Impact of CYP3A5 and MDR1(ABCB1) C3435T polymorphisms on the pharmacokinetics of tacrolimus in renal transplant recipients

Pharmacogenetics of Calcineurin inhibitors in kidney transplant recipients: the African gap. A narrative review

Calcineurin inhibitors (CNIs) are the mainstay of immunosuppression in kidney transplantation. Interpatient variability in the disposition of calcineurin inhibitors is a well-researched phenomenon and has a well-established genetic contribution. There is great diversity in the makeup of African genomes, but very little is known about the pharmacogenetics of CNIs and transplant outcomes. This review focuses on genetic variants of calcineurin inhibitors' metabolizing enzymes (CYP3A4, CYP3A5), related molecules (POR, PPARA) and membrane transporters involved in the metabolism of calcineurin inhibitors. Given the genetic diversity across the African continent, it is imperative to generate pharmacogenetic data, especially in the era of personalized medicine and emphasizes the need for studies specific to African populations. The study of allelic variants in populations where they have greater frequencies will help answer questions regarding their impact. We aim to fill the knowledge gaps by reviewing existing research and highlighting areas where African research can contribute.

A Population Pharmacokinetic Model to Predict the Individual Starting Dose of Tacrolimus for Tunisian Adults after Renal Transplantation

BACKGROUND

Tacrolimus is the most frequently used immunosuppressive drug for preventing renal rejection. However, its use is hampered by its narrow therapeutic index and large intra and interpatient variability in pharmacokinetics. The objective of this study was to externally validate a tacrolimus population pharmacokinetic model developed for the Dutch population and adjust the model for the Tunisian population for use in predicting the starting dose requirement after kidney transplantation.

METHODS

Data on tacrolimus exposure were obtained from kidney transplant recipients (KTRs) during the first 3 months post-transplantation. External validation of the Dutch model and its adjustment for the Tunisian population was performed using nonlinear mixed-effects modeling.

RESULTS

In total, 1901 whole-blood predose tacrolimus concentrations from 196 adult KTRs were analyzed. According to a visual predictive check, the Dutch model underestimated the starting dose for the Tunisian adult population. The effects of age, together with the CYP3A5*3 and CYP3A4*22 genotypes on tacrolimus clearance were significantly different in the Tunisian population than in the Dutch population. Based on a bodyweight-based dosing, only 21.9% of tacrolimus concentrations were within the target range, whereas this was estimated to be 54.0% with the newly developed model-based dosing. After adjustment, the model was successfully validated internally in a Tunisian population.

CONCLUSIONS

A starting-dose population pharmacokinetic model of tacrolimus for Tunisian KTRs was developed based on a previously published Dutch model. Using this starting dose could potentially increase the percentage of patients achieving target tacrolimus concentrations after the initial starting dose.

The pharmacogenetics of tacrolimus in renal transplant patients: association with tremors, new-onset diabetes and other clinical events

Our study is the first study to investigate the effect of SNPs in CYP3A5, CYP3A4, ABCB1 and POR genes on the incidence of tremors, nephrotoxicity, and diabetes mellitus. A total of 223 renal transplant patients receiving tacrolimus and mycophenolate mofetil (MMF) were recruited. Both adults and children patients participated in the study. Genotyping was performed using PROFLEX-PCR followed by RFLP. MPA and tacrolimus plasma concentrations were measured by immunoassay. The AUC0-12h of MMF was estimated by a Bayesian method. We found a statistically significant association between the CYP3A5*3 and CYP3A4*1B genotypes and the tacrolimus exposure. We found a lower occurrence of nephrotoxicity (p = 0.03), tremor (p = 0.01), and new-onset diabetes (p = 0.002) associated with CYP3A5*1 allele. The CYP3A4*1B allele was significantly associated with a lower occurrence of new-onset diabetes (p = 0.026). The CYP3A5*1 allele was significantly associated with an increased risk of acute and chronic rejection (p = 0.03 and p < 0.001, respectively). Our results support the usefulness of tacrolimus pharmacokinetics in pre-kidney transplant assessments.

The Impact of Single Nucleotide Polymorphisms on the Pharmacokinetics of Tacrolimus in Kidney Allograft Recipients of Northern-West, Iran

Purpose: Calcineurin inhibitors (CNIs) such as tacrolimus are a major immunosuppressive therapy after renal transplantation, which inhibit cytokine expression. The pharmacokinetics of such drugs is influenced by cytochrome P450 (CYP) enzymes, multi-drug resistance-1 (MDR-1), and C25385T pregnane X receptor (PXR). This study aimed to investigate the impact of single nucleotide polymorphisms (SNP) in these genes on the ratio of tacrolimus level per drug dosage (C/D ratio), acute graft rejection, and viral infections. Methods: Kidney transplantation recipients (n=65) under similar immunosuppressive treatment were included. Amplification refractory mutation systempolymerase chain reaction (ARMS-PCR) method was applied to amplify the loci containing the SNPs of interest. Results: Overall, 65 patients with a male/female ratio of 37/28 were included. The mean age was 38±1.75 years. The variant allele frequencies of CYP3A5*3, MDR-1 C3435T, and PXR C25385T were 95.38, 20.77, and 26.92%, respectively. No significant correlations were found between the studied SNPs and the tacrolimus C/D ratios. However, there was a significant difference in the C/D ratios at 2 and 8 weeks in homozygote CYP3A5 *3/*3 carriers (P=0.015). No significant association was found between the studied polymorphisms and viral infections and acute graft rejection (P>0.05). Conclusion: Homozygote CYP3A5 *3/*3 genotype could influence the tacrolimus metabolism rate (C/D ratio).

Use of Pharmacogenetics to Optimize Immunosuppressant Therapy in Kidney-Transplanted Patients

Immunosuppressant drugs (ISDs) are routinely used in clinical practice to maintain organ transplant survival. However, these drugs are characterized by a restricted therapeutic index, a high inter- and intra-individual pharmacokinetic variability, and a series of severe adverse effects. In particular, genetic factors have been estimated to play a role in this variability because of polymorphisms regarding genes encoding for enzymes and transporters involved in the ISDs pharmacokinetic. Several studies showed important correlations between genetic polymorphisms and ISDs blood levels in transplanted patients; therefore, this review aims to summarize the pharmacogenetics of approved ISDs. We used PubMed database to search papers on pharmacogenetics of ISDs in adults or pediatric patients of any gender and ethnicity receiving immunosuppressive therapy after kidney transplantation. We utilized as search term: “cyclosporine or tacrolimus or mycophenolic acid or sirolimus or everolimus and polymorphism and transplant”. Our data showed that polymorphisms in CYP3A5, CYP3A4, ABCB1, and UGT1A9 genes could modify the pharmacokinetics of immunosuppressants, suggesting that patient genotyping could be a helpful strategy to select the ideal ISDs dose for each patient.

