Variability in CYP2C9 allele frequency: A pilot study of its predicted impact on warfarin response among healthy South and North Indians

Stability of Anticoagulation Following Acenocoumarin in Stroke Patients: Role of Pharmacogenomics and Acquired Factors

OBJECTIVE

Pharmacogenomics plays an important role in drug metabolism. A stable anticoagulation is important for primary and secondary prevention of cardioembolic stroke and cerebral venous sinus thrombosis (CVST). We report the role of cytochrome P450 ( CYP2C9*2/*3 ) and vitamin K epoxide reductase subunit 1 ( VKORC1 ) genotypes and acquired causes in maintaining stability of anticoagulation following acenocoumarin in cardioembolic stroke and CVST.

METHODS

The study comprised 157 individuals with cardioembolic stroke and CVST who were on acenocoumarin. Their comorbidities, comedication, and dietary habits were noted. Prothrombin time and international normalized ratio (INR) were measured during follow-up, and the coagulation status was categorized as stable (>50% occasions in therapeutic range) and unstable (>50% below and above therapeutic range). Genotyping of VKORC1 , CYP2C9*2 , and CYP2C9*3 was done by polymerase chain reaction-restriction fragment length polymorphism. Bleeding and embolic complications were noted. The predictors of unstable INR were evaluated using multivariate analysis.

RESULTS

INR was stable in 47.8% and unstable in 52.2% of patients. Patients with mutant genotypes required low dose of acenocoumarin. The predictors of unstable INR were metallic valve (odds ratio [OR] 4.07, 95% confidence interval [CI] 1.23-13.49, P = 0.02), use of digoxin (OR 0.031, 95% CI 0.13-0.74, P = 0.09), proton pump inhibitor (OR 0.23, 95% CI 0.06-0.91, P = 0.037), sodium valproate (OR 0.22, 95% CI 0.05-0.85, P = 0.029), and CYP2C9*2 genotype (OR 5.57, 95% CI 1.19-26.06, P = 0.02).

CONCLUSIONS

Variant genotypes of VKORC1 , CYP2C9*2 , and CYP2C9*3 required lower dose of acenocoumarin, and CYP2C9*2 was associated with unstable INR. Comedication is a modifiable risk factor that needs attention.

Genetic and Nongenetic Determinants of Variable Warfarin Dose Requirements: A Report from North India

INTRODUCTION

Warfarin is widely used and will continue to be prescribed especially in developing countries due to its low cost. Given the huge patient load requiring anticoagulation, there is a need to develop strategies to optimize warfarin therapy for ensuring safe and effective anticoagulation. In the present work, we aimed at elucidating the association of genetic and nongenetic variables with warfarin dose requirement in patients attending the cardiovascular clinic in a tertiary care center of North India.

METHODS

This was a prospective study conducted over 1 year. Patient demographic and clinical details were captured in customized case record forms. Genotyping was done using the polymerase chain reaction-restriction fragment length polymorphism method. Pharmacogenetic influence of CYP2C9 (rs1799853 and rs1057910) and VKORC1 (rs9923231) variant alleles was studied. The association of genetic and nongenetic factors with warfarin dose was quantified using a stepwise multivariate linear regression model.

RESULTS

Two hundred and forty patients were screened. Data from 82 eligible patients were used for quantifying the association of genetic and nongenetic factors with warfarin dose. A descriptive model based on CYP2C9*3 (rs1057910) and VKORC1 (rs9923231) variant alleles and BMI was developed. The model explains nearly half of the interindividual variation in warfarin dose requirement.

CONCLUSION

The model explains nearly half of the interindividual variation in warfarin dose in patients with atrial fibrillation and or requiring valve replacement.

Association of HLA-B*51:01, HLA-B*55:01, CYP2C9*3, and Phenytoin-Induced Cutaneous Adverse Drug Reactions in the South Indian Tamil Population

