VKORC1 Polymorphisms Research Articles

The effect of CYP2C9, VKORC1 and CYP4F2 polymorphism and of clinical factors on warfarin dosage during initiation and long-term treatment after heart valve surgery

The dosage of warfarin is restricted due to its narrow therapeutic index, so, the required dose must be adapted individually to each patient. Variations in warfarin dosage are influenced by genetic factors, the changes in patient diet, anthropometric and clinical parameters. To determine whether VKORC1 G3730A and CYP4F2 G1347A genotypes contribute to warfarin dosage in patients during initiation and long-term anticoagulation treatment after heart valve surgery. From totally 307 patients, who underwent heart valve surgery, 189 patients (62%) who had been treated with warfarin more than 3months, were included into the study. A hierarchical stepwise multivariate linear regression model showed, that during initiation clinical factors can explain 17% of the warfarin dose variation. The addition of CYP2C9 and VKORC1 G-1639A genotype raises the accuracy about twice-to 32%. The CYP4F2 G1347A genotype can add again about 2-34%. During long-term treatment clinical factors explain about 26% of warfarin dose variation. If the CYP2C9 *2, *3, VKORC1*2 alleles are detected, model can explain about 49% in dose variation. The *3 allele of VKORC1 raises the accuracy by 1-50%. The carriers of CYP4F2 A1347A genotype required higher daily warfarin doses during initiation of warfarin therapy after heart valve surgery than comparing to G/G and G/A carriers, but during the longer periods of warfarin use, the dosage of warfarin depended significantly on VKORC1 *3 allele (G3730A polymorphism) and on the thyroid stimulating hormone level in the blood plasma.

Expanding Role of Pharmacogenomics in the Management of Cardiovascular Disorders

Cardiovascular disease is a leading cause of death worldwide. Many pharmacologic therapies are available that aim to reduce the risk of cardiovascular disease but there is significant inter-individual variation in drug response, including both efficacy and toxicity. Pharmacogenetics aims to personalize medication choice and dosage to ensure that maximum clinical benefit is achieved whilst side effects are minimized. Over the past decade, our knowledge of pharmacogenetics in cardiovascular therapies has increased significantly. The anticoagulant warfarin represents the most advanced application of pharmacogenetics in cardiovascular medicine. Prospective randomized clinical trials are currently underway utilizing dosing algorithms that incorporate genetic polymorphisms in cytochrome P450 (CYP)2C9 and vitamin k epoxide reductase (VKORC1) to determine warfarin dosages. Polymorphisms in CYP2C9 and VKORC1 account for approximately 40% of the variance in warfarin dose. There is currently significant controversy with regards to pharmacogenetic testing in anti-platelet therapy. Inhibition of platelet aggregation by aspirin in vitro has been associated with polymorphisms in the cyclo-oxygenase (COX)-1 gene. However, COX-1 polymorphisms did not affect clinical outcomes in patients prescribed aspirin therapy. Similarly, CYP2C19 polymorphisms have been associated with clopidogrel resistance in vitro, and have shown an association with stent thrombosis, but not with other cardiovascular outcomes in a consistent manner. Response to statins has been associated with polymorphisms in the cholesterol ester transfer protein (CETP), apolipoprotein E (APOE), 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, calmin (CLMN) and apolipoprotein-CI (APOC1) genes. Although these genes contribute to the variation in lipid levels during statin therapy, their effects on cardiovascular outcomes requires further investigation. Polymorphisms in the solute carrier organic anion transporter 1B1 (SLCO1B1) gene is associated with increased statin exposure and simvastatin-induced myopathy. Angiotensin-converting enzyme (ACE) inhibitors and β-adrenoceptor antagonists (β-blockers) are medications that are important in the management of hypertension and heart failure. Insertion and deletion polymorphisms in the ACE gene are associated with elevated and reduced serum levels of ACE, respectively. No significant association was reported between the polymorphism and blood pressure reduction in patients treated with perindopril. However, a pharmacogenetic score incorporating single nucleotide polymorphisms (SNPs) in the bradykinin type 1 receptor gene and angiotensin-II type I receptor gene predicted those most likely to benefit and suffer harm from perindopril therapy. Pharmacogenetic studies into β-blocker therapy have focused on variations in the β1-adrenoceptor gene and CYP2D6, but results have been inconsistent. Pharmacogenetic testing for ACE inhibitor and β-blocker therapy is not currently used in clinical practice. Despite extensive research, no pharmacogenetic tests are currently in clinical practice for cardiovascular medicines. Much of the research remains in the discovery phase, with researchers struggling to demonstrate clinical utility and validity. This is a problem seen in many areas of therapeutics and is because of many factors, including poor study design, inadequate sample sizes, lack of replication, and heterogeneity amongst patient populations and phenotypes. In order to progress pharmacogenetics in cardiovascular therapies, researchers need to utilize next-generation sequencing technologies, develop clear phenotype definitions and engage in multi-center collaborations, not only to obtain larger sample sizes but to replicate associations and confirm results across different ethnic groups.