Design, synthesis, and bioactivity evaluation of macrocyclic benzo[b]pyrido[4,3-e][1,4]oxazine derivatives as novel Pim-1 kinase inhibitors

Pim-1 kinase is a serine/threonine kinase which is vital in many tumors. The Pim-1 inhibitor 10-DEBC and its derivatives discovered in our previous work were modified through macrocyclization strategy. A series of benzo[b]pyridine[4,3-e][1,4]oxazine macrocyclic compounds were designed, synthesized, and evaluated as novel Pim-1 kinase inhibitors. Among these compounds, compound H5 exhibited the highest activity with an IC₅₀ value of 35 nM. In addition, the crystal complex structure of Pim-1 kinase bound with compound H3 was determined, and the structure-activity relationship of these macrocyclic compounds was analyzed, which provides the structural basis of further optimization of novel macrocyclic Pim-1 kinase inhibitors..

Assessment of the Link of ABCB1 and NR3C1 gene polymorphisms with the prednisolone resistance in pediatric nephrotic syndrome patients of Bangladesh: A genotype and haplotype approach

Introduction

Nephrotic syndrome is a common pediatric kidney disease. Investigations on several genetic polymorphisms revealed an inconsistent influence on the resistance of patients to steroids.

Objectives

This study aimed to identify the association of ABCB1 (1236C > T, 2677G > T, 3435C > T), NR3C1 (rs10482634, rs6877893), and CYP3A5 (CYP3A5*3) gene polymorphism as well as sociodemographic and clinicopathological parameters with the risk of developing prednisolone resistance in pediatric patients with nephrotic syndrome.

Methods

A case-control analysis was performed on 180 nephrotic syndrome patients. Among them, 30 patients were classified as prednisolone resistant group, and 150 were classified as prednisolone sensitive group. Genotyping was performed by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method.

Results

No significant association of 1236C > T polymorphism with the risk of prednisolone resistance (p > 0.05) was found. The GT heterozygous of 2677G > T was found to be significantly associated with the development of prednisolone resistance (OR = 3.9, p = 0.034). In the case of 3435C > T, a statistically significant association was observed in TC heterozygous and TT mutant homozygous genotypes (OR = 0.38, p = 0.047; OR = 3.06, p = 0.038, respectively) with prednisolone resistance. For rs10482634 polymorphism, the AG heterozygous and AG+GG genotypes were significantly linked with prednisolone resistance (OR = 2.40, p = 0.033; OR = 2.36, p = 0.034, respectively). We found no association with the risk of prednisolone resistance with rs6877893 and CYP3A5*3 polymorphism (p > 0.05). CTC and TGT haplotypes of ABCB1 and GA haplotype of NR3C1 were also associated with the increased risk of pediatric prednisolone resistance (OR = 4.47, p = 0.0003; OR = 2.71, p = 0.03; and OR = 4.22, p = 0.022, consecutively). We also observed the correlation of different sociodemographic and clinicopathological factors with prednisolone resistance in pediatric nephrotic syndrome.

Conclusion

Our findings showed a significant association of ABCB1 and NR3C1 gene polymorphisms with prednisolone resistant pediatric nephrotic syndrome.

Extrapolation of physiologically based pharmacokinetic model for tacrolimus from renal to liver transplant patients

Physiologically based pharmacokinetic (PBPK) modeling is useful for evaluating differences in drug exposure among special populations, but it has not yet been employed to evaluate the absorption process of tacrolimus. In this study, we developed a minimal PBPK model with a compartmental absorption and transit model for renal transplant patients using available data in the literature and clinical data from our hospital. The effective permeability value of tacrolimus absorption and parameters for the single adjusting compartment were optimized via sensitivity analyses, generating a PBPK model of tacrolimus for renal transplant patients with good predictability. Next, we extrapolated the pharmacokinetics of tacrolimus for liver transplant patients by changing the population demographic parameters of the model. When the physiological parameters of a population with normal liver function were changed to those of a population with impaired hepatic function (Child-Pugh class A) in the constructed renal transplant PBPK model, the predicted tacrolimus concentrations were consistent with the observed concentrations in liver transplant patients. In conclusion, the constructed tacrolimus PBPK model for renal transplant patients could predict the pharmacokinetics in liver transplant patients by slightly reducing the hepatic function, even at three weeks post-transplantation.

Temporary decrease in tacrolimus clearance in cytochrome P450 3A5 non-expressors early after living donor kidney transplantation: Effect of interleukin 6-induced suppression of the cytochrome P450 3A gene

Tacrolimus is important for immunosuppression in kidney transplantation. In this historical cohort and in vitro study, we evaluated the changes in tacrolimus pharmacokinetics early after living donor kidney transplantation and the effects of interleukin (IL)-6 on cytochrome P450 3A4 (CYP3A4) and cytochrome P450 3A5 (CYP3A5) expression. In the historical cohort study, 22 patients who met the inclusion criteria were classified into CYP3A5 expressors and non-expressors (n = 16 and 6, respectively). The blood tacrolimus concentration per dose ratio (C/D) temporarily increased post-kidney transplantation on days 3-4 only in CYP3A5 non-expressors. The effects of IL-6 on CYP3A4 and CYP3A5 expression were also investigated in vitro using HepG2 and Caco-2 cells. IL-6 induced a significant concentration- and time-dependent decrease in CYP3A4 and CYP3A5 expression in both cells. The mean CYP3A4 expression level at 12 hours after IL-6 exposure (% of 0 hour) was 44.0 and 62.6 in HepG2 and Caco-2 cells, respectively, whereas the CYP3A5 expression level was 30.7 and 52.4, respectively. We hypothesize that CYP3A5 non-expressors might exhibit a temporary decrease in the oral clearance of tacrolimus via an increase in serum IL-6 concentrations early after kidney transplantation. These results may help develop strategies to improve kidney transplant outcome.

Individualized treatment based on CYP3A5 single-nucleotide polymorphisms with tacrolimus in ulcerative colitis

Background/Aims

The pharmacokinetics of tacrolimus (TAC) is known to be largely influenced by single-nucleotide polymorphisms (SNPs) in CYP3A5. Patients starting TAC require careful dose adjustment, owing to the wide range of optimal dosages, depending on their CYP3A5 expression status. Here, we evaluated whether individualization of TAC dosages based on CYP3A5 SNPs would improve its therapeutic efficacy in ulcerative colitis.

Methods

Twenty-one patients were prospectively treated, with their initial dosage adjusted according to their CYP3A5 status (0.1, 0.15, and 0.2 mg/kg/day for CYP3A5*3/*3, CYP3A5*1/*3, and CYP3A5*1/*1, respectively). Their clinical outcomes were compared with those of patients treated with a fixed dose (0.1 mg/kg/day).

