A new warfarin dosing algorithm including VKORC1 3730 G > A polymorphism: comparison with results obtained by other published algorithms

Association between CYP2C9 and VKORC1 genetic polymorphisms and efficacy and safety of warfarin in Chinese patients

OBJECTIVES

Genetic variation has been a major contributor to interindividual variability of warfarin dosage requirement. The specific genetic factors contributing to warfarin bleeding complications are largely unknown, particularly in Chinese patients. In this study, 896 Chinese patients were enrolled to explore the effect of CYP2C9 and VKORC1 genetic variations on both the efficacy and safety of warfarin therapy.

METHODS AND RESULTS

Univariate analyses unveiled significant associations between two specific single nucleotide polymorphisms rs1057910 in CYP2C9 and rs9923231 in VKORC1 and stable warfarin dosage ( P  < 0.001). Further, employing multivariate logistic regression analysis adjusted for age, sex and height, the investigation revealed that patients harboring at least one variant allele in CYP2C9 exhibited a heightened risk of bleeding events compared to those with the wild-type genotype (odds ratio = 2.16, P  = 0.04). Moreover, a meta-analysis conducted to consolidate findings confirmed the associations of both CYP2C9 (rs1057910) and VKORC1 (rs9923231) with stable warfarin dosage. Notably, CYP2C9 variant genotypes were significantly linked to an increased risk of hemorrhagic complications ( P  < 0.00001), VKORC1 did not demonstrate a similar association.

CONCLUSION

The associations found between specific genetic variants and both stable warfarin dosage and bleeding risk might be the potential significance of gene detection in optimizing warfarin therapy for improving patient efficacy and safety.

Identification and in vitro functional assessment of 10 CYP2C9 variants found in Chinese Han subjects

Cytochrome P450 2C9 (CYP2C9) participates in about 15% of clinical drug metabolism, and its polymorphism is associated with individual drug metabolism differences, which may lead to the adverse drug reactions (ADRs). In this study, 1163 Chinese Han individuals were recruited to investigate their distribution pattern of CYP2C9 gene and find out the variants that may affect their drug metabolic activities. We successfully developed a multiplex PCR amplicon sequencing method and used it for the genetic screening of CYP2C9 in a large scale. Besides the wild type CYP2C9*1, totally 26 allelic variants of CYP2C9 were detected, which included 16 previously reported alleles and 10 new non-synonymous variants that had not been listed on the PharmVar website. The characteristics of these newly detected CYP2C9 variants were then evaluated after co-expressing them with CYPOR in S. cerevisiae microsomes. Immunoblot analysis revealed that except for Pro163Ser, Glu326Lys, Gly431Arg and Ile488Phe, most of newly detected variants showed comparable protein expression levels to wild type in yeast cells. Two typical CYP2C9 probe drugs, losartan and glimepiride, were then used for the evaluation of metabolic activities of variants. As a result, 3 variants Thr301Met, Glu326Lys, and Gly431Arg almost lost their catalytic activities and most of other variants exhibited significantly elevated activities for drug metabolism. Our data not only enriches the knowledge of naturally occurring CYP2C9 variants in the Chinese Han population, but also provides the fundamental evidence for its potential clinical usage for personalized medicine in the clinic.

Opposite Response to Vitamin K Antagonists: A Report of Two Cases and Systematic Review of Literature

Vitamin K antagonists (VKAs) are used in the prophylaxis and treatment of thromboembolic disorders. Despite a high efficacy, their narrow therapeutic window and high response variability hamper their management. Several patients experience fluctuations in dose−response and are at increased risk of over- or under-anticoagulation. Therefore, it is essential to monitor the prothrombin time/international normalized ratio to determine the so-called stable dose and to adjust the dosage accordingly. Three polymorphisms, CYP2C9∗2, CYP2C9∗3 and VKORC1-1639G>A, are associated with increased sensitivity to VKAs. Other polymorphisms are associated with a request for a higher dose and VKA resistance. We described the clinical cases of two patients who were referred to the Clinical Pharmacology and Pharmacogenetics Unit of the University Hospital of Salerno for pharmacological counseling. One of them showed hypersensitivity and the other one was resistant to VKAs. A systematic review was performed to identify randomized clinical trials investigating the impact of pharmacogenetic testing on increased sensitivity and resistance to VKAs. Although international guidelines are available and information on the genotype-guided dosing approach has been included in VKA drug labels, VKA pharmacogenetic testing is not commonly required. The clinical cases and the results of the systematically reviewed RCTs demonstrate that the pharmacogenetic-based VKA dosing model represents a valuable resource for reducing VKA-associated adverse events.

