Estimation of Warfarin Maintenance Dose Based on VKORC1 (−1639 G>A) and CYP2C9 Genotypes

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.

Interaction of the lysozyme with anticoagulant drug warfarin: Spectroscopic and computational analyses

Warfarin is a cardiovascular drug, used to treat or inhibit the coagulation of the blood. In this paper, we have studied the interaction of lysozyme with warfarin using several experimental (fluorescence, UV-visible and circular dichroism spectroscopies) and computational (molecular docking, molecular dynamics and DFT) approaches. Experimental studies have suggested that there was a strong interaction between lysozyme and warfarin. Inner filter effect played important role in fluorescence experimental data which show that the emission intensity of lysozyme decreased on the addition of warfarin, however, after inner filter effect correction the actual outcome turned out be the fluorescence enhancement. The extent of binding, increased with temperature rise. The interaction was primarily taken place via the dominance of hydrophobic forces. Small amount of warfarin didn't influence the secondary structure of lysozyme; however, the higher concentration of warfarin caused a decrease in the helicity of the protein and a consequent partial unfolding. Molecular docking studies were also performed which revealed that warfarin binds with lysozyme mainly with hydrophobic forces along with a significant contribution of hydrogen bonding. The flexibility of warfarin played important role in fitting the molecule into the binding pocket of lysozyme. Frontier molecular orbitals of warfarin, using DFT, in free as well as complexed form have also been calculated and discussed. Molecular dynamics simulations of unbound and warfarin bound lysozyme reveal a stable complex with slightly higher RMSD values in the presence of warfarin. Despite slightly increased RMSF values, the overall compactness and folding properties remain consistent, emphasizing strong binding towards lysozyme through the results obtained from intermolecular hydrogen bonding analysis. Essential dynamics analysis suggests warfarin induces slight structural changes without significantly altering the conformation, additionally supported by SASA patterns. Aside from the examination of global and essential motion, the MM/PBSA-based analysis of binding free energy elucidates the significant binding of warfarin to lysozyme, indicating a binding free energy of -13.3471 kcal/mol.

A Systematic Review of Polygenic Models for Predicting Drug Outcomes

Polygenic models have emerged as promising prediction tools for the prediction of complex traits. Currently, the majority of polygenic models are developed in the context of predicting disease risk, but polygenic models may also prove useful in predicting drug outcomes. This study sought to understand how polygenic models incorporating pharmacogenetic variants are being used in the prediction of drug outcomes. A systematic review was conducted with the aim of gaining insights into the methods used to construct polygenic models, as well as their performance in drug outcome prediction. The search uncovered 89 papers that incorporated pharmacogenetic variants in the development of polygenic models. It was found that the most common polygenic models were constructed for drug dosing predictions in anticoagulant therapies (n = 27). While nearly all studies found a significant association with their polygenic model and the investigated drug outcome (93.3%), less than half (47.2%) compared the performance of the polygenic model against clinical predictors, and even fewer (40.4%) sought to validate model predictions in an independent cohort. Additionally, the heterogeneity of reported performance measures makes the comparison of models across studies challenging. These findings highlight key considerations for future work in developing polygenic models in pharmacogenomic research.

An Adapted Neural-Fuzzy Inference System Model Using Preprocessed Balance Data to Improve the Predictive Accuracy of Warfarin Maintenance Dosing in Patients After Heart Valve Replacement

BACKGROUND

Tailoring warfarin use poses a challenge for physicians and pharmacists due to its narrow therapeutic window and substantial inter-individual variability. This study aimed to create an adapted neural-fuzzy inference system (ANFIS) model using preprocessed balance data to improve the predictive accuracy of warfarin maintenance dosing in Chinese patients undergoing heart valve replacement (HVR).

METHODS

This retrospective study enrolled patients who underwent HVR between June 1, 2012, and June 1, 2016, from 35 centers in China. The primary outcomes were the mean difference between predicted warfarin dose by ANFIS models and actual dose and the models' predictive accuracy, including the ideal predicted percentage, the mean absolute error (MAE), and the mean squared error (MSE). The eligible cases were divided into training, internal validation, and external validation groups. We explored input variables by univariate analysis of a general linear model and created two ANFIS models using imbalanced and balanced training sets. We finally compared the primary outcomes between the imbalanced and balanced ANFIS models in both internal and external validation sets. Stratified analyses were conducted across warfarin doses (low, medium, and high doses).

RESULTS

A total of 15,108 patients were included and grouped as follows: 12,086 in the imbalanced training set; 2820 in the balanced training set; 1511 in the internal validation set; and 1511 in the external validation set. Eight variables were explored as predictors related to warfarin maintenance doses, and imbalanced and balanced ANFIS models with multi-fuzzy rules were developed. The results showed a low mean difference between predicted and actual doses (< 0.3 mg/d for each model) and an accurate prediction property in both the imbalanced model (ideal prediction percentage, 74.39-78.16%; MAE, 0.37 mg/daily; MSE, 0.39 mg/daily) and the balanced model (ideal prediction percentage, 73.46-75.31%; MAE, 0.42 mg/daily; MSE, 0.43 mg/daily). Compared to the imbalanced model, the balanced model had a significantly higher prediction accuracy in the low-dose (14.46% vs. 3.01%; P < 0.001) and the high-dose warfarin groups (34.71% vs. 23.14%; P = 0.047). The results from the external validation cohort confirmed this finding.

CONCLUSIONS

The ANFIS model can accurately predict the warfarin maintenance dose in patients after HVR. Through data preprocessing, the balanced model contributed to improved prediction ability in the low- and high-dose warfarin groups.

Farmacogenômica e Doença Cardiovascular: Onde Estamos e Para Onde Vamos

A farmacogenômica (FGx) investiga a interação entre genes e medicamentos. Através da análise de regiões específicas do DNA, informações sobre o perfil de metabolização do paciente para um determinado fármaco podem ser descritas, assim como o perfil esperado de resposta ao tratamento. Objetivamente, esse tipo de teste pode ter impacto no tratamento de pacientes que não estão respondendo adequadamente a um determinado medicamento, seja pela ausência dos efeitos esperados ou em virtude do aparecimento de efeitos adversos. Neste cenário, o objetivo desta revisão é o de informar o cardiologista clínico sobre esta importante área do conhecimento e atualizá-lo sobre o tema, procurando preencher as lacunas no que diz respeito à relação custo-benefício da aplicação da FGx nas doenças cardiovasculares, além de fornecer informações para a implementação da terapia guiada pela FGx na prática clínica.