Results

The first blood trough level of CYP3A5 expressors, CYP3A5*1/*3 or CYP3A5*1/*1, and the overall rate in achieving the target blood trough level within a week in the individualized-dose group were significantly higher than those in the fixed-dose group (5.15±2.33 ng/mL vs. 9.63±0.79 ng/mL, P=0.035 and 12.5% vs. 66.7%, P=0.01). The remission rate at 2 weeks in the expressors was as high as that in the nonexpressors, CYP3A5*3/*3, in the individualized-dose group.

Conclusions

Individualized TAC treatment is effective against ulcerative colitis regardless of the CYP3A5 genotype.

Influence of CYP3A5 and ABCB1 Polymorphism on Tacrolimus Drug Dosing in South Indian Renal Allograft Recipients

Introduction:

Tacrolimus blood levels are influenced by polymorphisms involving Cytochrome 3A subfamily (CYP3A5) and P-Glycoprotein (ABCB-1) genes. However, their role in transplant outcomes was less studied in South Indian population. We studied the prevalence and impact of these polymorphisms in renal transplant recipients from South India.

Methods:

An analysis of CYP3A5, ABCB1 genotype done in 101 renal transplant recipients by polymerase chain reaction was correlated with blood tacrolimus trough levels (CLIA method), weight, concentration/dose (L/D) ratio, incidence of biopsy proven early acute rejections, and tacrolimus toxicity.

Results:

Prevalence of CYP3A5*1/*1, *1/*3 and *3/*3 and ABCB1 (3435C>T) TT, CT, CC genotypes were 12 (11.9%), 48 (47.5%), 41 (40.6%) and 16 (15.8%), 45 (44.6%), 40 (39.6%), respectively. Mean tacrolimus level, median concentration/dose (L/D) ratio were significantly lower in homozygous (CYP3A5*1/*1-6.01 ng/mL; 48.99 ng/mL/mg/kg/day) and heterozygous expresser group (CYP3A5*1/*3-5.84 ng/mL; 68.93 ng/mL/mg/kg/day) when compared with nonexpresser group [CYP3A5*3/*3-7.46 ng/mL (P < 0.001);181.3 ng/mL/mg/kg/day (P < 0.05]. No significant differences observed between the ABCB1 genotypic groups. Incidence of early acute rejections (30% vs. 9.76%; P 0.016) and tacrolimus-related toxicity (14.6% vs. 5%; P 0.039) were significantly higher in CYP3A5 expressers and nonexpressers, respectively. No correlation observed between the ABCB1 polymorphisms between rejection episodes or tacrolimus renal toxicity. Among 101 patients, 40.6% were non-expressers (poor metabolizers) (*3/*3).

Conclusions:

CYP3A5 polymorphisms correlated with tacrolimus dose requirements and blood levels, incidence of early acute rejection, and tacrolimus nephrotoxicity. CYP3A5 polymorphism analysis prior to renal transplant will aid more precise early tacrolimus dose calculation to balance between rejection and toxicity.

Effect of CYP3A4, CYP3A5, and ABCB1 Polymorphisms on Intravenous Tacrolimus Exposure and Adverse Events in Adult Allogeneic Stem Cell Transplant Patients

Pharmacogenetics influences oral tacrolimus exposure; however, little data exist regarding i.v. tacrolimus. We investigated the impact of genetic polymorphisms in CYP3A4, CYP3A5, and ABCB1 on i.v. tacrolimus exposure and toxicity in adult patients receiving an allogeneic hematopoietic stem cell transplant for hematologic malignancies. Germline DNA was extracted from buccal swabs and genotyped for CYP3A4, CYP3A5, and ABCB1 polymorphisms. Continuous i.v. infusion of tacrolimus .03 mg/kg/day was initiated on day +5 post-transplant, and steady-state blood concentrations were measured 4days later. We evaluated the association between phenotypes and prevalence of nontherapeutic target concentrations (below or above 5 to 15 ng/mL) as well as tacrolimus-related toxicities. Of 63 patients, 28.6% achieved the target concentration; 71.4% were >15ng/mL, which was more common in CYP3A4 intermediate/normal metabolizers (compared with rapid) and those with at least 1 ABCB1 C2677T loss-of-function allele (P < .05). ABCB1 C2677T was significantly associated with concentrations >15ng/mL (odds ratio, 6.2; 95% confidence interval, 1.8 to 23.6; P = .004) and tacrolimus-related toxicities (odds ratio, 7.5; 95% confidence interval, 1.6 to 55.2; P = .02). ABCB1 C2677T and CYP3A4 are important determinants of i.v. tacrolimus exposure, whereas ABCB1 C2677T also impacts tacrolimus-related toxicities in stem cell transplants.

Effectiveness of Measuring Genetic Polymorphisms in Metabolizing Enzymes of Tacrolimus within One Medical Facility

OBJECTIVES

Because genetic polymorphisms cause diverse activity in drug metabolizing enzymes, drug concentrations in the blood may be variable among patients. We analyzed the genotypes of CYP3A5 and MDR1, and investigated their relationship with whole blood drug concentrations.

METHODS

Eight patients were administered an oral dose of tacrolimus for one week or longer prior to enrollment in this study. Whole blood concentrations for tacrolimus were measured 12 hours post oral administration, on the same day as genotyping, within our hospital using a fully automated gene analyzer. The procedures became so rapid that collection of blood samples could be completed within the same day (approximately one hour).

RESULTS

The genotype frequency of CYP3A5 was ^*3/^*3 in five patients, ^*1/^*3 in two patients, and ^*1/^*1 in one patient. All five patients with ^*3/^*3 showed favorable increases in tacrolimus blood concentrations. In the two patients with ^*1/^*3, an increase in tacrolimus blood concentration was not readily achieved in one patient, but increased favorably in the other patient. In the patient with ^*1/^*1, tacrolimus was not detectable in the patient's blood. A favorable treatment effect was obtained by changing tacrolimus to cyclosporine. It is notable that genotypes in patients where tacrolimus was not detected in the blood were wild types: 2677G/G and 3435C/C in MDR1.

CONCLUSIONS

The measurement of genetic polymorphisms in metabolizing enzymes of tacrolimus, within one medical facility, is applicable for the selection of immunosuppressants and individual dosing for the treatment of autoimmune disease.

Economic Evaluation of Pharmacogenetic Tests in Patients Subjected to Renal Transplantation: A Review of Literature

Renal transplantation is the treatment of choice for the patients with end-stage renal failure. Genetic factors, among others, can influence variability in response to immunosuppressive drugs. Nowadays, due to restrictive health resources, the question arises whether routine pharmacogenetic analyses should be done in the renal transplant recipients or not. The aim of this literature review was to present the up-to-date information considering the economic feasibility of pharmacogenetic testing in patients subjected to renal transplantation. The organization United Network for Organ Sharing in the US estimated that total costs per renal transplant concerning these analyses were $334,300 in 2014. Pharmacogenetic testing prior to treatment initiation could be helpful to predict and assess treatment response and the risks for adverse drug reactions. This kind of testing before treatment initiation seems to be one of the most promising applications of pharmacokinetics. Although pharmacogenetic tests were found to be a cost-effective or cost-saving strategy in many cases, some authors represent another opinion. However, if the real costs of renal transplantation are recognized, the application of these tests in the standard daily practice could be considered more realistic, which additionally emphasizes the importance of future studies assessing their cost effectiveness.

