Tacrolimus Dosing in Adult Lung Transplant Patients Is Related to Cytochrome P4503A5 Gene Polymorphism

Immune outcomes of lung transplant recipients with different cytochrome P450 3A5 phenotypes after discontinuation of voriconazole antifungal prophylaxis

INTRODUCTION

Tacrolimus forms the backbone of immunosuppression regimens in lung transplant recipients (LTRs). It is extensively metabolized by cytochrome P450 (CYP) 3A5 enzymes, of which polymorphisms can significantly affect tacrolimus dose requirements. It is unknown how coadministration of tacrolimus with voriconazole, a potent CYP3A5 inhibitor, affects rejection rates or empiric dose adjustments needed after voriconazole discontinuation.

METHODS

This retrospective cohort study compares LTRs with poor (PR) versus intermediate/extensive (IE) CYP3A5 metabolizer phenotypes. The primary endpoint is cumulative immune outcomes within three months of voriconazole discontinuation; secondary endpoints include change in tacrolimus dose-to-concentration ratios after voriconazole discontinuation.

RESULTS

Thirty-four patients underwent full analysis: 13 IE and 21 PR metabolizers. A higher proportion of IE metabolizers were African American (46.2% vs. 9.5%, p = .03). There was no significant difference in composite immune outcomes, though there was a proportionally higher frequency of new donor-specific antibody development in PR metabolizers (14.3% vs 7.7%, p = .56). Both groups required approximately 2.5 to 3-fold tacrolimus dose increases post-voriconazole discontinuation to re-attain therapeutic levels.

CONCLUSION

This novel investigation sheds light on how CYP3A5 phenotype could be used to guide tacrolimus dosing, with the goal of preventing both toxicity and organ rejection.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

BACKGROUND

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

METHODS

We enrolled 14 adult lung transplant recipients who were treated with tacrolimus and then intensively collected blood samples within a 12-h dosing interval. The pharmacokinetic parameters of tacrolimus were calculated using non-compartmental analysis, and the influence of pathophysiological characteristics and CYP3A5*3 and CYP3A4*1G genotypes on the pharmacokinetics of tacrolimus was assessed. Using linear regression analysis, we investigated the correlation between tacrolimus concentration at different sampling points and measured the area under the time-concentration curve (AUC_0-12h).

RESULTS

Geometric mean of apparent clearance (CL/F) was 18.13 ± 1.65 L/h in non-CYP3A5*3/*3 carriers, five times higher than that in CYP3A5*3/*3 carriers (p < 0.001). Furthermore, the tacrolimus concentration 4 h after administration had the strongest correlation with AUC_0-12h (R² = 0.979).

CONCLUSION

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

Current perspective of immunomodulators for lung transplant

Lung transplantation is an effective treatment option for selected patients suffering from end-stage lung disease. More intensive immunosuppression is enforced after lung transplants owing to a greater risk of rejection than after any other solid organ transplants. The commencing of lung transplantation in the modern era was in 1983 when the Toronto Lung Transplant Group executed the first successful lung transplant. A total of 43,785 lung transplants and 1365 heart-lung transplants have been performed from 1 Jan 1988 until 31 Jan 2021. The aim of this review article is to discuss the existing immunosuppressive strategies and emerging agents to prevent acute and chronic rejection in lung transplantation.

Composite CYP3A phenotypes influence tacrolimus dose-adjusted concentration in lung transplant recipients

OBJECTIVES

Interpatient variability in tacrolimus pharmacokinetics is attributed to metabolism by cytochrome P-450 3A4/5 isoenzymes (encoded by CYP3A4 and CYP3A5). Guidelines for adjusting tacrolimus based on CYP3A5 test results are published; however, CYP3A4 variants also contribute to the variability in tacrolimus pharmacokinetics. The effects of composite phenotypes incorporating CYP3A5 and CYP3A4 increased (*1G, *1B) and decreased (*22) function variants have not been evaluated. The objective of this study is to investigate the impact of both increased and decreased function CYP3A variants on weight and dose-adjusted tacrolimus concentration (C0/D).

METHODS

We performed a single-center retrospective cohort study of lung transplant recipients to evaluate the median tacrolimus C0/D by composite CYP3A phenotype groups during the index transplant hospitalization. CYP3A4 and CYP3A5 alleles were used to classify patients into four CYP3A groups from least to most CYP3A activity. Exploratory analyses of ABCB1 and additional candidate genes were also assessed.