Current state and future perspective of cardiovascular medicines derived from natural products

The contribution of natural products (NPs) to cardiovascular medicine has been extensively documented, and many have been used for centuries. Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide. Over the past 40 years, approximately 50% of newly developed cardiovascular drugs were based on NPs, suggesting that NPs provide essential skeletal structures for the discovery of novel medicines. After a period of lower productivity since the 1990s, NPs have recently regained scientific and commercial attention, leveraging the wealth of knowledge provided by multi-omics, combinatorial biosynthesis, synthetic biology, integrative pharmacology, analytical and computational technologies. In addition, as a crucial part of complementary and alternative medicine, Traditional Chinese Medicine has increasingly drawn attention as an important source of NPs for cardiovascular drug discovery. Given their structural diversity and biological activity NPs are one of the most valuable sources of drugs and drug leads. In this review, we briefly described the characteristics and classification of NPs in CVDs. Then, we provide an up to date summary on the therapeutic potential and the underlying mechanisms of action of NPs in CVDs, and the current view and future prospect of developing safer and more effective cardiovascular drugs based on NPs.

Therapeutic strategies for thrombosis: new targets and approaches

Antiplatelet agents and anticoagulants are a mainstay for the prevention and treatment of thrombosis. However, despite advances in antithrombotic therapy, a fundamental challenge is the side effect of bleeding. Improved understanding of the mechanisms of haemostasis and thrombosis has revealed new targets for attenuating thrombosis with the potential for less bleeding, including glycoprotein VI on platelets and factor XIa of the coagulation system. The efficacy and safety of new agents are currently being evaluated in phase III trials. This Review provides an overview of haemostasis and thrombosis, details the current landscape of antithrombotic agents, addresses challenges with preventing thromboembolic events in patients at high risk and describes the emerging therapeutic strategies that may break the inexorable link between antithrombotic therapy and bleeding risk.

Genetic risk assessment towards warfarin application: Saudi Arabia study with a potential to predict and prevent side effects

Warfarin doses are greatly affected by polymorphism altering cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase complex subunit 1 (VKORC1) gene. This study evaluated the prevalence of alleles (either single or double) and carriers of single nucleotide polymorphisms (SNPs) in both genotypes CYP2C9 and VKORC1 in alkharj area, Saudi Arabia and its association with warfarin use risk. Total 112 samples were collected and genotyped using FlexiGene DNA Kit for isolation and StepOnePlus Real-Time PCR System by TaqMan allelic discrimination methods. The results indicated the frequency of 11%, 8% and 45% for CYP2C9 *2 *3 and VKORC1-1639 G > A polymorphism. And as a combination genotype it was 15.18% For both CYP2C9 and VKORC1 polymorphism, 27.67% for CYP2C9 and 42.86% for VKORC1. Non-carriers rate came to be at 30.3%. According to previously published dosing changes in warfarin for polymorphism carriers (single-double-triple). The predicted warfarin doses reduction in order of 1–1.6, 2–2.9, 2.9–3.7 mg/day. It was found that 72.3% of the study population was carrier of a type of polymorphism, 15.18% for two types of polymorphisms. These findings predict changes in warfarin metabolism and eventually dosing alteration among patients on warfarin. Both genotypes (CYP2C9 and VKORC1) require different dosing of warfarin than non-carriers in order to minimize the risk of warfarin overdosing and avoidance of the drug-related problems (DRPs).

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.

Missense mutation of VKORC1 leads to medial arterial calcification in rats

Vitamin K plays a crucial role in the regulation of vascular calcifications by allowing activation of matrix Gla protein. The dietary requirement for vitamin K is low because of an efficient recycling of vitamin K by vitamin K epoxide reductase (VKORC1). However, decreased VKORC1 activity may result in vascular calcification. More than 30 coding mutations of VKORC1 have been described. While these mutations have been suspected of causing anticoagulant resistance, their association with an increase in the risk of vascular calcification has never been considered. We thus investigated functional cardiovascular characteristics in a rat model mutated in VKORC1. This study revealed that limited intake in vitamin K in mutated rat induced massive calcified areas in the media of arteries of lung, aortic arch, kidneys and testis. Development of calcifications could be inhibited by vitamin K supplementation. In calcified areas, inactive Matrix Gla protein expression increased, while corresponding mRNA expression was not modified. Mutation in VKORC1 associated with a limited vitamin K intake is thus a major risk for cardiovascular disease. Our model is the first non-invasive rat model that shows spontaneous medial calcifications and would be useful for studying physiological function of vitamin K.

The Effect of Demographic Factors and VKORC1 1639 G>A Genotypes on Estimated Warfarin Maintenance Dose in Iranian Patients Under Warfarin Therapy

Warfarin is an anticoagulant that inhibits vitamin K-dependent clotting factors including factor (F) II, FVII, FIX and FX. Different factors can change the effect of this anticoagulant in clinic. Therefore we assessed impact of VKORC1 -1639 G>A polymorphism and demographic factors on required maintenance dose in Iranian patients under warfarin therapy. The study population included 95 patients with a mean age of 61.3 ± 12.6 years. Target INR range of 2-3 was considered for these patients. The frequency of VKORC1 -1639 G>A polymorphism was assessed by polymerase chain reaction-restriction length polymorphism (PCR-RFLP). Finally the obtain data were analyzed by SPSS software. Our study revealed that 30.5%, 49.5%, and 20% of the patients had VKORC1 (G/G), (G/A), and (A/A) genotypes, respectively. Carriers of VKORC1 G/G genotype required a higher warfarin dose as compared to A/A carriers (4.48 ± 1.32 and 2.7 ± 1.16 mg/day, respectively; P < 0.01). In addition, patients with higher age required lower warfarin therapeutic dose (r = - 0.3, P < 0.01). It seems that -1639 G>A polymorphism and demographic variables had significant effects on warfarin maintenance dose in Iranian patients under warfarin therapy.

Personalized Anticoagulation: Optimizing Warfarin Management Using Genetics and Simulated Clinical Trials

BACKGROUND

Clinical trials testing pharmacogenomic-guided warfarin dosing for patients with atrial fibrillation have demonstrated conflicting results. Non-vitamin K antagonist oral anticoagulants are expensive and contraindicated for several conditions. A strategy optimizing anticoagulant selection remains an unmet clinical need.

METHODS AND RESULTS

Characteristics from 14 206 patients with atrial fibrillation were integrated into a validated warfarin clinical trial simulation framework using iterative Bayesian network modeling and a pharmacokinetic-pharmacodynamic model. Individual dose-response for patients was simulated for 5 warfarin protocols-a fixed-dose protocol, a clinically guided protocol, and 3 increasingly complex pharmacogenomic-guided protocols. For each protocol, a complexity score was calculated using the variables predicting warfarin dose and the number of predefined international normalized ratio (INR) thresholds for each adjusted dose. Study outcomes included optimal time in therapeutic range ≥65% and clinical events. A combination of age and genotype identified different optimal protocols for various subpopulations. A fixed-dose protocol provided well-controlled INR only in normal responders ≥65, whereas for normal responders <65 years old, a clinically guided protocol was necessary to achieve well-controlled INR. Sensitive responders ≥65 and <65 and highly sensitive responders ≥65 years old required pharmacogenomic-guided protocols to achieve well-controlled INR. However, highly sensitive responders <65 years old did not achieve well-controlled INR and had higher associated clinical events rates than other subpopulations.