Effect of CYP2C9 and VKORC1 genetic polymorphisms on mean daily maintenance dose of acenocoumarol in South Indian patients

AimTo determine the effect of CYP2C9 and VKORC1 genetic polymorphisms on mean daily maintenance dose of acenocoumarol in South Indian patients with heart valve replacement. Materials and methodsThe study was conducted in 170 patients on therapy with acenocoumarol following heart valve replacement surgery. Single nucleotide polymorphisms (SNP) namely CYP2C9*2 (rs1799853), CYP2C9*3 (rs1057910), and VKORC1 (rs9923231) were identified by quantitative Real-Time Polymerase Chain Reaction (RT-PCR) method. ResultsPatients with at least one variant allele of CYP2C9 (*1*2 or *1*3) required 44% and 28.2% lower daily maintenance dose of acenocoumarol (2.0mg and 2.5mg, respectively) than the normal CYP2C9*1*1 genotype group (3.4mg) (p<0.05). Patients with VKORC1 GG genotype required higher dose (3.3mg) as compared to those with genotype VKORC1 GA (2.3mg) and VKORC1 AA (1.0mg) (p<0.001). Patients with both CYP2C9*1*2/*1*3 and VKORC1 GA genotype required 38% lower dose (2.46mg) than patients with CYP2C9*1*1 and VKORC1 GG genotype (3.52mg) (p<0.0001). The clinical (age, body mass index) and genetic variables (VKORC1-1639 G>A, CYP2C9*2, CYP2C9*3) contribute together to predict 30.4% of the required maintenance dose of acenocoumarol. ConclusionThe genetic polymorphisms of CYP2C9 and VKORC1 results in decreased requirement of daily maintenance dose of acenocoumarol. The polymorphism VKORC1 (–1639 G>A) was found to be the major predictor of acenocoumarol dose requirement in South Indian population.

Abstract TP406: Impact Of Warfarin Pharmacogenomics In The Time In Therapeutic Range In Korean Patients With Atrial Fibrillation.

Background: Warfain is highly effective for stroke prevention in patients with atrial fibrillation (AF), but also has narrow therapeutic window (usually INR 2-3). Even in clinical trials with selected, closely monitored patients, the times in therapeutic range (TTR) of those taking warfarin is less than two thirds. Single nucleotide polymorphisms in genes affecting warfarin metabolism (cytochrome-P450 2C9, CYP2C9) and response (vitamin-K epoxide reductase complex 1, VKORC1) have an important influence on warfarin therapy. Initial INR response to warfain was reportedly associated with genetic variability in VKORC1 than with CYP2C9. However, warfarin pharmacogenics associated with long-term intraindividual variation (TTR during the warfarin maintenance) is unsettled. Methods: Clinical and genetic data form 330 Korean patients with AF (200 had AF-related stroke) were collected and followed for average 36 months. Patients were included who had AF, who were eligible to take warfarin , in whom genetic testing was available, and who were followed for more than 6 months. Thromboembolism and hemorrhagic complication was monitored with clinical and laboratory findings, including thromboemoblic [CHADS2 and CHA2DS2-Vasc] and hemorrhagic [ATRIA] risk schemes, as confounders. Results: Genotypic frequencies of CYP2C9 *1/*1, *1/*3, and *3/*3 were 90%, 6.7%, 0.3%, respectively, whereas VKORC1 +1173 TT, CT, and CC were 84%, 15.2%, 0.6%, respectively. TTR varies greatly depending on the CYP2C9 polymorphism: TTR of INR 2-3 was 65±20% in *1/*1 carriers, 42±22% in *1/*3 carriers, and 1.4±2.2% in *3/*3 carriers. TTR of INR was not different depending on the VKORC1 polymorphism. Conclusions: Novel oral anticoagulants have recently been introduced. However, there is a lack of consensus regarding the indication of these novel agents in patients with AF. Our results indicated that TTR during warfarin maintenance was associated with genetic variability in CYP2C9 than with VKORC1. Warfarin alternatives could be particularly helpful in patients who have specific CYP2C9 polymorphism other than *1/*1. Further studies are needed testing the impact of warfarin genetic polymorphism in other ethnic group (i.e. white) where these CYP2C9 polymorphisms were prevalent.