RESULTS

Of the 92 included individuals, most (58) were CYP3A Group 2. The median tacrolimus C0/D differed significantly between CYP3A groups (P = 0.0001). CYP3A Group 2 median tacrolimus C0/D was 190.5 (interquartile range: 147.6-267.5) (ng/ml)/(mg/kg/d) and significantly higher than Group 4 [107.9 (90.4-116.1), P = 0.0001)]. Group 2 median tacrolimus C0/D did not significantly differ from Group 1 and Group 3 [373.5 (149.2-490.3) and 81.4 (62.6-184.1), respectively]. No significant differences in tacrolimus C0/D were found for the ABCB1 diplotypes.

CONCLUSION

These data indicate that a composite CYP3A phenotype incorporating both increase and decrease variant information from CYP3A4 in addition to CYP3A5 may significantly influence tacrolimus C0/D during the early postoperative period.

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.

Effect of hepar-protecting Wuzhi capsule on Pharmacokinetics and Dose-effect Character of Tacrolimus in Healthy Volunteers

Wuzhi capsule (WZC), a preparation of Fructus Schisandra sphenanthera extract, has been widely used for the treatment of viral and drug-induced hepatitis in China. This study aimed to determine the pharmacokinetic parameters of tacrolimus (TAC) when co-administered with WZC and its dose-effect of WZC on TAC in healthy volunteers. We assessed the effect of increased dosage of WZC (1, 2, 6, and 8 capsules once daily) on the relative oral exposure of TAC to explore the dose-response relationship between WZC and TAC using bioanalysis, pharmacokinetic, genotypical analyses. We elucidate the influence of CYP3A5 and MDR1 genetic polymorphisms on the WZC dose by maintaining C_trough of TAC in Chinese healthy volunteers. When co-administered with WZC, the T_max of TAC was increased significantly while the apparent oral clearance was decreased. The plasma TAC level in volunteers with high CYP3A5 expression was greatly lower than that in those with mutant CYP3A5. However, polymorphisms of MDR1 exon26 C3435T, exon21 G2677T/A and exon12 C1236T were not associated with plasma TAC levels. Our findings provide important information on interactions between modern medications and herbal products, thus facilitating a better usage of TAC in patients receiving WZC. This article is protected by copyright. All rights reserved.

Population pharmacokinetics and dosing regimen optimization of tacrolimus in Chinese lung transplant recipients

We aimed to (i) develop a population pharmacokinetic model of tacrolimus in Chinese lung transplant recipients and (ii) propose model-based dosing regimens for individualized treatment. We obtained 807 tacrolimus steady-state whole blood concentrations from 52 lung transplant patients and genotyped CYP3A5*3. Population pharmacokinetic analysis was performed using nonlinear mixed-effects modeling. Monte Carlo simulations were employed to determine the initial dosing regimens. Tacrolimus pharmacokinetics was described by a one-compartment model with first-order absorption and elimination processes. In CYP3A5*3/*3 70-kg patients with 30% hematocrit and voriconazole-free therapy, the mean estimated apparent clearance was 13.1 l h^-1 with 20.1% between-subject variability, which was lower than that in Caucasian lung transplant patients (17.5-36.5 l h^-1). Hematocrit, postoperative days, tacrolimus daily dose, voriconazole concomitant therapy, and CYP3A5*3 genotype were identified as significant covariates for tacrolimus clearance. To achieve target trough concentration (10-15 ng ml^-1) on the 8th day post-transplant, a higher initial dosage than the current regimen of 0.04 mg kg^-1 every 12 h is recommended for CYP3A5*1/*3 patients without voriconazole concomitant therapy. Given the nonlinear kinetics of tacrolimus and large variability, population pharmacokinetic model should be combined with therapeutic drug monitoring to optimize individualized therapy.

Immunosuppressive strategies in lung transplantation

Lung transplantation is a viable option for those with end-stage lung disease which is evidenced by the continued increase in the number of lung transplantations worldwide. However, patients and clinicians are constantly faced with acute and chronic rejection, infectious complications, drug toxicities, and malignancies throughout the lifetime of the lung transplant recipient. Conventional maintenance immunosuppression therapy consisting of a calcineurin inhibitor (CNI), anti-metabolite, and corticosteroids have become the standard regimen but newer agents and modalities continue to be developed. Here we will review induction agents, maintenance immunosuppressives, adjunctive therapies and other strategies to improve long-term outcomes.

Tacrolimus exposure early after lung transplantation and exploratory associations with acute cellular rejection

AIMS

To (i) describe tacrolimus (TAC) pre-dose concentrations (C₀), (ii) calculate apparent oral TAC clearance (CL/F_HCT) adjusted for measured haematocrit (HCTi) and standardised to a HCT of 45%, across three observation time points and (iii) explore if low TAC C₀ or high mean CL/F_HCT are associated with an increased risk of rejection episodes early after lung transplantation.

METHODS

TAC whole blood concentration-time profiles and transbronchial biopsies were performed prospectively at weeks 3, 6 and 12 after lung transplantation. The TAC pre-dose concentration (C₀) was measured, and CL/F_HCT was determined using non-compartmental analysis. The associations between TAC C₀ and CL/F_HCT and rejection status were explored using repeated measures logistic regression.

