Genetic polymorphism of the CYP2C9 subfamily of 3 different races in warfarin maintenance dose

Impact of CYP2C9 and VKORC1 Polymorphisms on Warfarin Sensitivity and Responsiveness in Jordanian Cardiovascular Patients during the Initiation Therapy

Warfarin is an oral anticoagulant frequently used in the treatment of different cardiovascular diseases. Genetic polymorphisms in the CYP2C9 and VKORC1 genes have produced variants with altered catalytic properties. A total of 212 cardiovascular patients were genotyped for 17 Single Nucleotide Polymorphisms (SNPs) within the CYP2C9 and VKORC1 genes. This study confirmed a genetic association of the CYP2C9*3 and VKORC1 rs10871454, rs8050894, rs9934438, and rs17708472 SNPs with warfarin sensitivity. This study also found an association between CYP2C9 and VKORC1 genetic haplotype blocks and warfarin sensitivity. The initial warfarin dose was significantly related to the CYP2C9*3 polymorphism and the four VKORC1 SNPs (p < 0.001). There were significant associations between rs4086116 SNP and TAT haplotype within CYP2C9 gene and rs17708472 SNP and CCGG haplotype within VKORC1 gene and warfarin responsiveness. However, possessing a VKORC1 variant allele was found to affect the international normalized ratio (INR) outcomes during initiation of warfarin therapy. In contrast, there was a loose association between the CYP2C9 variant and INR measurements. These findings can enhance the current understanding of the great variability in response to warfarin treatment in Arabs.

Influence of CYP2C9 and VKORC1 on patient response to warfarin: a systematic review and meta-analysis

Background

Warfarin is a highly effective anticoagulant however its effectiveness relies on maintaining INR in therapeutic range. Finding the correct dose is difficult due to large inter-individual variability. Two genes, CYP2C9 and VKORC1, have been associated with this variability, leading to genotype-guided dosing tables in warfarin labeling. Nonetheless, it remains unclear how genotypic information should be used in practice. Navigating the literature to determine how genotype will influence warfarin response in a particular patient is difficult, due to significant variation in patient ethnicity, outcomes investigated, study design, and methodological rigor. Our systematic review was conducted to enable fair and accurate interpretation of which variants affect which outcomes, in which patients, and to what extent.

Methodology/Principal Findings

A comprehensive search strategy was applied and 117 studies included. Primary outcomes were stable dose, time to stable dose and bleeding events. Methodological quality was assessed using criteria of Jorgensen and Williamson and data synthesized in meta-analyses using advanced methods. Pooled effect estimates were significant in most ethnic groups for CYP2C9*3 and stable dose (mutant types requiring between 1.1(0.7–1.5) and 2.3 (1.6–3.0)mg/day). Effect estimates were also significant for VKORC1 and stable dose for most ethnicities, although direction differed between asians and non-asians (mutant types requiring between 0.8(0.4–1.3) and 1.5(1.1–1.8)mg/day more in asians and between 1.5(0.7–2.2) and 3.1(2.7–3.6)mg/day less in non-asians). Several studies were excluded due to inadequate data reporting. Assessing study quality highlighted significant variability in methodological rigor. Notably, there was significant evidence of selective reporting, of outcomes and analysis approaches.

Conclusions/Significance

Genetic associations with warfarin response vary between ethnicities. In order to achieve unbiased estimates in different populations, a high level of methodological rigor must be maintained and studies should report sufficient data to enable inclusion in meta-analyses. We propose minimum reporting requirements, suggest methodological guidelines and provide recommendations for reducing the risk of selective reporting.

Clinical applications of pharmacogenomics guided warfarin dosing

AIM OF THE REVIEW

To assess the state of the literature concerning pharmacogenomic testing in patients requiring vitamin K antagonists, specifically warfarin.

METHOD

We conducted a literature search of MEDLINE and International Pharmaceutical Abstracts using the following words: warfarin, pharmacogenetic, and pharmacogenomic. The search results were reviewed by the authors and papers concerning pharmacogenomic testing in warfarin dosing were procured and reviewed. Additionally bibliographies of papers procured were also examined for other studies. The authors focused on clinical trials concerning the use of pharmacogenomic testing in warfarin dosing.

RESULTS

Although numerous studies have demonstrated that a significant portion of warfarin dosing variability can be explained by genetic polymorphisms, few prospective studies have been conducted that examine the integration of this information in practical dosing situations. Those that have, have shown that using pharmacogenomic information improves initial dosing estimates and decreases the need for frequent clinic visits and laboratory testing. Data showing a reduction in serious bleeding events is sparse. Cost-effectiveness analyses have generally shown a small but positive effect with pharmacogenomic testing in patients receiving warfarin.

CONCLUSION

Several studies have shown that pharmacogenomic testing for warfarin dosing is more accurate that other dosing schemes. Pharmacogenomic testing improves time to a therapeutic international normalized ratio while requiring fewer dosing adjustments. Patients who require higher or lower than usual doses seem to benefit the most. The cost-effectiveness of pharmacogenomic testing as well as preventing of outcomes such as bleeding or thrombosis are not yet elucidated. Pharmacists, especially those in a community setting can play a role in this new technology by educating prescribers and patients concerning pharmacogenomic testing, and by developing and using dosing protocols that incorporate its use.

Influence of CYP2C9 genotype on warfarin dose requirements--a systematic review and meta-analysis

PURPOSE

To quantify the influence of common cytochrome P450 2C9 (CYP2C9) polymorphisms on warfarin dose requirements.

METHODS

A systematic review and a meta-analysis, calculating the warfarin dose reduction associated with the five most common variant CYP2C9 genotypes.

RESULTS

Thirty-nine studies (7,907 patients) were included in the meta-analysis. Compared to the CYP2C9*1/*1 genotype, the CYP2C9*1/*2, CYP2C9*1/*3, CYP2C9*2/*2, CYP2C9*2/*3, and CYP2C9*3/*3 required warfarin doses that were 19.6 (95% confidence interval 17.4, 21.9), 33.7 (29.4, 38.1), 36.0 (29.9, 42.0), 56.7 (49.1, 64.3), and 78.1% (72.0, 84.3) lower, respectively. The impact of CYP2C9 genotype tended to be larger in patients without interacting drugs.

CONCLUSIONS

Previous studies have rarely been powered to determine the quantitative influence of specific CYP2C9 genotypes on warfarin dose requirements. The results from our pooled analysis are likely to be the most accurate to date and the methodology could serve as a model for future pharmacogenetic meta-analyses.