Potential Clinical and Economic Outcomes of CYP2C9 and VKORC1 Genotype-Guided Dosing in Patients Starting Warfarin Therapy

Cost-effectiveness analysis of CYP3A5 genotype-guided tacrolimus dosing in solid organ transplantation using real-world data

The objective of this study was to estimate the cost-effectiveness of CYP3A5 genotype-guided tacrolimus dosing in kidney, liver, heart, and lung transplant recipients relative to standard of care (SOC) tacrolimus dosing, from a US healthcare payer perspective. We developed decision-tree models to compare economic and clinical outcomes between CYP3A5 genotype-guided and SOC tacrolimus therapy in the first six months post-transplant. We derived inputs for CYP3A5 phenotype frequencies and physician use of genotype test results to inform clinical care from literature; tacrolimus exposure [high vs low tacrolimus time in therapeutic range using the Rosendaal algorithm (TAC TTR-Rosendaal)] and outcomes (incidences of acute tacrolimus nephrotoxicity, acute cellular rejection, and death) from real-world data; and costs from the Medicare Fee Schedule and literature. We calculated cost per avoided event and performed sensitivity analyses to evaluate the robustness of the results to changes in inputs. Incremental costs per avoided event for CYP3A5 genotype-guided vs SOC tacrolimus dosing were $176,667 for kidney recipients, $364,000 for liver recipients, $12,982 for heart recipients, and $93,333 for lung recipients. The likelihood of CYP3A5 genotype-guided tacrolimus dosing leading to cost-savings was 19.8% in kidney, 32.3% in liver, 51.8% in heart, and 54.1% in lung transplant recipients. Physician use of genotype results to guide clinical care and the proportion of patients with a high TAC TTR-Rosendaal were key parameters driving the cost-effectiveness of CYP3A5 genotype-guided tacrolimus therapy. Relative to SOC, CYP3A5 genotype-guided tacrolimus dosing resulted in a slightly greater benefit at a higher cost. Further economic evaluations examining intermediary outcomes (e.g., dose modifications) are needed, particularly in populations with higher frequencies of CYP3A5 expressers.

Cost Effectiveness of Pharmacogenetic Testing for Drugs with Clinical Pharmacogenetics Implementation Consortium (CPIC) Guidelines: A Systematic Review

The objective of this study was to evaluate the evidence on cost-effectiveness of pharmacogenetic (PGx)-guided treatment for drugs with Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines. A systematic review was conducted using multiple biomedical literature databases from inception to June 2021. Full articles comparing PGx-guided with nonguided treatment were included for data extraction. Quality of Health Economic Studies (QHES) was used to assess robustness of each study (0-100). Data are reported using descriptive statistics. Of 108 studies evaluating 39 drugs, 77 (71%) showed PGx testing was cost-effective (CE) (N = 48) or cost-saving (CS) (N = 29); 21 (20%) were not CE; 10 (9%) were uncertain. Clopidogrel had the most articles (N = 23), of which 22 demonstrated CE or CS, followed by warfarin (N = 16), of which 7 demonstrated CE or CS. Of 26 studies evaluating human leukocyte antigen (HLA) testing for abacavir (N = 8), allopurinol (N = 10), or carbamazepine/phenytoin (N = 8), 15 demonstrated CE or CS. Nine of 11 antidepressant articles demonstrated CE or CS. The median QHES score reflected high-quality studies (91; range 48-100). Most studies evaluating cost-effectiveness favored PGx testing. Limited data exist on cost-effectiveness of preemptive and multigene testing across disease states.

A Comparison of the Content and Consistency of Methodological Quality and Transferability Checklists for Reviewing Model-Based Economic Evaluations

OBJECTIVES

The aim of this study was to examine whether and how the content of six checklists (Caro, Consensus on Health Economic Criteria [CHEC]-Extended, European Network of Health Economic Databases [EURONHEED], National Institute for Health and Care Excellence [NICE], Philips, Welte) affect the consistency in findings on methodological quality and transferability, using 10 model-based economic evaluations of genetic-guided pharmacotherapy for venous thromboembolism.

METHODS

Each checklist was categorised by domain (structure, data, consistency, etc.) and type of assessment (presence vs. appropriateness) and was applied to each study by two independent reviewers who agreed on ratings via consensus, and discussion with a third reviewer when necessary. Methodological quality scores and rankings were examined using Spearman correlation tests, with subgroup analyses for domains and types of assessment. We compared overall ratings of transferability qualitatively, including how content may affect what is considered 'transferable'.

RESULTS

The checklists had similar proportions of items judging presence and appropriateness, but varying proportions of items across domains. For methodological quality, ranking consistencies were the highest between CHEC-Extended-Philips, Philips-NICE and NICE-Caro, with similar consistencies for domains and type of assessment. For transferability, NICE and Caro identified the same study, which scored high on EURONHEED, as transferable to the UK, while Welte, which considered methodological quality, identified none as transferable.

CONCLUSIONS

We found that the choice of checklist can affect findings on study quality and decisions about whether study results are transferable, indicating that different checklists may shortlist different sets of studies in formulating policy recommendations, leading to different policy decisions. Our systematic approach for evaluating the content of methodological quality and transferability checklists of economic evaluations can be extended to other checklists.

Ethnic Diversity and Warfarin Pharmacogenomics

Warfarin has remained the most commonly prescribed vitamin K oral anticoagulant worldwide since its approval in 1954. Dosing challenges including having a narrow therapeutic window and a wide interpatient variability in dosing requirements have contributed to making it the most studied drug in terms of genotype-phenotype relationships. However, most of these studies have been conducted in Whites or Asians which means the current pharmacogenomics evidence-base does not reflect ethnic diversity. Due to differences in minor allele frequencies of key genetic variants, studies conducted in Whites/Asians may not be applicable to underrepresented populations such as Blacks, Hispanics/Latinos, American Indians/Alaska Natives and Native Hawaiians/other Pacific Islanders. This may exacerbate health inequalities when Whites/Asians have better anticoagulation profiles due to the existence of validated pharmacogenomic dosing algorithms which fail to perform similarly in the underrepresented populations. To examine the extent to which individual races/ethnicities are represented in the existing body of pharmacogenomic evidence, we review evidence pertaining to published pharmacogenomic dosing algorithms, including clinical utility studies, cost-effectiveness studies and clinical implementation guidelines that have been published in the warfarin field.