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.

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.

Investigation of CYP 3A5 and ABCB1 gene polymorphisms in the long-term following renal transplantation: Effects on tacrolimus exposure and kidney function

The clinical use of tacrolimus (Tac) is complicated by the large inter-individual variability in its pharmacokinetics as well as by chronic adverse effects on renal function. The main goal of this study was to evaluate the potential influence of cytochrome P450 3A5 (CYP 3A5) and ATP-binding cassette transporter B1 (ABCB1) gene polymorphisms on Tac dose requirements and dose-adjusted concentrations in different long-term periods following renal transplantation. Another aim was to investigate whether these polymorphisms affect renal function in late post-transplant period. A total of 91 renal transplant recipients were enrolled for genotyping analysis, and 53 of these entered into a pharmacokinetic-pharmacogenetic study. Allele-specific polymerase chain reaction was used for CYP 3A5 and ABCB1 polymorphism determination. Pharmacokinetic data (dose, trough concentration and dose-adjusted concentration of Tac) and renal function parameters [creatinine (Cre) clearance and serum Cre level] were analyzed in relation to patient genotype at 6, 12 and 24 months after transplantation. Also, linear regression analysis was performed to evaluate the effect of CYP 3A5 and ABCB1 genotypes on Tac exposure and renal function up to 24 months post-transplant. Individuals carrying the CYP 3A5*1/*3 genotype had higher Tac dose requirements than CYP 3A5*3/*3 carriers at 6, 12 and 24 months after renal transplantation. The results revealed that ABCB1 polymorphism did not influence Tac dose requirements independently. Regression analysis showed that CYP 3A5 influenced the Tac dose-adjusted concentration as well as renal function up to 24 months post-transplant. These findings confirmed that CYP 3A5 polymorphism represents the most important determinant of Tac dose and exposure in the late period following renal transplantation. Furthermore, the obtained results indicate that the decline in renal function may be more pronounced in patients with CYP 3A5*1 in the long-term period after renal transplantation.

Choosing the right dose of tacrolimus

Choosing the right dose of tacrolimus 'adapted to each individual patient' is a central question after transplantation. The pharmacokinetic behaviour of tacrolimus in paediatric patients is significantly influenced by clinical factors growth and maturation, as well as genetic factors. Large interindividual variability and narrow therapeutic index make dosage individualisation mandatory in children. CYP3A5 expressers require a 1.8-fold higher tacrolimus dose than non-expressers. A visual patient-tailored dosing chart, taking into consideration the child's weight, recent haematocrit level and CYP3A5 genotype, was developed based on a population pharmacokinetic-pharmacogenetic model, and can be used routinely to individualise tacrolimus starting dose. Area under the concentration-time curve-based dosage adaptation through limited sampling strategy and Bayesian estimation is more reliable than trough concentration. Therapeutic drug monitoring and dosage adaptation can be included in routine post-transplantation consultation and should be considered in the urgent situations (eg, rejection, adverse event, lack of compliance, change of coadministration drug with potential drug-drug interaction and other situations).

Personalization of the immunosuppressive treatment in renal transplant recipients: the great challenge in "omics" medicine

Renal transplantation represents the most favorable treatment for patients with advanced renal failure and it is followed, in most cases, by a significant enhancement in patients’ quality of life. Significant improvements in one-year renal allograft and patients’ survival rates have been achieved over the last 10 years primarily as a result of newer immunosuppressive regimens. Despite these notable achievements in the short-term outcome, long-term graft function and survival rates remain less than optimal. Death with a functioning graft and chronic allograft dysfunction result in an annual rate of 3%–5%. In this context, drug toxicity and long-term chronic adverse effects of immunosuppressive medications have a pivotal role. Unfortunately, at the moment, except for the evaluation of trough drug levels, no clinically useful tools are available to correctly manage immunosuppressive therapy. The proper use of these drugs could potentiate therapeutic effects minimizing adverse drug reactions. For this purpose, in the future, “omics” techniques could represent powerful tools that may be employed in clinical practice to routinely aid the personalization of drug treatment according to each patient’s genetic makeup. However, it is unquestionable that additional studies and technological advances are needed to standardize and simplify these methodologies.

Clinical implementation of pharmacogenetics in kidney transplantation: calcineurin inhibitors in the starting blocks

Pharmacogenetics has generated many expectations for its potential to individualize therapy proactively and improve medical care. However, despite the huge amount of reported genetic associations with either pharmacokinetics or pharmacodynamics of drugs, the translation into patient care is still slow. In fact, strong evidence for a substantial clinical benefit of pharmacogenetic testing is still limited, with a few exceptions. In kidney transplantation, established pharmacogenetic discoveries are being investigated for application in the clinic to improve efficacy and to limit toxicity associated with the use of immunosuppressive drugs, especially the frequently used calcineurin inhibitors (CNIs) tacrolimus and ciclosporin. The purpose of the present review is to picture the current status of CNI pharmacogenetics and to discuss the most promising leads that have been followed so far.

Relative contributions of cytochrome CYP3A4 versus CYP3A5 for CYP3A-cleared drugs assessed in vitro using a CYP3A4-selective inactivator (CYP3cide)

Metabolism by cytochrome P4503A (CYP3A) is the most prevalent clearance pathway for drugs. Designation of metabolism by CYP3A commonly refers to the potential contribution by one or both of two enzymes, CYP3A4 and CYP3A5. The metabolic turnover of 32 drugs known to be largely metabolized by CYP3A was examined in human liver microsomes (HLMs) from CYP3A5 expressers (*1/*1 genotype) and nonexpressers (*3/*3 genotype) in the presence and absence of ketoconazole and CYP3cide (a selective CYP3A4 inactivator) to calculate the contribution of CYP3A5 to metabolism. Drugs with the highest contribution of CYP3A5 included atazanavir, vincristine, midazolam, vardenafil, otenabant, verapamil, and tacrolimus, whereas 17 of the 32 tested showed negligible CYP3A5 contribution. For specific reactions in HLMs from *1/*1 donors, CYP3A5 contributes 55% and 44% to midazolam 1'- and 4-hydroxylation, 16% to testosterone 6β-hydroxylation, 56% and 19% to alprazolam 1'- and 4-hydroxylation, 10% to tamoxifen N-demethylation, and 58% to atazanavir p-hydroxylation. Comparison of the in vitro observations to clinical pharmacokinetic data showed only a weak relationship between estimated contribution by CYP3A5 and impact of CYP3A5 genotype on oral clearance, in large part because of the scatter in clinical data and the low numbers of study subjects used in CYP3A5 pharmacogenetics studies. These data should be useful in guiding which drugs should be evaluated for differences in pharmacokinetics and metabolism between subjects expressing CYP3A5 and those who do not express this enzyme.

