Pharmacogenetics of antiplatelets and anticoagulants: a report on clopidogrel, warfarin and dabigatran

The safety of available pharmacotherapy for stroke prevention in atrial fibrillation

INTRODUCTION

Oral anticoagulant drugs reduce the risk of stroke associated with atrial fibrillation. Vitamin K antagonists, gold standard therapy for decades, have been deposed by the direct oral anticoagulants that exhibit superior safety profiles. However, hemorrhagic complications remain a major concern to anticoagulation.

AREAS COVERED

We searched available data in the literature to review the current knowledge on the safety profiles of available anticoagulants.

EXPERT OPINION

Despite a relevant leap forward with the introduction of DOACs, safety concerns persist in some fields of the current pharmacotherapy for stroke prevention in atrial fibrillation. In-depth knowledge of the safety profile of available anticoagulants and dealing with safety issues in patient subgroups is of utmost importance. Bleeding risk scores should not be dichotomously used to decide anticoagulation treatment but rather to promote shared decision, identify and correct modifiable risk factors, and set monitoring frequency. Additional issues that wait to be investigated in order to improve the safety of therapy include circulating levels of direct oral anticoagulants and anticoagulation in patient sub-groups: very elderly, frail, those with advanced kidney or liver disease, and so on. Safety may be improved from the in-depth knowledge of safety concerns and therapeutic options.

Effect of Genotype on the Pharmacokinetics and Bleeding Events of Direct Oral Anticoagulants: A Systematic Review and Meta-analysis

This meta-analysis aimed to investigate the effect of the genotype on the pharmacokinetics and bleeding events of direct oral anticoagulants (DOACs) and comprehensively searched electronic databases. Weighted mean difference (WMD) was used to assess the kinetic indicators, odds ratio, and 95% confidence interval (CI) were used to calculate the clinical outcomes. Thirteen articles with 1543 participants were finally included in this study. The peak concentration (C_max ) and area under the plasma concentration-time curve from time 0 to infinity of individuals with the ABCB1 rs 1045642 CT + TT were higher than that of the CC (WMD = -31.9, 95% CI [-49.94, -12.24], P = .02; WMD = -79.97, 95%CI [-152.38 to -7.56], P = .03, I² = 0). The C_max of individuals with mutated genes in ABCB1 2677-3435 is higher than that the wild type (WMD = -19.20, 95%CI [36.62 to -1.79], P = .03, I² = 0). Carriers of the CYP3A5 rs776746 GG genotype had a higher C_max than the GA gene (WMD = -51.22, 95%CI [-92.26 to -10.19], P = .01, I² = 0). Bleeding events were more common in the CES1 rs 2244613 AA + AC than in the CC (odds ratio, 2.62, 95%CI [1.06, 6.47], P = .04; I² = 0). The C_max of DOACs was affected by individuals with ABCB1 rs 1045642, ABCB1 2677-343, and cytochrome P450 3A5 rs 776746. Carriers of the ABCB1 rs 1045642 affected the change of area under the plasma concentration-time curve from time 0 to infinity of DOACs. Bleeding events were affected by CES1 rs 2244613.

The Impact of ABCB1 and CES1 Polymorphisms on Dabigatran Pharmacokinetics in Healthy Chinese Subjects

Dabigatran is a novel direct oral anticoagulant agent, whose plasma concentration is closely related to bleeding risk. Genetic polymorphisms can affect the level of plasma dabigatran. The purpose of this study was to understand the relationship between dabigatran-related genes and the plasma level of dabigatran in healthy Chinese subjects after taking a single oral dose. This study was performed with a single-center, single-dose, randomized, open-label, and four-period crossover trial design under both fasting and fed conditions. A total of 106 eligible healthy subjects were enrolled in the study and 104 were genotyped. One-way analysis of variance (ANOVA) was used to compare pharmacokinetic parameters among different genotypes and linear regression was applied to explore the multiplicative interaction between variables. In this study, we found that the genotype frequencies of CES1 rs2244613 and CES1 rs8192935 were significantly different between Chinese and Caucasians, but the genotype frequencies of ABCB1 rs1045642 and ABCB1 rs4148738 were similar in both populations. CES1 rs8192935 were associated with the peak concentration of dabigatran. There was no significant gender difference in the exposure level of dabigatran. Furthermore, food significantly delayed the absorption of dabigatran but had little effect on C_max and AUC_0-∞.

