Pharmacogenetics of warfarin: current status and future challenges

Warfarin-A natural anticoagulant: A review of research trends for precision medication

BACKGROUND

Warfarin is a widely prescribed anticoagulant in the clinic. It has a more considerable individual variability, and many factors affect its variability. Mathematical models can quantify the quantitative impact of these factors on individual variability.

PURPOSE

The aim is to comprehensively analyze the advanced warfarin dosing algorithm based on pharmacometrics and machine learning models of personalized warfarin dosage.

METHODS

A bibliometric analysis of the literature retrieved from PubMed and Scopus was performed using VOSviewer. The relevant literature that reported the precise dosage of warfarin calculation was retrieved from the database. The multiple linear regression (MLR) algorithm was excluded because a recent systematic review that mainly reviewed this algorithm has been reported. The following terms of quantitative systems pharmacology, mechanistic model, physiologically based pharmacokinetic model, artificial intelligence, machine learning, pharmacokinetic, pharmacodynamic, pharmacokinetics, pharmacodynamics, and warfarin were added as MeSH Terms or appearing in Title/Abstract into query box of PubMed, then humans and English as filter were added to retrieve the literature.

RESULTS

Bibliometric analysis revealed important co-occuring MeShH and index keywords. Further, the United States, China, and the United Kingdom were among the top countries contributing in this domain. Some studies have established personalized warfarin dosage models using pharmacometrics and machine learning-based algorithms. There were 54 related studies, including 14 pharmacometric models, 31 artificial intelligence models, and 9 model evaluations. Each model has its advantages and disadvantages. The pharmacometric model contains biological or pharmacological mechanisms in structure. The process of pharmacometric model development is very time- and labor-intensive. Machine learning is a purely data-driven approach; its parameters are more mathematical and have less biological interpretation. However, it is faster, more efficient, and less time-consuming. Most published models of machine learning algorithms were established based on cross-sectional data sourced from the database.

CONCLUSION

Future research on personalized warfarin medication should focus on combining the advantages of machine learning and pharmacometrics algorithms to establish a more robust warfarin dosage algorithm. Randomized controlled trials should be performed to evaluate the established algorithm of warfarin dosage. Moreover, a more user-friendly and accessible warfarin precision medicine platform should be developed.

Optimizing warfarin dosing for patients with atrial fibrillation using machine learning

While novel oral anticoagulants are increasingly used to reduce risk of stroke in patients with atrial fibrillation, vitamin K antagonists such as warfarin continue to be used extensively for stroke prevention across the world. While effective in reducing the risk of strokes, the complex pharmacodynamics of warfarin make it difficult to use clinically, with many patients experiencing under- and/or over- anticoagulation. In this study we employed a novel implementation of deep reinforcement learning to provide clinical decision support to optimize time in therapeutic International Normalized Ratio (INR) range. We used a novel semi-Markov decision process formulation of the Batch-Constrained deep Q-learning algorithm to develop a reinforcement learning model to dynamically recommend optimal warfarin dosing to achieve INR of 2.0-3.0 for patients with atrial fibrillation. The model was developed using data from 22,502 patients in the warfarin treated groups of the pivotal randomized clinical trials of edoxaban (ENGAGE AF-TIMI 48), apixaban (ARISTOTLE) and rivaroxaban (ROCKET AF). The model was externally validated on data from 5730 warfarin-treated patients in a fourth trial of dabigatran (RE-LY) using multilevel regression models to estimate the relationship between center-level algorithm consistent dosing, time in therapeutic INR range (TTR), and a composite clinical outcome of stroke, systemic embolism or major hemorrhage. External validation showed a positive association between center-level algorithm-consistent dosing and TTR (R2 = 0.56). Each 10% increase in algorithm-consistent dosing at the center level independently predicted a 6.78% improvement in TTR (95% CI 6.29, 7.28; p < 0.001) and a 11% decrease in the composite clinical outcome (HR 0.89; 95% CI 0.81, 1.00; p = 0.015). These results were comparable to those of a rules-based clinical algorithm used for benchmarking, for which each 10% increase in algorithm-consistent dosing independently predicted a 6.10% increase in TTR (95% CI 5.67, 6.54, p < 0.001) and a 10% decrease in the composite outcome (HR 0.90; 95% CI 0.83, 0.98, p = 0.018). Our findings suggest that a deep reinforcement learning algorithm can optimize time in therapeutic range for patients taking warfarin. A digital clinical decision support system to promote algorithm-consistent warfarin dosing could optimize time in therapeutic range and improve clinical outcomes in atrial fibrillation globally.

CAGI, the Critical Assessment of Genome Interpretation, establishes progress and prospects for computational genetic variant interpretation methods

BACKGROUND

The Critical Assessment of Genome Interpretation (CAGI) aims to advance the state-of-the-art for computational prediction of genetic variant impact, particularly where relevant to disease. The five complete editions of the CAGI community experiment comprised 50 challenges, in which participants made blind predictions of phenotypes from genetic data, and these were evaluated by independent assessors.

RESULTS

Performance was particularly strong for clinical pathogenic variants, including some difficult-to-diagnose cases, and extends to interpretation of cancer-related variants. Missense variant interpretation methods were able to estimate biochemical effects with increasing accuracy. Assessment of methods for regulatory variants and complex trait disease risk was less definitive and indicates performance potentially suitable for auxiliary use in the clinic.

CONCLUSIONS

Results show that while current methods are imperfect, they have major utility for research and clinical applications. Emerging methods and increasingly large, robust datasets for training and assessment promise further progress ahead.