Genetic-guided pharmacotherapy for venous thromboembolism: a systematic and critical review of economic evaluations

Despite the known contributions of genes, genetic-guided pharmacotherapy has not been routinely implemented for venous thromboembolism (VTE). To examine evidence on cost-effectiveness of genetic-guided pharmacotherapy for VTE, we searched six databases, websites of four HTA agencies and citations, with independent double-reviewers in screening, data extraction, and quality rating. The ten eligible studies, all model-based, examined heterogeneous interventions and comparators. Findings varied widely; testing was cost-saving in two base-cases, cost-effective in four, not cost-effective in three, dominated in one. Of 22 model variables that changed decisions about cost-effectiveness, effectiveness/relative effectiveness of the intervention was the most frequent, albeit of poor quality. Studies consistently lacked details on the provision of interventions and comparators as well as on model development and validation. Besides improving the reporting of interventions, comparators, and methodological details, future economic evaluations should examine strategies recommended in guidelines and testing key model variables for decision uncertainty, to advise clinical implementations.

Pharmacogenetic testing for adverse drug reaction prevention: systematic review of economic evaluations and the appraisal of quality matters for clinical practice and implementation

Background

Genetic testing has potential roles in identifying whether an individual would have risk of adverse drug reactions (ADRs) from a particular medicine. Robust cost-effectiveness results on genetic testing would be useful for clinical practice and policy decision-making on allocating resources effectively. This study aimed to update a systematic review on economic evaluations of pharmacogenetic testing to prevent ADRs and critically appraise the quality of reporting and sources of evidence for model input parameters.

Methods

We searched studies through Medline via PubMed, Scopus and CRD’s NHS Economic Evaluation up to October 2019. Studies investigating polymorphism-based pharmacogenetic testing, which guided drug therapies to prevent ADRs, using economic evaluation methods were included. Two reviewers independently performed data extraction and assessed the quality of reporting using the Consolidated Health Economic Evaluation Reporting Standards (CHEERS) guidelines and the quality of data sources using the hierarchy of evidence developed by Cooper et al.

Results

Fifty-nine economic evaluations of pharmacogenetic testing to avoid drug-induced ADRs were found between 2002 and 2018. Cost-utility and cost-effectiveness analyses were the most common methods of economic evaluation of pharmacogenetic testing. Most studies complied with the CHEERS checklist, except for single study-based economic evaluations which did not report uncertainty analysis (78%). There was a lack of high-quality evidence not only for estimating the clinical effectiveness of pharmacogenetic testing, but also baseline clinical data. About 14% of the studies obtained clinical effectiveness data of testing from a meta-analysis of case-control studies with direct comparison, which was not listed in the hierarchy of evidence used.

Conclusions

Our review suggested that future single study-based economic evaluations of pharmacogenetic testing should report uncertainty analysis, as this could significantly affect the robustness of economic evaluation results. A specific ranking system for the quality of evidence is needed for the economic evaluation of pharmacogenetic testing of ADRs. Differences in parameters, methods and outcomes across studies, as well as population-level and system-level differences, may lead to the difficulty of comparing cost-effectiveness results across countries.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12913-021-07025-8.

Systematic review of the evidence on the cost-effectiveness of pharmacogenomics-guided treatment for cardiovascular diseases

PURPOSE

To examine the evidence on the cost-effectiveness of implementing pharmacogenomics (PGx) in cardiovascular disease (CVD) care.

METHODS

We conducted a systematic review using multiple databases from inception to 2018. The titles and abstracts of cost-effectiveness studies on PGx-guided treatment in CVD care were screened, and full texts were extracted.

RESULTS

We screened 909 studies and included 46 to synthesize. Acute coronary syndrome and atrial fibrillation were the predominantly studied conditions (59%). Most studies (78%) examined warfarin-CYP2C9/VKORC1 or clopidogrel-CYP2C19. A payer's perspective was commonly used (39%) for cost calculations, and most studies (46%) were US-based. The majority (67%) of the studies found PGx testing to be cost-effective in CVD care, but cost-effectiveness varied across drugs and conditions. Two studies examined PGx panel testing, of which one examined pre-emptive testing strategies.

CONCLUSION

We found mixed evidence on the cost-effectiveness of PGx in CVD care. Supportive evidence exists for clopidogrel-CYP2C19 and warfarin-CYP2C9/VKORC1, but evidence is limited in other drug-gene combinations. Gaps persist, including unclear explanation of perspective and cost inputs, underreporting of study design elements critical to economic evaluations, and limited examination of PGx panel and pre-emptive testing for their cost-effectiveness. This review identifies the need for further research on economic evaluations of PGx implementation.

Genotype-guided warfarin therapy: current status

Warfarin pharmacogenomics has been an extensively studied field in the last decades as it is focused on personalized therapy to overcome the wide interpatient warfarin response variability and decrease the risk of side effects. In this expert review, besides briefly summarizing the current knowledge about warfarin pharmacogenetics, we also present an overview of recent studies that aimed to assess the efficacy, safety and economic issues related to genotype-based dosing algorithms used to guide warfarin therapy, including randomized and controlled clinical trials, meta-analyses and cost-effectiveness studies. To date, the findings still present disparities, mostly because of standard limitations. Thus, further studies should be encouraged to try to demonstrate the benefits of the application of warfarin pharmacogenomic dosing algorithms in clinical practice.

The Value of Evidence in the Decision-Making Process for Reimbursement of Pharmacogenetic Dosing of Warfarin

BACKGROUND

After early clinical trials that evaluated pharmacogenetic (PG) algorithms, many healthcare payers were reluctant to cover this technology and, consequently, PG dosing of warfarin could not be translated into clinical practice.

OBJECTIVE

The aim of this study was to estimate the value of upgrading evidence relating to PG dosing of warfarin from the healthcare payer perspective.

METHODS

Randomized controlled trials (RCTs) that evaluated PG dosing of warfarin were identified through a systematic literature search, and their findings were combined by a cumulative meta-analysis. A health economic model was used to estimate economic outcomes and to calculate the expected value of perfect information (EVPI) as a measure of the value of clinical trials for decision makers.