CONCLUSIONS

Under the assumptions of this simulation, patients with atrial fibrillation can be triaged to an optimal warfarin therapy protocol by age and genotype. Clinicians should consider alternative anticoagulation therapy for patients with suboptimal outcomes under any warfarin protocol.

Hematoma Expansion Following Intracerebral Hemorrhage: Mechanisms Targeting the Coagulation Cascade and Platelet Activation

Hematoma expansion (HE), defined as a greater than 33% increase in intracerebral hemorrhage (ICH) volume within the first 24 hours, results in significant neurological deficits, and enhancement of ICH-induced primary and secondary brain injury. An escalation in the use of oral anticoagulants has led to a surge in the incidences of oral anticoagulation-associated ICH (OAT-ICH), which has been associated with a greater risk for HE and worse functional outcomes following ICH. The oral anticoagulants in use include vitamin K antagonists, and direct thrombin and factor Xa inhibitors. Fibrinolytic agents are also frequently administered. These all act via differing mechanisms and thus have varying degrees of impact on HE and ICH outcome. Additionally, antiplatelet medications have also been increasingly prescribed, and result in increased bleeding risks and worse outcomes after ICH. Aspirin, thienopyridines, and GPIIb/IIIa receptor blockers are some of the most common agents in use clinically, and also have different effects on ICH and hemorrhage growth, based on their mechanisms of action. Recent studies have found that reduced platelet activity may be more effective in predicting ICH risk, hemorrhage expansion, and outcomes, than antiplatelet agents, and activating platelets may thus be a novel target for ICH therapy. This review explores how dysfunctions or alterations in the coagulation and platelet cascades can lead to, and/or exacerbate, hematoma expansion following intracerebral hemorrhage, and describe the mechanisms behind these effects and the drugs that induce them. We also discuss potential future therapy aimed at increasing platelet activity after ICH.

Prevalence and genotype distribution of human papillomavirus infection among women in northeastern Guangdong Province of China

BACKGROUND

Human papillomavirus (HPV) DNA testing is an important method in cervical cancer screening. However, the studies on prevalence and genotype distribution of HPV among women in northeastern Guangdong Province of China are very limited.

METHODS

A total of 28,730 women attending the Department of Gynecology of Meizhou People's Hospital (Huangtang Hospital), Meizhou Hospital Affiliated to Sun Yat-sen University between January 1st, 2013 and June 1st, 2015 were enrolled in this study. HPV type-specific distribution was tested using flow-through hybridization and gene chip.

RESULTS

The overall prevalence of HPV infection was 19.81%, among which 79.09% were infected with high-risk HPV subtypes in the subjects. The 5 most predominant genotypes were HPV16, 52, 58, 18 and 81. Most HPV infections were observed in women aged 41-50 and women aged 30-59 accounted for a proportion of over 80%.

CONCLUSIONS

Our findings suggested a high burden of HPV infection among women in northeastern Guangdong Province of China. We identified the top 5 HPV genotypes as well as the age-specific distribution of HPV infections in this area.

Pharmacogenomics of CYP2C9: Functional and Clinical Considerations

CYP2C9 is the most abundant CYP2C subfamily enzyme in human liver and the most important contributor from this subfamily to drug metabolism. Polymorphisms resulting in decreased enzyme activity are common in the CYP2C9 gene and this, combined with narrow therapeutic indices for several key drug substrates, results in some important issues relating to drug safety and efficacy. CYP2C9 substrate selectivity is detailed and, based on crystal structures for the enzyme, we describe how CYP2C9 catalyzes these reactions. Factors relevant to clinical response to CYP2C9 substrates including inhibition, induction and genetic polymorphism are discussed in detail. In particular, we consider the issue of ethnic variation in pattern and frequency of genetic polymorphisms and clinical implications. Warfarin is the most well studied CYP2C9 substrate; recent work on use of dosing algorithms that include CYP2C9 genotype to improve patient safety during initiation of warfarin dosing are reviewed and prospects for their clinical implementation considered. Finally, we discuss a novel approach to cataloging the functional capabilities of rare 'variants of uncertain significance', which are increasingly detected as more exome and genome sequencing of diverse populations is conducted.

A new algorithm to predict warfarin dose from polymorphisms of CYP4F2, CYP2C9 and VKORC1 and clinical variables: Derivation in Han Chinese patients with non valvular atrial fibrillation

Few pharmacogenomic dosing regimens of warfarin have been developed for Chinese patients with non valvular atrial fibrillation (NVAF). The objective of this study was to develop a new algorithm by polymorphisms of CYP2C9, VKORC1 and CYP4F2 to predict the daily stable dose of warfarin in Chinese patients with NVAF. A total of 325 Chinese NVAF patients on stable dose of warfarin with a target international normalised ratio of 1.5 to 3.0 were recruited and divided randomly into two cohorts. CYP2C9*3, VKORC1 –1639, VKORC1 1173 and CYP4F2 were detected by ligase detection reaction method. The new algorithm was developed with multivariate linear regression in cohort 1 (260 patients) and assessed with Pearson Correlation Analysis (PCA) in cohort 2 (65 patients). From 260 enrolled patients, the model (R2 = 51.7%) was developed as: Dose = 3.47 − 0.022 (AGE) + 0.017 (WT) + 0.189 (PTE) − 0.283 (β-blocker) − 0.471 (AMIO) − 0.586 (CYP2C9 *1/*3) − 0.296 (VKORC1 CT) – 0.648 (VKORC1 TT) + 0.219 (CYP4F2 TT). PCA displayed that the algorithm was good (r = 0.658). The residual plots revealed that the predicted doses by the algorithm tend to be overestimated when lower doses were administered to patients and to be underestimated in higher doses. The algorithm developed by us might predict warfarin dose used by Chinese NVAF patients.

Effects of safflower injection on the pharmacodynamics and pharmacokinetics of warfarin in rats

1. Safflower injection (SI) is extracted from Chinese herbal medicine safflower that comprises many active components. Warfarin is a common anticoagulant and has exhibited drug interactions with several herbal products. This study aimed to investigate the effects of SI on pharmacodynamics and pharmacokinetics of warfarin in rats. 2. Wistar rats were randomly divided into blank control group, SI group, warfarin control group and SI + warfarin group, respectively. In SI and SI + warfarin groups, rats were injected with SI (1.6 mL/kg/d, i.p.) for 14 days. Warfarin (0.2 mg/kg) was given orally on the eighth day. Saline was given as control. The blood samples were collected at various time points. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were measured. UPLC-MS/MS was used to determine the plasma concentrations of S(R)-warfarin, and the pharmacokinetic parameters were calculated. 3. PT, APTT in SI and SI + warfarin rats increased significantly compared with corresponding control rats. The pharmacokinetic parameters including C_max, t_1/2, AUC_0-t and AUC_0-∞ of S-warfarin and R-warfarin in SI + warfarin rats were higher than those in warfarin control rats. 4. These findings suggest that SI significantly increases the anticoagulant effect of warfarin by affecting its pharmacodynamic and pharmacokinetic parameters.