Pharmacogenomics of warfarin in populations of African descent.

Warfarin is the most commonly prescribed oral anticoagulant worldwide despite its narrow therapeutic index and the notorious inter- and intra-individual variability in dose required for the target clinical effect. Pharmacogenetic polymorphisms are major determinants of warfarin pharmacokinetic and dynamics and included in several warfarin dosing algorithms. This review focuses on warfarin pharmacogenomics in sub-Saharan peoples, African Americans and admixed Brazilians. These 'Black' populations differ in several aspects, notably their extent of recent admixture with Europeans, a factor which impacts on the frequency distribution of pharmacogenomic polymorphisms relevant to warfarin dose requirement for the target clinical effect. Whereas a small number of polymorphisms in VKORC1 (3673G > A, rs9923231), CYP2C9 (alleles *2 and *3, rs1799853 and rs1057910, respectively) and arguably CYP4F2 (rs2108622), may capture most of the pharmacogenomic influence on warfarin dose variance in White populations, additional polymorphisms in these, and in other, genes (e.g. CALU rs339097) increase the predictive power of pharmacogenetic warfarin dosing algorithms in the Black populations examined. A personalized strategy for initiation of warfarin therapy, allowing for improved safety and cost-effectiveness for populations of African descent must take into account their pharmacogenomic diversity, as well as socio-economical, cultural and medical factors. Accounting for this heterogeneity in algorithms that are 'friendly' enough to be adopted by warfarin prescribers worldwide requires gathering information from trials at different population levels, but demands also a critical appraisal of racial/ethnic labels that are commonly used in the clinical pharmacology literature but do not accurately reflect genetic ancestry and population diversity.

Creating a genotype-based dosing algorithm for acenocoumarol steady dose

Acenocoumarol is a commonly prescribed anticoagulant drug for the prophylaxis and treatment of venous and arterial thromboembolic disorders in several countries. In counterpart of warfarin, there is scarce information about pharmacogenetic algorithms for steady acenocoumarol dose estimation. The aim of this study was to develop an algorithm of prediction for acenocoumarol.The algorithm was created using the data from 973 retrospectively selected anticoagulated patients and was validated in a second independent cohort adding up to 2,683 patients. The best regression model to predict stable dosage in the Primary Cohort included clinical factors (age and body mass index, BSA) and genetic variants (VKORC1, CYP2C9* and CYP4F2 polymorphisms) and explained up to 50% of stable dose. In the validation study the clinical algorithm yielded an adjusted R²=0.15 (estimation´s standard error=4.5) and the genetic approach improved the dose forecast up to 30% (estimation´s standard error=4.6). Again, the best model combined clinical and genetic factors (R² = 0.48; estimation´s standard error=4) which provided the best results of doses estimates within 20% of the real dose in patients taking lower (≤ 7 mg/week) or higher (≥ 25 mg/week) acenocoumarol doses. In conclusion, we developed a prediction algorithm using clinical data and three polymorphisms in VKORC1, CYP2C9* and CYP4F2 genes that provided a steady acenocoumarol dose for about 50% of patients in the Validation Cohort. Such algorithm was especially useful to patients who need higher or lower acenocoumarol doses, those patients with higher time required until their stabilisation and are more prone to suffer a treatment derived complication.

A Case of Warfarin-Induced Bleeding in a Patient with CYP2C9 and VKORC1 Gene Polymorphism, Detected by a Point-of-Care Gene Test Device

A 69-year-old female Korean patient was initially prescribed warfarin for the prevention of systemic thromboembolism due to atrial fibrillation. One month later, multiple bruises and subcutaneous hematomas were evident, and laboratory testing revealed a prolonged prothrombin time (PT) of > 106s. After admission, the PT was corrected via fresh frozen plasma transfusion and intravenous vitamin K infusion. We sought to determine the cause of the PT prolongation, suspecting that genetic cause may have had an effect on the variation in the warfarin dose requirement. A point-of-care gene test device (Verigene Ⓡ system; Nanosphere, Northbrook, IL) revealed CYP2C9 *1/*3 heterozygosity and a VKORC1 A/A single nucleotide polymorphism. Although it is well established that CYP2C9 or VKORC1 gene polymorphisms can influence warfarin dose requirements, they can be easily neglected, with detrimental outcomes. Through our experience with CYP2C9 and VKORC1 polymorphism causing bleeding complications during warfarin treatment, we aim to emphasize the importance of pharmacogenetic testing to avoid this potential oversight. (Korean J Med 2013;85:87-91)