Pharmacogenomic Considerations for Anticoagulant Prescription in Patients with Hereditary Haemorrhagic Telangiectasia

Hereditary haemorrhagic telangiectasia (HHT) is a vascular dysplasia that commonly results in bleeding but with frequent indications for therapeutic anticoagulation. Our aims were to advance the understanding of drug-specific intolerance and evaluate if there was an indication for pharmacogenomic testing. Genes encoding proteins involved in the absorption, distribution, metabolism, and excretion of warfarin, heparin, and direct oral anticoagulants (DOACs) apixaban, rivaroxaban, edoxaban, and dabigatran were identified and examined. Linkage disequilibrium with HHT genes was excluded, before variants within these genes were examined following whole genome sequencing of general and HHT populations. The 44 genes identified included 5/17 actionable pharmacogenes with guidelines. The 76,156 participants in the Genome Aggregation Database v3.1.2 had 28,446 variants, including 9668 missense substitutions and 1076 predicted loss-of-function (frameshift, nonsense, and consensus splice site) variants, i.e., approximately 1 in 7.9 individuals had a missense substitution, and 1 in 71 had a loss-of-function variant. Focusing on the 17 genes relevant to usually preferred DOACs, similar variant profiles were identified in HHT patients. With HHT patients at particular risk of haemorrhage when undergoing anticoagulant treatment, we explore how pre-emptive pharmacogenomic testing, alongside HHT gene testing, may prove beneficial in reducing the risk of bleeding and conclude that HHT patients are well placed to be at the vanguard of personalised prescribing.

Simulating clinical trials for model-informed precision dosing: using warfarin treatment as a use case

Treatment response variability across patients is a common phenomenon in clinical practice. For many drugs this inter-individual variability does not require much (if any) individualisation of dosing strategies. However, for some drugs, including chemotherapies and some monoclonal antibody treatments, individualisation of dosages are needed to avoid harmful adverse events. Model-informed precision dosing (MIPD) is an emerging approach to guide the individualisation of dosing regimens of otherwise difficult-to-administer drugs. Several MIPD approaches have been suggested to predict dosing strategies, including regression, reinforcement learning (RL) and pharmacokinetic and pharmacodynamic (PKPD) modelling. A unified framework to study the strengths and limitations of these approaches is missing. We develop a framework to simulate clinical MIPD trials, providing a cost and time efficient way to test different MIPD approaches. Central for our framework is a clinical trial model that emulates the complexities in clinical practice that challenge successful treatment individualisation. We demonstrate this framework using warfarin treatment as a use case and investigate three popular MIPD methods: 1. Neural network regression; 2. Deep RL; and 3. PKPD modelling. We find that the PKPD model individualises warfarin dosing regimens with the highest success rate and the highest efficiency: 75.1% of the individuals display INRs inside the therapeutic range at the end of the simulated trial; and the median time in the therapeutic range (TTR) is 74%. In comparison, the regression model and the deep RL model have success rates of 47.0% and 65.8%, and median TTRs of 45% and 68%. We also find that the MIPD models can attain different degrees of individualisation: the Regression model individualises dosing regimens up to variability explained by covariates; the Deep RL model and the PKPD model individualise dosing regimens accounting also for additional variation using monitoring data. However, the Deep RL model focusses on control of the treatment response, while the PKPD model uses the data also to further the individualisation of predictions.

Missense VKOR mutants exhibit severe warfarin resistance but lack VKCFD via shifting to an aberrantly reduced state

Missense vitamin K epoxide reductase (VKOR) mutations in patients cause resistance to warfarin treatment but not abnormal bleeding due to defective VKOR activity. The underlying mechanism of these phenotypes remains unknown. Here we show that the redox state of these mutants is essential to their activity and warfarin resistance. Using a mass spectrometry-based footprinting method, we found that severe warfarin-resistant mutations change the VKOR active site to an aberrantly reduced state in cells. Molecular dynamics simulation based on our recent crystal structures of VKOR reveals that these mutations induce an artificial opening of the protein conformation that increases access of small molecules, enabling them to reduce the active site and generating constitutive activity uninhibited by warfarin. Increased activity also compensates for the weakened substrate binding caused by these mutations, thereby maintaining normal VKOR function. The uninhibited nature of severe resistance mutations suggests that patients showing signs of such mutations should be treated by alternative anticoagulation strategies.

Clinical significance of the series of CYP2C9*non3 variants, an unignorable predictor of warfarin sensitivity in Chinese population

Backgrounds

Gene polymorphisms are critical for variations in warfarin dose. To date, more than 70 CYP2C9 alleles have been identified. This study was designed to clarify the clinical significance of CYP2C9*non-3 variants to warfarin sensitivity in Chinese Han patients.

Methods

The entire CYP2C9 gene region was sequenced in 1,993 individuals, and clinical data and VKORC1 genotypes were collected from 986 patients with atrial fibrillation treated with warfarin. The SKAT-O method was used to analyze the effects of CYP2C9*non-3 variants on warfarin sensitivity.

Results

A total of 20 CYP2C9 variants were identified, of which four were novel. Carriers with CYP2C9*non-3 variants may have lower warfarin dose requirements, and similar to CYP2C9*3, CYP2C9*non-3 variants are clearly relevant to warfarin-sensitive and highly sensitive responders.

Conclusion

Our results showed that, besides CYP2C9*3, the series of CYP2C9*non-3 variants is an unignorable predictor for warfarin sensitivity in Chinese population. From a safety consideration, people carried such variants may need a preferred choice of NOACs when they started anticoagulation therapy.