Effect of MDR1 polymorphisms on the blood concentrations of tacrolimus in Turkish renal transplant patients

BACKGROUND

Tacrolimus, a calcineurin inhibitör, is prescribed to prevent allograft rejection in renal transplantation. Tacrolimus not only has a narrow therapeutic index, but also shows significant interindividual differences. The absorption and metabolism of this drug are affected by multidrug resistance (MDR) 1 gene polymorphisms that correlated with single-nucleotide polymorphisms (SNPs) affecting in vivo P-glycoprotein activity. This study investigated associations of MDR1 gene C3435T polymorphism with tacrolimus blood concentrations and dose requirements as well as acute rejection episodes among Turkish renal transplant patients.

METHODS

One hundred living-donor transplant recipients and 150 healthy control subjects underwent C3435T genotyping using polymerase chain reaction-restriction fragment length polymorphism. Blood concentrations of tacrolimus were determined with the cloned enzyme donor immunoassay.

RESULTS

The CC, CT, and TT genotype frequencies among patients were, respectively, 44.0%, 33.0%, and 23.0% versus 36.7%, 43.3%, and 20.0% among control subjects. There was no significant difference between (P = .061; P = .102; P = .211; respectively). The ratio of blood concentration to dose of tacrolimus for patients with mutant homozygous 3435 TT genotype was higher than that of wild-type 3435 CC genotype homozygous individuals. The doses for these patients were lower at 1, 3, and 12 months (P = .048; P = .03; P = .041, respectively). There were no significant differences between the groups regarding coprescription of drugs that affect tacrolimus concentrations, such as diltiazem. Acute rejection episodes were not associated with the CC vs CT or TT genotypes: odds ratio (OR), 0.517 (95% confidence interval [CI], 0.190-1.407; P = .192); OR 1.558 (95% CI, 0.587-4.136; P = .372); OR 1.346; (95% CI, 0.456-3.968; P = .590), respectively.

CONCLUSIONS

Determination of MDR1 polymorphism may help to achieve target of tacrolimus blood concentrations.

Macrocyclic drugs and clinical candidates: what can medicinal chemists learn from their properties?

Macrocycles are ideal in efforts to tackle "difficult" targets, but our understanding of what makes them cell permeable and orally bioavailable is limited. Analysis of approximately 100 macrocyclic drugs and clinical candidates revealed that macrocycles are predominantly used for infectious disease and in oncology and that most belong to the macrolide or cyclic peptide class. A significant number (N = 34) of these macrocycles are administered orally, revealing that oral bioavailability can be obtained at molecular weights up to and above 1 kDa and polar surface areas ranging toward 250 Å(2). Moreover, insight from a group of "de novo designed" oral macrocycles in clinical studies and understanding of how cyclosporin A and model cyclic hexapeptides cross cell membranes may unlock wider opportunities in drug discovery. However, the number of oral macrocycles is still low and it remains to be seen if they are outliers or if macrocycles will open up novel oral druggable space.

Effect of CYP3A5, CYP3A4, and ABCB1 genotypes as determinants of tacrolimus dose and clinical outcomes after heart transplantation

BACKGROUND

Tacrolimus (Tac) is mainly metabolized by cytochrome P450 3A isoenzymes. In a cohort of heart transplant recipients, we investigated the effect of CYP3A5, CYP3A4, and ABCB1/MDR1 polymorphisms on Tac dose requirements and the risk of developing new-onset diabetes after transplantation (NODAT).

METHODS

A total of 65 heart transplant recipients were genotyped for 3 single nucleotide polymorphisms (SNPs) in the CYP3A5 (SNP rs776746), CYP3A4 (SNP rs2740574), and ABCB1 (SNP rs104564). The mean Tac dose values were compared between the genotypes.

RESULTS

CYP3A5 3 homozygotes (nonexpressers; n = 55, 85%) received significantly higher Tac dose compared with CYP3A5 1 carriers (expressers). No different NODAT frequencies were found between the genotypes.

CONCLUSIONS

The CYP3A5 polymorphism was the main determinant of Tac dose requirements among heart transplant recipients. This common functional polymorphism had no influence on the risk of developing NODAT.

Pharmacokinetics of tacrolimus during pregnancy

BACKGROUND

Information on the pharmacokinetics of tacrolimus during pregnancy is limited to case reports despite the increasing number of pregnant women being prescribed tacrolimus for immunosuppression.

METHODS

Blood, plasma, and urine samples were collected over 1 steady-state dosing interval from women treated with oral tacrolimus during early to late pregnancy (n = 10) and postpartum (n = 5). Total and unbound tacrolimus as well as metabolite concentrations in blood and plasma were assayed by a validated liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) method. A mixed-effect linear model was used for comparison across gestational age and using postpartum as the reference group.

RESULTS

The mean oral clearance (CL/F) based on whole-blood tacrolimus concentration was 39% higher during mid-pregnancy and late pregnancy compared with postpartum (47.4 ± 12.6 vs. 34.2 ± 14.8 L/h, P < 0.03). Tacrolimus-free fraction increased by 91% in plasma (f(P)) and by 100% in blood (f(B)) during pregnancy (P = 0.0007 and 0.002, respectively). Increased fP was inversely associated with serum albumin concentration (r = -0.7, P = 0.003), which decreased by 27% during pregnancy. Pregnancy-related changes in f(P) and f(B) contributed significantly to the observed gestational increase in tacrolimus whole-blood CL/F (r² = 0.36 and 0.47, respectively, P < 0.01). In addition, tacrolimus whole-blood CL/F was inversely correlated with both hematocrit and red blood cell counts, suggesting that binding of tacrolimus to erythrocytes restricts its availability for metabolism. Treating physicians increased tacrolimus dosages in study participants during pregnancy by an average of 45% to maintain tacrolimus whole-blood trough concentrations in the therapeutic range. This led to striking increases in unbound tacrolimus trough concentrations and unbound area under the concentration-time curve, by 112% and 173%, respectively, during pregnancy (P = 0.02 and 0.03, respectively).

CONCLUSIONS

Tacrolimus pharmacokinetics are altered during pregnancy. Dose adjustment to maintain whole-blood tacrolimus concentration in the usual therapeutic range during pregnancy increases circulating free drug concentrations, which may impact clinical outcomes.

Validation of tacrolimus equation to predict troughs using genetic and clinical factors

AIM

Tacrolimus is an immunosuppressant used in transplantation. This article reports the validation of the authors' recently developed genetics-based tacrolimus equation that predicts troughs.

METHODS

Validation was performed in an independent cohort of 795 kidney transplant recipients receiving tacrolimus. The performance of the equation to predict initial troughs was assessed by calculating the bias and precision of the equation. For all troughs in the first 6 months post-transplant, a comparison was made between the troughs predicted using the equation versus those predicted using a basic apparent clearance model with no covariates.