VKORC1 and CYP2C9 Genotype Variations in Relation to Warfarin Dosing in Korean Stroke Patients

Background and PurposeVariant alleles of CYP2C9 and VKORC1 account for differences in anticoagulation response. We sought to establish a warfarin dosing formula for individualized target International Normalization Ratio of Prothrombin Times (INRs) using data from single nucleotide polymorphisms (SNPs) in VKORC1 and CYP2C9 in Korean patients.MethodsIschemic stroke patients displaying stable target INR for at least 3 months before enrollment were analyzed. Warfarin and vitamin K levels were measured to adjust for confounders. Phenotypes were defined using the 'warfarin response index' (WRI) defined as INR divided by the daily maintenance warfarin dose. We tested SNPs in CYP2C9 (3 sites: 430C>T (rs1799853), 1075A>C (rs1057910), 1076T>C) and VKORC1 (14 sites: 381C>T, 861C>A (rs17880887), 2653G>C, 3673A>G, 5496G>T, 5808T>G (r17882154), 6009C>T, 6484T>C (rs9934438), 6853C>T (rs17886369), 7566T>C, 8767G>C, 8814T>C, 9041G>A (rs17880624), and 9071G>T) using a standard sequencing method. Multivariate linear regression analysis was applied to establish the formula for warfarin dosage.ResultsAll 204 patients had excellent drug compliance. The mean INR was 2.22 (+0.56) and mean daily maintenance dose of warfarin was 3.92 mg (+1.54). Patients with low WRI were younger (P<0.001) with high body mass index (P=0.003), high prevalence of wild-type CYP2C9 polymorphism (1075A>C, P<0.001), and six heterozygote SNPs in VRORC1 (P<0.001), which were tightly interlinked (381T>C, 3673G>A, 6484T>C, 6853C>G. 7566C>T, 9041G>A) (r2=1). Based on these data, a warfarin dosing formula was established.ConclusionsWRI is influenced by age, body mass index and SNPs in VKORC1 and CYP2C9 in Korean stroke patients. The obtained warfarin dosing formula may be clinically applicable.

Association of FunctionalVKORC1Promoter Polymorphism with Occurrence and Clinical Aspects of Ischemic Stroke in a Greek Population

Genetic factors are considered to play an important role in determining the susceptibility to the occurrence, clinical course, and functional outcome of an acute ischemic stroke (IS). Undercarboxylation of specific vitamin K-dependent proteins, due to genetic polymorphisms of VKORC1, can affect both vascular calcification and thrombogenicity. We sought to determine the association of VKORC1 −1639G > A polymorphism with IS incidence, age of onset, severity of disease, and functional outcome after an acute IS. VKORC1 −1639G > A polymorphism was determined in 145 consecutive patients with first ever IS and 145 age- and sex-matched control subjects of Greek Caucasian origin using PCR-RFLP. Stroke severity and functional outcome were assessed on admission and at one month after stroke, respectively. Frequency of VKORC1 −1639G > A genotypes did not differ between IS patients and controls (OR = 1.12, P = 0.51). Moreover, carriage of the A allele was not associated with age of stroke onset, severity of disease (Scandinavian stroke scale score 32.2 versus 32.9, resp., P = 0.96), or poor outcome at 1 month post-stroke (52.9 versus 64.4%, resp., P = 0.31). In conclusion, VKORC1 −1639G > A polymorphism is not a genetic determinant of IS occurrence, age of onset, severity, or functional outcome of disease in a Greek population.

Impact of Genetic Factors (CYP2C9,VKORC1 and CYP4F2) on Warfarin Dose Requirement in the Turkish Population