The Random Effects Warfarin Days' Supply (REWarDS) Model: Development and Validation of a Novel Method for Estimating Exposure to Warfarin Using Administrative Data

Warfarin's complex dosing is a significant barrier to measurement of its exposure in observational studies using population databases. Using population-based administrative data (1996-2019) from British Columbia, Canada, we developed a method based on statistical modeling (Random Effects Warfarin Days' Supply (REWarDS)) that involves fitting a random-effects linear regression model to patients' cumulative dosage over time for estimation of warfarin exposure. Model parameters included a minimal universally available set of variables from prescription records for estimation of patients' individualized average daily doses of warfarin. REWarDS estimates were validated against a reference standard (manual calculation of the daily dose using the free-text administration instructions entered by the dispensing pharmacist) and compared with alternative methods (fixed window, fixed tablet, defined daily dose, and reverse wait time distribution) using Pearson's correlation coefficient (r), the intraclass correlation coefficient, and the root mean squared error. REWarDS-estimated days' supply showed strong correlation and agreement with the reference standard (r = 0.90 (95% confidence interval (CI): 0.90, 0.90); intraclass correlation coefficient = 0.95 (95% CI: 0.94, 0.95); root mean squared error = 8.24 days) and performed better than all of the alternative methods. REWarDS-estimated days' supply was valid and more accurate than estimates from all other available methods. REWarDS is expected to confer optimal precision in studies measuring warfarin exposure using administrative data.

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

Background

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

Methods

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

Results

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

Conclusion

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

Trial Registration

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

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.

Genome and systems biology of Melilotus albus provides insights into coumarins biosynthesis

Melilotus species are used as green manure and rotation crops worldwide and contain abundant pharmacologically active coumarins. However, there is a paucity of information on its genome and coumarin production and function. Here, we reported a chromosome-scale assembly of Melilotus albus genome with 1.04 Gb in eight chromosomes, containing 71.42% repetitive elements. Long terminal repeat retrotransposon bursts coincided with declining of population sizes during the Quaternary glaciation. Resequencing of 94 accessions enabled insights into genetic diversity, population structure, and introgression. Melilotus officinalis had relatively larger genetic diversity than that of M. albus. The introgression existed between M. officinalis group and M. albus group, and gene flows was from M. albus to M. officinalis. Selection sweep analysis identified candidate genes associated with flower colour and coumarin biosynthesis. Combining genomics, BSA, transcriptomics, metabolomics, and biochemistry, we identified a β-glucosidase (BGLU) gene cluster contributing to coumarin biosynthesis. MaBGLU1 function was verified by overexpression in M. albus, heterologous expression in Escherichia coli, and substrate feeding, revealing its role in scopoletin (coumarin derivative) production and showing that nonsynonymous variation drives BGLU enzyme activity divergence in Melilotus. Our work will accelerate the understanding of biologically active coumarins and their biosynthetic pathways, and contribute to genomics-enabled Melilotus breeding.

From Pharmacogenetics to Pharmaco-Omics:Milestones and Future Directions

The origins of pharmacogenetics date back to the 1950s, when it was established that inter-individual differences in drug response are partially determined by genetic factors. Since then, pharmacogenetics has grown into its own field, motivated by the translation of identified gene-drug interactions into therapeutic applications. Despite numerous challenges ahead, our understanding of the human pharmacogenetic landscape has greatly improved thanks to the integration of tools originating from disciplines as diverse as biochemistry, molecular biology, statistics, and computer sciences. In this review, we discuss past, present, and future developments of pharmacogenetics methodology, focusing on three milestones: how early research established the genetic basis of drug responses, how technological progress made it possible to assess the full extent of pharmacological variants, and how multi-dimensional omics datasets can improve the identification, functional validation, and mechanistic understanding of the interplay between genes and drugs. We outline novel strategies to repurpose and integrate molecular and clinical data originating from biobanks to gain insights analogous to those obtained from randomized controlled trials. Emphasizing the importance of increased diversity, we envision future directions for the field that should pave the way to the clinical implementation of pharmacogenetics.

Personalized medicine in cardiovascular disease: review of literature

Purpose

Personalized medicine (PM) is the concept of managing patients based on their characteristics, including genotypes. In the field of cardiology, advantages of PM could be found in the diagnosis and treatment of several conditions such as arrhythmias and cardiomyopathies; moreover, it may be beneficial to prevent adverse drug reactions (ADR) and select the best medication. Genetic background can help us in selecting effective treatments, appropriate dose requirements, and preventive strategies in individuals with particular genotypes.

Method

In this review, we provide examples of personalized medicine based on human genetics for the most used pharmaceutics in cardiology, including warfarin, clopidogrel, and statins. We also review cardiovascular diseases, including coronary artery disease, arrhythmia, and cardiomyopathies.

Conclusion

Genetic factors are as important as environmental factors and they should be tested and evaluated more in the future by improving in genetic testing tools.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-021-00840-0.

Profiling of warfarin pharmacokinetics-associated genetic variants: Black Africans portray unique genetic markers important for an African specific warfarin pharmacogenetics-dosing algorithm

BACKGROUND

Warfarin dose variability observed in patients is attributed to variation in genes involved in the warfarin metabolic pathway. Genetic variation in CYP2C9 and VKORC1 has been the traditional focus in evaluating warfarin dose variability, with little focus on other genes.

OBJECTIVE

We set out to evaluate 27 single nucleotide polymorphisms (SNPs) in the CYP2C cluster loci and 8 genes (VKORC1, ABCB1, CYP2C9, CYP2C19, CYP2C8, CYP1A2, CYP3A4, and CYP3A5) involved in pharmacokinetics of warfarin.

PATIENTS/METHODS

503 participants were recruited among black Africans and Mixed Ancestry population groups, from South Africa and Zimbabwe, and a blood sample taken for DNA. Clinical parameters were obtained from patient medical records, and these were correlated with genetic variation.

RESULTS

Among black Africans, the SNPs CYP2C rs12777823G>A, CYP2C9 c.449G>A (*8), CYP2C9 c.1003C>T (*11) and CYP2C8 c.805A>T (*2) were significantly associated with warfarin maintenance dose. Conversely, CYP2C9 c.430C>T (*2), CYP2C8 c.792C>G (*4) and VKORC1 g.-1639G>A were significantly associated with maintenance dose among the Mixed Ancestry. The presence of CYP2C8*2 and CYP3A5*6 alleles was associated with increased mean warfarin maintenance dose, whereas CYP2C9*8 allele was associated with reduced warfarin maintenance dose.