Phenytoin (PHT) is one of the most commonly reported aromatic anti-epileptic drugs (AEDs) to cause cutaneous adverse reactions (CADRs), particularly severe cutaneous adverse reactions (SCARs). Although human leukocyte antigen (HLA)-B*15:02 is associated with PHT-induced Steven Johnson syndrome/toxic epidermal necrosis (SJS/TEN) in East Asians, the association is much weaker than it is reported for carbamazepine (CBZ). In this study, we investigated the association of pharmacogenetic variants of the HLA B gene and CYP2C9*3 with PHT-CADRs in South Indian epileptic patients. This prospective case-controlled study included 25 PHT-induced CADRs, 30 phenytoin-tolerant patients, and 463 (HLA-B) and 82 (CYP2C9*3) normal-controls from previous studies included for the case and normal-control comparison. Six SCARs cases and 19 mild-moderate reactions were observed among the 25 cases. Pooled data analysis was performed for the HLA B*51:01 and PHT-CADRs associations. The Fisher exact test and multivariate binary logistic regression analysis were used to identify the susceptible alleles associated with PHT-CADRs. Multivariate analysis showed that CYP2C9*3 was significantly associated with overall PHT-CADRs (OR = 12.00, 95% CI 2.759–84.87, p = 003). In subgroup analysis, CYP2C9*3 and HLA B*55:01 were found to be associated with PHT-SCARs (OR = 12.45, 95% CI 1.138–136.2, p = 0.003) and PHT-maculopapular exanthema (MPE) (OR = 4.041, 95% CI 1.125–15.67, p = 0.035), respectively. Pooled data analysis has confirmed the association between HLA B*51:01/PHT-SCARs (OR = 6.273, 95% CI 2.24–16.69, p = <0.001) and HLA B*51:01/PHT-overall CADRs (OR = 2.323, 95% CI 1.22–5.899, p = 0.037). In this study, neither the case nor the control groups had any patients with HLA B*15:02. The risk variables for PHT-SCARs, PHT-overall CADRs, and PHT-MPE were found to be HLA B*51:01, CYP2C9*3, and HLA B*55:01, respectively. These alleles were identified as the risk factors for the first time in the South Indian Tamil population for PHT-CADRs. Further investigation is warranted to establish the clinical relevance of these alleles in this population with larger sample size.

Genetic polymorphisms and dosing of vitamin K antagonist in Indian patients after heart valve surgery

Purpose

Vitamin K antagonists (VKAs), such as warfarin and acenocoumarol, exert their anti-coagulant effect by inhibiting the subunit 1 of vitamin K epoxide reductase complex (VKORC1). CYP2C9 is a hepatic drug-metabolizing enzyme in the CYP450 superfamily and is the primary metabolizing enzyme of warfarin. Three single nucleotide polymorphisms, two in the CYP2C9 gene, namely CYP2C9*2 and CYP2C9*3, and one in the VKORC1 gene (c.- 1639G > A, rs9923231), have been identified to reduce VKA metabolism and enhance their anti-coagulation effect. The purpose of this study is to evaluate the prevalence of CYP2C9 and VKORC1 polymorphism in Indians receiving VKA-based anti-coagulation after valve surgery and to evaluate the usefulness of genetic information in managing VKA-based anti-coagulation.

Methods

In the current prospective observational study, 150 patients who underwent heart valve surgery and had stable INR were genotyped for VKORC1 (- 1639 G > A), CYP2C9*2, and CYP2C9*3. The VKA dosage was estimated from published algorithms and compared to the clinically stabilized dosage.

Results

Out of 150 patients, 101 (67.33%) were on warfarin and 49 (32.66%) were on acenocoumarol. Majority of the patients, the 83 in warfarin group and the 40 in acenocoumarol group, had a wild CYP2C9 diplotype. The rest had a mutant (CYP2C9*2 or CYP2C9*3) diplotype. Similarly, 67 patients in the warfarin group and 35 patients in the acenocoumarol group had wild type (G/G) of VKORC1 genotype. The rest had a mutant (G/A or A/A) VKORC1 genotype. In the warfarin group, based on the genotype, 51.5% of the patients were extensive or normal metabolizers, and 47.4% of the patients were intermediate metabolizers of VKAs. In the acenocoumarol group, 61.2% of the patients were extensive or normal metabolizers, and 38.8% of the patients were intermediate metabolizers. Individually, alleles of VKORC1 (- 1639 G > A), CYP2C9*2, and CYP2C9*3 had mean dosage reduction effect on VKA dosage, which co-related to the clinically stabilized dosages (P < 0.0001). Among the VKORC1 (- 1639 G > A) cohort, the reduction in warfarin mean weekly dosage was 13.48 mg as compared to the wild-type category (P < 0.0001) and similarly, the reduction in the mean weekly acenocoumarol dose was 6.07 mg (P < 0.03) as compared to the wild type after adjusting for age, gender, and body mass index.

