Creating a genotype-based dosing algorithm for acenocoumarol steady dose

Acenocoumarol Pharmacogenetic Dosing Algorithm versus Usual Care in Patients with Venous Thromboembolism: A Randomised Clinical Trial

Patients with venous thromboembolism (VTE) require immediate treatment with anticoagulants such as acenocoumarol. This multicentre randomised clinical trial evaluated the effectiveness of a dosing pharmacogenetic algorithm versus a standard-of-care dose adjustment at the beginning of acenocoumarol treatment. We included 144 patients with VTE. On the day of recruitment, a blood sample was obtained for genotyping (CYP2C9*2, CYP2C9*3, VKORC1, CYP4F2, APOE). Dose adjustment was performed on day 3 or 4 after the start of treatment according to the assigned group and the follow-up was at 12 weeks. The principal variable was the percentage of patients with an international normalised ratio (INR) within the therapeutic range on day 7. Thirty-four (47.2%) patients had an INR within the therapeutic range at day 7 after the start of treatment in the genotype-guided group compared with 14 (21.9%) in the control group (p = 0.0023). There were no significant differences in the time to achieve a stable INR, the number of INRs within the range in the first 6 weeks and at the end of study. Our results suggest the use of a pharmacogenetic algorithm for patients with VTE could be useful in achieving target INR control in the first days of treatment.

A Pharmacogenetically Guided Acenocoumarol Dosing Algorithm for Chilean Patients: A Discovery Cohort Study

Background

Vitamin K antagonists (VKA) are used as prophylaxis for thromboembolic events in patients with cardiovascular diseases. The most common VKA are warfarin and acenocoumarol. These drugs have a narrow therapeutic margin and high inter-individual response variability due to clinical and pharmacogenetic variables.

Objective

The authors aim to develop an algorithm comprised of clinical and genetic factors to explain the variability in the therapeutic dose of acenocoumarol among Chilean patients

Methodology

DNA was obtained from 304 patients as a discovery cohort with an international normalized ratio (INR) range of 2.0–3.0. The non-genetic (demographic and clinical) variables were also recorded. Genotype analyses were performed using real-time PCR for VKORC1 (rs9923231), VKORC1 (rs7294), GGCx (rs11676382), CYP4F2 (rs2108622), ABCB1 (rs1045642), CYP2C9*2 (rs1799853), ApoE (rs429358), and CYP2C9*3 (rs1057910).

Results

The clinical variables that significantly influenced the weekly therapeutic dose of VKA were age, sex, body mass index (BMI), and initial INR, collectively accounting for 19% of the variability, and the genetic variables with a significant impact were VKORC1 (rs9923231), CYP2C9*2 (rs1799853), and CYP2C9*3 (rs1057910), explaining for another 37% of the variability.

Conclusion

We developed an algorithm that explains 49.99% of the variability in therapeutic VKA dosage in the Chilean population studied. Factors that significantly affected the dosage included VKORC1, CYP2C9*2, and CYP2C9*3 polymorphisms, as well as age, sex, BMI, and initial INR.

Genome-Wide Association Study of VKORC1 and CYP2C9 on acenocoumarol dose, stroke recurrence and intracranial haemorrhage in Spain

Acenocoumarol is an oral anticoagulant with significant interindividual dose variations. Variants in CYP2C9 and VKORC1 have been associated with acenocoumarol maintenance dose. We analysed whether any of the 49 polymorphisms in CYP2C9 and VKORC1 previously associated with acenocoumarol maintenance dose in a Genome-Wide Association study (GWAs) in Dutch population are associated with stroke recurrence, intracranial haemorrhage (ICH) and acenocoumarol maintenance dose in a Spanish population. We performed a GWAs using Human Core Exome-chip (Illumina) in 78 patients stroke patients treated with acenocoumarol for secondary prevention enrolled as part of the prospective investigator-initiated study (IIS) SEDMAN Study. Patients were followed-up a median of 12.8 months. Three and eight patients had recurrent stroke and ICH events, respectively. We found 14 of the 49 published variants associated with acenocoumarol maintenance dose (p < 0.05). Six polymorphisms were associated with stroke recurrence and four variants with ICH (p < 0.05). In conclusion, variants in VKORC1 and CYP2C9 are associated with acenocoumarol maintenance dose, stroke recurrence and ICH in a Spanish cohort. These results highlight the relevance of studying pharmacogenetics associated with efficacy and safety of anticoagulant drugs and justify studies with larger sample size and different ethnic populations.