Effect of CES1 and ABCB1 genotypes on the pharmacokinetics and clinical outcomes of dabigatran etexilate in patients with atrial fibrillation and chronic kidney disease

Background Despite the well-studied safety profile of dabigatran, its interactions with genetic polymorphism parameters are poorly understood, especially in patients with moderate chronic kidney disease (CKD). The study assessed whether genetic factors can contribute to CKD and alter dabigatran concentration. Methods Patients with atrial fibrillation (AF) and stage 3 CKD treated with dabigatran 110 or 150 mg have been included in the study. Real-time polymerase chain reaction was used to evaluate single-nucleotide polymorphisms of the ABCB1 gene (rs1045642 and rs4148738) and CES1 gene (rs2244613). A plasma trough concentration/dose (C/D) ratio was used as a pharmacokinetic index. Results A total of 96 patients aged 51-89 years (median age: 75 years) were evaluated. Patients on a reduced regimen of 110 mg twice a day were older (79.8 vs. 67.9, p < 0.0001) and had lower creatinine clearance (49.7 vs. 62.3 mL/min/1.73 m2, p = 0.015). Patients with the rs2244613 CC genotype had lower C/D values (70% reduction in the mean C/D vs. AA genotype, p = 0.001). Linear stepwise regression has shown the CKD epidemiology collaboration to be the only significant predictor of C/D among genetic factors and kidney function characteristics. During the median follow-up of 15 months, there were 15 bleedings in 13 patients. Conclusions Polymorphism of CES1 rs2244613 can contribute to the safety of dabigatran in patients with AF and CKD. There was no influence of the aforementioned polymorphisms of ABCB1 on dabigatran trough plasma concentrations and C/D. Kidney function is a mainstay of clinical decision-making on direct oral anticoagulant (DOAC) dose, and further knowledge should be accumulated on the role of genetic factors.

Comparison of Two Different Techniques Of Warfarin Dosing Determination - A Chemometrics Study

A high prevalence of genetic polymorphisms increases sensitivity to warfarin therapy. In this study, we investigated 47 patients with effective long-term therapy by warfarin well-controlled by monitoring of International Normalised Ratio (INR). All patients were tested for gene polymorphisms VKORC1, CYP2C9*C2, and CYP2C9*C3, which were used for a dose calculation employing a program www.WarfarinDosing.org. The main goal was to investigate whether the warfarin doses determined by INR are in accordance with the doses calculated according to the pharmacogenetic algorithm. For this purpose, several chemometric tools, namely principal component analysis, cluster analysis, correlation analysis, correspondence analysis, Passing-Bablock regression, Bland-Altman method, descriptive statistics, and ANOVA were used. We also analysed the relationship between the dose of warfarin determined by INR and several constitutional and genetic factors. Statistically significant association between clinically optimized warfarin dose and indication for the treatment, age, and warfarin sensitivity determined by VKORC1, CYP2C9 gene polymorphisms were confirmed. Finally, we confirmed a good concordance between the INR determined warfarin doses and pharmacogenetic approach.

Genetic determinants of dabigatran safety (CES1 gene rs2244613 polymorphism) in the Russian population: multi-ethnic analysis

This study was aimed to investigate the prevalence of the CES1 gene (c.1168-33A > C, rs2244613) polymorphism among 12 different ethnic groups living in Russia to provide a basis for future clinical studies concerning genetic determinants of dabigatran safety. The study involved 1630 apparently healthy, unrelated, and chronic medication-free volunteers of both genders from 12 different ethnic groups in Russia: 136 Russians, 90 Avars, 50 Dargins, 46 Laks, 120 Kabardians, 112 Balkars, 244 Ossetians, 206 Mari, 204 Mordvinians, 238 Chuvashes, 114 Buryats and 70 Nanays. Genotyping was performed by using real-time polymerase chain reaction-based methods. The allelic prevalence of the ethnic groups was compared with Caucasus population participating in the RE-LY study. Statistically significant differences for the following gene polymorphism were found between all ethnic groups and RE-LY participants. Based on obtained results, it can be assumed that patients of all ethnic groups living in Russia taking dabigatran have a lower risk of bleeding.

Pharmacogenomics of Novel Direct Oral Anticoagulants: Newly Identified Genes and Genetic Variants