RESULTS

Eighteen patients provided 377 TAC whole blood concentrations. Considerable variability around the median (IQR) CL/F_HCT 6.8 (4.2-15.9) L h^-1, and the median C₀ 12.7 (9.9-16.6) μg L^-1 was noted. Despite adjustment for haematocrit, a significant decrease was observed in CL/F_HCT in all patients over time: CL/F_HCT 14 (5.4-23) at week 3, CL/F_HCT 7.7 (4.5-12) at week 6 and CL/F_HCT 3.9 (2.4-11) L h^-1 at week 12 (p < 0.01). Seven (38.9%) patients experienced a single grade 2 rejection, whilst 11 (61.1%) patients experienced no rejection. Higher TAC C₀ were associated with a reduced risk of rejection OR 0.68 (95% CI 0.51-0.91, p = 0.02), and greater mean CL/F_HCT was associated with an increased risk of rejection OR 1.34 (95% CI 1.01-1.81 p = 0.04).

CONCLUSION

Monitoring TAC C₀, HCT and CL/F_HCT in patients after lung transplantation may assist clinicians in detecting patients at risk of acute rejection and may guide future research into TAC and HCT monitoring after lung transplantation.

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

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

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.

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

BACKGROUND

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

SUMMARY

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

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.

Association of donor small ubiquitin-like modifier 4 rs237025 genetic variant with tacrolimus elimination in the early period after liver transplantation

BACKGROUNDS & AIMS

Individualized tacrolimus treatment can improve drug safety and efficacy. In this study, we aimed to investigate the association of donor and recipient small ubiquitin-like modifier 4 (SUMO4) rs237025 polymorphisms with tacrolimus elimination and the potential mechanism.

METHODS

A total of 297 liver transplant patients were enrolled in the study. CYP3A5 rs776746 and SUMO4 rs237025 were genotyped using TaqMan SNPs assays. The activity of nuclear factor-kB (NF-kB) was evaluated by luciferase assay. The expressions of CYP3A5 were detected by qRT-PCR and western blotting.

RESULTS

Tacrolimus C/D ratios was significantly lower for donor SUMO4 rs237025 AA carriers than AG/GG carriers at weeks 1, 2, 3. In multivariate analysis, donor and recipient CYP3A5 rs776747, donor SUMO4 rs237025 and total bilirubin were independent predictors of tacrolimus C/D ratios in the early post-transplantation period both in Cohort A and Cohort B. When combined donor CYP3A5 rs776746 and donor SUMO4 rs237025 genotypes, tacrolimus C/D ratios was highly significant at all investigated time points within the four groups. CYP3A5 mRNA expression in liver tissues was significantly higher for AA carriers than AG/GG patients under inflammatory stimuli after liver transplantation (LT). Furthermore, we demonstrated that SUMO4 rs237025 G allele could increase NF-κB transcriptional activity under inflammatory condition. And activation of NF-kB suppressed the expression of pregnane X receptor (PXR)-mediated CYP3A5 gene.

CONCLUSIONS

Donor SUMO4 rs237025 genetic variant was associated with higher Tac C/D ratios in the early period after LT, which might be related to the down-regulation of CYP3A5 enzyme through the NF-kB signalling pathway.

CYP3A4 genotype is associated with sildenafil concentrations in patients with heart failure with preserved ejection fraction

Despite its established inter-individual variability, sildenafil has been the subject of only a few pharmacogenetic investigations, with limited data regarding the genetic modulators of its pharmacokinetics. We conducted a pharmacogenetic sub-study of patients randomized to sildenafil (n=85) in the RELAX trial, which investigated the impact of high-dose sildenafil in patients with heart failure with preserved left ventricular ejection fraction (HFpEF). In the overall population, the CYP3A4 inferred phenotype appeared associated with the dose-adjusted peak concentrations of sildenafil at week 12 and week 24 (adjusted P=0.045 for repeated measures analysis), although this P-value did not meet our corrected significance threshold of 0.0167. In the more homogeneous Caucasian subgroup, this association was significant (adjusted P=0.0165 for repeated measures). Hence, CYP3A4 inferred phenotype is associated with peak sildenafil dose-adjusted concentrations in patients with HFpEF receiving high doses of sildenafil. The clinical impact of this association requires further investigation.