Long Short-Term Memory Network for Development and Simulation of Warfarin Dosing Model Based on Time Series Anticoagulant Data

Background

Warfarin is an effective treatment for thromboembolic disease but has a narrow therapeutic index, and dosage can differ tremendously among individuals. The study aimed to develop an individualized international normalized ratio (INR) model based on time series anticoagulant data and simulate individualized warfarin dosing.

Methods

We used a long short-term memory (LSTM) network to develop an individualized INR model based on data from 4,578 follow-up visits, including clinical and genetic factors from 624 patients whom we enrolled in our previous randomized controlled trial. The data of 158 patients who underwent valvular surgery and were included in a prospective registry study were used for external validation in the real world.

Results

The prediction accuracy of LSTM_INR was 70.0%, which was much higher than that of MAPB_INR (maximum posterior Bayesian, 53.9%). Temporal variables were significant for LSTM_INR performance (51.7 vs. 70.0%, P < 0.05). Genetic factors played an important role in predicting INR at the onset of therapy, while after 15 days of treatment, we found that it might unnecessary to detect genotypes for warfarin dosing. Using LSTM_INR, we successfully simulated individualized warfarin dosing and developed an application (AI-WAR) for individualized warfarin therapy.

Conclusion

The results indicate that temporal variables are necessary to be considered in warfarin therapy, except for clinical factors and genetic factors. LSTM network may have great potential for long-term drug individualized therapy.

Trial Registration

NCT02211326; www.chictr.org.cn:ChiCTR2100052089.

Comparison of multivariate linear regression and a machine learning algorithm developed for prediction of precision warfarin dosing in a Korean population

BACKGROUND

Personalized warfarin dosing is influenced by various factors including genetic and non-genetic factors. Multiple linear regression (LR) is known as a conventional method to develop predictive models. Recently, machine learning approaches have been extensively implemented for warfarin dosing due to the hypothesis of non-linear association between covariates and stable warfarin dose.

OBJECTIVE

To extend the multiple linear regression algorithm for personalized warfarin dosing in a Korean population and compare with a machine learning--based algorithm.

METHOD

From this cohort study, we collected information on 650 patients taking warfarin who achieved steady state including demographic information, indications, comorbidities, comedications, habits, and genetic factors. The dataset was randomly split into training set (90%) and test set (10%). The LR and machine learning (gradient boosting machine [GBM]) models were developed on the training set and were evaluated on the test set.

RESULT

LR and GBM models were comparable in terms of accuracy of ideal dose (75.38% and 73.85%), correlation (0.77 and 0.73), mean absolute error (0.58 mg/day and 0.64 mg/day), and root mean square error (0.82 mg/day and 0.9 mg/day), respectively. VKORC1 genotype, CYP2C9 genotype, age, and weight were the highest contributors and could obtain 80% of maximum performance in both models.

CONCLUSION

This study shows that our LR and GMB models are satisfactory to predict warfarin dose in our dataset. Both models showed similar performance and feature contribution characteristics. LR may be the appropriate model due to its simplicity and interpretability.

Pharmacogenetics of Warfarin in a Diverse Patient Population

INTRODUCTION

Many warfarin-related genotypes have shown to impact the average daily warfarin (ADW) dose requirements; however, information in non-Caucasian populations is limited.

OBJECTIVES

To identify the frequencies of 4 warfarin-related gene polymorphisms in an ethnically diverse patient population and to examine their impact with other clinical variables on ADW dose requirements.