Direct oral anticoagulants (DOAC) have shown an upward prescribing trend in recent years due to favorable pharmacokinetics and pharmacodynamics without requirement for routine coagulation monitoring. However, recent studies have documented inter-individual variability in plasma drug levels of DOACs. Pharmacogenomics of DOACs is a relatively new area of research. There is a need to understand the role of pharmacogenomics in the interpatient variability of the four most commonly prescribed DOACs, namely dabigatran, rivaroxaban, apixaban, and edoxaban. We performed an extensive search of recently published research articles including clinical trials and in-vitro studies in PubMed, particularly those focusing on genetic loci, single nucleotide polymorphisms (SNPs), and DNA polymorphisms, and their effect on inter-individual variation of DOACs. Additionally, we also focused on commonly associated drug-drug interactions of DOACs. CES1 and ABCB1 SNPs are the most common documented genetic variants that contribute to alteration in peak and trough levels of dabigatran with demonstrated clinical impact. ABCB1 SNPs are implicated in alteration of plasma drug levels of rivaroxaban and apixaban. Studies conducted with factor Xa, ABCB1, SLCOB1, CYP2C9, and VKORC1 genetic variants did not reveal any significant association with plasma drug levels of edoxaban. Pharmacokinetic drug-drug interactions of dabigatran are mainly mediated by p-glycoprotein. Strong inhibitors and inducers of CYP3A4 and p-glycoprotein should be avoided in patients treated with rivaroxaban, apixaban, and edoxaban. We conclude that some of the inter-individual variability of DOACs can be attributed to alteration of genetic variants of gene loci and drug-drug interactions. Future research should be focused on exploring new genetic variants, their effect, and molecular mechanisms that contribute to alteration of plasma levels of DOACs.

Pharmacogenetic studies with oral anticoagulants. Genome-wide association studies in vitamin K antagonist and direct oral anticoagulants

Oral anticoagulants (OAs) are the recommended drugs to prevent cardiovascular events and recurrence in patients with atrial fibrillation (AF) and cardioembolic stroke. We conducted a literature search to review the current state of OAs pharmacogenomics, focusing on Genome Wide Association Studies (GWAs) in patients treated with vitamin K antagonists (VKAs) and direct oral anticoagulants (DOACs).

VKAs: Warfarin, acenocoumarol, fluindione and phenprocoumon have long been used, but their interindividual variability and narrow therapeutic/safety ratio makes their dosage difficult. GWAs have been useful in finding genetic variants associated with VKAs response. The main genes involved in VKAs pharmacogenetics are: VKORC1, CYP2C19 and CYP4F2. Variants in these genes have been included in pharmacogenetic algorithms to predict the VKAs dose individually in each patient depending on their genotype and clinical variables.

DOACs: Dabigatran, apixaban, rivaroxaban and edoxaban have been approved for patients with AF. They have stable pharmacokinetics and do not require routine blood checks, thus avoiding most of the drawbacks of VKAs. Except for a GWAs performed in patients treated with dabigatran, there is no Genome Wide pharmacogenomics data for DOACs. Pharmacogenomics could be useful to predict the better clinical response and avoid adverse events in patients treated with anticoagulants, identifying the most appropriate anticoagulant drug for each patient. Current pharmacogenomics data show that the polymorphisms affecting VKAs or DOACs are different, concluding that personalized medicine based on pharmacogenomics could be possible. However, more studies are required to implement personalized medicine in clinical practice with OA and based on pharmacogenetics of DOACs.

Pharmacogenetics of novel oral anticoagulants: a review of identified gene variants & future perspectives

Novel oral anticoagulants (NOACs) are becoming a therapy of choice in everyday clinical practice after almost 50 years during which warfarin and related coumarin derivatives were used as the main anticoagulants. Advantages of NOACs over standard anticoagulants include their predictable pharmacodynamics and pharmacokinetics, stable plasma concentrations and less drug-drug and food-drug interactions. However, pharmacogenetics has its place in administration of NOACs, as considerable interindividual variations have been detected. In this review, previous findings in pharmacogenetics of dabigatran, rivaroxaban, apixaban and edoxaban are summarized, along with recommendations for studying genes encoding metabolically important enzymes for four selected NOACs. Future directions include identification of clinically relevant SNPs, and change in optimum dosage for patients who are carriers of significant variants.

Left Atrial Appendage Thrombus Formation in a Patient on Dabigatran Therapy Associated With ABCB1 and CES-1 Genetic Defect

Dabigatran, directly targeting thrombin, is widely used for the prevention of stroke in nonvalvular atrial fibrillation (NVAF). We reported a rare case of left atrial appendage thrombus formation in a persistent NVAF patient despite the 31 months uninterrupted treatment with dabigatran 110 mg twice daily. The patient is a carrier of ABCB1 variant alleles with 7 heterozygote single nucleotide polymorphisms (SNPs: rs4148738, rs2235046, rs1128503, rs10276036, rs1202169, rs1202168, rs1202167) as well as CES-1 variant alleles with 2 homozygote SNPs (rs2244613 and rs4122238) and 2 heterozygote SNPs (rs8192935 and rs4580160), which may contribute to the changes of dabigatran plasma concentration. In addition, Drug-drug interaction with atorvastatin may also play a role to decrease dabigatran plasma concentration. There are only four such cases till date, of which had thrombus in the left atrium, reported in the literature. We firstly reported the documented case in a Chinese patient carrying multiple alleles of ABCB1 and CES-1, who suffered from thrombus in the left atrial appendage despite long-term anticoagulation with dabigatran. More clinical data are required to elucidate the impact of CES-1 and ABCB1 polymorphism on dabigatran pharmacokinetics, especially for Asian.