CONCLUSION

African populations present with a diversity of variants that are important in predicting pharmacogenetics-based warfarin dosing in addition to those reported in CYP2C9 and VKORC1. It is therefore important, to include African populations in pharmacogenomics studies to be able to identify all possible biomarkers that are potential predictors for drug response.

Evaluating the effects of anticoagulant rodenticide bromadiolone in Wistar rats co-exposed to vitamin K: impact on blood-liver axis and brain oxidative status

The aim of this study was to investigate the beneficial effects of vitamin K relate to protection against detrimental effects of bromadiolone. Wistar rats (n = 30) were divided in three groups (n = 10): control group and two groups treated with bromadiolone (0.12 mg/kg) and bromadiolone + vitamin K (0.12 mg/kg + 100 mg/kg) over the period of four days. The main findings in the bromadiolone-exposed rats, such as damaged hepatocytes, high levels of globulin, total proteins and lymphocytes, and altered albumin/globulin ratio, collectively indicate an acute inflammatory process. Morphological changes in erythrocytes include microcytosis, hypochromia, hyperchromia, hemolysis, stomatocytosis, and spherocytosis. Significantly low values of RBC, Hct, and hemoglobin concentrations indicate impairments of the hematopoietic pathway causing combined anemia. The selected dose of bromadiolone caused a non-significant increase of catalase activity and a significant increase of the total protein content in brain tissue homogenates. Vitamin K supplementation reduced many of the harmful effects of bromadiolone. The cytoprotective role of vitamin K was proved to be of great importance for the preservation of structural changes on the membranes of hepatocytes and erythrocytes, in addition to the known role in the treatment of coagulopathies. The results of the study suggest valuable properties of vitamin K in the prevention and treatment of various types of anemia caused by bromadiolone toxicity. Future research is necessary to determine the adequate dose and treatment duration with vitamin K in disorders caused by the cumulative action of bromadiolone and possibly other pesticides.

Measuring Pharmacogene Variant Function at Scale Using Multiplexed Assays

As costs of next-generation sequencing decrease, identification of genetic variants has far outpaced our ability to understand their functional consequences. This lack of understanding is a central challenge to a key promise of pharmacogenomics: using genetic information to guide drug selection and dosing. Recently developed multiplexed assays of variant effect enable experimental measurement of the function of thousands of variants simultaneously. Here, we describe multiplexed assays that have been performed on nearly 25,000 variants in eight key pharmacogenes (ADRB2, CYP2C9, CYP2C19, NUDT15, SLCO1B1, TMPT, VKORC1, and the LDLR promoter), discuss advances in experimental design, and explore key challenges that must be overcome to maximize the utility of multiplexed functional data. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Influence of NQO1 Polymorphisms on Warfarin Maintenance Dose: A Systematic Review and Meta-Analysis (rs1800566 and rs10517)

This meta-analysis was conducted to analyze the effect of NQO1 polymorphism on the warfarin maintenance dosage. Using strict inclusion and exclusion criteria, we searched PubMed, EMBASE, and the Cochrane Library for eligible studies published prior to July 7, 2021. The required data were extracted, and experts were consulted when necessary. Review Manager Version 5.4 software was used to analyze the relationship between NQO1 polymorphisms and the warfarin maintenance dosage. Four articles involving 757 patients were included in the meta-analysis. Patients who were NQO1 rs10517 G carriers (AG carriers or GG carriers) required a 48% higher warfarin maintenance dose than those who were AA carriers. Patients with NQO1 rs1800566 CT carriers required a 13% higher warfarin dose than those who were CC carriers, with no associations observed with the other comparisons of the NQO1 rs1800566 genotypes. However, the results obtained by comparing the NQO1 rs1800566 genotypes require confirmation, as significant changes in the results were found in sensitivity analyses. Our meta-analysis suggests that the NQO1 rs10517and NQO1 rs1800566 variant statuses affect the required warfarin maintenance dose.

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

BACKGROUND

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

OBJECTIVE

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

METHOD

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

RESULT

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

CONCLUSION

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

Current practices of Western Australian general dentists regarding management of patients on anticoagulant/antiplatelet therapy

PURPOSE

Currently, there are little to no published studies outlining general dentists' knowledge in the management of patients on anticoagulant/antiplatelet therapies in Australia. The aim of this study was to investigate the current practices of Western Australian (WA) general dentists with regards to dental management of patients taking anticoagulants/antiplatelets.

MATERIALS AND METHODS

WA dentists were invited to undertake a survey to investigate their knowledge on the management of patients taking anticoagulant/antiplatelet. The questionnaire provided to WA general dentists consisted of pre-extraction advice on patients (direct oral anticoagulants [DOACs], antiplatelets, warfarin, dual antiplatelets and antiplatelet/anticoagulant). Results were analysed using descriptive statistics as well as chi-square tests.

RESULTS

Of the 89 participants, 40.5% had <5 years of general dental experience. Most WA general dentists (64%-71%) responded with 'no change' when performing extractions on patients on DOACs, antiplatelet therapy, warfarin, dual antiplatelets and antiplatelets/anticoagulants (P = 0.00). Furthermore, dentists with 6-10 years of experience were more likely to cease antiplatelet for 24 h before extractions (P < 0.05). Dentists who extracted 10-30 teeth per month were likely to stop antiplatelets and DOACs for more than 48 h compared to other groups (P < 0.05).

CONCLUSION

Most WA dentists would not cease anticoagulant/antiplatelet therapy when undergoing dental extractions.