Warfarin has a narrow therapeutic index and displays marked person-to-person variation in dose requirement. Functional polymorphisms at candidate genes can therefore offer utility as biomarkers to individualize warfarin treatment. The main objective of this study was to determine whether and to what extent variability in warfarin dose requirements was determined by polymorphisms in CYP2C9, VKORC1, CYP4F2 (rs2108622) and EPHX1 (rs2292566) in the Turkish population. Patients (n = 107) who had stable doses and international normalized ratio (INRs) at their last three consecutive visits were registered. Their demographic factors, concurrent medications, warfarin-related bleedings or thromboembolisms, smoking, alcohol intake and weekly green vegetable consumption were recorded. From a blood sample, DNA was isolated and genotyped by real-time PCR for polymorphisms of CYP2C9, VKORC1, CYP4F2 and EPHX1. A regression analysis was used to determine the independent effects of genetic and non-genetic factors on warfarin dose optimization. In our study, in addition to age, genetic variants of CYP2C9, VKORC1 and CYP4F2 were found to be significant predictor variables for the maintenance dose for warfarin, explaining 39.3% of dose variability. VKORC1 and CYP2C9 genotypes remain predictor variables of the warfarin dose, and we first found that CYP4F2 (rs2108622) contributes to dose variability in the Turkish population as well. These observations may be of benefit to future translation research with a view to global personalized medicine in regions hitherto understudied such as the Turkish population so as to rationalize initial warfarin dose and reduce the burden of frequent INR measurements.

Genetic and Clinical Determinants Influencing Warfarin Dosing in Children With Heart Disease

Warfarin is a common anticoagulant with narrow therapeutic window and variable anticoagulation effects. Single gene polymorphisms in cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase (VKORC1) have been shown to impact warfarin dosing in adults. Insufficient data exists on genetic and clinical factors which influence warfarin dosing in children. Pediatric patients with heart disease who received long-term warfarin therapy were tested for VKORC1 and CYP2C9 polymorphisms. Clinical and demographic data were reviewed in those children who achieved stable therapeutic international normalized ratio (INR). Multiple linear regression modeling was used to assess relationships between stable warfarin doses and genetic or clinical variables. Fifty children were tested for VKORC1 and CYP2C9 polymorphisms; 37 patients (M 26: F 11) had complete data, achieved stable therapeutic INR, and were included in dose variability analysis. There were predominance of white race 73% and male sex 70.3%. The mean age was 9.6 years (1.8-18.6 years). The mean weight was 37.8 kg (7.7-95 kg). Fontan physiology and mechanical cardiac valves were two most common indications for chronic warfarin therapy (25/37 or 67.6%). Twelve patients (32.4%) had ≥ 2 indications for warfarin therapy. Three patients had documented venous or arterial clots, and 5 patients had strokes. Congenital heart disease was present in 29 patients (78.4%), including Fontan physiology (20), complex biventricular physiology (4), and congenital mitral valve disease (5). Acquired heart disease was present in 8 patients (21.6%), including Kawasaki disease with coronary aneurysms (3), acquired mitral valve disease (3), and Marfan syndrome (2). Stable warfarin dose (mg/kg/day) was strongly associated with VKORC1 polymorphism (p < 0.0001) and goal therapeutic INR (p = 0.009). Negative correlations were observed between stable warfarin dose and age, weight, height, and BSA (p = 0.04, 0.02, 0.02, and 0.02 respectively). Factors which did not influence warfarin dose included CYP2C9 polymorphism (p = 0.17), concurrent medications (p = 0.85), sex (p = 0.4), race (p = 0.14), congenital heart disease (p = 0.09), and Fontan physiology (p = 0.76). The gene-dose effect was observed in children with homozygous wild type VKORC1 CC, who required higher warfarin dose compared to those carrying heterozygous TC or homozygous TT (p = 0.028 and 0.0004 respectively). The full multiple linear regression model revealed that VKORC1 genotypes accounted for 47% of dosing variability; CYPC29 accounted for 5%. Overall, the combination of VKORC1, CYP2C9, age, and target INR accounted for 82% of dosing variability. In children with heart disease, VKORC1 genotypes, age, and target INR are important determinants influencing warfarin dosing in children with heart disease. Future warfarin dosing algorithm in children should factor both genetic and clinical factors.

The impact of the CYP2C9 and VKORC1 polymorphisms on acenocoumarol dose requirements in a Romanian population