Conclusion

Single nucleotide polymorphism in the CYP2C9 gene and in the VKORC1 gene is present in nearly 40% of Indian patients. VKORC1 (- 1639 G > A), CYP2C9*2, and CYP2C9*3 genotypes have significant dosage-lowering effects on VKA-based anti-coagulation therapy. The trend in estimated dosages of VKAs co-related to that of observed the clinically stabilized dosage in the cohort. The pharmacogenomic calculators used in this study tend to overestimate the VKA dosages as compared to clinical dosage due to the limitations in the algorithms and in our study. A new algorithm based on a larger dataset capturing the vast genetic variability across the Indian population and relevant clinical factors could provide better results.

Association between polymorphisms of VKORC1 and CYP2C9 genes with warfarin maintenance dose in a group of warfarin users in Birjand city, Iran

Warfarin is the cardinal anticoagulant drug prescribed around the world. Due to stochastic bleeding in patients, it is essential to adjust the dose for every individual. The aim of the present study was to evaluate the frequency of CYP2C9 and VKORC1 gene polymorphisms and their association with warfarin maintenance dose in a sample of cardiovascular patients in Birjand, South-Khorasan province of Iran. Patients with a history of cardiovascular disorders who take warfarin daily were selected. CYP2C9 and VKORC1 gene polymorphisms were detected by polymerase chain reaction-restriction fragment length polymorphism in all participants. A total of 114 patients (mean age: 52.7 ± 14.9 years, M/F ratio: 0.76) participated in this study. Regarding CYP2C9 gene polymorphisms, the most frequent genotype was 1*/1* (80.4% in females and 62.5% in males). The frequency of 1*/2* and 2*/2* variants was 13% and 6.5% in females and 25% and 12.5% in males, respectively. The frequency of VKORC1 gene (1639 G > A), was 31.5%, 39.5%, and 29% for GG, GA, and AA in males, respectively. Besides, the mentioned genotype frequencies for females were 50%, 40.5%, and 9.5%, respectively. Moreover, there was a statistically significant correlation between VKORC1 gene -1639 G > A variant and warfarin maintenance dose (P < 0.001) but not for CYP2C9 variants. The results of the current study confirmed that the mutant variants of CYP2C9 are not frequent and do not have any impact on warfarin dose. In the case of VKORC1, the mutant allele (A) showed a positive correlation with warfarin dose adjustment.

Value of VKORC1 (-1639G>A) rs9923231 genotyping in predicting warfarin dose: A replication study in South Indian population

OBJECTIVE

Warfarin is the most commonly prescribed oral anticoagulant, although having a narrow therapeutic index and wide interindividual variability. The aim of this study was to replicate the utility of VKORC1 (-1639G>A) rs9923231 genotyping in predicting the mean daily dose and to evaluate its ability to categorize warfarin-treated patients to high-, intermediate-, or low-dose categories in the South Indian population.

MATERIALS AND METHODS

A cohort of 222 warfarin-treated patients was genotyped using restriction fragment length polymorphism method. The influence of the rs9923231 polymorphism on the variations in the mean daily dose was compared using one-way analysis of variance and linear regression analysis. Discriminatory ability of the rs9923231 polymorphism to group the patients into ordered dose categories was assessed by estimating the proportional odds ratios using the ordered logit regression analysis.

RESULTS

The frequency of AA genotype and A allele in the study sample was found to be 1.8% and 9.23%, respectively, which was similar to reports from other South Indian populations. The mean daily dose required to achieve the optimum international normalized ratio was significantly lower in AA homozygous genotype carriers (3.99 ± 1.67 mg/day) and GA heterozygous (4.26 ± 1.57 mg/day) compared to the GG genotype carriers (5.51 ± 2.13 mg/day), p = 0.003. The A allele carriers (GA+AA genotypes) had a 3.23 higher odds of being grouped as a low-dose requiring category compared to non-carriers (95% CI 1.49-6.98, p = 0.003).

CONCLUSIONS

These preliminary results strongly support the use of VKORC1 (-1639G>A) rs9923231 polymorphism for genetically guided initial warfarin dosing in South Indian patients with heart valve replacements.