Warfarin Dosing Algorithms Underpredict Dose Requirements in Patients Requiring ≥7 mg Daily: A Systematic Review and Meta-analysis

There is preliminary evidence to suggest that some published warfarin dosing algorithms produce biased maintenance dose predictions in patients who require higher than average doses. We conducted a meta-analysis of warfarin dosing algorithms to determine if there exists a systematic under- or overprediction of dose requirements for patients requiring ≥7 mg/day across published algorithms. Medline and Embase databases were searched up to September 2015. We quantified the proportion of over- and underpredicted doses in patients whose observed maintenance dose was ≥7 mg/day. The meta-analysis included 47 evaluations of 22 different warfarin dosing algorithms from 16 studies. The meta-analysis included data from 1,492 patients who required warfarin doses of ≥7 mg/day. All 22 algorithms were found to underpredict warfarin dosing requirements in patients who required ≥7 mg/day by an average of 2.3 mg/day with a pooled estimate of underpredicted doses of 92.3% (95% confidence interval 90.3-94.1, I² = 24%).

The VKORC1 and CYP2C9 genotypes significantly effect Vitamin K antagonist dosing only in patients over the age of 20years

INTRODUCTION

Given the qualitative differences in the role of VKORC1 and CYP2C9 polymorphisms in Vitamin K antagonists (VKA) dosing variation between adults and children, we were interested in determining at what age these polymorphism begin to play a more significant role.

METHODS

A prospective cohort study of 190 patients aged 1-86years receiving VKA for treatment of venous thromboembolism. Blood samples were collected beyond the acute thrombotic event when patients were on stable targeted INR (2-3) for plasma testing and VKORC1/CYP2C9 genotyping. Patient demographics including VKA dose were collected. Simple and multiple linear regression was used to assess the relationship of VKA dose with polymorphisms and weight, adjusted for quality of anticoagulation (INR, D-Dimer), liver (AST, ALT) and renal function.

RESULTS

In subjects 1-19years of age, weight explained 39.0% of dosing variation with VKORC1 and CYP2C9 playing a minor role. In contrast, in subjects 20-40years weight contributed 23%, VKORC1 44% and CYPC29 49% of the VKA dose variation.

CONCLUSION

Until the age of 19, weight has a far greater effect on VKA dosing variation than VKORC1 and CYP2C9 polymorphisms. During the age of 20-40years, VKORC1 and CYP2C9 play a significant role.

The Impact of Genetic and Non-Genetic Factors on Warfarin Dose Prediction in MENA Region: A Systematic Review

Background

Warfarin is the most commonly used oral anticoagulant for the treatment and prevention of thromboembolic disorders. Pharmacogenomics studies have shown that variants in CYP2C9 and VKORC1 genes are strongly and consistently associated with warfarin dose variability. Although different populations from the Middle East and North Africa (MENA) region may share the same ancestry, it is still unclear how they compare in the genetic and non-genetic factors affecting their warfarin dosing.

Objective

To explore the prevalence of CYP2C9 and VKORC1 variants in MENA, and the effect of these variants along with other non-genetic factors in predicting warfarin dose.

Methods

In this systematic review, we included observational cross sectional and cohort studies that enrolled patients on stable warfarin dose and had the genetics and non-genetics factors associated with mean warfarin dose as the primary outcome. We searched PubMed, Medline, Scopus, PharmGKB, PHGKB, Google scholar and reference lists of relevant reviews.

Results

We identified 17 studies in eight different populations: Iranian, Israeli, Egyptian, Lebanese, Omani, Kuwaiti, Sudanese and Turkish. Most common genetic variant in all populations was the VKORC1 (-1639G>A), with a minor allele frequency ranging from 30% in Egyptians and up to 52% and 56% in Lebanese and Iranian, respectively. Variants in the CYP2C9 were less common, with the highest MAF for CYP2C9*2 among Iranians (27%). Variants in the VKORC1 and CYP2C9 were the most significant predictors of warfarin dose in all populations. Along with other genetic and non-genetic factors, they explained up to 63% of the dose variability in Omani and Israeli patients.

Conclusion

Variants of VKORC1 and CYP2C9 are the strongest predictors of warfarin dose variability among the different populations from MENA. Although many of those populations share the same ancestry and are similar in their warfarin dose predictors, a population specific dosing algorithm is needed for the prospective estimation of warfarin dose.

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.

The Pharmacist's Perspective on Pharmacogenetics Implementation

The future for pharmacogenetics will continue to expand. Pharmacists can apply and incorporate drug knowledge in collaboration with other health providers using pharmacogenetics. Patients benefit with enhanced therapeutic outcomes that could lead to more streamlined drug approaches, fewer follow-up visits, cost savings, and shorter times to achieve therapeutic outcomes. As more drug-gene pathways are discovered and use of this knowledge increases, the potential for algorithm development for medication use will occur, resulting in better patient outcomes, higher standard of care, and reflect evidence-based medicine.

Development of neuro-fuzzy model to explore gene-nutrient interactions modulating warfarin dose requirement

AIM

To investigate the influence of alterations in vitamin K (K1, K2 and K3) in modulating warfarin dose requirement.

PATIENTS & METHODS

Reverse phase HPLC to determine the plasma vitamin K; PCR-RFLP to detect polymorphisms; and the neuro-fuzzy model to predict warfarin dose were used.

RESULTS

The developed neuro-fuzzy model showed a mean absolute error of 0.000024 mg/week. CYP2C9*2 and CYP2C9*3 mediated warfarin sensitivity was observed when vitamin K is in high and low tertiles, respectively. VKORC1-1639G>A exhibited warfarin sensitivity in all combinations. Higher vitamin K1 was observed in CYP4F2 V433M polymorphism. The requirement of warfarin is low in GGCX 8016 GG genotype compared with GA and AA genotypes.

CONCLUSION

Vitamin K profile along with genetic testing ensures precision in warfarin dose optimization.

Warfarin Pharmacogenetics Reevaluated: Subgroup Analysis Reveals a Likely Underestimation of the Maximum Pharmacogenetic Benefit by Clinical Trials

OBJECTIVES

Various patient subgroups were examined to determine which ones obtain the largest pharmacogenetic improvements in warfarin dose accuracy. Subgrouping schemes of recent clinical trials were analyzed for comparison.