RESULTS

For initial troughs, the equation had a low bias (0.2 ng/ml) and high precision (1.8 ng/ml). For all troughs, the equation predicted troughs significantly better than the basic apparent clearance model.

CONCLUSION

The tacrolimus equation had good bias and precision in predicting initial troughs and performed better than a basic apparent clearance model for all the troughs.

Genetic polymorphisms influence the steroid treatment of children with idiopathic nephrotic syndrome

BACKGROUND

Idiopathic nephrotic syndrome (INS) is the most frequent type of nephrotic syndrome that occurs in children. Its response to treatment with steroids varies. The aim of this study was to analyze the correlation between steroid metabolism-related genes and the response to steroid treatment.

METHODS

The patient cohort comprised 74 children with INS, of whom were 58 steroid-sensitive (SS) cases and 16 steroid-resistant (SR) cases. The genetic polymorphisms analyzed were those of the CYP3A5 gene (A6986G) and ABCB1 gene (C1236T, G2677T/A, and C3435T), and the polymorphisms between SS and SR children were compared.

RESULTS

C1236T in ABCB1 was associated with steroid resistance in INS children [odds ratio (OR) 2.65, 95 % confidence interval (CI) 1.01-6.94; p = 0.042] The frequency of the T allele was significantly higher in SR subjects than in SS subjects (0.81 vs. 0.62, respectively). A6986G in CYP3A5 showed a trend of association, but this association did not reach statistical significance (OR 2.63, 95 % CI 0.94-7.37; p = 0.059). No significant correlation was found between treatment response and G2677T/A or C3435T in ABCB1.

CONCLUSIONS

Our results indicate that among our pediatric patients with INS the C1236T polymorphism in the ABCB1 gene was associated with steroid resistance, while the A6986G polymorphism in the CYP3A5 gene showed a trend of association, but did not reach statistical significance, requiring further analysis.

Meta-analysis of the effect of MDR1 C3435 polymorphism on tacrolimus pharmacokinetics in renal transplant recipients

BACKGROUND

The published data revealed conflicting results of the polymorphism of MDR1 exon 26 SNP C3435T on the pharmacokinetics of tacrolimus in different post transplant times; thus, the aim was to perform a meta-analysis of different post transplant times to investigate the influence of SNP C3435T on the tacrolimus pharmacokinetics.

METHODS

A literature search was conducted to locate the relevant papers by using the PUBMED and EMBASE electronic source until 2011. The pharmacokinetic parameters, including dose administration, concentration and concentration to dose ratio were extracted and a meta-analysis was performed by using STATA10.0.

RESULTS

A total of 13 papers concerning 1327 individuals were included in the meta-analysis. The overall results showed SNP C3435T could influence the pharmacokinetic parameters in different post transplant times, the subjects with CC genotype had lower concentration dose ratio and need higher tacrolimus dose than the CT and TT genotype.

CONCLUSIONS

Our meta-analysis of available studies has demonstrated a definite correlation between the SNP C3435T in MDR1 gene and pharmacokinetics of tacrolimus. However, additional studies with large sample size and better study designs are warranted to verify our finding.

Dosing equation for tacrolimus using genetic variants and clinical factors

AIM

To develop a dosing equation for tacrolimus, using genetic and clinical factors from a large cohort of kidney transplant recipients. Clinical factors and six genetic variants were screened for importance towards tacrolimus clearance (CL/F).

METHODS

Clinical data, tacrolimus troughs and corresponding doses were collected from 681 kidney transplant recipients in a multicentre observational study in the USA and Canada for the first 6 months post transplant. The patients were genotyped for 2,724 single nucleotide polymorphisms using a customized Affymetrix SNP chip. Clinical factors and the most important SNPs (rs776746, rs12114000, rs3734354, rs4926, rs3135506 and rs2608555) were analysed for their influence on tacrolimus CL/F.

RESULTS

The CYP3A5*1 genotype, days post transplant, age, transplant at a steroid sparing centre and calcium channel blocker (CCB) use significantly influenced tacrolimus CL/F. The final model describing CL/F (l h(-1)) was: 38.4 ×[(0.86, if days 6-10) or (0.71, if days 11-180)]×[(1.69, if CYP3A5*1/*3 genotype) or (2.00, if CYP3A5*1/*1 genotype)]× (0.70, if receiving a transplant at a steroid sparing centre) × ([age in years/50](-0.4)) × (0.94, if CCB is present). The dose to achieve the desired trough is then prospectively determined using the individuals CL/F estimate.

CONCLUSIONS

The CYP3A5*1 genotype and four clinical factors were important for tacrolimus CL/F. An individualized dose is easily determined from the predicted CL/F. This study is important towards individualization of dosing in the clinical setting and may increase the number of patients achieving the target concentration. This equation requires validation in an independent cohort of kidney transplant recipients.

Lower tacrolimus daily dose requirements and acute rejection rates in the CYP3A5 nonexpressers than expressers

BACKGROUND

CYP3A5 genetic polymorphisms contribute to marked interindividual differences in the metabolism of and response to tacrolimus in humans.

OBJECTIVE

This study was aimed to clarify the impact of the CYP3A5*3 variant on tacrolimus dose requirements and acute rejection rates in patients with organ transplantation.

METHODS

A literature search was performed up to August 2009 by using the Cochrane library, PubMed, Medline, and EMBase.

RESULTS

Twenty-three studies (a total of 1779 patients) were included in this meta-analysis. Eighteen studies (1443 patients) were involved in renal transplantation and five studies (336 patients) in liver transplantation. Results of meta-analysis demonstrated that, in renal transplant patients, despite the presence of significant heterogeneity, CYP3A5 expressers required higher mean tacrolimus daily doses by 0.045 mg/kg (95% confidence interval (CI), 0.033-0.056) than nonexpressers. Furthermore, sub-analysis of the time of posttransplantation showed that CYP3A5 expressers required higher daily doses than nonexpressers by 0.010, 0.084, 0.041, 0.037, and 0.044 mg/kg at week 2, and at month 1, 3, 6, and 12, respectively. Subset analysis of the ethnicity of organ recipients indicated that mean tacrolimus daily doses were 0.056, 0.037, and 0.077 mg/kg higher in CYP3A5 expressers than non- expressers for white, Chinese, and Japanese patients, respectively. In contrast, for liver transplant patients, higher tacrolimus daily doses were required not only in CYP3A5 expressers of the organ donors than nonexpressers by 0.024 mg/kg (95% CI, 0.019-0.028), but also in CYP3A5 expresser of the organ recipients than nonexpresser by 0.012 mg/kg (95% CI, 0.005-0.018). However, a significant difference in the acute organ rejection rate was observed only at one month (odds ratio, 3.27; 95% CI, 1.57-6.81; P=0.002).