RESULTS

Nine RCTs were identified and included in our analysis. The estimated difference in the percentage of time in the therapeutic range was 5.6 percentage points in 2007, decreasing to 4.3 percentage points when all studies were included. At a reimbursement price of €160 per PG testing, the EVPI for the clinical benefit was estimated at €80 and €90 per patient in 2007 and 2014, respectively. A reduction in the price of PG testing to €40, which was observed in this period, resulted in an EVPI of €3 per patient.

CONCLUSIONS

The estimated cumulative effect of PG dosing has remained similar since 2007, but additional evidence has contributed to a more precise estimation. While these variations should not affect the reimbursement decision, a large decline in the cost of PG testing in recent years calls for reconsideration.

Cost-effectiveness of pharmacogenetic-guided treatment: are we there yet?

Pharmacogenetics (PGx) has the potential to personalize pharmaceutical treatments. Many relevant gene-drug associations have been discovered, but PGx-guided treatment needs to be cost-effective as well as clinically beneficial to be incorporated into standard health-care. We reviewed economic evaluations for PGx associations listed in the US Food and Drug Administration (FDA) Table of Pharmacogenomic Biomarkers in Drug Labeling. We determined the proportion of evaluations that found PGx-guided treatment to be cost-effective or dominant over the alternative strategies, and estimated the impact on this proportion of removing the cost of genetic testing. Of the 137 PGx associations in the FDA table, 44 economic evaluations, relating to 10 drugs, were identified. Of these evaluations, 57% drew conclusions in favour of PGx testing, of which 30% were cost-effective and 27% were dominant (cost-saving). If genetic information was freely available, 75% of economic evaluations would support PGx-guided treatment, of which 25% would be cost-effective and 50% would be dominant. Thus, PGx-guided treatment can be a cost-effective and even a cost-saving strategy. Having genetic information readily available in the clinical health record is a realistic future prospect, and would make more genetic tests economically worthwhile.

A Systematic Review of Economic Evaluations of Pharmacogenetic Testing for Prevention of Adverse Drug Reactions

BACKGROUND

Pharmacogenetics offers the potential to improve health outcomes by identifying individuals who are at greater risk of harm from certain medicines. Routine adoption of pharmacogenetic tests requires evidence of their cost effectiveness.

OBJECTIVE

The present review aims to systematically review published economic evaluations of pharmacogenetic tests that aim to prevent or reduce the incidence of ADRs.

METHODS

We conducted a systematic literature review of economic evaluations of pharmacogenetic tests aimed to reduce the incidence of adverse drug reactions. Literature was searched using Embase, MEDLINE and the NHS Economic Evaluation Database with search terms relating to pharmacogenetic testing, adverse drug reactions, economic evaluations and pharmaceuticals. Titles were screened independently by two reviewers. Articles deemed to meet the inclusion criteria were screened independently on abstract, and full texts reviewed.

RESULTS

We identified 852 articles, of which 47 met the inclusion criteria. There was evidence supporting the cost effectiveness of testing for HLA-B*57:01 (prior to abacavir), HLA-B*15:02 and HLA-A*31:01 (prior to carbamazepine), HLA-B*58:01 (prior to allopurinol) and CYP2C19 (prior to clopidogrel treatment). Economic evidence was inconclusive with respect to TPMT (prior to 6-mercaptoputine, azathioprine and cisplatin therapy), CYP2C9 and VKORC1 (to inform genotype-guided dosing of coumarin derivatives), MTHFR (prior to methotrexate treatment) and factor V Leiden testing (prior to oral contraception). Testing for A1555G is not cost effective before prescribing aminoglycosides.

CONCLUSIONS

Our systematic review identified robust evidence of the cost effectiveness of genotyping prior to treatment with a number of common drugs. However, further analyses and (or) availability of robust clinical evidence is necessary to make recommendations for others.

Economic evaluation of pharmacogenomic-guided warfarin treatment for elderly Croatian atrial fibrillation patients with ischemic stroke

BACKGROUND & METHODS

Economic evaluation in genomic medicine is an emerging discipline to assess the cost-effectiveness of genome-guided treatment. Here, we developed a pharmaco-economic model to assess whether pharmacogenomic (PGx)-guided warfarin treatment of elderly ischemic stroke patients with atrial fibrillation in Croatia is cost effective compared with non-PGx therapy. The time horizon of the model was set at 1 year.

RESULTS

Our primary analysis indicates that 97.07% (95% CI: 94.08-99.34%) of patients belonging to the PGx-guided group have not had any major complications, compared with the control group (89.12%; 95% CI: 84.00-93.87%, p < 0.05). The total cost per patient was estimated at €538.7 (95% CI: €526.3-551.2) for the PGx-guided group versus €219.7 (95% CI: €137.9-304.2) for the control group. In terms of quality-adjusted life-years (QALYs) gained, total QALYs was estimated at 0.954 (95% CI: 0.943-0.964) and 0.944 (95% CI: 0.931-0.956) for the PGx-guided and the control groups, respectively. The true difference in QALYs was estimated at 0.01 (95% CI: 0.005-0.015) in favor of the PGx-guided group. The incremental cost-effectiveness ratio of the PGx-guided versus the control groups was estimated at €31,225/QALY.

CONCLUSION

Overall, our data indicate that PGx-guided warfarin treatment may represent a cost-effective therapy option for the management of elderly patients with atrial fibrillation who developed ischemic stroke in Croatia.

Economic evaluation of a pharmacogenetic dosing algorithm for coumarin anticoagulants in The Netherlands

AIM

To investigate the cost-effectiveness of a pharmacogenetic dosing algorithm versus a clinical dosing algorithm for coumarin anticoagulants in The Netherlands.

MATERIALS & METHODS

A decision-analytic Markov model was used to analyze the cost-effectiveness of pharmacogenetic dosing of phenprocoumon and acenocoumarol versus clinical dosing.