CYP3A pharmacogenetic association with tacrolimus pharmacokinetics differs based on route of drug administration

Tacrolimus is prescribed to the majority of transplant recipients to prevent graft rejection, and although patients are maintained on oral administration, nonoral routes of administration are frequently used in the initial post-transplant period. CYP3A5 genotype is an established predictor of oral tacrolimus dose requirements, and clinical guideline recommendations exist for CYP3A5-guided dose selection. However, the association between CYP3A5 and nonoral tacrolimus administration is currently poorly understood, and differs from the oral tacrolimus relationship. In addition to CYP3A5, other pharmacogenes associated with CYP3A activity, including CYP3A4, CYP3A7 and POR have also been identified as predictors of tacrolimus exposure. This review will describe the current understanding of the relationship between these pharmacogenes and tacrolimus pharmacokinetics after oral and nonoral administration.

Individualizing immunosuppression in lung transplantation

Immunosuppression management after lung transplantation continues to evolve, with an increasing number of agents available for use in various combinations allowing for more choice and individualization of immunosuppressive therapy. Therapeutic developments have led to improved outcomes including lower acute rejection rates and improved survival. However, a one size fits all approach for any immunosuppressive strategy may not be best suited to the individual patient and ultimately patient specific factors must be considered when designing the immunosuppressive regimen. Recipient factors including age, race, co-morbidities, immunologic risk, genetic polymorphisms, concomitant and previous pharmacotherapy, and overall immunosuppression burden should be considered. There are several significant drug-drug interactions with select immunosuppressive agents utilized in lung transplant pharmacotherapy that must be considered when choosing and devising a dosing strategy for an individual immunosuppressive agent. Herein, considerations for immunosuppression management in the individual patient will be reviewed.

ATP-binding cassette subfamily B member 1 1236C/T polymorphism significantly affects the therapeutic outcome of tacrolimus in patients with refractory ulcerative colitis

BACKGROUND AND AIM

Tacrolimus is now considered to be one of the main therapeutic options for refractory ulcerative colitis. Both cytochrome P-450 3A5 (CYP3A5) and ATP-binding cassette subfamily B member 1 (ABCB1) associated with tacrolimus metabolism are known to have several genetic polymorphisms. However, it remains controversial whether these polymorphisms affect the therapeutic efficacy for ulcerative colitis. We aimed to investigate the influence of both CYP3A5 and ABCB1 polymorphisms on the efficacy of tacrolimus in ulcerative colitis treatment under the tight dose-adjusting strategy.

METHODS

Sixty-one Japanese patients with ulcerative colitis treated with tacrolimus were enrolled retrospectively. Tacrolimus treatment was performed using the tight dose-adjusting strategy. Genotyping for CYP3A5*3, ABCB1 1236C>T, 2677G>A,T, and 3435C>T were performed, and the clinical outcomes at 12 weeks after the initiation of tacrolimus were compared among the genotypes.

RESULTS

There was no association between the CYP3A5 genotypes and therapeutic efficacy. In contrast, a significant association was observed with the ABCB1 1236C > T polymorphism and therapeutic efficacy. The ABCB1 1236CC+CT groups (n = 41) had a significantly higher response rate (73% vs 35%; P = 0.004) and remission rate (61% vs 20%; P = 0.002) than the TT group (n = 20). The multivariate logistic regression analysis also revealed that ABCB1 1236C>T was identified as an independent factor associated with remission.

CONCLUSIONS

ABCB1 1236C>T polymorphism significantly affects the therapeutic efficacy of tarcolimus at 12 weeks under the tight dose-adjusting treatment for ulcerative colitis.

Influence of the CYP3A4/5 genetic score and ABCB1 polymorphisms on tacrolimus exposure and renal function in Brazilian kidney transplant patients

BACKGROUND

Polymorphisms in genes encoding transport proteins and metabolizing enzymes involved in tacrolimus (TAC) disposition may be important sources of individual variability during treatment.

OBJECTIVE

The aim of this study was to investigate the effect of combined CYP3A4 and CYP3A5 variants, using a CYP3A4/5 genetic score, and ABCB1 polymorphisms on therapeutic TAC monitoring and their relationship with clinical outcomes.

MATERIAL AND METHODS

Brazilian kidney transplant recipients (n=151), who received TAC over 3 months after transplantation, were genotyped for CYP3A4 rs2242480 (g.20230G>A), CYP3A5 rs15524 (g.31611C>T) and rs776746 (g.6986A>G), ABCB1 rs1128503 (c.1236C>T), rs1045642 (c.3435C>T), and rs2032582 (c.2677G>T/A) polymorphisms.