METHODS

Patients were recruited from 2 anticoagulation clinics in the Los Angeles area. Blood samples were collected and genotyped for vitamin K epoxide reductase (VKORC1), CYP2C9*2, CYP2C9*3, and CYP4F2 after informed consent. Charts were reviewed to collect demographic, clinical, and warfarin dosing data.

RESULTS

A total of 291 patients were included (120 Caucasians, 127 Hispanics, and 44 Asians). In patients with wild-type genotypes for VKORC1, CYP2C9*2, CYP2C9*3, and CYP4F2, the highest warfarin requirement was found in Caucasians, lower in Hispanics, and lowest in Asians. Homozygous VKORC1 variant carriers were detected in 15%, 15%, and 79% in Caucasians, Hispanics, and Asians, respectively. Progressive lowering of ADW doses were associated with each VKORC1 variant in Caucasians and Hispanics, but the results in wild-type/ heterozygote Asians were unclear. CYP2C9 variants were associated with lower ADW doses; frequencies of CYP2C9*2 and CYP2C9*3 mutations were higher in Caucasians than in Hispanics but rare to none in Asians. The frequencies of CYP4F2 variant were similar across all ethnicities, but their impact on warfarin dose requirement were insignificant. Clinical factors such as age, body surface area, history of coronary artery disease, deep vein thrombosis or atrial fibrillation, and concomitant amiodarone or HMG-CoA reductase inhibitors had varying impact on the ADW requirements in the ethnicities studied.

CONCLUSIONS

Our study demonstrated differences among 3 ethnic groups in terms of ADW dose requirements and the impact of associated clinical variables. The results suggest that a single model for all ethnicities may not provide the best performance in predicting warfarin dose requirements.

Pharmacogenetics of warfarin dosing in patients of African and European ancestry

Despite the introduction of direct acting oral anticoagulants, warfarin remains the most commonly prescribed oral anticoagulant. However, warfarin therapy is plagued by the large inter- and intrapatient variability. The variability in dosing fueled research to identify clinical and genetic predictors and develop more accurate dosing algorithms. Observational studies have demonstrated the significant impact of single nucleotide polymorphisms in CYP2C9 and VKORC1 on warfarin dose in patients of European ancestry and African-Americans. This evidence supported the design and conduct of clinical trials to assess whether genotype-guided dosing results in improved anticoagulation control and outcomes. The trial results have shown discordance by race, with pharmacogenetic algorithms improving dose and anticoagulation control among European ancestry patients compared with African-American patients. Herein, we review the evidence from observational and interventional studies, highlight the need for inclusion of minority race groups and propose the need to develop race specific dosing algorithms.

Association between genetic polymorphisms of CYP2C9 and VKORC1 and safety and efficacy of warfarin: Results of a 5 years audit

Objective

Genetic polymorphisms of CYP2C9 and VKORC1 play major role in pharmacokinetics and pharmacodynamics of warfarin, respectively. Purpose of our study was to assess the utility of pretesting patients for the above mutations in predicting tendency for bleeding and achieving target INR.

Methods

This was an audit of data collected between July 2011 and December 2016. For safety and efficacy, patients were divided into two subgroups: those with or without bleeding and those who achieved target INR or not. Chi square test was applied to compare the between group differences and crude Odds Ratio (cOR) calculated.

Results

Among 521 patients evaluated, most common indication for warfarin therapy was valvular heart disease (210/521 = 40%); 36% (187/521) had at least one bleeding episode; 56% (269/479) had below target INR. 26% (136/521) had polymorphic alleles of CYP2C9 and 69% (358/521) had the GG haplotype of VKORC1. Polymorphic alleles of CYP2C9 or AG/AA haplotype had twice the odds of bleeding (cOR = 2.14 and 2.44 respectively) relative to those with wild CYP2C9 allele or GG haplotype. Combined CYP2C9 mutant alleles and/or AG/AA haplotypes had thrice the odds of bleeding (cOR = 3.12) relative to those with wild CYP2C9 alleles and GG haplotype. Those with GG haplotype had twice the odds (cOR = 1.81) and those with GG haplotype along with wild CYP2C9 allele had four times the odds (cOR = 4.27) of not achieving the target INR relative to those with other haplotype/alleles. All these associations were statistically significant (p < 0.05).