RESULTS

Pharmacogenetic dosing increased costs by €33 and quality-adjusted life-years (QALYs) by 0.001. The incremental cost-effectiveness ratios were €28,349 and €24,427 per QALY gained for phenprocoumon and acenocoumarol, respectively. At a willingness-to-pay threshold of €20,000 per QALY, the pharmacogenetic dosing algorithm was not likely to be cost effective compared with the clinical dosing algorithm.

CONCLUSION

Pharmacogenetic dosing improves health only slightly when compared with clinical dosing. However, availability of low-cost genotyping would make it a cost-effective option.

Economic Evaluations of Pharmacogenetic and Pharmacogenomic Screening Tests: A Systematic Review. Second Update of the Literature

Objective

Due to extended application of pharmacogenetic and pharmacogenomic screening (PGx) tests it is important to assess whether they provide good value for money. This review provides an update of the literature.

Methods

A literature search was performed in PubMed and papers published between August 2010 and September 2014, investigating the cost-effectiveness of PGx screening tests, were included. Papers from 2000 until July 2010 were included via two previous systematic reviews. Studies’ overall quality was assessed with the Quality of Health Economic Studies (QHES) instrument.

Results

We found 38 studies, which combined with the previous 42 studies resulted in a total of 80 included studies. An average QHES score of 76 was found. Since 2010, more studies were funded by pharmaceutical companies. Most recent studies performed cost-utility analysis, univariate and probabilistic sensitivity analyses, and discussed limitations of their economic evaluations. Most studies indicated favorable cost-effectiveness. Majority of evaluations did not provide information regarding the intrinsic value of the PGx test. There were considerable differences in the costs for PGx testing. Reporting of the direction and magnitude of bias on the cost-effectiveness estimates as well as motivation for the chosen economic model and perspective were frequently missing.

Conclusions

Application of PGx tests was mostly found to be a cost-effective or cost-saving strategy. We found that only the minority of recent pharmacoeconomic evaluations assessed the intrinsic value of the PGx tests. There was an increase in the number of studies and in the reporting of quality associated characteristics. To improve future evaluations, scenario analysis including a broad range of PGx tests costs and equal costs of comparator drugs to assess the intrinsic value of the PGx tests, are recommended. In addition, robust clinical evidence regarding PGx tests’ efficacy remains of utmost importance.

Cost effectiveness of novel oral anticoagulants for stroke prevention in atrial fibrillation depending on the quality of warfarin anticoagulation control

BACKGROUND

Vitamin K antagonists, such as warfarin, are standard treatments for stroke prophylaxis in patients with atrial fibrillation. Patient outcomes depend on quality of warfarin management, which includes regular monitoring and dose adjustments. Recently, novel oral anticoagulants (NOACs) that do not require regular monitoring offer an alternative to warfarin. The aim of this study was to evaluate whether cost effectiveness of NOACs for stroke prevention in atrial fibrillation depends on the quality of warfarin control.

METHODS

We developed a Markov decision model to simulate warfarin treatment outcomes in relation to the quality of anticoagulation control, expressed as percentage of time in the therapeutic range (TTR). Standard treatment with adjusted-dose warfarin and improved anticoagulation control by genotype-guided dosing were compared with dabigatran, rivaroxaban, apixaban and edoxaban. The analysis was performed from the Slovenian healthcare payer perspective using 2014 costs.

RESULTS

In the base case, the incremental cost-effectiveness ratio for apixaban, dabigatran and edoxaban was below the threshold of €25,000 per quality-adjusted life-years compared with adjusted-dose warfarin with a TTR of 60%. The probability that warfarin was a cost-effective option was around 1%. This percentage rises as the quality of anticoagulation control improves. At a TTR of 70%, warfarin was the preferred treatment in half the iterations.

CONCLUSION

The cost effectiveness of NOACs for stroke prevention in patients with nonvalvular atrial fibrillation who are at increased risk for stroke is highly sensitive to warfarin anticoagulation control. NOACs are more likely to be cost-effective options in settings with poor warfarin management than in settings with better anticoagulation control, where they may not represent good value for money.

Personalized antiplatelet and anticoagulation therapy: applications and significance of pharmacogenomics

In recent years, substantial effort has been made to better understand the influence of genetic factors on the efficacy and safety of numerous medications. These investigations suggest that the use of pharmacogenetic data to inform physician decision-making has great potential to enhance patient care by reducing on-treatment clinical events, adverse drug reactions, and health care-related costs. In fact, integration of such information into the clinical setting may be particularly applicable for antiplatelet and anticoagulation therapeutics, given the increasing body of evidence implicating genetic variation in variable drug response. In this review, we summarize currently available pharmacogenetic information for the most commonly used antiplatelet (ie, clopidogrel and aspirin) and anticoagulation (ie, warfarin) medications. Furthermore, we highlight the currently known role of genetic variability in response to next-generation antiplatelet (prasugrel and ticagrelor) and anticoagulant (dabigatran) agents. While compelling evidence suggests that genetic variants are important determinants of antiplatelet and anticoagulation therapy response, significant barriers to clinical implementation of pharmacogenetic testing exist and are described herein. In addition, we briefly discuss development of new diagnostic targets and therapeutic strategies as well as implications for enhanced patient care. In conclusion, pharmacogenetic testing can provide important information to assist clinicians with prescribing the most personalized and effective antiplatelet and anticoagulation therapy. However, several factors may limit its usefulness and should be considered.

Pharmacogenetic-guided dosing of coumarin anticoagulants: algorithms for warfarin, acenocoumarol and phenprocoumon

Coumarin derivatives, such as warfarin, acenocoumarol and phenprocoumon are frequently prescribed oral anticoagulants to treat and prevent thromboembolism. Because there is a large inter-individual and intra-individual variability in dose-response and a small therapeutic window, treatment with coumarin derivatives is challenging. Certain polymorphisms in CYP2C9 and VKORC1 are associated with lower dose requirements and a higher risk of bleeding. In this review we describe the use of different coumarin derivatives, pharmacokinetic characteristics of these drugs and differences amongst the coumarins. We also describe the current clinical challenges and the role of pharmacogenetic factors. These genetic factors are used to develop dosing algorithms and can be used to predict the right coumarin dose. The effectiveness of this new dosing strategy is currently being investigated in clinical trials.

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.