Effect of CYP4F2, VKORC1, and CYP2C9 in Influencing Coumarin Dose: A Single-Patient Data Meta-Analysis in More Than 15,000 Individuals

The cytochrome P450 (CYP)4F2 gene is known to influence mean coumarin dose. The aim of the present study was to undertake a meta-analysis at the individual patients level to capture the possible effect of ethnicity, gene-gene interaction, or other drugs on the association and to verify if inclusion of CYP4F2*3 variant into dosing algorithms improves the prediction of mean coumarin dose. We asked the authors of our previous meta-analysis (30 articles) and of 38 new articles retrieved by a systematic review to send us individual patients' data. The final collection consists of 15,754 patients split into a derivation and validation cohort. The CYP4F2*3 polymorphism was consistently associated with an increase in mean coumarin dose (+9% (95% confidence interval (CI) 7-10%), with a higher effect in women, in patients taking acenocoumarol, and in white patients. The inclusion of the CYP4F2*3 in dosing algorithms slightly improved the prediction of stable coumarin dose. New pharmacogenetic equations potentially useful for clinical practice were derived.

Pharmacogenetics in the Treatment of Cardiovascular Diseases and Its Current Progress Regarding Implementation in the Clinical Routine

There is a special interest in the implementation of pharmacogenetics in clinical practice, although there are some barriers that are preventing this integration. A large part of these pharmacogenetic tests are focused on drugs used in oncology and psychiatry fields and for antiviral drugs. However, the scientific evidence is also high for other drugs used in other medical areas, for example, in cardiology. In this article, we discuss the evidence and guidelines currently available on pharmacogenetics for clopidogrel, warfarin, acenocoumarol, and simvastatin and its implementation in daily clinical practice.

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.

Effect of CYP2C9, VKORC1, CYP4F2, and GGCX gene variants and patient characteristics on acenocoumarol maintenance dose: Proposal for a dosing algorithm for Moroccan patients

We investigated the impact of non-genetics factors, and single nucleotide polymorphisms (SNPs) in VKORC1, CYP2C9, CYP4F2, and GGCX on acenocoumarol dosage in Moroccan adult's patients, in order to develop an algorithm to predict acenocoumarol dose for Moroccan patients. Our study consisted of 217 Moroccan patients taking a maintenance dose of acenocoumarol for various indications. The patients were genotyped for VKORC1 -1639 G>A, VKORC1 1173 C>T, CYP2C9*2, CYP2C9*3, CYP4F2 1347 G>A and GGCX 12970 C>G SNPs. The statistical analysis was performed using the SPSS software. The age and SNPs in VKORC1 and CYP2C9 were significantly associated with the weekly acenocoumarol dose requirement (p = 0.023, p = 0.0001 and p = 0.001 respectively). There was no association found between the weekly acenocoumarol dose and the CYP4F2 or GGCX variants (p-value > 0.05). Non-parametric analysis confirmed the accumulate effect of variant alleles at VKORC1 -1639 G>A, VKORC1 1173 C>T and CYP2C9 SNPs on the acenocoumarol dose requirement. With 90.24% less dose required for one patient carrying homozygote variant at VKORC1 -1173 (TT) and CYP2C9 *x/*x haplotype. The multiple linear regression analysis showed that mutation in VKORC1 -1639, VKORC1 1173 SNPs, or in CYP2C9 haplotype reduces the mean acenocoumarol weekly dose to 25.4%, 23.4% and 6.2%, respectively. The R2 for multiple regression analysis final model was found to be 35.9%. In this work we were able to establish the factors influencing interindividual sensitivity to the anticoagulant therapy that can help physicians to predict optimal dose requirement for long term therapy.