Conclusions

Pretesting patients for genetic polymorphisms could aid in individualizing warfarin therapy.

Frequency of Common VKORC1 Polymorphisms and Their Impact on Warfarin Dose Requirement in Pakistani Population

Polymorphisms in vitamin K epoxide reductase complex subunit 1 (VKORC1) gene lead to interindividual variability in warfarin dose requirement. The characterization of genotype frequency distribution is required in different populations for construction of customized dosing algorithms to enhance the efficacy and reduce the toxicity of warfarin therapy. This study was carried out in Pakistani population to evaluate the contribution of common VKORC1 polymorphisms to warfarin therapy. A total of 550 stable patients taking warfarin were enrolled after medical history, physical examination, and laboratory investigations. Single blood sample was collected after informed consent. Genomic DNA was extracted and genotype analysis for VKORC1 1173C>T and VKORC1-1639G>A polymorphisms was done by polymerase chain reaction-restriction fragment length polymorphism assay. A number of samples were also analyzed by direct DNA sequencing for validation of results. Data were analyzed using SPSS version 20. Genotype frequency distributions of VKORC1 1173C>T and VKORC1-1639G>A were found to be different from other populations. Both of these polymorphisms did not demonstrate significant effect on warfarin dose requirement. Although Cytochrome P450 2C9 (CYP2C9) and VKORC1 polymorphisms together attributed only 3.8% variability in warfarin dose but it was statistically significant ( p value = .004). It is concluded that there is a need to study genotype frequency distribution and their effect on warfarin dose variability among different populations due to diversity in outcome. At the same time, no effect on warfarin dose variation explained by VKORC1 polymorphisms and small variability explained by studied genotypes stresses the need for exploration of more genetic and nongenetic factors in Pakistani population.

Frequency of Common CYP2C9 Polymorphisms and Their Impact on Warfarin Dose Requirement in Pakistani Population

Polymorphisms in cytochrome P450 (CYP) 2C9 (CYP2C9) gene result in interindividual variability in warfarin dose requirement. There is a need for characterization of genotype frequency distribution in different populations for construction of customized dosing algorithms to enhance the efficacy and reduce the toxicity of warfarin therapy. This study was carried out in Pakistani population to evaluate the contribution of common CYP2C9 polymorphisms to warfarin therapy. A total of 550 stable patients taking warfarin were enrolled after medical history, physical examination, and laboratory investigations. Single blood sample was collected after informed consent. Genomic DNA was extracted, and genotype analysis for CYP2C9*2 and CYP2C9*3 polymorphisms was done by polymerase chain reaction-restriction fragment length polymorphism assay. A number of samples were also analyzed by direct DNA sequencing for validation of the results. Data were analyzed using SPSS version 20. Genotype frequency distribution of CYP2C9*2 and CYP2C9*3 was found to be different from other populations. Of these 2 polymorphisms, CYP2C9*2 did not demonstrate significant effect on warfarin dose requirement, whereas CYP2C9*3 did show significant effect ( P value = .012). It is concluded that there is a need to study genotype frequency distribution and their effect on warfarin dose variability among different populations due to diversity in outcome.

Impact of the CYP4F2 gene polymorphisms on the warfarin maintenance dose: A systematic review and meta-analysis