Pharmacogenetic-guided selection of warfarin versus novel oral anticoagulants for stroke prevention in patients with atrial fibrillation: a cost-effectiveness analysis

OBJECTIVES

To compare clinical and economic outcomes of two anticoagulation therapy strategies, (i) pharmacogenetic-guided selection (PG-AC) of warfarin versus novel oral anticoagulants (NOACs), and (ii) usual anticoagulation care (usual AC) in patients with atrial fibrillation (AF), from the perspective of US healthcare payers.

METHODS

A Markov model was used to simulate long-term outcomes in a hypothetical cohort of 65-year-old patients with newly diagnosed AF: (i) all usual AC patients received warfarin therapy, and (ii) all PG-AC patients were genotyped. Patients with normal warfarin sensitivity genotypes would receive warfarin. Patients with high or low warfarin sensitivity genotypes would receive NOAC. Model inputs were derived from clinical trials published in the literature. The outcome measure was incremental cost per quality-adjusted life-year (QALY) gained (ICER).

RESULTS

PG-AC gained higher QALYs with higher cost (9.912 QALYs and USD94 396) when compared with usual AC (9.721 QALYs and USD93 853) in base-case analysis. The ICER of PG-AC was 2843 USD/QALY. The ICER of PG-AC would exceed 50 000 USD/QALY if the monthly cost of NOAC was more than USD285 or the risk of stroke with NOAC versus warfarin was more than 0.93. In 10 000 Monte Carlo simulations, PG-AC was cost-effective 96.4% of the time and usual AC was cost-effective 3.6% of the time. PG-AC was more costly than usual AC with a mean cost difference of USD1927 (95% confidence interval 1.877-1.977, P<0.001), and gained higher QALYs by 0.209 (95% confidence interval 0.208-0.210, P<0.001).

CONCLUSION

Compared with warfarin therapy with time in therapeutic range of 60%, using genotype to triage AF patients to warfarin or NOAC appears to be highly cost-effective.

Is individualized medicine more cost-effective? A systematic review

BACKGROUND

Individualized medicine (IM) is a rapidly evolving field that is associated with both visions of more effective care at lower costs and fears of highly priced, low-value interventions. It is unclear which view is supported by the current evidence.

OBJECTIVE

Our objective was to systematically review the health economic evidence related to IM and to derive general statements on its cost-effectiveness.

DATA SOURCES

A literature search of MEDLINE database for English- and German-language studies was conducted.

STUDY APPRAISAL AND SYNTHESIS METHOD

Cost-effectiveness and cost-utility studies for technologies meeting the MEDLINE medical subject headings (MeSH) definition of IM (genetically targeted interventions) were reviewed. This was followed by a standardized extraction of general study characteristics and cost-effectiveness results.

RESULTS

Most of the 84 studies included in the synthesis were from the USA (n = 43, 51 %), cost-utility studies (n = 66, 79 %), and published since 2005 (n = 60, 71 %). The results ranged from dominant to dominated. The median value (cost-utility studies) was calculated to be rounded $US22,000 per quality-adjusted life year (QALY) gained (adjusted to $US, year 2008 values), which is equal to the rounded median cost-effectiveness in the peer-reviewed English-language literature according to a recent review. Many studies reported more than one strategy of IM with highly varying cost-effectiveness ratios. Generally, results differed according to test type, and tests for disease prognosis or screening appeared to be more favorable than tests to stratify patients by response or by risk of adverse effects. However, these results were not significant.

LIMITATIONS

Different definitions of IM could have been used. Quality assessment of the studies was restricted to analyzing transparency.

CONCLUSIONS

IM neither seems to display superior cost-effectiveness than other types of medical interventions nor to be economically inferior. Instead, rather than 'whether' healthcare was individualized, the question of 'how' it was individualized was of economic relevance.

Genotype-guided use of oral antithrombotic therapy: a pharmacoeconomic perspective

Pharmacogenomics focuses on tailoring therapy to the individual as opposed to the historical model of fitting the individual to the therapy, and it offers the potential to maximize medication efficacy while reducing adverse events. By its very nature, personalized medicine is conducive to a patient-centered care model. Oral antithrombotics as a class could benefit immensely from this type of approach because an imbalance of safety and efficacy in either direction can yield deadly consequences. Since the current healthcare climate in the USA requires thoughtful allocation of resources, pharmacoeconomic analysis has become critical for all stakeholders, and the adoption of new technologies hinges upon economic impact. This article summarizes the current state of genetics in oral antithrombotic therapy, including clinical relevance as well as cost-effectiveness from a US healthcare system perspective, and provides insight into the future of pharmacogenomics in treating and preventing thromboembolic disorders.

Cost-effectiveness of pharmacogenetics-guided warfarin therapy vs. alternative anticoagulation in atrial fibrillation

Pharmacogenetics-guided warfarin dosing is an alternative to standard clinical algorithms and new oral anticoagulants for patients with nonvalvular atrial fibrillation. However, clinical evidence for pharmacogenetics-guided warfarin dosing is limited to intermediary outcomes, and consequently, there is a lack of information on the cost-effectiveness of anticoagulation treatment options. A clinical trial simulation of S-warfarin was used to predict times within therapeutic range for different dosing algorithms. Relative risks of clinical events, obtained from a meta-analysis of trials linking times within therapeutic range with outcomes, served as inputs to an economic analysis. Neither dabigatran nor rivaroxaban were cost-effective options. Along the cost-effectiveness frontier, in relation to clinically dosed warfarin, pharmacogenetics-guided warfarin and apixaban had incremental cost-effectiveness ratios of £13,226 and £20,671 per quality-adjusted life year gained, respectively. On the basis of our simulations, apixaban appears to be the most cost-effective treatment.

Dabigatran versus warfarin under standard or pharmacogenetic-guided management for the prevention of stroke and systemic thromboembolism in patients with atrial fibrillation: a cost/utility analysis using an analytic decision model

BACKGROUND

Atrial fibrillation (AF) is the most common form of heart arrhythmia and a leading cause of stroke and systemic embolism. Chronic anticoagulation is recommended for preventing those complications. Our study aimed to compare the cost/utility (CU) of three main anticoagulation options: 1) standard warfarin dosing (SD-W) 2) warfarin dosage under the guidance of CYP2C9 and VKORC1 genotyping (GT-W) and 3) dabigatran 150 mg twice a day.