To investigate the genotype-phenotype correlation in Romanian patients treated with acenocoumarol. We studied 301 consecutive patients who required treatment with acenocoumarol, admitted within the Municipal Hospital of Cluj-Napoca and the Heart Institute "Niculae Stănciou" in Cluj-Napoca over a 3-year period. For each patient we recorded clinical parameters which could interfere with the achievement of stable therapeutic international normalized ratio (INR). We performed genetic analysis which consisted of genotyping the CYP2C9 gene and the VKORC1 gene. Patients were divided in three groups according to the acenocoumarol dose needed to reach a stable INR: the low dose group (≤7mg/week), the medium dose group (>7mg and <28mg/week) and the high acenocoumarol dose group (>28mg/week). We found that patients' age was significantly different between groups (p<0.001). No differences existed between groups regarding the pathologies which required anticoagulation therapy or the concomitant treatment. The following parameters increased the odds of receiving a low dose of acenocoumarol: patient's age over 65years (OR, 3.2; p=0.01; 95%CI: 1.24-8.25), the presence of the CYP2C9*3 allele (OR, 3.4; p=0.006; 95%CI: 1.41-8.34), and the GA or AA genotype of c.-1639G>A polymorphism of VKORC1 (OR, 6.5; p=0.01; 95%CI: 1.38-30.5; respectively OR, 11.6; p=0.003; 95%CI: 2.26-59.58). A high acenocoumarol dose was less likely to be administered to an elderly patient (OR, 0.24; p=0.001; 95%CI: 0.1-0.56) or to a patient with the GA or AA genotype (OR, 0.2; p<0.001; 95CI%: 0.09-0.45; respectively OR, 0.05; p=0.006; 95%CI: 0.007-0.43). The stable therapeutic dose of acenocoumarol is dependent of patient's age, the presence of the CYP2C9*3 allele and the c.-1639G>A polymorphism of VKORC1.

Impact of the CYP4F2 p.V433M Polymorphism on Coumarin Dose Requirement: Systematic Review and Meta-Analysis

A systematic review and a meta-analysis were performed to quantify the accumulated information from genetic association studies investigating the impact of the CYP4F2 rs2108622 (p.V433M) polymorphism on coumarin dose requirement. An additional aim was to explore the contribution of the CYP4F2 variant in comparison with, as well as after stratification for, the VKORC1 and CYP2C9 variants. Thirty studies involving 9,470 participants met prespecified inclusion criteria. As compared with CC-homozygotes, T-allele carriers required an 8.3% (95% confidence interval (CI): 5.6-11.1%; P<0.0001) higher mean daily coumarin dose than CC homozygotes to reach a stable international normalized ratio (INR). There was no evidence of publication bias. Heterogeneity among studies was present (I(2) = 43%). Our results show that the CYP4F2 p.V433M polymorphism is associated with interindividual variability in response to coumarin drugs, but with a low effect size that is confirmed to be lower than those contributed by VKORC1 and CYP2C9 polymorphisms.

C0178 CYP2C9 and VKORC1 gene polymorphisms in the healthy Russian and Buryat respondents in Transbaikalia

It is now widely studied the prevalence of polymorphisms of genes CYP2C9 and VKORC1 among the Russian population, as they play an important role in warfarin therapy in patients with chronic atrial fibrillation. According to the literature the incidence of CYP2C9*2 (Ile359Leu) -11% in the Russian population, which corresponds to that of the European. As a result of genotyping studies conducted in the Moscow regionVKORC1 (polymorphic marker G3730A) genotype GG was detected in 31% of respondens, the genotype GA - 55%, and genotype AA - 14% of people.

CYP2C9 and VKORC1 polymorphisms influence warfarin dose variability in patients on long-term anticoagulation

The main aim of this study was to determine whether CYP2C9 and VKORC1 polymorphisms influence warfarin dose variability during initial dose-finding phase and during maintenance treatment after 360 days. Two hundred and six consecutive patients who were beginning warfarin therapy were selected. They were assessed for general and clinical characteristics; prescribed warfarin dose; response to therapy on days 7-10, 30, 60, 180, and 360; adverse events; and CYP2C9 2, 3, 5, 6, 8, 11, and VKORC1 1639G >A assays. During the first 30 days of anticoagulation, the relative variability of warfarin dose was significantly associated with CYP2C9*2 and CYP2C9*3 polymorphisms (p = 0.02) and with VKORC1 1639G >A genotypes (p = 0.04). Warfarin variability was also statistically different according to predicted metabolic phenotype and to VKORC1 genotypes after 360 days of treatment, and in the phase between 180 and 360 days (long-term dose variability). Both CYP2C9 and VKORC1 polymorphisms were associated with the international normalized ratio (INR) made between 7 and 10 days/initial dose ratio, adjusted for covariates (p < 0.01 and p = 0.02, respectively). Patients carrying VKORC1 and CYP2C9 variants presented lower required dose (at the end of follow-up of 360 days) compared to patients carrying wild-type genotypes (p = 0.04 and p = 0.03, respectively). Genetic information on CYP2C9 and VKORC1 is important both for the initial dose-finding phase and during maintenance treatment with warfarin.