Warfarin is an oral anticoagulant with significant interpatient variability in dosage. A large number of studies have confirmed that the individual warfarin dose is mainly affected by the cytochrome P450 complex subunit 2C9 and vitamin K epoxide reductase complex subunit 1. However, the association between cytochrome P450 4F2 (CYP4F2) gene polymorphisms and warfarin dosage in the Asian population remains controversial. To investigate the impact of the CYP4F2 polymorphism rs2108622 (p.V433M) on warfarin dose requirement, a systematic review and meta-analysis were conducted. According to the strict inclusion and exclusion criteria set, a comprehensive literature search was performed, and the studies published before August 5, 2015 were searched for in PubMed, EMBASE and the China National Knowledge Infrastructure databases. The references were checked by two independent reviewers. The association between the warfarin maintenance dose and CYP4F2 polymorphism was analyzed. Twenty-two studies were included in the meta-analysis. Compared with the CYP4F2 genotype CC, carriers of the CT and TT genotypes required a 9 [95% confidence interval (CI): 6.0-13.0] and 20% (95% CI, 13.0-27.0) higher warfarin dose, respectively. In the combined analysis, T carriers (CT+TT) required an 11% (95% CI, 8.0-14.0) higher warfarin dose compared to the CC genotype. In addition, there was a 10% (95% CI, 5.0-15.0) higher warfarin dose in TT carriers compared to the CT genotype (all P<0.05). The results of the meta-analysis suggest that the effects of the CYP4F2 polymorphism on individual warfarin dose have a statistically significant difference, and the effect degree is variable in the subgroups. Further studies are expected to explore whether the pharmacogenetics model including the CYP4F2 polymorphism can strengthen the prediction of warfarin dose.

Effects of VKORC1 Genetic Polymorphisms on Warfarin Maintenance Dose Requirement in a Chinese Han Population

Background

VKORC1 is reported to be capable of treating several diseases with thrombotic risk, such as cardiac valve replacement. Some single-nucleotide polymorphisms (SNPs) in VKORC1 are documented to be associated with clinical differences in warfarin maintenance dose. This study explored the correlations of VKORC1–1639 G/A, 1173 C/T and 497 T/G genetic polymorphisms with warfarin maintenance dose requirement in patients undergoing cardiac valve replacement.

Material/Methods

A total of 298 patients undergoing cardiac valve replacement were recruited. During follow-up, clinical data were recorded. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was applied to detect VKORC1–1639 G/A, 1173 C/T and 497 T/G polymorphisms, and genotypes were analyzed.

Results

Correlations between warfarin maintenance dose and baseline characteristics revealed statistical significances of age, gender and operation methods with warfarin maintenance dose (all P<0.05). Warfarin maintenance dose in VKORC1–1639 G/A AG + GG carriers was obviously higher than in AA carriers (P<0.001). As compared with patients with TT genotype in VKORC1 1173 C/T, warfarin maintenance dose was apparently higher in patients with CT genotype (P<0.001). Linear regression analysis revealed that gender, operation method, method for heart valve replacement, as well as VKORC1–1639 G/A and 1173 C/T gene polymorphisms were significantly related to warfarin maintenance dose (all P<0.05).

Conclusions

VKORC1 gene polymorphisms are key genetic factors to affect individual differences in warfarin maintenance dose in patients undergoing cardiac valve replacement; meanwhile, gender, operation method and method for heart valve replacement might also be correlate with warfarin maintenance dose.

Influence of VKORC1 gene polymorphisms on the effect of oral vitamin K supplementation in over-anticoagulated patients

Significant inter-individual variability on the effect of vitamin K to reverse overanticoagulation has been identified. Genetic polymorphisms of the vitamin K epoxide reductase complex subunit 1 (VKORC1) gene might explain in part this variability. The objective of this study was to evaluate the influence of VKORC1 -1639G>A and 3730G>A polymorphisms on the effect of oral vitamin K supplementation in overanticoagulated patients. We performed an interventional trial of oral vitamin K supplementation in over-anticoagulated outpatients (international normalized ratio [INR] ≥ 4). Subjects received vitamin K (2.5-5.0 mg) according to baseline INR and were genotyped by real time polymerase chain reaction (PCR). INR values were determined at 3, 6, 24 and 72 h after supplementation. We evaluated 33 outpatients, 61 % were males, with a mean age of 62 ± 12 years old. There was a significant decrease in INR values over time for both polymorphisms after oral vitamin K. At 3 h after supplementation, patients carrying the G allele for the -1639G>A polymorphism had a greater decrease in INR values compared to AA patients (p < 0.05 for difference among groups; p < 0.001 for time variation; p = 0.001 for time × group interaction), with differences of -1.01 for GG versus AA (p = 0.003) and -0.84 for GA versus AA (p = 0.024). Mean INR value at 24 h was 1.9 ± 0.6 and at 72 h was 2.1 ± 0.7, with no differences among genotypes. No significant interaction was identified between the 3730G>A polymorphism and vitamin K supplementation. Our study indicated that the VKORC1 -1639G>A polymorphism plays a role in the response to acute vitamin K supplementation in over-anticoagulated patients, with faster decrease of INR value in patients carrying the G allele.