METHODS

A Markov state transition model was built to simulate the expected C/U of dabigatran, SD-W and GT-W anticoagulation therapy for the prevention of stroke and systemic thromboembolism in patients with atrial fibrillation over a period of 5 years under the perspective of the public health care system. Model inputs were derived from extensive literature search and government's data bases. Outcomes considered were the number of total major events (thromboembolic and hemorrhagic events), total costs in Canadian dollars (1CAD$ = 1$US), total quality-adjusted life years (QALYs), costs/QALYs and incremental costs/QALYs gained (ICUR).

RESULTS

Raw base case results show that SD-W has the lowest C/U ratio. However, the dabigatran option might be considered as an alternative, as its cost per additional QALY gained compared to SD-W is CAD $ 4 765, i.e. less than 50 000, the ICUR threshold generally accepted to adopt an intervention. At the same threshold, GT-W doesn't appear to be an alternative to SD-W. Our results were robust to one-way and multi-way sensitivity analyses.

CONCLUSION

SD-W has the lowest C/U ratio among the 3 options. However, dabigatran might be considered as an alternative. GT-W is not C/U and should not currently be recommended for the routine anticoagulotherapy management of AF patients.

Cost–effectiveness of pharmacogenetic-guided dosing of phenprocoumon in atrial fibrillation

Aim: To investigate the cost–effectiveness of pharmacogenetic-guided phenprocoumon dosing versus standard anticoagulation care in Dutch patients with atrial fibrillation. Materials & methods: Using a decision-analytic Markov model, cost–effectiveness of pharmacogenetic-guided therapy versus standard care was estimated. Results: Compared with standard care, the pharmacogenetic-guided dosing strategy increased quality-adjusted life-years (QALYs) only very slightly and increased costs by €15. The incremental cost–effectiveness ratio was €2658 per QALY gained. In sensitivity analyses, the cost of genotyping had the largest influence on the cost–effectiveness ratio. In a probabilistic sensitivity analysis, the incremental costs of genotype-guided dosing were less than €20,000 per QALY gained in 75.6% of the simulations. Conclusion: Pharmacogenetic-guided dosing of phenprocoumon has the potential to increase health slightly and may be able to achieve this in a cost-effective way. Owing to the many uncertainties it is too early to conclude whether or not patients starting phenprocoumon should be genotyped.

Original submitted 20 December 2012; Revision submitted 8 April 2013

Cost-effectiveness of pharmacogenetics in anticoagulation: international differences in healthcare systems and costs

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

Willingness-to-pay and preferences for warfarin pharmacogenetic testing in Chinese warfarin patients and the Chinese general public

Aim: Genetic factors have been found to affect warfarin maintenance dose and a key factor for the successful clinical implementation of warfarin pharmacogenetic testing (WPGT) is economic sustainability. We aimed to estimate the willingness-to-pay (WTP) and preferences for WPGT in Singaporean Chinese subjects. Methods & subjects: A total of 197 warfarin patients and 187 members of the public completed a questionnaire. The discrete choice methodology was used and the choice model was estimated using hierarchical Bayes. Marginal WTP, attribute importance and WTP for three hypothetical WPGTs were calculated from the estimated utilities. Results: Both patients and the public placed most emphasis on side effects, followed by cost, number of International Normalized Ratio tests and ‘nature of test’. WTP for WPGT ranged from S$160 to S$730. Conclusion: WPGTs are likely to be economically sustainable.

Scientific challenges and implementation barriers to translation of pharmacogenomics in clinical practice

The mapping of the human genome and subsequent advancements in genetic technology had provided clinicians and scientists an understanding of the genetic basis of altered drug pharmacokinetics and pharmacodynamics, as well as some examples of applying genomic data in clinical practice. This has raised the public expectation that predicting patients' responses to drug therapy is now possible in every therapeutic area, and personalized drug therapy would come sooner than later. However, debate continues among most stakeholders involved in drug development and clinical decision-making on whether pharmacogenomic biomarkers should be used in patient assessment, as well as when and in whom to use the biomarker-based diagnostic tests. Currently, most would agree that achieving the goal of personalized therapy remains years, if not decades, away. Realistic application of genomic findings and technologies in clinical practice and drug development require addressing multiple logistics and challenges that go beyond discovery of gene variants and/or completion of prospective controlled clinical trials. The goal of personalized medicine can only be achieved when all stakeholders in the field work together, with willingness to accept occasional paradigm change in their current approach.

Cost-effectiveness of dabigatran versus genotype-guided management of warfarin therapy for stroke prevention in patients with atrial fibrillation

BACKGROUND

Dabigatran is associated with lower rate of stroke comparing to warfarin when anticoagulation control is sub-optimal. Genotype-guided warfarin dosing and management may improve patient-time in target range (TTR) and therefore affect the cost-effectiveness of dabigatran compared with warfain. We examined the cost-effectiveness of dabigatran versus warfarin therapy with genotype-guided management in patients with atrial fibrillation (AF).

METHODOLOGY/PRINCIPAL FINDINGS

A Markov model was designed to compare life-long economic and treatment outcomes of dabigatran (110 mg and 150 mg twice daily), warfarin usual anticoagulation care (usual AC) with mean TTR 64%, and genotype-guided anticoagulation care (genotype-guided AC) in a hypothetical cohort of AF patients aged 65 years old with CHADS(2) score 2. Model inputs were derived from literature. The genotype-guided AC was assumed to achieve TTR = 78.9%, adopting the reported TTR achieved by warfarin service with good anticoagulation control in literature. Outcome measure was incremental cost per quality-adjusted life-year (QALY) gained (ICER) from perspective of healthcare payers. In base-case analysis, dabigatran 150 mg gained higher QALYs than genotype-guided AC (10.065QALYs versus 9.554QALYs) at higher cost (USD92,684 versus USD85,627) with ICER = USD13,810. Dabigatran 110 mg and usual AC gained less QALYs but cost more than dabigatran 150 mg and genotype-guided AC, respectively. ICER of dabigatran 150 mg versus genotype-guided AC would be >USD50,000 (and genotype-guided AC would be most cost-effective) when TTR in genotype-guided AC was >77% and utility value of warfarin was the same or higher than that of dabigatran.