METHODS

The accuracy of a pharmacogenetic dose algorithm was determined retrospectively in comparison to that of a clinical algorithm in subgroups of the International Warfarin Pharmacogenetics Consortium (IWPC) patient database (n = 2,274) and of newly studied clinic patients (n = 146).

RESULTS

White patients with low-dose genotypes (*1*3/AA, *2*2/AA, *2*3/GA, *2*3/AA, *3*3/GG, *3*3/GA, and *3*3/AA) achieved the largest pharmacogenetic improvements in warfarin dose accuracy. Mean absolute dosing error (MAE) in this subgroup of IWPC and newly studied patients was reduced 75.7% and 89.7%, respectively. White IWPC patients with >2 variants or ≥2 mg/day absolute difference between pharmacogenetic and clinical dose predictions obtained MAE reductions of 71.1% and 65.3%, respectively. By comparison, unstratified populations and subgroups of a major clinical trial, when replicated in IWPC patients, obtained smaller MAE reductions of 31.8% to 48.2%. Blacks and Asians obtained substantially smaller dose accuracy improvements overall than whites.

CONCLUSIONS

Patient subgroups were identified that obtained the largest pharmacogenetic improvements in warfarin dose accuracy. These subgroups have not been analyzed in clinical trials to date, likely resulting in underestimation of the pharmacogenetic benefit.

Development and Comparison of Warfarin Dosing Algorithms in Stroke Patients

PURPOSE

The genes for cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase complex subunit 1 (VKORC1) have been identified as important genetic determinants of warfarin dosing and have been studied. We developed warfarin algorithm for Korean patients with stroke and compared the accuracy of warfarin dose prediction algorithms based on the pharmacogenetics.

MATERIALS AND METHODS

A total of 101 patients on stable maintenance dose of warfarin were enrolled. Warfarin dosing algorithm was developed using multiple linear regression analysis. The performance of all the algorithms was characterized with coefficient of determination, determined by linear regression, and the mean of percent deviation was used to predict doses from the actual dose. In addition, we compared the performance of the algorithms using percentage of predicted dose falling within ±20% of clinically observed doses and dividing the patients into a low-dose group (≤3 mg/day), an intermediate-dose group (3-7 mg/day), and high-dose group (≥7 mg/day).

RESULTS

A new developed algorithms including the variables of age, body weight, and CYP2C9 and VKORC1 genotype. Our algorithm accounted for 51% of variation in the warfarin stable dose, and performed best in predicting dose within 20% of actual dose and intermediate-dose group.

CONCLUSION

Our warfarin dosing algorithm may be useful for Korean patients with stroke. Further studies to elucidate clinical utility of genotype-guided dosing and find the additional genetic association are necessary.

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.

Artificial neural network-based pharmacogenomic algorithm for warfarin dose optimization

AIM

To develop more precise pharmacogenomic algorithm for prediction of safe and effective dose of warfarin.

MATERIALS & METHODS

An artificial neural network (ANN) algorithm was developed by using age, gender, BMI, plasma vitamin K levels, thyroid status and ten genetic variables as the inputs and therapeutic warfarin dose as the output. Hyperbolic tangent function was used to build an ANN architecture.

RESULTS

This model explained 93.5% variability in warfarin dosing and predicted warfarin dose accurately in 74.5% patients whose international normalized ratio (INR) was less than 2.0 and in 83.3% patients whose INR was more than 3.5. This algorithm reduced the out-of-range INRs (odds ratio [OR]: 0.49; 95% CI: 0.30-0.79; p = 0.003), the rate of adverse drug reactions (OR: 0.00; 95% CI: 0.00-1.21; p = 0.06) and time to reach first therapeutic INR (OR: 6.73; 95% CI: 2.17-22.31; p < 0.0001). This algorithm was found to be applicable in both euthyroid and hypothyroid status. S-warfarin/7-hydroxywarfarin ratio was found to increase in subjects with CYP2C9*2 and CYP2C9*3 justifying the warfarin sensitivity attributed to these variants.

CONCLUSION

An application of ANN for warfarin dosing improves predictability and provides safe and effective dosing.

Comparison of Nine Statistical Model Based Warfarin Pharmacogenetic Dosing Algorithms Using the Racially Diverse International Warfarin Pharmacogenetic Consortium Cohort Database

Objective

Multiple linear regression (MLR) and machine learning techniques in pharmacogenetic algorithm-based warfarin dosing have been reported. However, performances of these algorithms in racially diverse group have never been objectively evaluated and compared. In this literature-based study, we compared the performances of eight machine learning techniques with those of MLR in a large, racially-diverse cohort.

Methods

MLR, artificial neural network (ANN), regression tree (RT), multivariate adaptive regression splines (MARS), boosted regression tree (BRT), support vector regression (SVR), random forest regression (RFR), lasso regression (LAR) and Bayesian additive regression trees (BART) were applied in warfarin dose algorithms in a cohort from the International Warfarin Pharmacogenetics Consortium database. Covariates obtained by stepwise regression from 80% of randomly selected patients were used to develop algorithms. To compare the performances of these algorithms, the mean percentage of patients whose predicted dose fell within 20% of the actual dose (mean percentage within 20%) and the mean absolute error (MAE) were calculated in the remaining 20% of patients. The performances of these techniques in different races, as well as the dose ranges of therapeutic warfarin were compared. Robust results were obtained after 100 rounds of resampling.

Results

BART, MARS and SVR were statistically indistinguishable and significantly out performed all the other approaches in the whole cohort (MAE: 8.84–8.96 mg/week, mean percentage within 20%: 45.88%–46.35%). In the White population, MARS and BART showed higher mean percentage within 20% and lower mean MAE than those of MLR (all p values < 0.05). In the Asian population, SVR, BART, MARS and LAR performed the same as MLR. MLR and LAR optimally performed among the Black population. When patients were grouped in terms of warfarin dose range, all machine learning techniques except ANN and LAR showed significantly higher mean percentage within 20%, and lower MAE (all p values < 0.05) than MLR in the low- and high- dose ranges.

Conclusion

Overall, machine learning-based techniques, BART, MARS and SVR performed superior than MLR in warfarin pharmacogenetic dosing. Differences of algorithms’ performances exist among the races. Moreover, machine learning-based algorithms tended to perform better in the low- and high- dose ranges than MLR.

Validation of warfarin pharmacogenetic algorithms in 586 Han Chinese patients

AIM

To compare the accuracy of the nine selected algorithms for predicting warfarin dose with 586 Han Chinese patients.

MATERIALS & METHODS

Genotyping of VKORC1 1639G>A, CYP2C9*2 and CYP2C9*3 variants was performed. Both the mean absolute error and ideal estimation value were used for comparison.

RESULTS

The top three performers were from East Asians. The algorithms from Caucasians generally performed better in the medium-dose subgroup (>3 and <7 mg/day), while the algorithms from East Asians generally performed better in the low-dose subgroup (≤ 3 mg/day). None of the algorithms performed well in the high-dose subgroup (≥ 7 mg/day).