Polymorphic analysis of CYP2C9 gene in Vietnamese population

Genetic variations in CYP2C9 are associated to inter-individual variability of drugs metabolism and response. The only report has been done previously mainly focusing on the common variant alleles of CYP2C9 in Vietnamese Kinh subjects. However, little is known about the complete spectrum of this gene polymorphism in different ethnic groups of Vietnam. We sequenced the promoter region and all exons of CYP2C9 in 100 healthy unrelated Vietnamese Kinh subjects. Additionally, common CYP2C9 variants, *2 and *3, were also analyzed by RFLP-PCR in extra 194 Kinh subjects and 279 of other four ethnic groups in Vietnam. The results of these common variants observed from five ethnic groups were compared with other populations in the world. Seven previously reported alleles and two genotypes were determined in Kinh subjects. The percentage of CYP2C9*1 and CYP2C9*3 alleles are 96.5 and 3.5%, respectively. We found one novel non-synonymous variant in exon 7 leading to amino acid change at 363 position from proline to histidine. Functional analysis by SIFT and Polyphen-2 indicated that this mutation is intolerant and probably damaging. Prevalence of CYP2C9*2 observed in Vietnamese population was significantly lower compared with that of other populations in the South and West of Asia as well as in Europe. This study provides information of genetic distribution pattern of CYP2C9 in Vietnamese, which would be useful for optimizing drug therapies in Vietnam.

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.

The effect of CYP2C9*2, CYP2C9*3, and VKORC1-1639 G>A polymorphism in patients under warfarin therapy in city of Kermanshah

Polymorphism in the genes encoding CYP2C9 enzyme and VKORC1 reductase significantly influence warfarin dose requirement since patients with CYP2C9*2, CYP2C9*3 and VKORC1 mutant alleles require lower warfarin maintenance doses. Studies have reported the ethnic variations in the frequency of these genes within the various populations in Iran and other parts of the world. However, no such study has been done yet on Kurdish population in Kermanshah. From Kurdish population of Kermanshah province in Iran, a total of 110 patients who had heart surgery and taking warfarin, were genotyped for polymorphisms of VKORC1-1639 G>A, CYP2C9*2, and CYP2C9*3. Polymorphism genotyping was performed by sequencing as well as polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) using restriction enzymes of MspI, AVAII and KpnI, respectively. The frequencies of VKORC1-1639 GG, GA, and AA genotypes were 42%, 36%, and 22%, respectively and for CYP2C9 1*/1*, 1*/2*, 2*/2*, 1*/3*, 3*/3*, 2*/3* were 71%, 17%, 5.4%, 1.8%, 4.5%, and 0%, respectively. The frequency of VKORC1-1639A allele was 42.3% and the frequencies of CYP2C9*2 and *3 alleles were 14% and 5.4%, respectively. It was indicated that low warfarin dose requirements are strongly associated with the presence of CYP2C9 and VKORC1-1639 variant alleles. Our results confirmed the supply to understand the distribution of genomic biomarkers related to the drugs metabolism for future planning health programs.

DNA sensors to assess the effect of VKORC1 and CYP2C9 gene polymorphisms on warfarin dose requirement in Chinese patients with atrial fibrillation

The optimal dose of warfarin depends on polymorphisms in the VKORC1 (the vitamin K epoxide reductase complex subunit (1) and CYP2C9 (cytochrome P450 2C9) genes. To minimize the risk of adverse reactions, warfarin dosages should be adjusted according to results from rapid and simple monitoring methods. However, there are few pharmacogenetic-guided warfarin dosing algorithms that are based on large cohorts from the Chinese population, especially patients with atrial fibrillation. This study aimed to validate a pharmacogenetic-guided warfarin dosing algorithm based on results from a new rapid electrochemical detection method used in a multicenter study. Three SNPs (CYP2C9 *2, *3 and VKORC1 c.-1639G > A) were genotyped by electrochemical detection using a sandwich-type format that included a 3' short thiol capture probe and a 5' ferrocene-labeled signal probe. A total of 1285 samples from four clinical hospitals were evaluated. Concordance rates between the results from the electrochemical DNA biosensor and the sequencing test were 99.8%. The results for gene distribution showed that most Chinese patients had higher warfarin susceptibility because mutant-type and heterozygotes were present in the majority of subjects (99.4%) at locus c.-1639G > A. When the International Warfarin Pharmacogenetics Consortium algorithm was used to estimate therapeutic dosages for 362 patients with AF and the values were compared with their actual dosages, the results revealed that 56.9% were similar to actual dosages (within the 20% range). A novel electrochemical detection method of CYP2C9 *2, *3and VKORC1 c.-1639G > A alleles was evaluated. The warfarin dosing algorithm based on data gathered from a large patient cohort can facilitate the reasonable and effective use of warfarin in Chinese patients with AF.