RESULTS

Frequencies of CYP3A4 g.20230A, CYP3A5 g.31611C, and g.6986A were 0.37, 0.26, and 0.28, respectively. These alleles were associated with TAC rapid metabolization and were used for CYP3A4/5 genetic score construction. A higher CYP3A4/5 genetic score was associated with higher TAC dose and lower concentrations for dose administered (Co/D, P<0.05). Ninety days after transplantation, the presence of two or more rapid metabolization alleles contributed toward 27.7% of Co/D variability and was associated with a lower estimated glomerular filtration rate values (P<0.05). For ABCB1, the frequencies of c.1236T, c.3435T, and c.2677T/A alleles were 0.42, 0.42, and 0.33/0.04. At 30 days after transplantation, patients carrying ABCB1 c.1236TT+c.3435TT+(c.2677TT+TA) genotypes had higher TAC Co/D than those with common or heterozygous genotypes (P<0.05).

CONCLUSION

The results show the impact of the CYP3A4/5 genetic score on TAC exposure and renal function in Brazilian patients. Furthermore, ABCB1 polymorphisms, in a combined analysis, influenced TAC Co/D at 30 days after transplantation.

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

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

Influence of IL-18 and IL-10 Polymorphisms on Tacrolimus Elimination in Chinese Lung Transplant Patients

Aims. The influence of interleukin-10 (IL-10) and interleukin-18 (IL-18) polymorphisms on tacrolimus pharmacokinetics had been described in liver and kidney transplantation. The expression of cytokines varied in different kinds of transplantation. The influence of IL-10 and IL-18 genetic polymorphisms on the pharmacokinetic parameters of tacrolimus remains unclear in lung transplantation. Methods. 51 lung transplant patients at Shanghai Pulmonary Hospital were included. IL-18 polymorphisms (rs5744247 and rs1946518), IL-10 polymorphisms (rs1800896, rs1800872, and rs3021097), and CYP3A5 rs776746 were genotyped. Dose-adjusted trough blood concentrations (C/D ratio, mg/kg body weight) in lung transplant patients during the first 4 postoperative weeks were calculated. Results. IL-18 rs5744247 allele C and rs1946518 allele A were associated with fast tacrolimus metabolism. Combined analysis showed that the numbers of low IL-18 mRNA expression alleles had positive correlation with tacrolimus C/D ratios in lung transplant recipients. The influence of IL-18 polymorphisms on tacrolimus C/D ratios was observed in CYP3A5 expresser recipients, but not in CYP3A5 nonexpresser recipients. No clinical significance of tacrolimus C/D ratios difference of IL-10 polymorphisms was found in our data. Conclusions. IL-18 polymorphisms may influence tacrolimus elimination in lung transplantation patients.

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 Single Nucleotide Polymorphisms (SNPs) on Immunosuppressive Therapy in Lung Transplantation

Lung transplant patients present important variability in immunosuppressant blood concentrations during the first months after transplantation. Pharmacogenetics could explain part of this interindividual variability. We evaluated SNPs in genes that have previously shown correlations in other kinds of solid organ transplantation, namely ABCB1 and CYP3A5 genes with tacrolimus (Tac) and ABCC2, UGT1A9 and SLCO1B1 genes with mycophenolic acid (MPA), during the first six months after lung transplantation (51 patients). The genotype was correlated to the trough blood drug concentrations corrected for dose and body weight (C0/Dc). The ABCB1 variant in rs1045642 was associated with significantly higher Tac concentration, at six months post-transplantation (CT vs. CC). In the MPA analysis, CT patients in ABCC2 rs3740066 presented significantly lower blood concentrations than CC or TT, three months after transplantation. Other tendencies, confirming previously expected results, were found associated with the rest of studied SNPs. An interesting trend was recorded for the incidence of acute rejection according to NOD2/CARD15 rs2066844 (CT: 27.9%; CC: 12.5%). Relevant SNPs related to Tac and MPA in other solid organ transplants also seem to be related to the efficacy and safety of treatment in the complex setting of lung transplantation.

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.

Pharmacogenetics in solid organ transplantation: genes involved in mechanism of action and pharmacokinetics of immunosuppressive drugs

Allogenic solid organ transplantation has become the routine procedure in patients with end stage organ disease. Although the transplanted organ compensates deficient body functions, its allogenic nature requires institution of immune tolerance, nowadays provided by immunosuppressive drug administration. Both the safety and efficacy of immunosuppressive treatment depend on many factors, and maintaining levels of immunosuppressants within therapeutic range is the essential target for success in graft function preservation. It is obvious that drug and metabolite concentrations depend on efficiency of individual patient metabolism. Recently, many studies were undertaken to investigate the relationship between genetic factors, drug pharmacokinetics and therapy outcome, and interindividual variability apparently can be explained, at least in part, by genetically determined polymorphisms of xenobiotic-metabolizing enzymes, transport proteins and also in some cases, drug targets. This review presents the recent state of knowledge in the field of pharmacogenetics related to solid organ transplantation.