Role of CYP4F2, CYP2C19, and CYP1A2 polymorphisms on acenocoumarol pharmacogenomic algorithm accuracy improvement in the Greek population: need for sub-phenotype analysis

BACKGROUND

We have earlier developed a pharmacogenomic algorithm for acenocoumarol dose prediction in Greek patients that included CYP2C9/VKORC1 genetic information. This study aims at analyzing the potential effect of CYP4F2, CYP2C19, and CYP1A2 gene polymorphisms on acenocoumarol dose requirements and at further improving the Greek-specific pharmacogenomic algorithm.

METHODS

A total of 205 Greek patients taking acenocoumarol (140 who reached and 65 who did not reach stable dose), participants of acenocoumarol EU-PACT trial, were included in the study. CYP4F2, CYP2C19, and CYP1A2 polymorphisms were genotyped by use of the PCR-RFLP method. All patients were previously genotyped for CYP2C9/VKORC1 polymorphisms.

RESULTS

In the pooled sample, CYP4F2, CYP2C19, and CYP1A2 polymorphisms do not affect independently acenocoumarol dose requirements. For CYP4F2, significant effects were found on patients' ability to reach stable dose and on acenocoumarol dose requirements when CYP2C9/VKORC1 sub-phenotypes were analyzed. Specifically, when the patients were stratified according to their CYP2C9/VKORC1 functional bins, in sensitive responders, CYP4F2*3 allele carriers (CYP4F2 *1/*3 and *3/*3 genotypes) were more frequent in the patient group who reached stable dose (p=0.049). Additionally, in CYP2C9 intermediate metabolizers (IMs), after adjusting for age, weight, and VKORC1 genotypes, CYP4F2 genotypes were significantly associated with acenocoumarol stable dose (β: 0.07; 95% CI: 0.006-0.134; p=0.033).

CONCLUSIONS

CYP4F2 gene shows a prominent weak association with acenocoumarol dose requirements. Sub-phenotype analysis is potentially important in determining additional gene polymorphisms that are associated with acenocoumarol dose requirements.

Genotype-guided therapy improves initial acenocoumarol dosing

A few trials so far have evaluated the effectiveness of algorithms designed to calculate doses in oral anticoagulant therapy, with negative or contradictory results. We compared a genotype-guided algorithm vs physician management for the initiation of acenocoumarol. In a twoarm, prospective, randomised study with patients with atrial fibrillation who started therapy, the first dose was administered to all patients according to the physician’s criteria. At 72 hours, the corresponding dose was calculated based on INR in the standard care group (SC, N=92), whereas genetic data (VKORC1, CYP2C9 and CYP4F2) were also considered for the genotype-guided dosing (pharmacogenetic) group (PGx, N=87) by using an algorithm previously validated in 2,683 patients. The primary outcomes were: patients with steady dose, the time needed to reach the same and the percentage of therapeutic INRs. After 90 days, 25 % of the SC and 39 % of the PGx patients reached the steady dose (p=0.038). Kaplan-Meier analysis showed that PGx group needed fewer days to reach therapeutic INR (p=0.033). Additionally, PGx had a higher percentage of therapeutic INRs than SC patients (50 % and 45 %, respectively) (p=0.046). After six months the proportion of steadily anticoagulated patients remained significantly higher in PGx (p=0.010). In conclusion, genotype-guided dosing was associated with a higher percentage of patients with steady dose than routine practice when starting oral anticoagulation with acenocoumarol.

Influence of two variants of CYP450 oxidoreductase on the stable dose of acenocoumarol in a Spanish population

AIM

To evaluate the influence of two variants of P450 oxidoreductase (POR), rs2868177 and POR*28, on the stable dosage of acenocoumarol.

PATIENTS & METHODS

For this observational, cross-sectional study, patients were undergone stable anticoagulant treatment with acenocoumarol. Univariate and multiple regression analyses were performed to assess the influence of POR polymorphisms.

RESULTS

About 340 patients were enrolled. Multiple regression had a coefficient of determination (R²) of 51.5% and an Akaike information criterion of 234.22. The inclusion of POR*28 polymorphisms increased the R² to 52.0% and reduced the Akaike information criteria to 230.58. The POR*28 heterozygote showed statistical significance in the algorithm.