CONCLUSION

Algorithms built for specific ethnic groups and preassigned-dose groups are suggested for better prediction.

VKORC1 -1639G/A and 1173 C/T Genetic Polymorphisms Influence Individual Differences in Warfarin Maintenance Dose

OBJECTIVE

In this study, we investigated two VKORC1 gene polymorphisms, -1639G/A and 1173C/T, for effects on warfarin maintenance dosage in valvular heart disease (VHD) patients after cardiac valve replacement (CVR).

METHODS

A total of 219 VHD patients receiving warfarin therapy after CVR surgery were recruited to this study between June 2010 and December 2013. Basic clinical data, prothrombin time, warfarin maintenance dose, and blood samples were collected from all patients. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analyses were used to analyze the VKORC1 -1639G/A and 1173C/T polymorphisms. SPSS version 19.0 software was used for statistical analysis of the data.

RESULTS

Patients with either the AG+or GG genotype (n=32) of the VKORC1 -1639G/A polymorphism required a significantly higher warfarin dose compared to patients with the AA genotype (n=187) (4.36±1.03 mg/day vs. 2.95±0.94 mg/day; p<0.001). Similarly, patients carrying the CT genotype (n=28) of the VKORC1 1173C/T polymorphism also required a significantly higher warfarin dose compared to those with the TT genotype (n=191) (4.19±0.99 mg/day vs. 3.00±0.94 mg/day; p<0.001). Linear regression analysis showed that gender, age, weight, and VKORC1 -1639G/A and 1173C/T polymorphisms were correlated with individual differences in warfarin maintenance dose (all p<0.05).

CONCLUSION

We present evidence that the two VKORC1 polymorphisms, -1639G/A and 1173C/T, are key genetic factors influencing individual differences in warfarin maintenance dose in VHD patients who underwent CVR. Gender, age, and weight also independently correlated with warfarin maintenance dose.

Development of a pharmacogenetic-based warfarin dosing algorithm and its performance in Brazilian patients: highlighting the importance of population-specific calibration

BACKGROUND

The main aims of the present study were to develop a pharmacogenetic-based warfarin dosing algorithm and to validate it in a highly admixed population.

MATERIALS & METHODS

We included two patient cohorts treated with warfarin (first cohort, n = 832; and second cohort, n = 133).

RESULTS

Our algorithm achieved a determination coefficient of 40% including the variables age, gender, weight, height, self-declared race, amiodarone use, enzyme inducers use, VKORC1 genotypes and predicted phenotypes according to CYP2C9 polymorphisms.

CONCLUSION

Data suggest that our developed algorithm is more accurate than the IWPC algorithm when the application is focused on patients from the Brazilian population. Population-specific derivation and/or calibration of warfarin dosing algorithms may lead to improved performance compared with general use dosing algorithms currently available. Original submitted 26 November 2014; Revision submitted 9 April 2015.

Clinical Application of Genotype-guided Dosing of Warfarin in Patients with Acute Stroke

BACKGROUND

Patients with certain types of stroke need urgent anticoagulation and it is extremely important for them to achieve fast and stable anticoagulant effect and receive individualized treatment during the initiation of warfarin therapy.

METHODS

We conducted a prospective study among 210 acute stroke patients who had an indication for anticoagulation and compared the impact of CYP2C9 and VKORC1 genotype-guided warfarin dosing (PhG) with fixed dosing (NPhG) on anticoagulation control and clinical outcome between groups.

RESULTS

PhG achieved target INR values earlier, i.e., on average in 4.2 (4.1-4.7, 95% CI) days compared to NPhG (5.2 days [4.7-6.4, 95% CI]) (p = 0.0009), spent a higher percentage of time in the therapeutic INR range (76.3% [74.7-78.5, 95% CI] vs. 67.1% [64.5-69.6, 95% CI] in NPhG), and spent less time overdosed (INR > 3.1) (PhG 0.4 [0.1-0.7, 95% CI], NPhG 1.7 [1.1-2.3, 95% CI] days; p >0.000). PhG reached stable maintenance dose faster (10 [9.9-10.7, 95% CI] vs. 13.9 [13.3-14.7, 95% CI] days in controls; p = 0.0049) and had a better clinical outcome in relation to neurological deficit on admission as compared to NPhG.

CONCLUSION

We confirmed that warfarin therapy with genotype-guided dosing instead of fixed dosing reduces the time required for stabilization and improves anticoagulant control with better clinical outcome in early stages of warfarin therapy introduction among acute stroke patients, which is essential for clinical practice.

PGWD: integrating personal genome for warfarin dosing

Warfarin is a drug normally used in the prevention of thrombosis and the formation of blood clots. The dosage of warfarin is strongly affected by genetic variants of CYP2C9 and VKORC1 genes. Current technologies for detecting the variants of these genes are mainly based on real-time PCR. In recent years, due to the rapidly dropping cost of whole genome sequencing and genotyping, more and more people get their whole genome sequenced or genotyped. However, current software for warfarin dosing prediction is based on low-throughput genetic information either from real-time PCR, or melting curve methods. There is no bioinformatics tool available that can take the high-throughput genome sequencing data as input and determine the accurate dosage of warfarin. Here, we present PGWD, a web tool that analyzes personal genome sequencing data, and integrates with clinical information for warfarin dosing.

A review of a priori regression models for warfarin maintenance dose prediction

A number of a priori warfarin dosing algorithms, derived using linear regression methods, have been proposed. Although these dosing algorithms may have been validated using patients derived from the same centre, rarely have they been validated using a patient cohort recruited from another centre. In order to undertake external validation, two cohorts were utilised. One cohort formed by patients from a prospective trial and the second formed by patients in the control arm of the EU-PACT trial. Of these, 641 patients were identified as having attained stable dosing and formed the dataset used for validation. Predicted maintenance doses from six criterion fulfilling regression models were then compared to individual patient stable warfarin dose. Predictive ability was assessed with reference to several statistics including the R-square and mean absolute error. The six regression models explained different amounts of variability in the stable maintenance warfarin dose requirements of the patients in the two validation cohorts; adjusted R-squared values ranged from 24.2% to 68.6%. An overview of the summary statistics demonstrated that no one dosing algorithm could be considered optimal. The larger validation cohort from the prospective trial produced more consistent statistics across the six dosing algorithms. The study found that all the regression models performed worse in the validation cohort when compared to the derivation cohort. Further, there was little difference between regression models that contained pharmacogenetic coefficients and algorithms containing just non-pharmacogenetic coefficients. The inconsistency of results between the validation cohorts suggests that unaccounted population specific factors cause variability in dosing algorithm performance. Better methods for dosing that take into account inter- and intra-individual variability, at the initiation and maintenance phases of warfarin treatment, are needed.

