3A5 and P‐glycoprotein (P‐gp), encoded by ABCB1 gene. In the present study, we hypothesized that genetic variability in CYP3A5 and ABCB1 genes may be associated with CNI‐related neurotoxicity. Methods: The effects of the polymorphisms, such as CYP3A5 A6986G, ABCB1 C1236T, G2677T/A, and C3435T, associated with CNI‐related neurotoxicity were evaluated in 63 patients with hematopoietic stem cell transplantation. Results: Of the 63 cases, 15 cases developed CNI‐related neurotoxicity. In the CsA patient group (n = 30), age (p = 0.008), hypertension (p = 0.017), renal dysfunction (p < 0.001), ABCB1 C1236T (p < 0.001), and G2677T/A (p = 0.014) were associated with neurotoxicities. The CC genotype at ABCB1 C1236T was associated with it, but not significantly so (p = 0.07), adjusted for age, hypertension, and renal dysfunction. In the FK506 patient group (n = 33), CYP3A5 A6986G (p < 0.001), and ABCB1 C1236T (p = 0.002) were associated with neurotoxicity. At least one A allele at CYP3A5 A6986G (expressor genotype) was strongly associated with it according to logistic regression analysis (p = 0.01; OR, 8.5; 95% CI, 1.4–51.4). Conclusion: The polymorphisms in CYP3A5 and ABCB1 genes were associated with CNI‐related neurotoxicity. This outcome is probably because of CYP3A5 or P‐gp functions or metabolites of CNIs.     

肾移植术后他克莫司神经毒性与CYP3A5基因多态性的相关性研究

目的 总结CYP3A5基因多态性检测与肾移植患者术后他克莫司神经系统毒性的相关性.方法 回顾性分析我院2017年至2020年116例肾移植术后应用他克莫司的患者.采用DNA直接测序法检测患者CYP3A5基因多态性,观察不同基因的患者术后不同时间段的他克莫司药物浓度及神经毒性反应.结果 肾移植术后使用他克莫司的患者神经毒...     

The Prognostic Role of CYP Enzyme in Kidney Transplantation: A Single Centre Experience

BackgroundThe main goal of immunosuppressive agents is to reach a balance of preserving allograft function while minimizing adverse effects. The purpose of our research is to corroborate the role of CYP3A enzyme in developing individual medication therapy via measuring medicine levels in patients’ blood samples.MethodsThis retrospective analysis studies 15 kidney transplant recipients. We carried out genotyping (CYP3A5, CYP3A4) after isolating DNA and RNA in patient and donor blood samples; we also determined CYP3A4 messenger RNA expression in case of recipients. Tacrolimus blood levels, dosage, and tacrolimus concentration normalized by dose and the body weight (C₀/D ratio) were evaluated.ResultsIn this research, recipients were divided into 2 groups based on their CYP3A5 genotype. Those who carry CYP3A5*1 allele (*1/*1 or *1/*3) are CYP3A5 expressors, whereas those who are homozygous for the nonfunctional CYP3A5*3 allele are CYP3A5 nonexpressors. There were 3 patients with functioning CYP3A5 enzyme (patients with CYP3A5*1/*3 genotype) where increased tacrolimus metabolism was expected. Our data show that C₀/D ratio of CYP3A5 nonexpressors was around 3 times higher than of CYP3A5 expressors.Looking at CYP3A4 enzyme, we found 1 patient carried CYP3A4*22/*22 genotype where we expected decreased CYP3A4 expression. It is clear that this patient had adequate therapy medication levels (9.50 μg/L) despite having received very low dosage of tacrolimus (0.03 mg/weight/d).ConclusionsOur results confirmed the importance of determining CYP status of recipients after a transplant because individual differences were observed in tacrolimus treatment that were partly influenced by CYP status of recipients.     

Effect of CYP3A5*1 expression on tacrolimus required dose after liver transplantation: A systematic review and meta‐analysis

We systematically collected eligible data to measure the effect of CYP3A5*1 expression on personalized tacrolimus therapy. Six databases were searched for studies on adult liver transplant recipients and donors of liver graft which reported tacrolimus dose requirement, trough blood concentration, and/or concentration/dose (C/D) ratio in expressers and nonexpressers of CYP3A5*1. Eligible data were pooled by meta‐analysis. Sixteen observational studies (1309 recipients, 1044 donors of liver graft) were included in the analyses. Tacrolimus C/D ratio was lower, and the dose was higher in recipient expressers of CYP3A5*1 and/or carriers of expresser liver graft at 1‐4 weeks and 2‐4, 6, and 12 months post‐transplantation. Tacrolimus blood concentration was lower at the first two weeks. Pair expressers were affected by about twofold, and the effect was different between ethnic groups. CYP3A5*1 expression in recipients increased tacrolimus required dose by 0.023 at first, 0.022 at third, and 0.012 mg/kg/day at sixth month. Its expression in graft tissue increased tacrolimus required dose by 0.024 at first, 0.035 at third, and 0.032 mg/kg/day at sixth month. Considering CYP3A5*1 polymorphism can be helpful in individualization of tacrolimus efficient dose prior to administration, and it can remove initial high‐risk lag time (over/underdose period before reaching target blood level) at first few days post‐transplantation.     