CONCLUSION

The POR*28 heterozygote appears to be associated with the stable dose of acenocoumarol, but its clinical contribution to the prediction of the dosing of this drug is minimal.

Dosing algorithms for vitamin K antagonists across VKORC1 and CYP2C9 genotypes

Essentials Prospective studies of pharmacogenetic-guided (PG) coumarin dosing produced varying results. EU-PACT acenocoumarol and phenprocoumon trials compared PG and non-PG dosing algorithms. Sub-analysis of EU-PACT identified differences between trial arms across VKORC1-CYP2C9 groups. Adjustment of the PG algorithm might lead to a higher benefit of genotyping.

SUMMARY

Background The multicenter, single-blind, randomized EU-PACT trial compared the safety and efficacy of genotype-guided and non-genetic dosing algorithms for acenocoumarol and phenprocoumon in patients with atrial fibrillation or deep vein thrombosis. The trial showed no differences in the primary outcome between the two dosing strategies. Objectives To explore possible reasons for the lack of differences between trial arms by performing a secondary analysis of EU-PACT data in order to evaluate the performance of both dosing algorithms across VKORC1-CYP2C9 genetic subgroups. Patients/Methods Anticoagulation control measured according to an International Normalized Ratio (INR) below (INR of < 2), within (INR of 2-3) and above (INR of > 3) the therapeutic range was compared across VKORC1-CYP2C9 subgroups. Owing to a low number of patients in each subgroup, trials for acenocoumarol and phenprocoumon were combined for analysis. Results Four weeks after therapy initiation, genotype-guided dosing increased the mean percentage of time in the therapeutic INR range (PTIR) in the VKORC1 GG-CYP2C9*1*1 subgroup as compared with the non-genetic dosing (difference of 14.68%, 95% confidence interval [CI] 5.38-23.98). For the VKORC1 AA-CYP2C9*1*1 subgroup, there was a higher risk of under-anticoagulation with the genotype-guided algorithm (difference of 19.9%; 95% CI 11.6-28.2). Twelve weeks after therapy initiation, no statistically significant differences in anticoagulation control between trial arms were noted across the VKORC1-CYP2C9 genetic subgroups. Conclusions EU-PACT genetic-guided dose initiation algorithms for acenocoumarol and phenprocoumon could have predicted the dose overcautiously in the VKORC1 AA-CYP2C9*1*1 subgroup. Adjustment of the genotype-guided algorithm could lead to a higher benefit of genotyping.

A novel acenocoumarol pharmacogenomic dosing algorithm for the Greek population of EU-PACT trial

Aim: To generate and validate a pharmacogenomic-guided (PG) dosing algorithm for acenocoumarol in the Greek population. To compare its performance with other PG algorithms developed for the Greek population. Patients & methods: A total of 140 Greek patients participants of the EU-PACT trial for acenocoumarol, a randomized clinical trial that prospectively compared the effect of a PG dosing algorithm with a clinical dosing algorithm on the percentage of time within INR therapeutic range, who reached acenocoumarol stable dose were included in the study. Results: CYP2C9 and VKORC1 genotypes, age and weight affected acenocoumarol dose and predicted 53.9% of its variability. EU-PACT PG algorithm overestimated acenocoumarol dose across all different CYP2C9/VKORC1 functional phenotype bins (predicted dose vs stable dose in normal responders 2.31 vs 2.00 mg/day, p = 0.028, in sensitive responders 1.72 vs 1.50 mg/day, p = 0.003, in highly sensitive responders 1.39 vs 1.00 mg/day, p = 0.029). The PG algorithm previously developed for the Greek population overestimated the dose in normal responders (2.51 vs 2.00 mg/day, p < 0.001). Conclusion: Ethnic-specific dosing algorithm is suggested for better prediction of acenocoumarol dosage requirements in patients of Greek origin.

Can pharmacogenetics help patients under chronic treatment with coumarin anticoagulants?