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.

Is there a role for MDR1, EPHX1 and protein Z gene variants in modulation of warfarin dosage? a study on a cohort of the Egyptian population

BACKGROUND

There is considerable inter-individual variability in warfarin dosages necessary to achieve target therapeutic anticoagulation. Polymorphisms in genes, which master warfarin pharmacokinetics and pharmacodynamics, might influence warfarin dose variation. Genes encoding drug transporters, such as human multidrug resistance (MDR1), as well as epoxide hydrolase 1 (EPHX1), which is a putative subunit of the vitamin K epoxide reductase, and Protein Z (PZ), which is a vitamin K-dependent plasma glycoprotein, are among those candidate genes.

OBJECTIVE

The purpose of this study was to investigate the contribution of MDR1 C3435T, EPHX1 H139R and PZ A-13G gene polymorphisms in warfarin dose variation in a cohort of the Egyptian population.

METHODS

Eighty-four patients whose international normalized ratio (INR) was in the range of 2-3, 41 males and 43 females, with a mean (±SD) age of 40.9 (13.3) years were recruited into this study. MDR1 C3435T, EPHX1 H139R and PZ A-13G gene polymorphisms were detected by polymerase chain reaction-restriction fragment length polymorphism. Primarily, linear regression analysis, including the variables age, gender, MDR1 C3435T, EPHX1 H139R and combined MDR1 C3435T, EPHX1 H139R and PZ A-13G genotypes, was used to assess the effective factors for warfarin maintenance dose. Secondly, the previously examined cytochrome P450 (CYP) 2C9 A1075C and vitamin K epoxide reductase complex subunit 1 (VKORC1) C1173T were added to the regression analysis.

RESULTS

Warfarin dose/week was not influenced by each of the MDR1 C3435T, EPHX1 H139R, and PZ A-13G gene polymorphisms when examined separately. However, when these single nucleotide polymorphisms (SNPs) were combined, MDR1 TT/EPHX1 RH,RR/PZ AA subjects showed statistically significant increase in warfarin dose/week when compared with MDR1 CC/EPHX1 RH,RR/PZ AA subjects [median (25th-75th percentiles): 49.0 (42.0-59.5) vs. 35.0 (24.5-42.0) mg/week, respectively] (p = 0.014). In contrast, in the presence of wild-type EPHX1 HH, there was a decrease in warfarin dose/week in MDR1 TT subjects when compared with CT and CC subjects [median (25th-75th percentiles): 22.0 (17.5-30.6), 42.0 (35.0-49.0) and 42.0 (28.0-54.3) mg/week, respectively] (p = 0.005 and 0.030, respectively). Age had a significant contribution (p = 0.048) to the overall variability in warfarin dose. Calculated weekly dose = 52.928 - (0.289 × age) + (9.709 × combined genotype). The multivariate linear regression equation of warfarin maintenance dose accounted for about 8 % of variation in dose (R (2) = 0.079), age accounted for 5 % of variation, while combined genotypes added the extra 3 %. However, the new regression equation accounted for 20.9 % of variation in dose. Age accounted for 5 %, while VKORC1 C1173T accounted for an extra 13 % of variation and MDR1 C3435T accounted for the remaining 3 % of variation. Calculated dose = 64.909 - (0.282 × age) - (13.390 × VKORC1) - (7.164 × MDR1). Correlation analysis showed a close and significant relationship between the calculated and actual warfarin dose (r = 0.457; p < 0.0005).