Impact of cytochrome P450 3A and ATP-binding cassette subfamily B member 1 polymorphisms on tacrolimus dose-adjusted trough concentrations among Korean renal transplant recipients

Background

Tacrolimus is a substrate of cytochrome P450 3A (CYP3A) and P-glycoprotein (P-gp), encoded by the CYP3A and ATP-binding cassette subfamily B member 1 (ABCB1) genes, respectively. This study was aimed to investigate the impact of CYP3A and ABCB1 polymorphisms on the tacrolimus pharmacokinetics and clinical outcomes in Korean renal transplant recipients.

Methods

We analyzed data from a cohort of 70 renal transplant recipients receiving tacrolimus. CYP3A4*4, CYP3A4*5, CYP3A4*18, CYP3A5*3, ABCB1 C1236>T, ABCB1 G2677>T/A, and ABCB1 C3435>T polymorphisms were genotyped and correlated to dose-adjusted tacrolimus trough concentration at months 1, 3, 6, and 12 after transplantation.

Results

Patients with the CYP3A5*3 alleles showed higher dose-adjusted tacrolimus concentrations for 12 months and higher trough levels until 6 months after transplantation. ABCB1 polymorphisms and haplotypes were not associated with tacrolimus concentrations. In a multivariate analysis, the presence of ≥1 CYP3A5*3 allele was a significant independent variable affecting dose-adjusted tacrolimus concentrations. Glomerular filtration rate, acute rejection, opportunistic infection, and graft survival were not affected by CYP3A5 polymorphisms. Calcineurin inhibitor toxicity, which showed higher tendency in patients with CYP3A5*1 alleles, might be associated with higher tacrolimus dose per kilogram.

Conclusions

The CYP3A5 genotype is a major factor in determining the dose requirement of tacrolimus, and genotyping may be of value in individualization of immunosuppressive therapy of renal transplant patients.     

Effect of CYP3A5 Genotype on Renal Allograft Recipients Treated With Tacrolimus

Objective

Tacrolimus concentrations are associated with CYP3A5 genotype. The purpose of this study was to evaluate the outcomes and drug concentrations/doses among a posttransplant population with various CYP3A5 genotypes within 12 months.

Methods

Sixty seven kidney recipients receiving immunosuppression with tacrolimus + mycophenolate mofetil + prednisolone were grouped according to their CYP3A5 genotypes (*1/*1; *1/*3; *3/*3). The initial dose of tacrolimus (0.15 mg/kg/d) was adjusted according to achieve a target therapeutic window. All patients underwent a protocol biopsy at 1 month posttransplantation. We assayed serum creatinine and tacrolimus blood trough concentrations to calculate the concentration per dosage during follow-up. We also investigated the incidence of acute rejection episodes and the nephrotoxicity of tacrolimus according to the renal biopsy.

Results

There was no significant difference among serum creatinine concentrations. Tracrolimus blood concentrations showed a significant difference at day 7 and 1 month with no significant difference at 3, 6, or 12 months among the three groups. The CYP3A5*3/*3 group showed the largest concentration per dosage (C/D) and CYP3A5*1/*1, the smallest C/D. There was a significant difference among the three groups. The occurrence of an acute rejection episode within 3 months showed a significant difference among the three groups but not from 3 to 12 months after transplantation. Nephrotoxicity was greatest among the CYP3A5*3/*3 group.

Conclusion

CYP3A5 influenced the blood concentrations of tacrolimus. Our study suggested to choose the initial dosage according to the CYP3A5 genotype to obtain a better outcome and reduce the incidences of acute rejection episodes and nephrotoxicity.     

肾移植受者CYP3A5基因多态性对术后他克莫司药物代谢的影响

目的 研究肾移植受者细胞色素P450 3A(CMP3A)酶系中的CYP3A5基因多态性对术后他克莫司(Tac)药物代谢的影响,并探讨测定CYP3A5基因型的方法 .方法 选取97例肾移植术后常规使用Tac+吗替麦考酚酯+泼尼松三联免疫抑制方案的受者.用焦磷酸测序法测定受者CYP3A5基因型;用均相酶扩大免疫分析法(EMIT)测定受者全血Tac浓度谷值(C0);比较不同基因型的受者肾移植术后第7天、第14天、1个月、3个月和6个月时的Tac C0,与Tac校正剂量的比值(Tac G0/Tac校正剂量).结果 焦磷酸测序法能够快速准确的测定肾移植受者CYP3A5基因型;97例肾移植受者CYP3A5基因型分别为:CYP3A5+1/*1型17例(17.5%),CYP3A5* 1/*3型35例(36.1%),CYP3A5*3/*3型45例(46.4%).CYP3A5*1/*1型和CYP3A5*1/*3型受者肾移植术后Tac G0/Tac校正剂量均显著低于CYP3A5*3/*3型受者.结论 肾移植受者CYP3A5基因型对Tac药物代谢具有显著的影响.采用焦磷酸法测定肾移植受者CYP3A5基因多态性,有助于确定不同个体移植术后理想的Tac起始剂量,实现Tac个体化用药.     