Deciphering Genetic Variants of Warfarin Metabolism in Children With Ventricular Assist Devices

Warfarin is prescribed in patients with ventricular assist devices (VADs). Dosage depends on several factors including the underlying genotype. These include polymorphisms of genes encoding cytochrome P450 enzymes, the main ones being CYP2C9, VKORC1, and CYP4F2. The objectives of this study were to evaluate the prevalence of CY2CP9 1*2*3*, VKORC1, and CYP4F2 in children with VADs and the time to reach the target international normalized ratio. We performed a retrospective/prospective study in children with VADs. We recorded polymorphisms, disease, type of VAD, ethnicity, age, gender, height, weight, INR values, bleeding, and thromboembolic episodes. Informed consent was obtained. We enrolled 34 children (19 male, 15 female), with a median age of 2 years (range 0.3-17 years) and median weight of 6.9Kg. The Berlin Heart was the most commonly implanted VAD (22/34; 64%), and the most common diagnosis was dilated cardiomyopathy. Statistical analysis confirmed a significant partial correlation with VKORC1 CC (p = 0.019). The CYP2C9*2 CT genotype showed a late rise in target INR values (p = 0.06), while the CYP2C9*2 CC showed a tendency toward an early INR rise (p = 0.024). We provide new information on the contribution of the warfarin polymorphisms in children with VAD implantation. Pharmacogenomic dosing for children using warfarin has the potential to improve clinical care in VAD patients. Patients with the CYP2C9*2 CT genotype may need more time or higher doses to reach target INR, while clinicians may need to be aware of the potential for a rapid rise in INR in patients with the CYP2C9*2 CC genotype.

Competitive tight-binding inhibition of VKORC1 underlies warfarin dosage variation and antidotal efficacy

Dose control of warfarin is a major complication in anticoagulation therapy and overdose is reversed by the vitamin K antidote. Improving the dosage management and antidotal efficacy requires mechanistic understanding. Here we find that effects of the major predictor of warfarin dosage, SNP -1639 G>A, follow a general correlation that warfarin 50% inhibitory concentration decreases with cellular level of vitamin K epoxide reductase (VKORC1), suggesting stoichiometric inhibition. Characterization of the inhibition kinetics required the use of microsomal VKORC1 with a native reductant, glutathione, that enables effective warfarin inhibition in vitro. The kinetics data can be fitted with the Morrison equation, giving a nanomolar inhibition constant and demonstrating that warfarin is a tight-binding inhibitor. However, warfarin is released from purified VKORC1-warfarin complex with increasing amount of vitamin K, indicating competitive inhibition. The competition occurs also in cells, resulting in rescued VKORC1 activity that augments the antidotal effects of vitamin K. Taken together, warfarin is a competitive inhibitor that binds VKORC1 tightly and inhibits at a stoichiometric (1:1) concentration, whereas exceeding the VKORC1 level results in warfarin overdose. Thus, warfarin dosage control should use VKORC1 level as a major indicator, and improved antidotes may be designed based on their competition with warfarin.

Evaluation of Warfarin Anticoagulation at University of Gondar Comprehensive Specialized Hospital, North-West Ethiopia

PURPOSE

To assess the quality of warfarin anticoagulation and its clinical outcomes on patients treated with warfarin at the University of Gondar comprehensive specialized hospital, North-west Ethiopia.

METHODS

We reviewed medical records of patients treated with warfarin between June 1, 2016, and May 30, 2018, at the University of Gondar comprehensive specialized hospital. The quality of anticoagulation was evaluated using the percentage of time spent in the therapeutic range. Data were entered into Statistical Product and Service Solutions (SPSS), version 20. Descriptive statistics were used to describe the socio-demographic and clinical characteristics of study participants. Multivariable logistic regression analysis was performed to identify independent predictors of quality of anticoagulation. Statistical significance was declared when the p-value was less than 0.05 at 95% confidence interval (CI).

RESULTS

From a total of 202 patients' charts reviewed, women accounted for 134 (67.3%). The mean participants' age was 44.33 years (±17.05years SD). The median time spent in the therapeutic range was 37.91 with an IQR of (0.00-65.86). More than two-third (143, (70.8%)) of participants had poor anticoagulation quality (time spent in the therapeutic range is less than 65%). Twenty-seven patients (13.4%) experienced adverse medication events of bleeding and thromboembolic events. Logistic regression analysis showed that potential medication interaction [p= 0.003 95% CI Adjusted odds ratio (AOR): 0.32 (0.152-0.689)] and presence of co-morbidity [p= 0.037 95% CI AOR: 0.70 (1.046-4.105)] were significantly associated with quality of anticoagulation.

CONCLUSION

The quality of warfarin anticoagulation at the University of Gondar comprehensive specialized hospital was poor. A strong effort is needed to improve the quality of anticoagulation. Patients who had other co-morbidity conditions and potentially interacting medication need special attention.

Research Progress of Herbal Medicines on Drug Metabolizing Enzymes: Consideration Based on Toxicology

The clinical application of herbal medicines is increasing, but there is still a lack of comprehensive safety data and in-depth research into mechanisms of action. The composition of herbal medicines is complex, with each herb containing a variety of chemical components. Each of these components may affect the activity of metabolizing enzymes, which may lead to herb-drug interactions. It has been reported that the combined use of herbs and drugs can produce some unexpected interactions. Therefore, this study reviews the progress of research on safety issues caused by the effects of herbs on metabolizing enzymes with reference to six categories of drugs, including antithrombotic drugs, non-steroidal anti-inflammatory drugs, anti-diabetic drugs, statins lipid-lowering drugs, immunosuppressants, and antineoplastic drugs. Understanding the effects of herbs on the activity of metabolizing enzymes could help avoid the toxicity and adverse drug reactions resulting from the co-administration of herbs and drugs, and help doctors to reduce the risk of prescription incompatibility.