CONCLUSION

Warfarin dose/week was significantly influenced by the combined MDR1 C3435T and EPHX1 H139R gene polymorphism since no polymorphism of PZ A-13G SNP was detected in our studied Egyptian population. Future studies with larger sample size will be needed to confirm our findings before definitive conclusions can be made.

Genetic epidemiology of pharmacogenetic variations in CYP2C9, CYP4F2 and VKORC1 genes associated with warfarin dosage in the Indian population

Aim: Warfarin, a widely used anticoagulant, exhibits large interindividual variability in dose requirements. CYP2C9 and VKORC1 polymorphisms in various ethnic groups have been extensively studied as genetic markers associated with variable drug response. However, allele frequencies of these variants have not been assessed in major ethnic groups in the Indian population. Materials & methods: To study the functional variants known to affect warfarin dosing, we reanalyzed genotype microarray datasets generated as a part of genome-wide association studies as well as data from the Indian Genome Variation database. We examined data from 2680 individuals across 24 ethnically diverse Indian subpopulations. Results: Allelic distribution of VKORC1 (-1639G>A) showed a greater degree of variation across Indian subpopulations, with frequencies as low as 6.5% in an out-group subpopulation to >70% in Tibeto–Burmans. Risk allele frequency of CYP4F2*3 (V433M) was higher in north Indians (0.30–0.44), as compared with other world populations, such as African–American (0.12), Caucasian (0.34) and Hispanic (0.23). TheVKORC1 variant (-1639A) was shown to be prevalent amongst Tibeto–Burmans, whereas CYP2C9 (R144C, I359L) and CYP4F2 (V433M) variants were observed in considerable variability amongst Indo–Europeans. The frequency of CYP2C9*3 (I359L) in north Indians was found to be higher than in most Asian populations. Furthermore, geographical distribution patterns of these variants in north India showed an increased trend of warfarin extensive metabolizers from the Himalayan to Gangetic region. Combined allele frequency (CYP2C9*3 and CYP4F2*3) data suggest that poor metabolizers varied in the range of 0.38–1.85% in Indo–Europeans. Conclusion: Based on genotypic distribution, the majority of the Indian subpopulation might require higher doses for stable anticoagulation, whereas careful assessment is required for Tibeto–Burmans who are expected to have intermediate dose requirement. This is the largest global genetic epidemiological study examining variants associated with warfarin that could potentially be valuable to clinicians in optimizing dosage strategies.

Original submitted 4 April 2014; Revision submitted 23 May 2014

Improvement of anticoagulant treatment using a dynamic decision support algorithm: a Danish Cohort study

INTRODUCTION

Warfarin is the most widely prescribed vitamin K antagonist and in the United States and Europe more than 10 million people are currently in long-term oral anticoagulant treatment. This study aims to retrospectively validate a dynamic statistical model providing dosage suggestions to patients in warfarin treatment.

MATERIALS AND METHODS

The model was validated on a cohort of 553 patients with a mean TTR of 83%. Patients in the cohort were self-monitoring and managed by a highly specialised anticoagulation clinic. The predictive model essentially consists of three parts handling INR history, warfarin dosage and biological noise, which allows for prediction of future INR values and optimal warfarin dose to stay on INR target. Further, the model is based on parameters initially being set to population values and gradually individualised during monitoring of patients.

PRIMARY OUTCOME

Time in therapeutic range was used as surrogate quality measure of the treatment, and model-suggested dosage of warfarin was used to assess the accuracy of the model performance.

RESULTS

The accuracy of the model predictions measured as median absolute error was 0.53 mg/day (interquartile range from 0.25 to 1.0). The model performance was evaluated by the difference between observed and predicted warfarin intake in the preceding week of an INR measurement. In more than 70% of the cases where INR measurements were outside the therapeutic range, the model suggested a more reasonable dose than the observed intake.

CONCLUSION

Applying the proposed dosing algorithm can potentially further increase the time in INR target range beyond 83%.