Impact of the CYP3A5, CYP3A4, COMT, IL-10 and POR genetic polymorphisms on tacrolimus metabolism in Chinese renal transplant recipients

Tacrolimus is a widely used immunosuppressive drug for preventing the rejection of solid organ transplants. The efficacy of tacrolimus shows considerable variability, which might be related to genetic variation among recipients. We conducted a retrospective study of 240 Chinese renal transplant recipients receiving tacrolimus as immunosuppressive drug. The retrospective data of all patients were collected for 40 days after transplantation. Seventeen SNPs of CYP3A5, CYP3A4, COMT, IL-10 and POR were identified by the SNaPshot assay. Tacrolimus blood concentrations were obtained on days 1-3, days 6-8 and days 12-14 after transplantation, as well as during the period of the predefined therapeutic concentration range. Kruskal-Wallis test was used to examine the effect of genetic variation on the tacrolimus concentration/dose ratio (C 0/D) at different time points. Chi-square test was used to compare the proportions of patients who achieved the target C 0 range in the different genotypic groups at weeks 1, 2, 3 and 4 after transplantation. After correction for multiple testing, there was a significant association of C 0/D with CYP3A5*3, CYP3A4*1G and CYP3A4 rs4646437 T>C at different time points after transplantation. The proportion of patients in the IL-10 rs1800871-TT group who achieved the target C 0 range was greater (p = 0.004) compared to the IL-10 rs1800871-CT and IL-10 rs1800871-CC groups at week 3 after transplantation. CYP3A5*3, CYP3A4 *1G, CYP3A4 rs4646437 T>C and IL-10 rs1800871 C>T might be potential polymorphisms affecting the interindividual variability in tacrolimus metabolism among Chinese renal transplant recipients.

A published pharmacogenetic algorithm was poorly predictive of tacrolimus clearance in an independent cohort of renal transplant recipients

AIMS

An algorithm based on the CYP3A5 genotype to predict tacrolimus clearance to inform the optimal initial dose was derived using data from the DeKAF study (Passey et al. Br J Clin Pharmacol 2011; 72: 948-57) but was not tested in an independent cohort of patients. Our aim was to test whether the DeKAF dosing algorithm could predict estimated tacrolimus clearance in renal transplant recipients at our centre.

METHODS

Predicted tacrolimus clearance based on the DeKAF algorithm was compared with dose-normalized trough whole-blood concentrations (estimated clearance) on day 7 after transplantation in a single-centre cohort of 255 renal transplant recipients.

RESULTS

There was a weak correlation (r = 0.431) between clearance based on dose-normalized trough whole-blood concentrations and DeKAF algorithm-predicted clearance. The means of the tacrolimus clearance predicted by the DeKAF algorithm and the estimated tacrolimus clearance based on the dose-normalized trough blood concentrations were plotted against the differences in the clearance as a Bland-Altman plot. Logarithmic transformation was performed owing to the increased difference in tacrolimus clearance as the mean clearance increased. There was a highly significant systematic error (P < 0.0005) characterized by a sloped regression line [gradient, 0.88 (95% confidence interval, 0.75-1.01)] on the Bland-Altman plot.

CONCLUSIONS

The DeKAF algorithm was unable to predict the estimated tacrolimus clearance accurately based on real tacrolimus doses and blood concentrations in our cohort of patients. Other genes are known to influence the clearance of tacrolimus, and a polygenic algorithm may be more predictive than those based on a single genotype.

A Markov chain model to evaluate the effect of CYP3A5 and ABCB1 polymorphisms on adverse events associated with tacrolimus in pediatric renal transplantation

The SNP A6986G of the CYP3A5 gene (*3) results in a non-functional protein due to a splicing defect whereas the C3435T was associated with variable expression of the ABCB1 gene, due to protein instability. Part of the large interindividual variability in tacrolimus efficacy and toxicity can be accounted for by these genetic factors. Seventy-two individuals were examined for A6986G and C3435T polymorphism using a PCR-RFLP-based technique to estimate genotype and allele frequencies in the Jordanian population. The association of age, hematocrit, platelet count, CYP3A5, and ABCB1 polymorphisms with tacrolimus dose- and body-weight-normalized levels in the subset of 38 pediatric renal transplant patients was evaluated. A Markov model was used to evaluate the time-dependent probability of an adverse event occurrence by CYP3A5 phenotypes and ABCB1 genotypes. The time-dependent probability of adverse event was about double in CYP3A5 non-expressors compared to the expressors for the first 12 months of therapy. The CYP3A5 non-expressors had higher corresponding normalized tacrolimus levels compared to the expressors in the first 3 months. The correlation trend between probability of adverse events and normalized tacrolimus concentrations for the two CYP3A5 phenotypes persisted for the first 9 months of therapy. The differences among ABCB1 genotypes in terms of adverse events and normalized tacrolimus levels were only observed in the first 3 months of therapy. The information on CYP3A5 genotypes and tacrolimus dose requirement is important in designing effective programs toward management of tacrolimus side effects particularly for the initial dose when tacrolimus blood levels are not available for therapeutic drug monitoring.