The influence of VKORC1 and CYP2C9 mutations on warfarin response after total hip and knee arthroplasty

AIMS

This study characterizes the influence of genotype at two loci on warfarin response after arthroplasty.

METHODS

121 postarthroplasty patients given warfarin thromboprophylaxis were reviewed for international normalized ratio (INR) values on the first three days postoperatively. Significant differences among genotypes in INR values on each of the first three postoperative days were assessed.

RESULTS

Wild-type patients at both loci (∼23% of patients) had yet to reach therapeutic INR (1.5-2.0) by postoperative day three more frequently than those with a mutation conferring hyper-responsiveness (61% vs. 30%; P ≤ .01).

CONCLUSIONS

Wild-type patients are not anticoagulated in a sufficiently prompt manner after arthroplasty.

What causes intracerebral bleeding after thrombolysis for acute ischaemic stroke? Recent insights into mechanisms and potential biomarkers

The overall population benefit of intravascular recombinant tissue plasminogen activator (rtPA) on functional outcome in ischaemic stroke is clear, but there are some treated patients who are harmed by early symptomatic intracranial haemorrhage (ICH). Although several clinical and radiological factors increase the risk of rtPA-related ICH, none of the currently available risk prediction tools are yet useful for practical clinical decision-making, probably reflecting our limited understanding of the underlying mechanisms. Finding new methods to identify patients at highest risk of rtPA-related ICH, or new measures to limit risk, are urgent challenges in acute stroke therapy research. In this article, we focus on the potential underlying mechanisms of rtPA-related ICH, highlight promising candidate risk biomarkers and suggest future research directions.

Influence of Absorption, Distribution, Metabolism, and Excretion Genomic Variants on Tacrolimus/Sirolimus Blood Levels and Graft-versus-Host Disease after Allogeneic Hematopoietic Cell Transplantation

Allelic variants of genes implicated in drug absorption, distribution, metabolism, and excretion (ADME) determine the pharmacokinetic variability of many medications and are increasingly recognized as important factors determining the success or failure of medical treatments. Both tacrolimus and sirolimus have narrow therapeutic ranges maintained by therapeutic drug monitoring (TDM). Using an ADME panel that covers >99% of the PharmaADME working group core list (188 single nucleotide polymorphism [SNP] and 12 copy number variant [CNV] assays in 36 pharmacogenetically relevant genes), we studied 177 patients who underwent allogeneic hematopoietic cell transplantation (HCT) using tacrolimus/sirolimus-based graft-versus-host disease (GVHD) prophylaxis. We tested for possible associations between ADME variants and tacrolimus/sirolimus drug levels, concentration/dose (C/D) ratio, and clinical endpoints, including acute GVHD. A total of 62 SNP and 6 CNV assays were evaluable after removing the variants, which were homozygous in (nearly) all samples. For sirolimus, rs2032582 (ABCB1) T-carriers versus non-T-carriers were associated with higher blood levels (P = .01), with similar results for C/D ratio. Generalized estimating equation analysis supported these findings. For tacrolimus, rs776746 CYP3A5*3/*3 and CYP3A5*3/*1 were associated with higher blood levels than CYP3A5*1/*1 (P = .002). By multivariable analysis, rs776746 CYP3A5*3/*3 and CYP3A5*3/*1 were independently associated with decreased acute GVHD compared with CYP3A5*1/*1, after adjustment for conditioning, donor type, race/ethnicity, and age. We demonstrated association of specific ADME genetic polymorphisms with blood levels of tacrolimus/sirolimus, and incidence of acute GVHD after HCT, in spite of TDM and dose adjustment. A larger ongoing study will determine whether these associations have clinical utility beyond TDM.

Identification and characterization of a novel CYP2C9 allelic variant in a warfarin-sensitive patient

Aim: To determine the genetic basis of the low warfarin dose requirement in a Chinese patient. Materials & methods: Bi-directional sequencing of CYP2C9, VKORC1 and CYP4F2 genes was performed. CYP2C9 variants were highly expressed in yeast and insect-cell microsomes. Three typical CYP2C9 probe drugs were used to evaluate the catalytic activity. Results: A novel missense mutation (1400T>C) was identified in CYP2C9 and had been named as new allele *60. When expressed in yeast and insect cells, compared with wild-type enzyme, variant CYP2C9.60 exhibited lower protein expression capacity and showed significantly decreased metabolic activities for the hydroxylation of S-warfarin, tolbutamide and diclofenac. Conclusion: The novel mutation can greatly decrease the enzymatic activity of the CYP2C9 enzyme both in vitro and in vivo.