Cost–Effectiveness of Pharmacogenetics in Anticoagulation: International Differences in Healthcare Systems and Costs

Genotyping patients for CYP2C9 and VKORC1 polymorphisms can improve the accuracy of dosing during the initiation of anticoagulation with vitamin K antagonists (coumarin derivatives). The anticipated degree of improvement in the safety of anticoagulation with coumarins through genotyping may vary depending on the quality of patient care, which varies both with and among countries. The management and the cost of anticoagulant care can therefore influence the cost-effectiveness of genotyping within any given country. In this article, we provide an overview of the cost-effectiveness of pharmacogenetics-guided dosing of coumarin derivatives. We describe the organization of anticoagulant care in the UK, Sweden, The Netherlands, Greece, Germany and Austria, where a genotype-guided dosing algorithm is currently being investigated as part of the EU-PACT trial. We also explore the costs of anticoagulant care for the treatment of atrial fibrillation in these countries.

VKORC1 rs2359612C allele is associated with increased risk of coronary artery disease in the presence of coronary calcification

VKORC1 genetic polymorphisms affect warfarin dose response, aortic calcification, and the susceptibility of coronary artery disease as shown in our previous study. Little is known regarding the association of VKORC1 polymorphisms with coronary artery calcification (CAC) and the role of CAC in the association with coronary artery disease (CAD). Due to a natural haplotype block in the VKORC1 gene in Chinese, polymorphism rs2359612 was analyzed in a case-control study and a prospective study. The case-control study included 464 CAD patients with non-calcified plaque (NCP), 562 CAD patients with mixed calcified plaque (MCP), 492 subjects with calcified plaque (CP), and 521 controls. The rs2359612C was only associated with increased risk of MCP, the CAD in the presence of CAC; the odds ratio was 1.397 (95 % CI 1.008-1.937, P < 0.05), which was replicated in the second independent population. On the contrary, a negative correlation was observed between rs2359612 and log-transformed Agatston score, and rs2359612 was negatively associated with the number of calcified vessels. Moreover, in a prospective study including 849 CAD patients undergoing revascularization, rs2359612C predicted a higher incidence of cardiovascular events in MCP subgroup; the relative risk was 1.435 (95 % CI 1.008-2.041, P = 0.045), which was not observed in the NCP subgroup. We conclude that the rs2359612C was associated with a higher risk of CAD in the presence of CAC and a higher incidence of cardiovascular events in CAD patients with CAC, but a lower coronary calcification. VKORC1 polymorphisms may be associated with the endophenotype of CAD, calcification-related atherosclerosis.

Responsiveness to low-dose warfarin associated with genetic variants of VKORC1, CYP2C9, CYP2C19, and CYP4F2 in an Indonesian population

The aim of this study was to assess the pharmacokinetics and pharmacodynamics of warfarin associated with genetic polymorphisms in VKORC1, CYP2C9, CYP2C19, and CYP4F2 in Indonesian patients treated with low-dose warfarin. Genotyping of VKORC1, CYP2C9, CYP2C19, and CYP4F2 was carried out in 103 patients treated with a daily dose of 1-2 mg warfarin, 89 of whom were treated with a fixed daily dose of warfarin (1 mg). The plasma concentrations of S- and R-warfarin and S- and R-7-hydroxywarfarin were used as pharmacokinetic indices, while prothrombin time expressed as the international normalized ratio (PT-INR) was used as a pharmacodynamic index. In patients treated with a fixed daily dose of warfarin (1 mg), a higher PT-INR was associated with VKORC1-1639 AA [median 1.35; interquartile range (IQR) 1.21-1.50] than with the GA (1.18; IQR 1.12-1.32; p < 0.01) and GG (1.02; IQR = 1.02-1.06; p < 0.01) polymorphisms, and with CYP2C9*1/*3 (1.63; IQR 1.45-1.85) compared to *1/*1 (1.23; IQR 1.13-1.43; p < 0.05). The S-warfarin concentration was significantly higher in patients with CYP2C9*1/*3 than in those with *1/*1 (p < 0.05). With low-dose warfarin administration, there was no significant difference in the concentrations of warfarin metabolites among any of the genotype variants. The genotype variations of CYP2C19 and CYP4F2 were not significantly associated with the PT-INR. For low-dose warfarin treatment, the VKORC1-1639 G > A and CYP2C9 genotype variations affected the pharmacokinetics and pharmacodynamics of warfarin, while we could not find significant effects of CYP4F2 or CYP2C19 genotype variations on warfarin (metabolite) concentrations or PT-INR.