CONCLUSION

Tacrolimus daily dose requirements may vary with the presence of the CYP3A5*3 variant, ethnicity of the organ recipients, and the time of posttransplantation. In addition, the acute organ rejection rate may be higher in CYP3A5 expressers than nonexpressers over the first month after transplantation.

Pharmacogenetics and individualized therapy in children: immunosuppressants, antidepressants, anticancer and anti-inflammatory drugs

Pharmacogenetic polymorphisms that change the amino acid sequences in coding regions only account for part of the interindividual differences in disease susceptibility and drug response. Additional pharmacogenomic and epigenetic factors are also involved. In children, pharmacogenetic studies are limited, although it has been clear for many years that the interactions between developmental patterns of drug-metabolizing enzymes and transporters have a major impact on dose exposure with age-specific dosage requirements. This article will analyze the factors affecting variability in drug response in children and focus on the pharmacogenetic polymorphisms of immunosuppressants, antidepressants, anticancer and anti-inflammatory drugs. Additional pharmacogenetic and epigenetic studies should be performed to allow the individualization of therapy in children.

Pharmacokinetic differences corroborate observed low tacrolimus dosage in Native American renal transplant patients

We have observed in clinical practice that Native Americans require lower dosages of tacrolimus to attain similar target blood trough levels compared to whites after renal transplant. Because there are no pharmacokinetic studies of tacrolimus in this ethnic group, we investigated whether this clinical observation could be corroborated by pharmacokinetic differences between Native Americans and other ethnic and racial groups. We recruited 24 adult Native American kidney transplant recipients on stable oral doses of tacrolimus for at least 1 month posttransplant. We conducted a 12-h steady-state pharmacokinetic profile for all of the patients and estimated pharmacokinetic parameters using NONMEM. The concentration-time data were fit to a linear two compartment model with first-order absorption and lag time using an empirical Bayesian approach. The mean estimate of oral clearance (CL/F) was 11.1 l/h. Compared with previously reported data in other ethnic and racial groups, the Native American cohort has approximately one third the clearance of other groups. Our pharmacokinetic study reveals the clinically observed low dose of tacrolimus in Native American renal transplant patients is associated with a decreased oral tacrolimus clearance. There is scant information available on the genetic or environmental characteristics unique to this ethnic group that affect pharmacokinetics compared to other, better-studied groups, and elucidation of these factors will provide information to further facilitate individualized drug treatment for tacrolimus and a wide range of other drugs with similar clearance processes.

Using genetic and clinical factors to predict tacrolimus dose in renal transplant recipients

AIMS

Tacrolimus has a narrow therapeutic window and shows significant interindividual difference in dose requirement. In this study we aim to first identify genetic factors that impact tacrolimus dose using a candidate gene association approach, and then generate a personalized algorithm combining identified genetic and clinical factors to predict individualized tacrolimus dose.

MATERIALS & METHODS

We screened 768 SNPs in 15 candidate genes in metabolism, transport and calcineurin inhibition pathways of tacrolimus, for association with tacrolimus dose in a discovery cohort of 96 patients.

RESULTS

Four polymorphisms in CYP3A5 and one polymorphism in CYP3A4 were identified to be significantly associated with tacrolimus stable dose (p < 8.46 × 10(-5)). The same SNPs were identified when dose-normalized trough tacrolimus concentration was analyzed. The CYP3A5*1 allele was associated with significantly higher stable dose, bigger dose increase, higher risk of being underdosed and lower incidence of post-transplant hyperlipidemia. ABCB1 polymorphisms were not associated with stable dose. No significant difference was found between CYP3A5 expressers and nonexpressers in incidence of acute rejection and time to first rejection. Age, ethnicity and CYP3A inhibitor use could predict 30% of tacrolimus dosing variability. Adding the identified genetic polymorphisms to the algorithm increased the predictability to 58%. In two validation cohorts of 77 and 64 patients, the algorithm containing both genetic and clinical factors produced correlation coefficients of 0.63 and 0.42, respectively. This algorithm gave a prediction of the stable doses closer to the actual doses when compared with another algorithm based only on the CYP3A5 genotype.

CONCLUSION

CYP3A5 genotype is the most significant genetic factor that impacts tacrolimus dose among the genes studied. This study generated the first pharmacogenomics model that predicts tacrolimus stable dose based on age, ethnicity, genotype and comedication use. Our results highlight the importance of incorporating both genetic and clinical, demographic factors into dose prediction.

Pharmacogenetics of tacrolimus: ready for clinical translation?

Tacrolimus (Tac) exhibits an interindividual pharmacokinetic variability that affects the dose required to reach the target concentration in blood. Tac is metabolized by two enzymes of the cytochrome P450 family, CYP3A5 and CYP3A4. The effect of the CYP3A5 genotype on Tac bioavailability has been demonstrated, and the main determinant of this pharmacogenetic effect is a single-nucleotide polymorphism (SNP) in intron 3 of CYP3A5 (6986 A>G; SNP rs776746; also known as CYP3A5*3). The mean dose-adjusted blood Tac concentration was significantly higher among CYP3A5*3 homozygotes than that of carriers of the wild-type allele (CYP3A5*1). In a recent prospective study, a group of kidney transplant patients received a Tac dose either according to the CYP3A5 genotype (the adapted group) or according to the standard regimen (the control group). All patients received induction therapy with mycophenolate mofetil, corticosteroids, and either basiliximab or intravenous anti-thymocyte globulin. Patients in the adapted-dose group required 3–8 days (median 6 days) to reach the target range compared with 3–25 days (median 7 days) in the control group (P=0.001). The total number of dose modifications was also lower in the adapted-dose group. This study also suggested that the CYP3A5 genotype might contribute minimally to the reduction of early acute rejection. However, additional studies are necessary to determine whether the pharmacogenetic approach could help reduce the necessity for induction therapy and co-immunosuppressors.

Pharmacogenetics of tacrolimus after renal transplantation: analysis of polymorphisms in genes encoding 16 drug metabolizing enzymes

BACKGROUND

Tacrolimus (Tac) is an immunosuppressive drug used to prevent post-transplant (PT) organ rejection. Continuous Tac monitoring is necessary to adjust the dose and prevent toxicity or rejection. Tac is metabolized by cytochrome-P450 (CYP) enzymes, and variation at the CYP and other drug metabolizing enzymes could influence Tac bio-availability and dose requirements. Our aim was to define the effect of DNA variants at 16 drug metabolising enzymes on Tac dose in patients with kidney transplants.

METHODS

The REDINREN Pharmacogenetics Project was a multicenter study designed to evaluate the effect of DNA polymorphisms on Tac dose requirements. A total of 200 patients who received a first cadaveric kidney and Tac as primary immunosuppressive drug were genotyped for 96 DNA polymorphisms on 16 genes. Significant associations were further replicated in a second group of 200 patients. The Tac daily dose was adjusted to achieve a blood concentration of 10-15 ng/mL in the period 0-3 months PT, and 5-10 ng/mL thereafter. The dose of tacrolimus dose and blood concentrations were compared between genotypes at 1 week, 6 months, and 1 year PT.