Effect of CYP2C9, VKORC1, CYP4F2 and GGCX genetic variants on warfarin maintenance dose and explicating a new pharmacogenetic algorithm in South Indian population

OBJECTIVE

To determine the influence of genetic polymorphisms on warfarin maintenance dose and to explicate an algorithm using the pharmacogenetic and clinical factors to determine the maintenance and/or starting dose of warfarin in South Indian patients receiving warfarin therapy.

METHODS

Patients receiving stabilized warfarin therapy (n=257) were included in the study. Single nucleotide polymorphisms (SNPs) of CYP2C9 (rs1799853 and rs1057910), VKORC1 (rs9923231, rs7196161, rs2884737, rs9934438, rs8050894, rs2359612 and rs7294), CYP4F2 (rs2108622) and GGCX (rs11676382) were genotyped by the quantitative real time-PCR method.

RESULTS

The mean daily maintenance dose of warfarin was found to be 4.7 ± 2.1 mg/day. Patients with the CYP2C9*1/*2, *1/*3 and *2/*3 variant genotypes required a 51.0 (2.8 mg), 60.9 (2.3 mg) and 62.2 % (2.2 mg) lower daily maintenance dose of warfarin, respectively, than those patients with the CYP2C9*1/*1 wild-type genotype (5.2 mg) (p<0.0001). The genetic variants of CYP2C9, VKORC1 and GGCX were associated with decreased warfarin dose, except for rs7196161, rs7294 and rs2108622 which were associated with an increased warfarin dose. Genetic variations of CYP2C9 (*2 and *3), VKORC1 (rs9923231, rs7294, rs9934438 and rs2359612), CYP4F2, GGCX and non-genetic factors such as age, body weight, clinical status (post mechanical valve replacement) could explain up to 62.1 % of the overall variation (adjusted r (2) 60.2 %, p<0.0001) in warfarin maintenance dose.

CONCLUSION

Genetic polymorphisms of CYP2C9, VKORC1, CYP4F2 and GGCX are important predictive factors of warfarin maintenance dose, and the developed algorithm will be useful to predict the required maintenance and/or starting warfarin dose in South Indian populations.

Warfarin anticoagulant therapy: a Southern Italy pharmacogenetics-based dosing model

Background and Aim

Warfarin is the most frequently prescribed anticoagulant worldwide. However, warfarin therapy is associated with a high risk of bleeding and thromboembolic events because of a large interindividual dose-response variability. We investigated the effect of genetic and non genetic factors on warfarin dosage in a South Italian population in the attempt to setup an algorithm easily applicable in the clinical practice.

Materials and Methods

A total of 266 patients from Southern Italy affected by cardiovascular diseases were enrolled and their clinical and anamnestic data recorded. All patients were genotyped for CYP2C9*2,*3, CYP4F2*3, VKORC1 -1639 G>A by the TaqMan assay and for variants VKORC1 1173 C>T and VKORC1 3730 G>A by denaturing high performance liquid chromatography and direct sequencing. The effect of genetic and not genetic factors on warfarin dose variability was tested by multiple linear regression analysis, and an algorithm based on our data was established and then validated by the Jackknife procedure.

Results

Warfarin dose variability was influenced, in decreasing order, by VKORC1-1639 G>A (29.7%), CYP2C9*3 (11.8%), age (8.5%), CYP2C9*2 (3.5%), gender (2.0%) and lastly CYP4F2*3 (1.7%); VKORC1 1173 C>T and VKORC1 3730 G>A exerted a slight effect (<1% each). Taken together, these factors accounted for 58.4% of the warfarin dose variability in our population. Data obtained with our algorithm significantly correlated with those predicted by the two online algorithms: Warfarin dosing and Pharmgkb (p<0.001; R² = 0.805 and p<0.001; R² = 0.773, respectively).

Conclusions

Our algorithm, which is based on six polymorphisms, age and gender, is user-friendly and its application in clinical practice could improve the personalized management of patients undergoing warfarin therapy.