Pharmacogenomics and heart failure in congenital heart disease

Congenital heart disease (CHD) constitutes a lifelong challenge in heart failure management. Current therapy is based mainly on physiologic principles extrapolated from the management of left ventricular failure in adult populations with either ischemic or nonischemic cardiomyopathy. However, there is good evidence of genomic variability in the origin and progression of CHD that suggests the need for a individualized approach to treatment. The developing science of pharmacogenomics presents an opportunity for CHD management broadly, and especially in the context of heart failure. There is growing evidence that individualizing drug therapy for these patients might be beneficial, and that prediction of response to therapy might be possible by incorporating genomic data into the treatment algorithm for individual patients.

Sequential Analysis of Tacrolimus Dosing in Adult Lung Transplant Patients WithABCB1Haplotypes

The genetic polymorphisms in the ABCB1 gene, which encodes for the membrane pump, P-glycoprotein, have been previously demonstrated to have an association with tacrolimus dosing in organ transplant patients. This study associated the haplotype and genotype for ABCB1 G2677T and C3435T variants with a sequential analysis of tacrolimus blood level (ng/mL) per mg/day dosage ([L/D]) administered to 91 adult lung transplant patients at 1, 3, 6, 9, and 12 months after transplantation. Haplotype 22 carriers had a significantly higher tacrolimus [L/D] value in comparison with nonhaplotype 22 carriers (P = .04) only at 1 month after transplant. Sequential analysis demonstrated that ABCB1 genotypes 00 and 01 had low tacrolimus [L/D] values at 1 and 3 months, but these values increased substantially at 6, 9, and 12 months after transplantation. This was not true of the other genotypes with the exception of genotypes 10 and 21, which had small numbers of patients but had consistently low tacrolimus [L/D]. Haplotype analysis also suggested that the homozygous for ABCB1 2677 variant allele had more of an impact on tacrolimus [L/D] in haplotype analysis than that of ABCB1 3435. In conclusion, sequential analysis of tacrolimus [L/D] with haplotypes can explain previous clinical observations of changes in tacrolimus dosage over time but suggests that this effect is limited to individual patient haplotypes. Sequential analysis of drug dosing and haplotypes relationships can provide important information about the induction or inhibition of drug-drug and disease-drug interactions among specific haplotypes.

Influence of CYP3A5 6986A > G and ABCB1 3435C > T Polymorphisms on Adverse Events Associated With Tacrolimus in Jordanian Pediatric Renal Transplant Patients

The aim of the study is to investigate the influence of ABCB1(3435) and CYP3A5(6986) polymorphisms, tacrolimus troughs and clinical factors on the time of adverse events associated with tacrolimus in pediatric kidney transplant patients. Clinical data, adverse events, tacrolimus troughs, corresponding doses, ABCB1 3435C > T and CYP3A5 6986A > G genotypes were collected from 38 pediatric kidney transplant patients in a retrospective study for over 2 years post-transplant. We used a marginal Cox proportional hazard model to evaluate the influence of clinical factors and single nucleotide polymorphisms (SNPs) on tacrolimus-associated adverse events. CYP3A5 genotype, the Bayesian predicted tacrolimus concentrations, hematocrit and mean corpuscular volume are significant risk factors of adverse events over a 2-year-period. CYP3A5*1 genotype was associated with 36% relative risk of CYP3A5*3/*3 genotype. In the 9-month period, the additional factor, ABCB1 3435TT genotype, was shown to be associated with 38% relative risk of the CC and CT genotypes. For graft loss, acute and chronic rejection, only tacrolimus concentration and hematocrit, but not CYP3A5 or ABCB1 polymorphisms, are important factors influencing their occurrences.

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.

Effect of a new functional CYP3A4 polymorphism on calcineurin inhibitors' dose requirements and trough blood levels in stable renal transplant patients

AIMS

CYP3A4 is involved in the oxidative metabolism of many drugs and xenobiotics including the immunosuppressants tacrolimus (Tac) and cyclosporine (CsA). The objective of the study was to assess the potential influence of a new functional SNP in CYP3A4 on the pharmacokinetic parameters assessed by dose requirements and trough blood levels of both calcineurin inhibitors (CNI) in stable renal transplant patients.

PATIENTS & METHODS

A total of 99 stable renal transplant patients receiving either Tac (n = 49) or CsA (n = 50) were genotyped for the CYP3A4 intron 6 C>T (rs35599367) and CYP3A5*3 SNPs. Trough blood levels ([Tac](0) or [CsA](0) in ng/ml), dose-adjusted [Tac](0) or [CsA](0) (ng/ml per mg/kg bodyweight) as well as doses (mg/kg bodyweight) required to achieve target concentrations were compared among patients according to allelic status for CYP3A4 and CYP3A5.