The allele frequency of CYP2C9 and VKORC1 in the Southern Khorasan population

The genetic factors are determinants in required dosage changes of warfarin among which are polymorphisms of CYP2C9 and VKORC1 genes. The present study aimed to determine the allele and genotype frequency of CYP2C9 and VKORC1 genes in Birjand population. This study was conducted on 120 individuals who referred to Imam Reza and Vali-Asr hospitals for PT/INR test. After extracting the genomic DNA, the considered sequences were amplified by PCR, and restriction fragment length polymorphism analysis was done by AvaII and KpnI enzymes to determine allele polymorphisms. Moreover, related sequences of VKORC1, after amplification, were sequenced for determining the genotype. Allelic and genotypic frequencies as well as Hardy-Weinberg equilibrium, observed heterozygosity, expected heterozygosity, and polymorphism information content were calculated by PowerMarker V 3.25 software. Amongst 120 individuals in this study with the mean age of 58.12 ± 12.7 years, 80.8%, 9.1%, and 10% exhibited the alleles of 1, 2, and 3 CYP2C9 gene, respectively. The genotype frequencies of 1/1, 1/2, 2/2, 3/1, 3/2, and 3/3 of this gene were found to be 64.1, 15.8, 0, 17.5, 2.5, and 0 %, respectively. In -1639 G>A region, VKORC1 had normal homozygote genotype (GG) and in 1173 C>T region, heterozygote (CT) with the frequency of 48.7% and 45.9% had the most prevalence. Compared with other populations, there is a considerable difference between the allele frequency of CYP2C9 and VKORC1 genetic variance. Since 35.8% of the selected populations carry an abnormal allele causing sensitivity to warfarin, the specialists at medical centers must be informed about the genotypes of patients before prescribing warfarin.

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.

Evaluation of cytochrome P450 2C9 activity in normal, healthy, adult Western Indian population by both phenotyping and genotyping

Objectives:

Cytochrome P450 2C9 (CYP2C9) is a member of cytochrome P450 (CYP) family that accounts for nearly 18% of the total CYP protein content in the human liver microsomes and catalyzes almost 15–20% of the drugs. Considering the paucity of data on the polymorphisms of CYP2C9 in Western Indian population, the present study was conducted to evaluate the prevalence of CYP2C9 polymorphisms (*1, *2 and *3) and correlate it with the activity using flurbiprofen (FLB) as a probe drug.

Materials and Methods:

A 100 mg FLB capsule was administered to 298 healthy adult participants. Venous blood samples were analyzed at 2 h postdose for the estimation of FLB and 4-hydroxy FLB. Metabolic ratio (MR) was calculated to determine the extent of poor metabolizer (PM) and rapid metabolizer status using probit plot. Genotyping of CYP2C9 polymorphism was performed using polymerase chain reaction-restriction fragment length polymorphism technique.

Results:

Of the total 298 participants, phenotype was assessable in 288 and genotype was performed in 289 participants. The median (range) MR of the study population was 6.6 (1.65–66.05). Five participants were found to be PMs by phenotype. Of the total 289 participants, 209 (72.3%) (66.7, 77.2) had CYP2C9*1/*1, 25 (8.7%) (5.8, 12.7) with CYP2C9*1/*2, 55 (19%) (14.8, 24.1) had CYP2C9*1/*3, 3 (1%) (0.3, 3.3) had CYP2C9*2/*3 genotype. A significant association between phenotype and genotype was observed.

Conclusion:

To conclude, the present study found significant association of CYP2C9 activity by both phenotype and genotype and these findings have to be corroborated in different kinds of patients.