Vitamin K antagonists are highly effective antithrombotic drugs. However, appropriate dosing is difficult to establish owing to its narrow therapeutic window as well as widespread inter- and intra-individual variability in dosage. Compared with dosing solely based on clinical information, pharmacogenetics can help improve the therapy with coumarins by decreasing the time to reach a stable dose and reducing the risk of bleeding. Most of the studies about genotyping of patients using vitamin K antagonists have focused on predicting the stable dose. Two genes have been shown to have the most influence on dosing: VKORC1 and CYP2C9. Furthermore, genotyping of more genes, such as CYP4F2 and APOE, is also being included in some dosing algorithms. The role of genotype beyond the initial dose-titration phase is less clear. Thus, a proven genetically determined risk of unstable dose or bleeding could help with the selection of patients who require more frequent monitoring of dose. On the other hand, patients who have a genetically determined stable dose could self-monitor their international normalized ratio (INR), making the therapy less expensive and more convenient.

A New Pharmacogenetic Algorithm to Predict the Most Appropriate Dosage of Acenocoumarol for Stable Anticoagulation in a Mixed Spanish Population

There is a strong association between genetic polymorphisms and the acenocoumarol dosage requirements. Genotyping the polymorphisms involved in the pharmacokinetics and pharmacodynamics of acenocoumarol before starting anticoagulant therapy would result in a better quality of life and a more efficient use of healthcare resources. The objective of this study is to develop a new algorithm that includes clinical and genetic variables to predict the most appropriate acenocoumarol dosage for stable anticoagulation in a wide range of patients. We recruited 685 patients from 2 Spanish hospitals and 1 primary healthcare center. We randomly chose 80% of the patients (n = 556), considering an equitable distribution of genotypes to form the generation cohort. The remaining 20% (n = 129) formed the validation cohort. Multiple linear regression was used to generate the algorithm using the acenocoumarol stable dosage as the dependent variable and the clinical and genotypic variables as the independent variables. The variables included in the algorithm were age, weight, amiodarone use, enzyme inducer status, international normalized ratio target range and the presence of CYP2C9*2 (rs1799853), CYP2C9*3 (rs1057910), VKORC1 (rs9923231) and CYP4F2 (rs2108622). The coefficient of determination (R2) explained by the algorithm was 52.8% in the generation cohort and 64% in the validation cohort. The following R2 values were evaluated by pathology: atrial fibrillation, 57.4%; valve replacement, 56.3%; and venous thromboembolic disease, 51.5%. When the patients were classified into 3 dosage groups according to the stable dosage (<11 mg/week, 11-21 mg/week, >21 mg/week), the percentage of correctly classified patients was higher in the intermediate group, whereas differences between pharmacogenetic and clinical algorithms increased in the extreme dosage groups. Our algorithm could improve acenocoumarol dosage selection for patients who will begin treatment with this drug, especially in extreme-dosage patients. The predictability of the pharmacogenetic algorithm did not vary significantly between diseases.

The SAMe-TT2R2 Score Predicts Poor Anticoagulation Control in AF Patients: A Prospective 'Real-world' Inception Cohort Study

OBJECTIVES

International guidelines recommend that an average individual time in therapeutic range should be >65% to 70% for optimal efficacy and safety outcomes while taking a vitamin K antagonist. The Sex, Age (<60 years); Medical history (at least 2 of the following: hypertension, diabetes, coronary artery disease/myocardial infarction, peripheral arterial disease, congestive heart failure, previous stroke, pulmonary disease, hepatic or renal disease); Treatment (interacting drugs, eg, amiodarone for rhythm control) [all 1 point]; and the current Tobacco use (2 points) and Race (non-Caucasian; 2 points) (SAMe-TT2R2) score would help decision making by identifying those patients with newly diagnosed atrial fibrillation who could do well on vitamin K antagonists. The study objective was to validate the predictive value of the SAMe-TT2R2 score for discriminating those who would achieve a high time in the therapeutic range (≥65%) in a prospective "real-world" cohort of patients with atrial fibrillation initiating oral anticoagulation therapy with vitamin K antagonists.

METHODS

We studied an inception cohort of consecutive patients with nonvalvular atrial fibrillation who initiated oral anticoagulation in our outpatient anticoagulation clinic. The baseline SAMe-TT2R2 score was calculated. At 6 months, we calculated the time in therapeutic range using a linear method.