CONCLUSIONS/SIGNIFICANCE

The likelihood of genotype-guided anticoagulation service to be accepted as cost-effective would increase if the quality of life on warfarin and dabigatran therapy are compatible and genotype-guided service achieves high TTR (>77%).

Clinical Pharmacogenomics of Warfarin and Clopidogrel

Genetic polymorphisms significantly influence responses to warfarin and clopidogrel. Polymorphisms in the cytochrome P450 (CYP) 2C9 and vitamin K epoxide reductase genes change warfarin pharmacokinetics and pharmacodynamics, respectively. Because these polymorphisms influence warfarin dose requirements, they may primarily help determine therapeutic warfarin doses in patients who newly start on the drug. To assist in estimating therapeutic warfarin doses, the warfarin label provides a pharmacogenomic dosing table and various warfarin pharmacogenomic dosing algorithms are available. On the other hand, polymorphisms in the CYP2C19 gene affect clopidogrel pharmacokinetics. These polymorphisms may be useful to identify clopidogrel nonresponders who may benefit from taking an alternative antiplatelet agent such as prasugrel and ticagrelor. Although both drugs have pharmacogenomic tests available for clinical use, their clinical utilities have not been established and are currently being actively studied. In this review, clinical application of warfarin and clopidogrel pharmacogenomics will be focused. With the current level of evidence, potential patients who may get benefit from warfarin and clopidogrel pharmacogenomic testing will be discussed. In addition, the interpretation of the warfarin and clopidogrel test results and the current barriers to widespread use of warfarin and clopidogrel pharmacogenomic testing will be discussed.

Role of pharmacogenomics in the management of traditional and novel oral anticoagulants

Warfarin is the most commonly prescribed oral anticoagulant. However, it remains a difficult drug to manage mostly because of its narrow therapeutic index and wide interpatient variability in anticoagulant effects. Over the past decade, there has been substantial progress in our understanding of genetic contributions to variable warfarin response, particularly with regard to warfarin dose requirements. The genes encoding for cytochrome P450 (CYP) 2C9 (CYP2C9) and vitamin K epoxide reductase complex subunit 1 (VKORC1) are the major genetic determinants of warfarin pharmacokinetics and pharmacodynamics, respectively. Numerous studies have demonstrated significant contributions of these genes to warfarin dose requirements. The CYP2C9 gene has also been associated with bleeding risk with warfarin. The CYP4F2 gene influences vitamin K availability and makes minor contributions to warfarin dose requirements. Less is known about genes influencing warfarin response in African-American patients compared with other racial groups, but this is the focus of ongoing research. Several warfarin pharmacogenetic dosing algorithms and United States Food and Drug Administration-cleared genotyping tests are available for clinical use. Clinical trials are ongoing to determine the clinical utility and cost-effectiveness of genotypeguided warfarin dosing. Results from these trials will likely influence clinical uptake and third party payer reimbursement for genotype-guided warfarin therapy. There is still a lack of pharmacogenetic data for the newly approved oral anticoagulants, dabigatran and rivaroxaban, and with other oral anticoagulants in the research and development pipeline. These data, once known, could be of great importance as routine monitoring parameters for these agents are not available.

Optimization of anticoagulation with warfarin for stroke prevention: pharmacogenetic considerations

Warfarin is a cornerstone of oral anticoagulation for stroke prevention. Anticoagulation with warfarin in patients with atrial fibrillation is over twice as effective in secondary prevention of stroke as any other tested alternatives, including all other antithrombotic drugs or surgical interventions. General belief is that warfarin is capable of preventing 20 ischemic strokes for every hemorrhagic one it causes. However, warfarin is one of the most feared agents as a result of its woeful safety profile and difficulties in maintaining the proper daily dose. Recent research in pharmacogenetics predominantly focused on elucidating the influence of individual genetic predispositions to administered warfarin. Although the incorporation of genotype information improves the accuracy of adequate dose prediction, an improvement in anticoagulation control or a reduction in hemorrhagic complications has not been yet convincingly demonstrated. It is clear that identifying an individual patient's risk for hemorrhage on warfarin will require more broad clinical and genetic studies. Future research focused on patients with stroke should concentrate on defining the possible differences, especially focusing on predicting bleeding events in general and intracranial hemorrhages in particular. The purpose of this review is to summarize the existing evidence about pharmacogenetics of warfarin in general, especially focusing on stroke prevention.

Warfarin dosing algorithm using clinical, demographic and pharmacogenetic data from Chinese patients

CYP2C9 and VKORC1 genotypes could be used to predict warfarin requirement. The objective was to develop and validate a warfarin dosing algorithm using genetic, clinical and demographic data of Chinese patients from an anticoagulation clinic in Hong Kong. Blood samples were collected from 100 patients on stable maintenance dose of warfarin, recruited from an anticoagulation clinic, for genotyping CYP2C9 and VKORC1. Clinical and demographic data were obtained by face-to-face interview and medical chart review. Data of 80 patients (study cohort) were randomly selected for deriving a dosing algorithm. Comparison between predicted dose and actual stable doses was conducted in a validation cohort (n = 20). Sixty-nine (69%) of all 100 patients were homozygous for VKORC1 1173-TT, 25 (25%) were VKORC1 1173-CT heterozygotes and six (6%) were homozygous for VKORC1 1173-CC. 6 (6%) patients were CYP2C9 1*/3* and 94 (94%) were CYP2C9 1*/1*. CYP2C9 and VKORC1 genotype, age, weight and vitamin K intake were identified by stepwise regression modelling to produce the best model for estimating warfarin dose (R (2) = 68%, P < 0.001). In the validation cohort (n = 20), actual stable dose was significantly associated with predicted dose (R = 0.6, P = 0.005). Five of 11 (45.6%) and 5/9 (55.6%) patients whose mean warfarin requirements were ≤ 3 mg/day and >3 mg/day, respectively, were within <20% of actual doses. In conclusion, a genotype-guided dosing algorithm for warfarin therapy was developed for Chinese patients to explain 68% of dosage variation. The predicted doses differed from the actual doses by no more than 20% in 50% of patients.