Implications of Polymorphisms in the BCKDK and GATA-4 Gene Regions on Stable Warfarin Dose in African Americans

VKORC1 and CYP2C9 genotypes explain less variability in warfarin dose requirements in African Americans compared with Europeans. Variants in BCKDK and GATA-4 gene regions, purported to regulate VKORC1 and CYP2C9 expression, have been shown to play an important role in warfarin dose requirements in Europeans and Asians, respectively. We sought to determine whether rs56314408 near BCKDK or GATA-4 rs2645400 influence warfarin dose requirements in 200 African Americans. Unlike the strong linkage disequilibrium (LD) between rs56314408 and VKORC1 rs9923231 in Europeans, they were not in LD in African Americans. No associations were found on univariate analysis. On multivariable analysis, rs56314408 was associated (P = 0.027) with dose in a regression model excluding VKORC1 rs9923231, and GATA-4 rs2645400 was associated (P = 0.032) with dose in a model excluding CYP2C (CYP2C9*2, *3, *5, *6, *8, and *11, CYP2C rs12777823) variants. Neither variant contributed to dose in the model that included both VKORC1 rs9923231 and CYP2C variants. Our results do not support contributions of the studied variants to warfarin dose requirements in African Americans. However, they illustrate the value of studies in African descent populations, who have low LD in their genome, in teasing out genetic variation underlying drug response associations. They also emphasize the importance of confirming associations in persons of African ancestry.

Non-vitamin K antagonist oral anticoagulants for stroke prevention in atrial fibrillation: safety issues in the elderly

INTRODUCTION

Non-vitamin K antagonist oral anticoagulants (NOACs) are increasingly used for stroke prevention in patients with atrial fibrillation (AF). Since NOACs are predominantly used in the elderly with AF at high risk for stroke and bleeding and with comorbidities requiring polypharmacy, it is important to assess their safety and efficacy in this population.

AREAS COVERED

We review changes in pharmacokinetics and pharmacodynamics observed with senescence and the effect on NOACs and drug and food interactions. We also provide an update on challenges related to NOAC use in situations that increases the risk for bleeding or require temporary discontinuation and address practical issues in the elderly AF patients managed on NOACs. Clinical studies and trials with cardiovascular outcomes reported from January 1990 to August 2020 were identified through the Medline database using PubMed, Cochrane Library, and EMBASE database.

EXPERT OPINION

NOACs are highly effective in preventing stroke in AF patients with non-inferior or superior efficacy to warfarin, with reduced risk of major bleeding. However, in the older-elderly, evidence comes mainly from observational studies or extrapolation from studies in populations with minimal functional limitations or comorbidities. The high upfront cost and out-of-pocket expense for copayment or deductibles also limit the use of this effective therapy in a substantial number of patients. The cost reduction may further improve long-term use for NOACs in stroke prevention in elderly patients with AF.

Coumarin-based Scaffold as α-glucosidase Inhibitory Activity: Implication for the Development of Potent Antidiabetic Agents

BACKGROUND

Delaying the absorption of glucose through α-glucosidase enzyme inhibition is one of the therapeutic approaches in the management of Type 2 diabetes, which can reduce the incidence of postprandial hyperglycemia. The existence of chronic postprandial hyperglycemia impaired the endogenous antioxidant defense by inducing oxidative stress-induced pancreatic β-cell destruction through uncontrolled generation of free radicals such as ROS, which in turn, leads to various macrovascular and microvascular complications. The currently available α -glucosidase inhibitors, for instance, acarbose, have some side effects such as hypoglycemia at higher doses, liver problems, meteorism, diarrhea, and lactic acidosis. Therefore, there is an urgent need to discover and develop potential α-glucosidase inhibitors.

OBJECTIVE

Based on suchmotifs, researchers are intrigued to search for the best scaffold that displays various biological activities. Among them, coumarin scaffold has attracted great attention. The compound and its derivatives can be isolated from various natural products and/or synthesized for the development of novel α-glucosidase inhibitors.

RESULTS

This study focused on coumarin and its derivatives as well as on their application as potent antidiabetic agents and has also concentrated on the structure-activity relationship.

CONCLUSION

This review describes the applications of coumarin-containing derivatives as α - glucosidase inhibitors based on published reports which will be useful for innovative approaches in the search for novel coumarin-based antidiabetic drugs with less toxicity and more potency.

An Overview of Coumarin as a Versatile and Readily Accessible Scaffold with Broad-Ranging Biological Activities

Privileged structures have been widely used as an effective template for the research and discovery of high value chemicals. Coumarin is a simple scaffold widespread in Nature and it can be found in a considerable number of plants as well as in some fungi and bacteria. In the last years, these natural compounds have been gaining an increasing attention from the scientific community for their wide range of biological activities, mainly due to their ability to interact with diverse enzymes and receptors in living organisms. In addition, coumarin nucleus has proved to be easily synthetized and decorated, giving the possibility of designing new coumarin-based compounds and investigating their potential in the treatment of various diseases. The versatility of coumarin scaffold finds applications not only in medicinal chemistry but also in the agrochemical field as well as in the cosmetic and fragrances industry. This review is intended to be a critical overview on coumarins, comprehensive of natural sources, metabolites, biological evaluations and synthetic approaches.

Effect of Vitamin K Epoxide Reductase Complex 1 Polymorphism on Warfarin Dose Requirement among Patients in Tertiary Care Hospital

Background

Warfarin, anticoagulant is used for thromboembolic disorders. Inter-individual variation in clinical response to warfarin is due to various factors, including polymorphism of Vitamin K epoxide reductase complex 1 (VKORC1)-1639G>A. The aim of our study was to evaluate the effect of VKORC1 polymorphism on the maintenance dose of warfarin.

Materials and Methods

Cross-sectional study conducted by the departments of Pharmacology, Cell Biology and Molecular Genetics on patients attending cardiology clinic, receiving warfarin for at least 2 months. Genomic deoxyribonucleic acid was extracted and genotyping was done by Polymerase Chain Reaction - Restriction Fragment Length Polymorphism. The correlation between VKORC1 gene polymorphism and warfarin maintenance dose was analyzed.