RESULTS

We included 459 patients, of whom 222 (47%) were male. Their median age was 76 years (interquartile range, 70-82 years), median Cardiac failure or dysfunction, Hypertension, Age over 75 years [Doubled], Diabetes, Stroke [Doubled] - Vascular disease, Age between 65-74 and Sex category [Female] (CHA2DS2-VASc) score was 4 (3-5), and median Hypertension, Abnormal Renal/Liver Function, Stroke, Bleeding History or Predisposition, Labile INR, Elderly, Drugs/Alcohol Concomitantly (HAS-BLED) score was 3 (2-3). The median SAME-TT2R2 score was 2 (1-2). At 6 months, the mean ± standard deviation time in therapeutic range was 64% ± 17% overall, and 248 patients (54%) had a time in therapeutic range value >65%. Patients with a SAME-TT2R2 score 0 to 1 had a mean time in therapeutic range of 67% ± 18%, whereas patients with a SAME-TT2R2 score ≥2 had a mean time in therapeutic range of 61% ± 16% (P < .001). The odds ratio for having a low time in therapeutic range value was 2.10 (95% confidence interval, 1.44-3.06; P < .001) for those patients with a SAME-TT2R2 score ≥2.

CONCLUSIONS

In a prospective "real-world" inception cohort of patients with atrial fibrillation initiating oral anticoagulation with acenocoumarol, we have validated the clinical value of the SAME-TT2R2 score for the identification of patients who would have poor-quality anticoagulation. Thus, rather than imposing a "trial of vitamin K antagonists" for such patients (and exposing such patients to thromboembolic risks), we can a priori identify those patients who can (not cannot) do well on a vitamin K antagonists. Such patients would benefit from additional strategies for improving anticoagulation control with vitamin K antagonists or alternative oral anticoagulant drugs.

Acenocoumarol Pharmacogenetic Dosing Algorithms and Their Application in Two Bulgarian Patients with Low Anticoagulant Requirements

BACKGROUND

The anticoagulant therapy with acenocoumarol is generally associated with a high risk of bleeding and thromboembolic events.

PURPOSE

We applied eight already existing acenocoumarol dosing algorithms to Bulgarian patients with low acenocoumarol dose requirements and investigated which of these algorithms would predict most precisely the dose anticoagulant.

MATERIALS AND METHODS

Two patients with Bulgarian origin were referred to the outpatient clinical laboratory of "St. Ekaterina" University Hospital for Cardiovascular Surgery and Cardiology, Sofia, Bulgaria. After obtaining written informed consent, both patients were genotyped for polymorphisms in genes for Cytochrome P450 2C9 (CYP2C9), Vitamin K epoxide reductase (VKORC1), Apolipoprotein E (APOE), and Cytochrome P450 4F2 (CYP4F2).

RESULTS

All applied acenocoumarol dosing algorithms predicted relatively similar doses of coumarin anticoagulant in both patients. However, van Schie et al.'s algorithm allowed more accurate calculation of the optimal dose in our patients with extremely low acenocoumarol requirements. Genotyping of selected polymorphic variants in CYP2C9 and VKORC1 showed that both patients were compound heterozygotes for CYP2C9 (CYP2C9*2/*3) and homozygotes for both variants in VKORC1 (VKORC1 1173 T/T, and VKORC1-1639 A/A). This combination of genotypes suggested high sensitivity to acenocoumarol leading to the low anticoagulant dose requirements (0.25 and 1 mg/day, respectively) needed to reach the target International Normalized Ratio of 2.5-3.5.

CONCLUSIONS

The genotyping of polymorphic variants in VKORC1 and CYP2C9, together with clinical and demographic parameters, can serve for more precise definition of the individual starting and maintenance doses of coumarin derivatives in each patient.

Extrapolation of acenocoumarol pharmacogenetic algorithms

INTRODUCTION

Acenocoumarol (ACN) has a narrow therapeutic range that is especially difficult to control at the start of its administration. Various dosing pharmacogenetic-guided dosing algorithms have been developed, but further work on their external validation is required. The aim of this study was to evaluate the extrapolation of pharmacogenetic algorithms for ACN as an alternative to the development of a specific algorithm for a given population.