RESULTS

Dose-adjusted concentrations were 2.0- and 1.6-fold higher in T-variant allele carriers for the CYP3A4 intron 6 C>T SNP compared with homozygous CC for Tac and CsA, respectively. When CYP3A4/CYP3A5 genotypes were combined, the difference was even more striking as the so-defined CYP3A poor metabolizer group presented dose-adjusted concentration 1.6- and 4.1-fold higher for Tac, and 1.5- and 2.2-fold higher for CsA than the intermediate metabolizer and extensive metabolizer groups, respectively. Multiple linear regression analysis revealed that, taken together, both CYP3A4 intron 6 and CYP3A5*3 SNPs explained more than 60 and 20% of the variability observed in dose-adjusted [Tac](0) and [CsA](0), respectively.

CONCLUSION

The CYP3A4 intron 6 C>T polymorphism is associated with altered Tac and CsA metabolism. CYP3A4 intron 6 C>T along with CYP3A5*3 (especially for Tac) pharmacogenetic testing performed just before transplantation may help identifying patients at risk of CNI overexposure and contribute to limit CNI-related nephrotoxicity by refining the starting dose according to their genotype. Original submitted 5 May 2011; Revision submitted 29 June 2011.

Effect of gene polymorphisms on the levels of calcineurin inhibitors in Indian renal transplant recipients

The outcome of renal transplantation is improved by cyclosporine and tacrolimus. However, its success is limited by drug-induced nephrotoxicity. Therefore, monitoring their levels is important. These levels are influenced mainly by CYP3A4, CYP3A5 and MDR- 1 genes. These levels also affect target molecules of CNIs, mainly IL-2. Inter-individual differences in these levels have been attributed to SNPs in these genes and hence study of these SNPs assumes significance. So far no study has been carried out on Indian renal transplant recipients covering the SNPs of the genes involved in metabolism, efflux and drug target of CNIs, hence the data is lacking for Indian population. The aim is to study A-392G SNP of CYP3A4, A6986G SNP of CYP3A5, C3435T SNP of MDR-1 and T-330G SNP of IL-2 genes and correlate with CNI blood levels. Hundred healthy subjects and 100 consecutive renal transplant recipients; 56 on CsA and 44 on tacrolimus were genotyped by PCR followed by restriction enzyme assay for mentioned SNPs. No significant difference was observed between level/dose (L/D) ratio of CNIs and CYP3A4 and IL-2 SNPs. However, median L/D ratio for tacrolimus was significantly higher in subjects with CYP3A5*3/*3 (n = 24) (P = 0.011) and MDR- 1 3435TT (n = 18) (P = 0.0122). The findings from this study show that homozygous mutant patients for CYP3A5 and MDR-1 gene SNPs could be managed with lower tacrolimus dose to avoid nephrotoxicity.

Developmental pharmacogenetics of immunosuppressants in pediatric organ transplantation

Cyclosporine, tacrolimus, sirolimus, and mycophenolate mofetil are the primary immunosuppressants used on pediatric organ transplantation. Therapeutic drug monitoring is used in daily practice, because their clinical use is hampered by a narrow therapeutic index and large variability. Tailoring immunosuppressive therapy to the individual patient to optimize efficacy and minimize toxicity is therefore essential. Because research in pharmacogenetics already identified polymorphisms impacting their pharmacokinetic parameters in adults, developmental pharmacogenetics of immunosuppressants holds promises for optimizing dosage regimens and improving clinical outcome in children. In this review, we focus on the impact of age and pharmacogenetics on these immunosuppressants in children undergoing organ transplantation.

Design of Allele Specific PCR for Rapid Detection of CYP3A5 (A6986G) and Mdr-1 (C3435T) Polymorphisms

Single nucleotide polymorphisms in CYP3A5 (A6986G) and MDR-1 (C3435T) genes have been shown to be associated with the pharmacokinetics of tacrolimus in case of renal transplant recipients. Knowing these genotypes of the recipients before undergoing transplantation, is therefore essential for physicians to adjust the starting dose of tacrolimus in order to avoid drug induced nephrotoxicity. We have designed an allele specific PCR method for easier and rapid detection of these polymorphisms. 20 Indian renal transplant recipients on tacrolimus who developed nephrotoxicity within 1 month of transplantation and 58 Indian non-transplant subjects having the risk factors for kidney disease i.e. hypertension or diabetes or the family history of these, have been studied for these SNPs by allele specific PCR method. The data suggest that the heterozygosity of CYP3A5 and mutant allele frequency of MDR-1 SNP is higher in transplant patients as well as in general population.