Effect of CYP2C9-VKORC1 interaction on warfarin stable dosage and its predictive algorithm

This study aimed to identify the effect of CYP2C9-VKORC1 interaction on warfarin dosage requirement and its predictive algorithm by investigating four populations. Generalized linear model was used to evaluate the relationship between the interaction and warfarin stable dosage (WSD), whereas multiple linear regression analysis was applied to construct the WSD predictive algorithm. To evaluate the effect of CYP2C9-VKORC1 interaction on the predictive algorithms, we compared the algorithms with and without the interaction. The interaction was significantly associated with WSD in the Chinese and White cohorts (P values < 0.05). In the algorithms that considered the interaction, the predictive success rates improved by only 0.12% in the Chinese patients and by a maximum of 0.02% in the White patients under four different CYP2C9 classifications. Thus, VKORC1-CYP2C9 interaction can affect WSD. However, the discrepancy between the predictive results obtained using the predictive algorithm with and without CYP2C9-VKORC1 interaction was negligible and can therefore be disregarded.

Effect of CYP2C9 and VKORC1 genetic variations on warfarin dose requirements in Indian patients

BACKGROUND

Warfarin, an oral anticoagulant is used in patients who are at increased risk of developing blood clots. The management of warfarin therapy is challenging because it shows large inter and intra individual variability in patient response due to factors like age, gender, diet, concurrent drug interactions and variations in CYP2C9 and VKORC1 genes. Studies implicate that polymorphisms in VKORC1 and CYP2C9 genes are associated with reduced doses of warfarin. The aim of our current study was to characterize the effects of VKORC1 and CYP2C9 gene variations that contribute to variability in warfarin dosing in Indian patients.

METHODS

Genomic DNA was extracted from 103 patients undergoing warfarin therapy. Their mean daily warfarin dose, INR and demographics were recorded and genotyping of VKORC1 and CYP2C9 gene was performed by PCR-RFLP method.

RESULTS

Individuals with wild type genotypes required highest mean warfarin dosage of 4.72 mg/day while VKORC1 variants required 3.6 mg/day to maintain their therapeutic INR. CYP2C9*2 genotype was not found to affect the warfarin maintenance dosages. The odds ratio for developing supra therapeutic INR in patients carrying VKORC1 variant allele when compared to wild types was 13.96 (95% CI; 4.85 - 44.65. Other factors affecting warfarin dosages were age and weight.

CONCLUSION

Inclusion of pharmacogenetic data along with clinical parameters would help better predict warfarin doses in Indian patients.

The impact of VKORC1-1639G > A genetic polymorphism upon warfarin dose requirement in different ethnic populations

OBJECTIVE

Published data on the association between vitamin K epoxide reductase complex 1 (VKORC1)-1639G > A polymorphism and warfarin dose requirement are inconclusive. To derive a more precise estimation of the relationship, a meta-analysis was performed.

METHODS AND RESULTS

Studies were identified in English-language articles by search of PubMed and Embase database (inception to July 2013). A total of 32 prospective clinical trials involving 5005 patients were identified and included for analysis. Overall, the weighted mean maintenance dosage of warfarin in patients with the -1639AA genotype decreased 2.62 mg/d compared with that in the -1639GG genotype patients (95% CI -3.10 to -2.14; P < 0.00001) when 24 eligible studies were pooled into the meta-analysis. Furthermore, significantly lower warfarin dose requirement was found in patients with GA genotype versus GG genotype (WMD, -1.32; 95% CI -1.67 to -0.96; P < 0.00001). In the subgroup analysis by ethnicity, statistically significant lower maintenance dosage of warfarin in patients with the AA genotype versus GG genotype were found in both Caucasians (WMD, -2.47; 95% CI -2.92 to -2.03; P < 0.00001) and Asians (WMD, -2.84; 95% CI -4.57 to -1.11; P = 0.001).

CONCLUSIONS

This meta-analysis indicated that the VKORC1-1639G > A genetic polymorphism is associated with the variation of interindividual warfarin dose requirement in different ethnic populations.

VKORC1 and CYP2C9 genotypes in Egyptian patients with warfarin resistance

Warfarin is the most commonly prescribed anticoagulant drug; however, a narrow therapeutic range and a high risk of bleeding or stroke complicate its clinical use. Warfarin resistance was defined as prolonged warfarin requirements of more than 15 mg/day to achieve therapeutic anticoagulation or failure to achieve therapeutic anticoagulation with more than 20 mg/day. The resistance is associated with polymorphisms of the vitamin K epoxide reductase-oxidase complex (VKORC1) and cytochrome P450-2C9 (CYP2C9) genes, which affect warfarin pharmacodynamics and pharmacokinetics, respectively. Identification of the VKORC1 -1639 (A/G) and CYP2C9 (*1/*2/*3) allelic variants was performed using the PGX-Thrombo Strip in 41 patients with warfarin resistance compared with 30 patients with normal warfarin response out of 352 diagnosed cases of deep vein thrombosis. In warfarin-resistant patients, the VKORC1-1639 genotype frequencies were GG 0.756, GA 0.244 and AA 0.0, whereas in warfarin responder patients, they were: GG 0.333, GA 0.400 and AA 0.276 with P ≤ 0.001. The CYP2C9 genotype frequencies showed nonsignificant difference in both group of patients (P = 0.31). Our results suggest that the VKORC1-1639 GG and the wild type CYP2C9*1*1genotypes are associated with the high-dose requirement for warfarin therapy, and that VKORC1-1639 GG is responsible for warfarin resistance and failure in Egyptian patients.

A new nested allele-specific multiplex polymerase chain reaction method for haplotyping of VKORC1 gene to predict warfarin sensitivity

The vitamin K epoxide reductase complex 1 gene (VKORC1) is commonly assessed to predict warfarin sensitivity. In this study, a new nested allele-specific multiplex polymerase chain reaction (PCR) method that can simultaneously identify single nucleotide polymorphisms (SNPs) at VKORC1 381, 861, 5808, and 9041 for haplotype analysis was developed and validated. Extracted DNA was amplified in the first PCR DNA, which was optimized by investigating the effects of varying the primer concentrations, annealing temperature, magnesium chloride concentration, enzyme concentration, and the amount of DNA template. The amplification products produced from the first round of PCR were used as templates for a second PCR amplification in which both mutant and wild-type primers were added in separate PCR tubes, followed by optimization in a similar manner. The final PCR products were resolved by agarose gel electrophoresis and further analysed by using a VKORC1 genealogic tree to infer patient haplotypes. Fifty patients were identified to have H1H1, one had H1H2, one had H1H7, 31 had either H1H7 or H1H9, one had H1H9, eight had H7H7, and one had H8H9 haplotypes. This is the first method that is able to infer VKORC1 haplotypes using only conventional PCR methods.