Results

A total of 102 patients with a mean age of 47.72 ± 10.31 years, of which 58 (56.86%) were male. The frequency of VKORC1 G>A for GG, GA, and AA genotypes was 74.51%, 19.61%, and 5.88%, respectively. Variant allele AA was less frequent than the wild type. Mean weekly warfarin dose was 23.12 ± 8.08, 22.93 ± 8.21, and 15.6 ± 5.35 mg in patients with GG, GA, and AA genotypes, respectively. Patients with GG genotype required therapeutic dose compared to variant type (P = 0.001). Multiple stepwise regression model showed 26.3% variability in warfarin dose was due to VKORC1 genotype (R = 0.513, R² = 0.263, adjusted R² = 0.256, P = 0.0001).

Conclusion

VKORC1 polymorphism alone influence 26.3% variability in warfarin dose and AA genotype patients required lower dose.

Genotype-Guided Dosing of Warfarin in Chinese Adults: A Multicenter Randomized Clinical Trial

BACKGROUND

Warfarin is an effective treatment for thromboembolic disease but has a narrow therapeutic index; optimal anticoagulation dosage can differ tremendously among individuals. We aimed to evaluate whether genotype-guided warfarin dosing is superior to routine clinical dosing for the outcomes of interest in Chinese patients.

METHODS

We conducted a multicenter, randomized, single-blind, parallel-controlled trial from September 2014 to April 2017 in 15 hospitals in China. Eligible patients were ≥18 years of age, with atrial fibrillation or deep vein thrombosis without previous treatment of warfarin or a bleeding disorder. Nine follow-up visits were performed during the 12-week study period. The primary outcome measure was the percentage of time in the therapeutic range of the international normalized ratio during the first 12 weeks after starting warfarin therapy.

RESULTS

A total of 660 participants were enrolled and randomly assigned to a genotype-guided dosing group or a control group under standard dosing. The genotype-guided dosing group had a significantly higher percentage of time in the therapeutic range than the control group (58.8% versus 53.2% [95% CI of group difference, 1.1-10.2]; P=0.01). The genotype-guided dosing group also achieved the target international normalized ratio sooner than the control group. In subgroup analyses, warfarin normal sensitivity group had an even higher percentage of time in the therapeutic range during the first 12 weeks compared with the control group (60.8% versus 48.9% [95% CI, 1.1-24.4]). The incidence of adverse events was low in both groups.

CONCLUSIONS

The outcomes of genotype-guided warfarin dosing were superior to those of clinical standard dosing. These findings raise the prospect of precision warfarin treatment in China. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02211326.

The gut microbes, Enterococcus and Escherichia-Shigella, affect the responses of heart valve replacement patients to the anticoagulant warfarin

Numerous algorithms based on patient genetic variants have been established with the aim of reducing the risk of GI bleeding and thromboembolism during warfarin administration. However, approximately 35 % of individual warfarin sensitivity still remains unexplained. Few of warfarin algorithms take into account gut microbiota profiles. The identification of certain microbiome will provide new targets and new strategies for reducing the risk of bleeding and thromboembolism during warfarin administration. In this study, we collected plasma and stool samples from 200 inpatients undergoing heart valve replacement (HVR), which were classified as low responder (LR), high responder (HR) and normal responder (NR). Significant differences were observed in the diversity and relative abundance of the gut microbiota among the three groups. The genus Escherichia-Shigella was enriched significantly in the LRs (P = 3.189e^-11), while the genus Enterococcus was enriched significantly in the HRs (P = 1.249e^-11). The amount of VK2 synthesized by gut microbiota in LR group was much higher than that in HR group (P = 0.005). Whole genome shotgun sequencing indicated that the relative abundance of enzymes and modules associated with VK biosynthesis was significantly higher in LRs than in HRs or NRs. The 12 microbial markers were identified through tenfold cross-validation with a random forest model. The results provided a new microbial diagnostic model that can be used to inform modulation of warfarin dosage on the basis of patient intestinal flora composition.

The Genetics of Warfarin Dose-Response Variability in Africans: An Expert Perspective on Past, Present, and Future

Coumarins such as warfarin are prescribed for prevention and treatment of thromboembolic disorders. Warfarin remains the most widely prescribed and an anticoagulant of choice in Africa. Warfarin use is, however, limited by interindividual variability in pharmacokinetics and a narrow therapeutic index. The difference in patients' pharmacodynamic responses to warfarin has been attributed to genetic variation in warfarin metabolism and molecular targets (e.g., CYP2C9 and VKORC1) and host-environment interactions. This expert review offers a synthesis of human genetics studies in Africans with respect to pharmacogenetics-informed warfarin dosing. We identify areas that need future research attention or could benefit from harnessing existing pharmacogenetics knowledge toward rational and optimal therapeutics with warfarin in African patients. A literature search was conducted until January 2019. A total of 343 articles were retrieved from nine African countries: Botswana, Ethiopia, Egypt, Ghana, Kenya, South Africa, Sudan, Tanzania, and Mozambique. We found 19 studies on genetics of warfarin treatment specifically among Africans. Genes examined included CYP2C9, VKORC1, CYP4F2, APOE, CALU, GGCX, and EPHX1. CYP2C9*2 and *3 alleles were highly frequent among Egyptians, while rare in other African populations. CYP2C9*5, *8, *9, and *11, and VKORC1 Asp36Tyr genetic variants explained warfarin variability in Africans better, compared to CYP2C9*2 and *3. In Africa, there is limited pharmacogenetics data on warfarin. Therefore, future research and funding commitments should be prioritized to ensure safe and effective use of warfarin in Africa. Lessons learned in Africa from the science of pharmacogenetics would inform rational therapeutics in hematology, cardiology, and surgical specialties worldwide.