High prevalence of VKORC1*3 (G9041A) genetic polymorphism in north Indians: A study on patients with cardiac disorders on acenocoumarol

Coumarin derivatives such as warfarin and acenocoumarol are used in various disorders such as deep venous thrombosis, pulmonary embolism, atrial fibrillation and artificial heart valves. They have improved prognosis of patients with thromboembolic disease. An individual's response to coumarins depends on several factors. The non-genetic factors include age, gender, body mass index, diet and interacting drugs. Among the genetic factors, the cytochrome P450 system and vitamin K epoxide reductase complex subunit 1 play a key role in drug metabolism. This was a prospective hospital based study in which allele and genotypic frequencies of CYP2C9 gene polymorphisms; 430C>T and 1075A>C and VKORC1 gene polymorphisms; 1639G>A, 9041G>A and 6009C>T in 106 alleles of north Indian patients with valve replacement on acenocoumarol were determined and their effect on acenocoumarol dosing was studied. To the best of our knowledge, this is first report of VKORC1 9041G>A and 6009C>T gene polymorphisms and their effect on acenocoumarol dosing from north India. In 53 patients with valve replacement on acenocoumarol with stable INR, the allele frequency of CYP2C9*2 and CYP2C9*3 gene polymorphisms was 0.05 and 0.17 respectively and that of VKORC1 *2,*3 and *4 gene polymorphisms was 0.15, 0.72 and 0.11 respectively. The presence of CYP2C9*3 or VKORC1*2 gene polymorphism were associated with decrease in acenocoumarol dose requirements (p values 0.03 and 0.02 respectively).This study confirmed the association of lower mean weekly dosages of acenocoumarol in patients with CYP2C9*3 and VKORC1*2 gene polymorphisms. An unusually high frequency of 9041A polymorphism in VKORC1 was found in study population.

A Critical Evaluation of Pharmacogenetic Information in Package Inserts for Selected Drugs Marketed in India and Its Comparison With US FDA-Approved Package Inserts

Our objective was to compare the pharmacogenetic information provided in the package inserts (PIs) of 7 drugs marketed in the United States and India, namely, abacavir, capecitabine, carbamazepine, clopidogrel, irinotecan, valproic acid, and warfarin. We evaluated the pharmacogenetic information provided in Indian PIs for the highest level where it was included, robustness and completeness, clinical validity, and clinical utility and compared it with corresponding data of US PIs. Pharmacogenetic studies carried out in India were identified using PubMed. Pharmacogenetic information was provided in Indian PIs of all the drugs except irinotecan. It appeared in the same section as in US PIs for abacavir, capecitabine, carbamazepine (HLA-*3101), valproic acid (urea cycle disorders), and warfarin (protein C and protein S), whereas it appeared at lower levels for other drug-gene combinations. The robustness of pharmacogenetic testing was graded convincing for abacavir, adequate for carbamazepine and clopidogrel, and incomplete for the remaining drugs, and only abacavir and clopidogrel PIs provided full details of supporting studies. These details, when provided in the Indian PIs were identical to those in the US PIs. The Indian PIs did not provide data on Indian patients, although published studies are available. Both US and Indian PIs lacked critical information on the clinical validity and utility of pharmacogenetic testing. The pharmacogenetic information should provide country/ethnicity-specific data so that they are useful to clinicians. Where data are not available, the prevalence of genetic variation in the population of a country needs to be determined and should then be translated to the PIs.

The effect of CYP2C9 and VKORC1 genetic polymorphisms on warfarin dose requirements in a pediatric population

OBJECTIVE

The aim was to investigate the frequency of genetic polymorphisms of cytochrome P4502C9 (CYP2C9) and vitamin K epoxide reductase complex subunit1 (VKORC1) and determine the effect of these polymorphisms on warfarin dose requirements in pediatric patients.

METHODS

Fifty-eight pediatric patients with cardiac disease, thrombophilia, or other conditions, taking a stable warfarin dose, aged 0.2-18 years, and with international normalized ratio (INR) between 2 and 3 and 149 healthy children as a control group were included in this prospective, observational study. Patients receiving drugs that interact with warfarin, having chronic liver or renal disease, obesity, or thyroid dysfunctions were excluded. Polymerase chain reaction (real time and restriction fragment length polymorphism) was used to analyze the CYP2C9*2, CYP2C9*3, and VKORC1 polymorphisms. The ideal warfarin dose was calculated according to the patient's age, height, and the presence of CYP2C9*2, CYP2C9*3, and VKORC1 genetic polymorphisms. The mean daily administered doses and ideal doses were compared. Analysis of variance, Student's t-test, logistic regression analysis, and Pearson's correlation analysis were used for statistical analyses.