MATERIAL AND METHODS

The predictive performance, deviation, accuracy, and clinical significance of five pharmacogenetic algorithms (EU-PACT, Borobia, Rathore, Markatos, Krishna Kumar) were compared in 189 stable ACN patients representing all indications for anticoagulant treatment.

RESULTS

The correlation between the dose predictions of the five pharmacogenetic models ranged from 7.7 to 70.6% and the percentage of patients with a correct prediction (deviation ≤20% from actual ACN dose) ranged from 5.9 to 40.7%. EU-PACT and Borobia pharmacogenetic dosing algorithms were the most accurate in our setting and evidenced the best clinical performance.

CONCLUSIONS

Among the five models studied, the EU-PACT and Borobia pharmacogenetic dosing algorithms demonstrated the best potential for extrapolation.

Estimation and validation of acenocoumarol dosing algorithms in Bulgarian patients with cardiovascular diseases

Aim & Methods: A total of 169 Bulgarian patients were genotyped for CYP2C9*2,*3, VKORC1-1639G>A and VKORC11173C>T. The effect of genetic and nongenetic factors on acenocoumarol dose variability was tested in a derivation cohort of patients and the obtained algorithm was validated in a test cohort.

RESULTS & DISCUSSION

It was found that VKORC-1639G>A (25.5%), CYP2C9*2 (7.8%), CYP2C9*3 (6.1%), age (13.6%) and diagnosis (6.0%) significantly affected acenocoumarol dose variability in the derivation cohort. These factors with additional factors, such as sex (0.1%, p = 0.76), weight (2.6%, p = 0.14) and amiodarone use (3.0%, p = 0.059) accounted for 46.5% and 23.0% of the dose variability for genetic and clinical models, respectively.

CONCLUSION

Based on the results of this investigation, validated clinical and pharmacogenetic algorithms for the prediction of a stable anticoagulant dose were developed, specifically designed for the Bulgarian population.

An acenocoumarol dosing algorithm exploiting clinical and genetic factors in South Indian (Dravidian) population

OBJECTIVE

The objective of this study was to determine the influence of CYP2C9, VKORC1, CYP4F2, and GGCX genetic polymorphisms on mean daily dose of acenocoumarol in South Indian patients and to develop a new pharmacogenetic algorithm based on clinical and genetic factors.

METHODS

Patients receiving acenocoumarol maintenance therapy (n = 230) were included in the study. Single nucleotide polymorphisms (SNP) of CYP2C9, VKORC1, CYP4F2, and GGCX were genotyped by real-time polymerase chain reaction (RT-PCR) method.

RESULTS

The mean daily acenocoumarol maintenance dose was found to be 3.7 ± 2.3 (SD) mg/day. The CYP2C9 *1*2, CYP2C9 *1*3, and CYP2C9 *2*3 variant genotypes significantly reduced the dose by 56.7 % (2.0 mg), 67.6 % (1.6 mg), and 70.3 % (1.5 mg) than wild-type carriers 4.1 mg, p < 0.0001. The genetic variants of CYP2C9 and GGCX (rs11676382) were found to be associated with lower acenocoumarol dose, whereas CYP4F2 (rs2108622) was associated with higher doses. Age, body mass index (BMI), variation of CYP2C9, VKORC1, CYP4F2, and GGCX were the major determinants of acenocoumarol maintenance dose, accounting for 61.8 % of its variability (adjusted r (2) = 0.615, p < 0.0001). Among the VKORC1 variants, rs9923231 alone contributed up to 28.6 % of the acenocoumarol dose variation.

CONCLUSION

VKORC1 rs9923231 polymorphism had the highest impact on acenocoumarol daily dose. A new pharmacogenetic algorithm was established to determine the acenocoumarol dose in South Indian population.

Pharmacogenetic-guided dosing of coumarin anticoagulants: algorithms for warfarin, acenocoumarol and phenprocoumon

Coumarin derivatives, such as warfarin, acenocoumarol and phenprocoumon are frequently prescribed oral anticoagulants to treat and prevent thromboembolism. Because there is a large inter-individual and intra-individual variability in dose-response and a small therapeutic window, treatment with coumarin derivatives is challenging. Certain polymorphisms in CYP2C9 and VKORC1 are associated with lower dose requirements and a higher risk of bleeding. In this review we describe the use of different coumarin derivatives, pharmacokinetic characteristics of these drugs and differences amongst the coumarins. We also describe the current clinical challenges and the role of pharmacogenetic factors. These genetic factors are used to develop dosing algorithms and can be used to predict the right coumarin dose. The effectiveness of this new dosing strategy is currently being investigated in clinical trials.