Warfarin Anticoagulation in Children: Is there a Role For a Personalized Approach to Dosing?

There is an increasing need for safe and effi­ cacious anticoagulant therapy in childhood. Despite the advent of the new oral anti­ coagulants, the vitamin K antagonists (VKAs), most often warfarin, remain the agents of choice for long­term anticoagulant therapy in children [1]. Maintenance of anticoagulation intensity within the therapeutic range is essential in order to ensure efficacy and safety of warfarin treat­ ment. Poor anticoagulation control can result in hemorrhage due to overdosing and thrombo­ embolic events due to underdosing. There is wide interindividual variability in warfarin dose requirement in children, some of which results from age­dependent differences in the disposi­ tion and activity of warfarin. Factors that influ­ ence warfarin­dose requirement in children have been little studied until recently [2]. In adults, polymorphisms in CYP2C9 and VKORC1, the key genes involved in the meta­ bolism and action of warfarin, are responsible for a large part of the interindividual variability in dose requirement [3,4]. Pharmacogenetics­based warfarin­dosing algorithms have been developed and evaluated in adults [5]. Recent studies have highlighted an advantage to this approach over standard empirical warfarin dosing in terms of improving the accuracy of dose prediction and reducing hemorrhagic complications during warfarin initiation [6]. The availability of plat­ forms upon which to perform rapid genotyping has made pharmacogenetics­based dosing a real potential for clinical practice [7]. Studies of the factors that influence warfarin­ dose requirement in children have consistently confirmed the presence of a relationship between age and the maintenance dose as a function of bodyweight. Streif et al. reported that the weight­adjusted warfarin dose required to main­ tain a target International Normalized Ratio (INR) range of 2–3 was highest in youngest children (age ≤1 year, 0.33 ± 0.20 mg/kg) and fell with increasing age (age 2–5 years, 0.15 ± 0.10 mg/kg; age 6–12 years, 0.13 ± 0.06 mg/kg; age 13–18 years, 0.09 ± 0.05 mg/kg) [8]. This effect has been confirmed by subsequent studies suggesting that younger children may have an increased capacity for warfarin clearance com­ pared with older children. Although weight­ adjusted warfarin dose shows an inverse rela­ tionship with age, the mean dose of warfarin required to maintain a therapeutic target INR still rises overall with increasing age [2].

Validation of pharmacogenetic algorithms and warfarin dosing table in Egyptian patients

Warfarin remains a difficult drug to use due to the large variability in dose response. Clear understanding of the accuracy of warfarin pharmacogenetic dosing methods might lead to appropriate control of anticoagulation. This study aims to evaluate the accuracy of warfarin dosing table and two pharmacogenetic algorithms, namely the algorithms of Gage et al. (Clin Pharmacol Ther 84:326-331, 2008), and the International Warfarin Pharmacogenetics Consortium algorithm (IWPC) in a real Egyptian clinical setting. Additionally, three non-pharmacogenetic dosing methods (the Gage, IWPC clinical algorithms and the empiric 5 mg/day dosing) were evaluated. Sixty-three Egyptian patients on a stable therapeutic warfarin dose were included. Patients were recruited from the outpatient clinic of the critical care medicine department. CYP2C9 and VKORC1 polymorphisms were genotyped by real time PCR system. Predicted doses by all dosing methods were calculated and compared with the actual therapeutic warfarin doses. The Gage algorithm (adjusted R(2) = 0.421, and mean absolute error (MAE) = 3.3), and IWPC algorithm (adjusted R(2) = 0.419, MAE = 3.2) produced better accuracy than did the warfarin dosing table (adjusted R(2) = 0.246, MAE = 3.5), the two clinical algorithms (R(2) = 0.24, MAE = 3.7) and the fixed dose approach (MAE = 3.9). However, all dosing models produced comparable clinical accuracy with respect to proportion of patients within 1 mg/day of actual dose (ideal dose). Non-pharmacogenetic methods severely over-predicted dose (defined as ≥2 mg/day more than actual dose) compared to the three pharmacogenetic models. In comparison to non-pharmacogenetic methods, the three pharmacogenetic models performed better regarding the low dose group in terms of percentage of patients within ideal dose. In the high dose group, none of the dosing models predicted warfarin doses within ideal dose. Our study showed that genotype-based dosing improved prediction of warfarin therapeutic dose beyond that available with the fixed-dose approach or the clinical algorithms, especially in the low-dose group. However, the two pharmacogenetic algorithms were the most accurate.