RESULTS

The frequency of the CYP2C9 and VKORC1 genetic polymorphisms was determined as CYP2C9*1/*1 (54.6%), *1/*2 (16.4%), *1/*3 (24.2%), *2/*3 (2.9%), *3/*3 (1.9%), wild-type VKORC1 (26.6%), heterozygote alleles (52.7%), and mutant alleles (20.8%). Patients with allelic variants were found to require lower warfarin doses, and a 64.5% correlation was found between the calculated ideal doses and the administered warfarin doses.

CONCLUSION

Considering CYP2C9 and VKORC1 genetic polymorphisms prior to commencing warfarin treatment will make it easier to reach target INRs and reduce the rate of complications.

Pharmacogenetics of drug metabolizing enzymes in the United Kingdom population: review of current knowledge and comparison with selected European populations

Data on frequency of pharmacogenetic polymorphisms in the UK population are limited. However, availability of whole genome sequencing data on 94 UK controls of European ethnicity from the 1000 genomes project together with similar data on other populations provides a valuable new source of data in this area and allows direct comparison of allele frequencies with those for other European populations. The ethnic diversity of the UK population also needs to be considered, and 1000 genomes includes data on South Asians, the most common ethnic group in the UK after White Europeans. Allele frequencies for polymorphisms in genes relevant to phase I and phase II drug metabolism for UK, Finnish, Spanish and South Asian populations were obtained from the literature and 1000 genomes. Generally there was good agreement between the literature and 1000 genomes reports. CYP2D6*4, the most common CYP2D6 poor metabolizer allele among Europeans, appears more common in the UK than in Spain and Finland, whereas, as suggested previously, CYP2C19*2 and CYP2C9*2 appear more common in Finland and Spain, respectively, than in the UK. South Asians show low frequencies of CYP2C9*2 and CYP2C19*17 but higher frequencies of CYP2C19*2 compared with UK residents of European ethnicity. Though personalizing drug treatment on the basis of individual genotype rather than ethnicity may be more appropriate, differences in allele frequencies across continents should be considered when designing clinical trials of new drugs.

Cost-effectiveness analysis of pharmacogenetic-guided warfarin dosing in Thailand

INTRODUCTION

Pharmacogenetic (PGx) test is a useful tool for guiding physician on an initiation of an optimal warfarin dose. To implement of such strategy, the evidence on the economic value is needed. This study aimed to determine the cost-effectiveness of PGx-guided warfarin dosing compared with usual care (UC).

METHODS

A decision analytic model was used to compare projected lifetime costs and quality-adjusted life years (QALYs) accrued to warfarin users through PGx or UC for a hypothetical cohort of 1,000 patients. The model was populated with relevant information from systematic review, and electronic hospital-database. Incremental cost-effectiveness ratios (ICERs) were calculated based on healthcare system and societal perspectives. All costs were presented at year 2013. A series of sensitivity analyses were performed to determine the robustness of the findings.

RESULTS

From healthcare system perspective, PGx increases QALY by 0.002 and cost by 2,959 THB (99 USD) compared with UC. Thus, the ICER is 1,477,042 THB (49,234 USD) per QALY gained. From societal perspective, PGx results in 0.002 QALY gained, and increases costs by 2,953 THB (98 USD) compared with UC (ICER 1,473,852 THB [49,128 USD] per QALY gained). Results are sensitive to the risk ratio (RR) of major bleeding in VKORC1 variant, the efficacy of PGx-guided dosing, and the cost of PGx test.

CONCLUSION

Our finding suggests that PGx-guided warfarin dosing is unlikely to be a cost-effective intervention in Thailand. This evidence assists policy makers and clinicians in efficiently allocating scarce resources.

CYP2C9*3 polymorphism presenting as lethal subdural hematoma with low-dose warfarin

Warfarin is the most common and cheap oral anticoagulant currently used in clinical practice. A high inter-individual variation is seen in the response to warfarin. Recently, pharmacogenetics has gained importance in managing patients on warfarin, both in predicting the optimum required dose as well as in decreasing the risk of bleeding. This case report is a description of a 49-year-old patient who had a lethal subdural hematoma with low-dose warfarin. He was subsequently found to have CYP2C9 gene polymorphism (*1/*3). This case report stresses the importance of pre-prescription assessment of genetic analysis for those initiated on warfarin.

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.