Analysis of gene-gene interactions using gene-trait similarity regression

OBJECTIVE

Gene-gene interactions (G×G) are important to study because of their extensiveness in biological systems and their potential in explaining missing heritability of complex traits. In this work, we propose a new similarity-based test to assess G×G at the gene level, which permits the study of epistasis at biologically functional units with amplified interaction signals.

METHODS

Under the framework of gene-trait similarity regression (SimReg), we propose a gene-based test for detecting G×G. SimReg uses a regression model to correlate trait similarity with genotypic similarity across a gene. Unlike existing gene-level methods based on leading principal components (PCs), SimReg summarizes all information on genotypic variation within a gene and can be used to assess the joint/interactive effects of two genes as well as the effect of one gene conditional on another.

RESULTS

Using simulations and a real data application to the Warfarin study, we show that the SimReg G×G tests have satisfactory power and robustness under different genetic architecture when compared to existing gene-based interaction tests such as PC analysis or partial least squares. A genome-wide association study with approx. 20,000 genes may be completed on a parallel computing system in 2 weeks.

Effect of VKORC1, CYP2C9 and CYP4F2 genetic variants in early outcomes during acenocoumarol treatment

Aim: To analyze VKORC1, CYP2C9 and CYP4F2 polymorphisms in relation to the main outcomes in the first stages of acenocoumarol therapy. Patients & methods: Nine hundred and forty one patients who had started therapy and in whom time to stable dosage, time to over-anticoagulation and adverse events occurred during 3 first months were retrospectively analyzed. Results: VKORC1 AA patients needed fewer days to reach stable dosage (p = 0.017). International normalized ratio [INR] at 72 h, and VKORC1 and CYP2C9 genotypes conditioned INR values >2.5 (p < 0.001, p = 0.002 and p < 0.001, respectively), whereas CYP4F2 T carriers had a low risk of the same outcome (p = 0.009). In regards to combined genotypes, CYP4F2 had a significant effect on over-anticoagulation at the beginning of therapy except for the VKORC1 AA and CYP2C9*3 combination. Conclusion: In addition to VKORC1 and CYP2C9, CYP4F2 gene has a slight but significant role in reaching INR >2.5 during the first weeks of acenocoumarol therapy.

Original submitted 22 July 2013; Revision submitted 14 November 2013

Vitamin K antagonists in heart disease: current status and perspectives (Section III). Position paper of the ESC Working Group on Thrombosis--Task Force on Anticoagulants in Heart Disease

Oral anticoagulants are a mainstay of cardiovascular therapy, and for over 60 years vitamin K antagonists (VKAs) were the only available agents for long-term use. VKAs interfere with the cyclic inter-conversion of vitamin K and its 2,3 epoxide, thus inhibiting γ-carboxylation of glutamate residues at the amino-termini of vitamin K-dependent proteins, including the coagulation factors (F) II (prothrombin), VII, IX and X, as well as of the anticoagulant proteins C, S and Z. The overall effect of such interference is a dose-dependent anticoagulant effect, which has been therapeutically exploited in heart disease since the early 1950s. In this position paper, we review the mechanisms of action, pharmacological properties and side effects of VKAs, which are used in the management of cardiovascular diseases, including coronary heart disease (where their use is limited), stroke prevention in atrial fibrillation, heart valves and/or chronic heart failure. Using an evidence-based approach, we describe the results of completed clinical trials, highlight areas of uncertainty, and recommend therapeutic options for specific disorders. Although VKAs are being increasingly replaced in most patients with non-valvular atrial fibrillation by the new oral anticoagulants, which target either thrombin or FXa, the VKAs remain the agents of choice for patients with atrial fibrillation in the setting of rheumatic valvular disease and for those with mechanical heart valves.