供受体CYP3A5基因多态性与肝移植患者术后他克莫司浓度/剂量比的关系

目的研究肝移植供、受体CYP3A5基因多态性对受者术后他克莫司浓度/剂量比的影响。方法研究对象为2009年2月至6月期间在中山大学附属第三医院肝移植中心接受肝移植手术的32例受者及其对应供体。记录患者术后1周、2周、4周、12周他克莫司用量,并测定相应时间点的他克莫司谷浓度值,计算他克莫司浓度/剂量比。采用聚合酶链反应-限制性内切酶片段长度多态性方法对肝移植供、受体进行CYP3A5基因分型,比较不同基因型对受者术后他克莫司浓度/剂量比的影响。结果供、受者基因型分布比较差异均无统计学意义（P〉0.05）。CYP3A5＊3等位基因总发生频率为76%（97/128）,CYP3A5＊1等位基因总发生频率为24%（31/128）。受者术后2、4、12周他克莫司浓度/剂量比与供体CYP3A5基因型明显相关,与供体为携带＊3/＊3基因型的受者比较,供体为＊1/＊1和＊1/＊3基因型的受者该值明显降低,比较差异有统计学意义（均为P〈0.05）,后两者比较差异无统计学意义（P〉0.05）。术后1、2、4、12周,不同CYP3A5基因型受体的他克莫司浓度/剂量比比较,差异均无统计学意义（均为P〉0.05）。结论供体CYP3A5基因多态性是影响肝移植术后患者他克莫司血药浓度的重要遗传因素。供体携带＊1等位基因,其受者需更高剂量他克莫司才能达到目标血药浓度。     

A pharmacogenetic strategy for immunosuppression based on the CYP3A5 genotype

Pharmacogenetics has the potential to complement therapeutic drug monitoring in achieving target blood concentrations of the immunosuppressive drugs during the critical early period after transplantation when adequate drug exposure is essential to prevent rejection. The most attractive candidate for a pharmacogenetic strategy is tacrolimus dosing based on the CYP3A5 genotype.     

Tacrolimus pharmacogenetics: polymorphisms associated with expression of cytochrome p4503A5 and P-glycoprotein correlate with dose requirement

BACKGROUND: There is marked heterogeneity in blood concentrations of tacrolimus following standard body-weight-based dosing. This is most apparent in black patients, who have a higher dose requirement when compared with other ethnic groups. Differences in intestinal P-glycoprotein and hepatic and intestinal cytochrome P4503A activity have been postulated as contributing to this problem. METHODS: The dose-normalized blood concentrations of tacrolimus at 3 months after renal transplantation were related to CYP3AP1 and multiple drug resistance (MDR)-1 genotypes determined by polymerase chain reaction followed by restriction fragment length polymorphism analysis. RESULTS: We found that a single nucleotide polymorphism in the CYP3AP1 pseudogene (A/G(44)) that previously has been noted to be more common in African Americans and strongly associated with hepatic CYP3A5 activity correlated well with the tacrolimus dose requirement. A weaker association was found for a polymorphism in the MDR-1 gene, which influences intestinal P-glycoprotein expression. CONCLUSIONS: The CYP3AP1 genotype is a major factor in determining the dose requirement for tacrolimus, and genotyping may be of value in planning patient-specific drug dosing.     

Higher number of tacrolimus dose adjustments in kidney transplant recipients who are extensive and intermediate CYP3A5 metabolizers

Kidney transplant recipients carrying the CYP3A5*1 allele have lower tacrolimus troughs, and higher dose requirements compared to those with the CYP3A5*3/*3 genotype. However, data on the effect of CYP3A5 alleles on post-transplant tacrolimus management are lacking. The effect of CYP3A5 metabolism phenotypes on the number of tacrolimus dose adjustments and troughs in the first 6 months post-transplant was evaluated in 78 recipients (64% Caucasians). Time to first therapeutic concentration, percentage of time in therapeutic range (TTR), and estimated glomerular filtration rate (eGFR) were also evaluated. Fifty-five kidney transplant recipients were CYP3A5 poor metabolizers (PM), 17 were intermediate metabolizers (IM), and 6 were extensive metabolizers (EM). Compared to PMs, EMs/IMs had significantly more dose adjustments (6.1 vs. 8.1, p = .015). Overall, 33.82% of trough measurements resulted in a dose change. There was no difference in the number of tacrolimus trough measurements between PMs and EM/IMs. The total daily tacrolimus dose requirements were higher in EMs and IMs compared to PMs (<.001). TTR was ∼50% in the PMs and EMs/IMs groups. CYP3A5 EM/IM metabolizers have more tacrolimus dose changes and higher dose requirements which increases clinical management complexity. Larger studies are needed to assess the cost and benefits of including genotyping data to improve clinical management.