RESULTS

The CYP3A5 genotype (SNP rs776746) was the strongest predictor of Tac dose requirements. Patients who were CYP3A5*3*3 (CYP3A5 non-expressors) received significantly higher Tac dose at 1 week, 6 months, and 1 year PT (p<0.0001). At 1 week, 41% of the CYP3A5 non-expressors achieved target blood concentrations compared to 26% of the CYP3A5 expressors (p=0.007). We also found a significant effect of CYP3A4 genotype (SNP rs2740574) on Tac dose requirements in patients who were CYP3A5 non-expressors. None of the other polymorphisms were related to Tac dose requirements or modified the effect of the CYP3A5 genotype.

CONCLUSIONS

rs776746 (CYP3A5) and rs2740574 (CYP3A4) were the only SNPs associated with Tac dosage. The genotyping of these polymorphisms could be a useful pharmacogenetic tool to determine the Tac dose immediately after transplantation.

Impact of the CYP3A4*1G polymorphism and its combination with CYP3A5 genotypes on tacrolimus pharmacokinetics in renal transplant patients

Aim: Tacrolimus is a substrate of CYP3A4 and CYP3A5. The present study investigated the impact of the CYP3A4*1/*1G polymorphism compared with CYP3A5 genotypes on the dose-adjusted pharmacokinetics of tacrolimus. The effects of the polymorphism on the variability in tacrolimus pharmacokinetics among patients with the CYP3A5*1 allele (CYP3A5 expresser) and among those with CYP3A5*3/*3 genotype (nonexpresser) were also studied. Materials & methods: A total of 136 renal allograft recipients were given repeated doses of tacrolimus every 12 h. On day 28 after the renal transplantation, blood tacrolimus concentrations were measured, and dose-adjusted pharmacokinetics were determined and compared with the corresponding genotype. Results: The dose-adjusted AUC0–12 and C0 of tacrolimus were significantly lower in patients with the CYP3A4*1G allele and CYP3A5 expressers than those with the CYP3A4*1/*1 genotype and nonexpressers, respectively. In a multiple regression analysis, the dose-adjusted AUC0–12 and C0 values were associated with CYP3A4*1/*1 (p = 0.018 and 0.040, respectively) and CYP3A5*3/*3 (p < 0.001 each). The standardized regression coefficient for the AUC0–12 of tacrolimus was approximately twofold less for CYP3A4*1/*1 than CYP3A5*3/*3. The lowest dose-adjusted AUC0–12 was found in CYP3A5 expressers with the CYP3A4*1G allele. Conclusion: The CYP3A4*1/*1G polymorphism was associated with the pharmacokinetics of tacrolimus, however, its contribution to dose-adjusted pharmacokinetics was approximately twofold less than that of the CYP3A5*1/*3 polymorphism. Although its effect on CYP3A4 activity is not clear, CYP3A4*1/*1G may be a candidate for a polymorphism affecting the interindividual variability in tacrolimus pharmacokinetics among CYP3A5 expressers.

Original submitted 5 January 2011; Revision submitted 22 February 2011

The interactions of age, genetics, and disease severity on tacrolimus dosing requirements after pediatric kidney and liver transplantation

Purpose

In children, data on the combined impact of age, genotype, and disease severity on tacrolimus (TAC) disposition are scarce. The aim of this study was to evaluate the effect of these covariates on tacrolimus dose requirements in the immediate post-transplant period in pediatric kidney and liver recipients.

Methods

Data were retrospectively collected describing tacrolimus disposition, age, CYP3A5 and ABCB1 genotype, and pediatric risk of mortality (PRISM) scores for up to 14 days post-transplant in children receiving liver and renal transplants. Initial TAC dosing was equal in all patients and adjusted using therapeutic drug monitoring. We determined the relationship between covariates and tacrolimus disposition.

Results

Forty-eight kidney and 42 liver transplant recipients (median ages 11.5 and 1.5 years, ranges 1.5–17.7 and 0.05–14.8 years, respectively) received TAC post-transplant. In both transplant groups, younger children (<5 years) needed higher TAC doses than older children [kidney: 0.15 (0.07–0.35) vs. 0.09 (0.02–0.20) mg/kg/12h, p = 0.046, liver: 0.12 (0.04–0.32) vs. 0.09 (0.01–0.18) mg/kg/12h, p = 0.038]. In kidney but not liver transplants, CYP3A5 expressors needed significantly higher TAC doses than nonexpressors [0.15 (0.07–0.20) vs. 0.09 (0.02–0.35) mg/kg/12h, P = 0.001]. In these patients, age and CYP3A5 genotype were independently associated with TAC dosing requirement. In liver, but not kidney transplant patients, homozygous ABCB1 T-T-T haplotype carriers needed higher TAC doses than noncarriers [0.26 (0.15–0.32) vs. 0.11 (0.01–0.25) mg/kg/12h, p = 0.013].

Conclusion

CYP3A5 genotype may explain variation in tacrolimus disposition early after transplant in pediatric kidney recipients, independent of age-related variation. In contrast, in pediatric liver recipients, variation in tacrolimus disposition appears related to age and ABCB1 genotype. These findings illustrate the importance of the interplay among age, genotype, and transplant organ on tacrolimus disposition.

Influence of CYP3A5 and MDR1(ABCB1) polymorphisms on the pharmacokinetics of tacrolimus in Chinese renal transplant recipients

The aims of this study were to investigate the influence of CYP3A5 and MDR1 genetic polymorphisms on tacrolimus pharmacokinetics in Chinese renal transplant recipients, so as to help rational administration in clinical practice. We calculated pharmacokinetic parameters of tacrolimus from blood concentrations in steady state at day 28. Polymerase chain reaction restriction fragment length polymorphisms were used for CYP3A5 and MDR1 analysis. The results showed that the dose-adjusted area under the concentration time curve (AUC(0-12)) and renal clearance showed a significant difference between CYP3A5*1 carriers and the CYP3A5*3/*3 genotype (P < .01). In the following study, a distinction was made between carriers of CYP3A5*1/ vs CYP3A5*3/*3 seeking to investigate the influence of the MDR13435T>C polymorphism on tacrolimus pharmacokinetics. MDR1 3435T>C polymorphism did not affect any tacrolimus pharmacokinetic parameter in either group. Renal transplant recipients who were CYP3A5*1 carriers required a higher dose of tacrolimus than CYP3A5*3/*3, indicating a significantly lower dose-adjusted AUC(0-12) of tacrolimus. In contrast, MDR1 3435T>C polymorphism was not an important factor in tacrolimus pharmacokinetics. Pharmacogenetic methods may be used prospectively to aid dose selection and individualize immunosuppressive therapy.