A systematic review of cost-effectiveness analyses of pharmacogenetic-guided dosing in treatment with coumarin derivatives

Anticoagulant therapy with coumarin derivatives is often sub- or supra-therapeutic, resulting in an increased risk of thromboembolic events or hemorrhage, respectively. Pharmacogenetic-guided dosing has been proposed as an effective way of reducing bleeding rates. Clinical trials to confirm the safety, efficacy and effectiveness of this strategy are ongoing, but in addition, it is also necessary to consider the cost-effectiveness of this strategy. This article describes the findings of a systematic review of published cost-effectiveness analyses of pharmacogenetic-guided dosing of coumarin derivatives. Similarities and differences in the approaches used were examined and the quality of the analyses was assessed. The results of the analyses are not sufficient to determine whether or not pharmacogenetic-guided dosing of coumarins is cost effective. More reliable cost-effectiveness estimates need to become available before it is possible to recommend whether or not this strategy should be applied in clinical practice.

Clinical and economic consequences of pharmacogenetic-guided dosing of warfarin

Patients using warfarin for oral anticoagulant therapy need to be frequently monitored because of warfarin's narrow therapeutic range and the large variation in dose requirements among patients. Patients receiving the wrong dose have an increased risk of bleeding or thromboembolic events. The required dose is influenced by environmental factors, such as gender, age, diet and concomitant medication, as well as genetic factors. Pharmacogenetic testing prior to warfarin initiation might improve dosing accuracy and, therefore, safety and efficacy of warfarin treatment. Meckley et al. studied the clinical consequences and costs of genotyping before warfarin treatment. The results of their study suggest that pharmacogenetic-guided dosing of patients initiating warfarin could improve health (quality-adjusted life-years) but at a high cost per quality-adjusted life-year gained. Owing to the inevitable assumptions that have to be made in all cost-effectiveness models, great uncertainty remains regarding the cost-effectiveness of pharmacogenetic-guided warfarin dosing.

Only connect: personal genomics and the future of American medicine

Access to one's own complete genome was unheard of just a few years ago. At present we have a smattering of identifiable complete human genomes, but the coming months and years will undoubtedly bring thousands more. What will this mean for the practice of medicine in the US? No one knows, but given the remarkable drop in the cost of DNA sequencing over the last few years, it seems a safe bet that within the next decade, primary care physicians will order patients' whole genome sequences with no more fanfare than they would a complete blood count. But the challenges of transforming that easily accessible information into cost savings and better health outcomes will be daunting. Obviously, we lack interpretive abilities and phenotypic information commensurate with our skill in amassing DNA sequences. Worse, we have exacerbated these problems by failing to embrace the increasing ubiquity of genomic information, the populace's interest in it, and its relevance to virtually every medical specialty. The success of personal genomics will require a profound cultural shift by every entity with a stake in human health.

Implementing genotype-guided antithrombotic therapy

Genotyping has the potential to improve the efficacy and safety of major antithrombotic drugs. For warfarin, the stable maintenance dose varies from 1-10 mg/day. The VKORC1 -1639G>A allele and the CYP2C9*2 and *3 alleles (cumulative frequency: 90% in Asians, 65% in Europeans and 20% in Africans), explain 45% of response variability in European and 30% in African populations. The large clinical trials COAG and EU-PACT will define the extent to which pharmacogenetic dosing affects the safety and efficacy of warfarin and coumarin derivatives. The platelet inhibitor clopidogrel requires activation by the CYP2C19 enzyme. CYP2C19*2 and *3 alleles (cumulative frequency: 20-50%) produce null enzyme activity, and their presence attenuates platelet inhibition and increases cardiovascular events. The US FDA-mandated drug labeling recognizes the relevance of genotyping in the selection and dosing of both warfarin and clopidogrel.

Increased frequency of CYP2C9 variant alleles and homozygous VKORC1*2B carriers in warfarin-treated patients with excessive INR response

BACKGROUND

Several studies have linked mutations in the genes encoding cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase complex 1 (VKORC1) to a reduced warfarin dose requirement and an increased risk of bleeding with warfarin treatment, but the implementation of genotyping as routine practice is still controversial. The objective of this study was to investigate whether the frequencies of CYP2C9 variant alleles (*2 and *3), and VKORC1 haplotypes (*2A/B) were increased in a population of warfarin-treated patients with an excessive INR response.

METHODS

All patients with INR values >5 detected by routine monitoring at Diakonhjemmet Hospital, Oslo, Norway, between October 2006 and January 2009 were prospectively enrolled in the study (n = 131, 'cases'). A group of patients with normal INR values (2-3) were randomly included as the reference population (n = 130, 'controls'). The frequencies of CYP2C9 variant alleles *2 (430C > T) and *3 (1075A > C), VKORC1 haplotypes *2A (1173G > T) and *2B (1173G > T + 497T >G), and the respective genotypes were compared between the study groups by chi-square tests [odds ratio (OR) of cases vs. controls with 95% confidence intervals (CI) calculated for the various end-points].

RESULTS

About two thirds of the patients in the high INR group were in the maintenance phase of the treatment (>3 weeks from first warfarin dose to measurement of INR >5). The frequency of CYP2C9 variant alleles (sum of *2 and *3) was significantly higher in patients with high INR cases than in the controls (OR 1.6, 95% CI 1.03-2.52; p = 0.036). Observed frequencies for each of the variant alleles were also higher in the cases than in the controls (i.e., 2C9*3: OR 1.97, 95% CI 0.91-2.41, p = 0.073; 2C9*2: OR 1.36, 95% CI 0.88-1.58, p = 0.246). There were no significant differences in VKORC1*2 haplotype frequencies between the two subgroups, but the number of homozygous VKORC1*2B carriers was significantly higher in cases than in controls (OR 2.72, 1.02-7.24; p = 0.039).

CONCLUSION

The presence of CYP2C9 variant alleles and the homozygous VKORC1*2B genotype was associated with elevated INR values in warfarin-treated patients. These results support the implementation of genotyping as a tool to identify patients with an increased risk of excessive anticoagulation during warfarin treatment.