Inter and intra ethnic variation of vitamin K epoxide reductase complex and cytochrome P450 4F2 genetic polymorphisms and their prevalence in South Indian population

BACKGROUND:

Genetic variation in the vitamin K epoxide reductase complex (VKORC1) and cytochrome P450 4F2 (CYP4F2) genes were found to be strongly associated with the oral anticoagulant (OA) dose requirement. The distribution of genetic variation in these two genes was found to show large inter- and intra-ethnic difference.

MATERIALS AND METHODS:

A total of 470 unrelated, healthy volunteers of South Indians of either sex (age: 18-60 years) were enrolled for the study. A 5 ml of venous blood was collected and the genomic deoxyribonucleic acid (DNA) was extracted by using phenol-chloroform extraction method. Real-time quantitative polymerase chain reaction (RT-PCR) method was used for genotyping.

RESULTS:

The variant allele frequencies of VKORC1 rs2359612 (T), rs8050894 (C), rs9934438 (T) and rs9923231 (A) were found to be 11.0%, 11.8%, 11.7% and 12.0%, respectively. The variant allele VKORC1 rs7294 was (80.1%) more frequent and the variant allele CYP4F2 * 3 was found to be 41.8% in South Indians. The allele, genotype and haplotype frequencies of VKORC1 and CYP4F2 gene were distinct from other compared HapMap populations (P < 0.0001).

CONCLUSION:

The findings of our study provide the basic genetic information for further pharmacogenetic based investigation of OA therapy in the population.

Pharmacogenomics of anti-platelet and anti-coagulation therapy

Arterial thrombosis is a major component of vascular disease, especially myocardial infarction (MI) and stroke. Current anti-thrombotic therapies such as warfarin and clopidogrel are effective in inhibiting cardiovascular events; however, there is great inter-individual variability in response to these medications. In recent years, it has been recognized that genetic factors play a significant role in drug response, and, subsequently, common variants in genes responsible for metabolism and drug action have been identified. These discoveries along with new diagnostic targets and therapeutic strategies hold promise for more effective individualized anti-coagulation and anti-platelet therapy.

Genetics-based pediatric warfarin dosage regimen derived using pharmacometric bridging

BACKGROUND

Warfarin dosage regimens using CYP2C9 and VKORC1 polymorphisms have been extensively studied in adults and is included in US Food and Drug Administration-approved warfarin labeling. However, no dosage algorithm is available for pediatric patients.

OBJECTIVE

To derive a genetics-based pediatric dosge regimen for warfarin, including starting dose and titration scheme.

METHODS

A model-based approach was developed based on a previously validated warfarin dosage model in adults, with subsequent comparison to pediatric data from pediatric warfarin dose, genotyping, and international normalized ratio (INR) results. The adult model was based on a previously established model from the CROWN (CReating an Optimal Warfarin dosing Nomogram) trial. Pediatric warfarin data were obtained from a study conducted at the Children's Hospital of Los Angeles with 26 subjects. Variant alleles of CYP2C9 (rs1799853 or *2, and rs1057910 or *3) and the VKORC1 single nucleotide polymorphism (SNP) rs9923231 (-1639 G>A) were assessed, where the rs numbers are reference SNP identification tags assigned by the National Center for Biotechnology Information.

RESULTS

A pediatric warfarin model was derived using the previously validated model and clinical pharmacology considerations. The model was validated, and clinical trial simulation and stochastic modeling were used to optimize pediatric dosage and titration. The final dosage regimen was optimized based on simulations targeting a high (≥60%) proportion of INRs within the therapeutic range by week 2 of warfarin therapy while minimizing INRs >3.5 or <2.

CONCLUSIONS

The proposed pediatric warfarin dosage scheme based on individual CYP2C9 (alleles *1,*2,*3) and VKORC1 rs9923231 (-1639 G>A) genotypes may offer improved dosage compared to current treatment strategies, especially in patients with variant CYP2C9 and VKORC1 alleles. This pilot study provides the foundation for a larger prospective evaluation of genetics-based warfarin dosage in pediatric patients.

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.

The pharmacokinetics and pharmacodynamics of single dose (R)- and (S)-warfarin administered separately and together: relationship to VKORC1 genotype

AIMS

1) To determine the pharmacokinetics and pharmacodynamics of (R)- and (S)-warfarin given alone and in combination and 2) to determine whether the relative potency of (R)- and (S)-warfarin is dependent on VKORC1 genotype.

METHODS

A three way crossover study was conducted in which 17 healthy male subjects stratified by VKORC1 1173 C>T genotype and all CYP2C9 1*/1* received (R)-warfarin 80 mg, (S)-warfarin 12.5 mg and rac-warfarin sodium 25 mg. Plasma (R)- and (S)-warfarin unbound and total concentrations and prothrombin time were determined at multiple time points to 168 h.

RESULTS

Pharmacokinetic parameters for (R)- and (S)-warfarin were similar to the literature. (R)-warfarin 80 mg alone resulted in a mean AUC(PT) (0,168 h) of 3550 s h (95% CI 3220, 3880). Rac-warfarin sodium 25 mg containing (S)-warfarin 11.7 mg produced a greater effect on AUC(PT) (0,168 h) than (S)-warfarin 12.5 mg (mean difference 250 s.h, 95% CI 110, 380, P < 0.002) given alone. In a mixed effects model the ratio of response between (R)- and (S)-warfarin (AUC(PT((R)-warfarin)) : AUC(PT((S)-warfarin))) was 1.21 fold higher (95% CI 1.05, 1.41, P < 0.02) in subjects of VKORC1 TT genotype compared with the CC genotype.

CONCLUSIONS

(R)-warfarin has a clear PD effect and contributes to the hypoprothrombinaemic effect of rac-warfarin. VKORC1 genotype is a covariate of the relative R/S potency relationship. Prediction of drug interactions with warfarin needs to consider effects on (R)-warfarin PK and VKORC1 genotype.

Adherence and variability in warfarin dose requirements: assessment in a prospective cohort

AIM

Although several genetic and nongenetic factors are associated with warfarin dose, approximately 40% of variability remains unexplained. An as yet unexplored factor is medication adherence. Here, we investigate the influence of adherence on response to warfarin and on pharmacogenetic analyses of association.

PATIENTS & METHODS

A total of 311 patients starting warfarin were followed-up prospectively, and adherence was measured at 1, 8 and 26 weeks. The association between adherence and warfarin response was tested, and the additional proportion of variability in response explained by adherence was assessed.

RESULTS

Significant associations were found between adherence and achievement of stable dose and time taken to achieve it, with nonadherers taking longer. Adjusting for adherence increased the proportion of explained variability in treatment response by up to 8%.

CONCLUSION

Given the significant contribution of adherence to drug response, we recommend that consideration is given to the value of assessing adherence when designing future pharmacogenetic studies of warfarin and other drugs.

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

Background and Purpose

Variant 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.

Methods

Ischemic 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.

Results

All 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.

Conclusions

WRI 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.