Analysis of the Barley Malt Rootlet Proteome

Barley seeds are one of the main ingredients of the malting industry for brewing beer. The barley rootlets that are separated from the kilned seeds at the end of the malting process and used as animal feed are one of the byproducts of this industry. In this study, the proteome of rootlets derived from two stages of the malting process, germination and kilning, from a popular malting barley variety were analyzed. A label-free shotgun proteomics strategy was used to identify more than 800 proteins from the barley rootlets. A high coverage and high confidence Gene Ontology annotations of the barley genome was used to facilitate the functional annotation of the proteins that were identified in the rootlets. An analysis of these proteins using Kellogg Encyclopedia of Genes and Genomes (KEGG) and Plant Reactome databases indicated the enrichment of pathways associated with phytohormones, protein biosynthesis, secondary metabolism, and antioxidants. Increased levels of jasmonic acid and auxin in the rootlets further supported the in silico analysis. As a rich source of proteins and amino acids use of these by-products of the malting industry for animal feed is validated. This study also indicates rootlets as a potential source of naturally occurring phenylpropanoids and antioxidants that can be further exploited in the development of functional foods.

Pharmacogenetic Warfarin Dosing Algorithm in the Russian Population

Background. To date, there are many pharmacogenetic algorithms for selecting the dose of warfarin. However, there is very little information about the predictive accuracy of the algorithms. We decided to evaluate the predictive accuracy of the Gage algorithm, using a calculator, located on the web site (http://www.warfarindosing.org) in two ethnic groups (Caucasians and Asians), living in Russia.

Aim. To compare the actual warfarin dose (AWD) to the calculated warfarin dose (CWD), using the algorithm in two ethnic groups taking warfarin.

Materials and methods. We included 114 patients (66 Caucasians and 48 Asians): the mean age was

60.91 ± 12.34 years; 61 (53.51 %) men, and 53 (46.49 %) women. The comparative characteristics of the algorithm were tested using the mean absolute error (MAE) between AWD and CWD, and percentage of patients, whose CWD fell within 20 % of AWD (percentage within 20 %). Genotyping for CYP2C9*2, CYP2C9*3, CYP4F*2 and VKORC1 was performed by real-time polymerase chain reaction (RT-PCR) method using Pharmacogenetics Warfarin reagent kits (DNA technology, Russia).

Results. The Gage algorithm produced the predictive accuracy with MAE = 1.02 ± 0.16 mg/day and percentage within 20 % for Asian patients was 39.6 %. We obtained MAE = 1.33 ± 0.16 mg/day and percentage within 20 % for Caucasian patients was 40.9 %. In two ethnic groups (Caucasians and Asians) of the Russian population, overall performance of warfarin pharmacogenetic dosing by the Gage algorithm was similar.

Conclusions. Despite the performance limitation of the current warfarin pharmacogenetic dosing Gage algorithm, constant international normalized ratio monitoring is important.

Sodium dehydroacetate induces coagulation dysfunction by inhibiting liver vitamin K epoxide reductase complex subunit 1 in Wistar rats

Sodium dehydroacetate (Na-DHA), an antibiotic agent that combats growth of bacteria, fungi, and yeast, is used as a preservative in animal feed, food, and cosmetics. We previously reported that Na-DHA induces coagulation anomalies in Wistar rats, but the anticoagulant mechanism of Na-DHA remains to be established. Here we report that Na-DHA prolonged prothrombin time (PT) and activated partial thromboplastin time (APTT) in male and female Wistar rats. In addition, Na-DHA decreased vitamin K (VK) levels and increased the levels of protein induced by vitamin K absence/antagonist-II (PIVKA-II) in rat serum. Moreover, we found that treatment with VK not only reversed Na-DHA-decreased serum VK and -increased PIVKA-II levels, but also attenuated Na-DHA-prolonged PT and APTT, suggesting that Na-DHA-decreased serum VK level contributes to the anticoagulation due to Na-DHA. Further we found that Na-DHA inhibited vitamin K epoxide reductase complex subunit 1 (VKORC1), a key enzyme in VK recycling, in the liver tissue of Wistar rats, as evidenced by reduced mRNA and protein levels of VKORC1 following Na-DHA treatment. Taken together, our data indicate that Na-DHA inhibits liver VKORC1, resulting in a decrease of serum VK levels, leading to abnormal coagulation in rats.

Implementation of genotype-guided dosing of warfarin with point-of-care genetic testing in three UK clinics: a matched cohort study

BACKGROUND

Warfarin is a widely used oral anticoagulant. Determining the correct dose required to maintain the international normalised ratio (INR) within a therapeutic range can be challenging. In a previous trial, we showed that a dosing algorithm incorporating point-of-care genotyping information ('POCT-GGD' approach) led to improved anticoagulation control. To determine whether this approach could translate into clinical practice, we undertook an implementation project using a matched cohort design.

METHODS

At three clinics (implementation group; n = 119), initial doses were calculated using the POCT-GGD approach; at another three matched clinics (control group; n = 93), patients were dosed according to the clinic's routine practice. We also utilised data on 640 patients obtained from routinely collected data at comparable clinics. Primary outcome was percentage time in target INR range. Patients and staff from the implementation group also provided questionnaire feedback on POCT-GGD.

RESULTS

Mean percentage time in INR target range was 55.25% in the control group and 62.74% in the implementation group; therefore, 7.49% (95% CI 3.41-11.57%) higher in the implementation group (p = 0.0004). Overall, patients and staff viewed POCT-GGD positively, suggesting minor adjustments to allow smooth implementation into practice.

CONCLUSIONS

In the first demonstration of the implementation of genotype-guided dosing, we show that warfarin dosing determined using an algorithm incorporating genetic and clinical factors can be implemented smoothly into clinic, to ensure target INR range is reached sooner and maintained. The findings are like our previous randomised controlled trial, providing an alternative method for improving the risk-benefit of warfarin use in daily practice.

Pharmacogenetics in the Treatment of Cardiovascular Diseases and Its Current Progress Regarding Implementation in the Clinical Routine

There is a special interest in the implementation of pharmacogenetics in clinical practice, although there are some barriers that are preventing this integration. A large part of these pharmacogenetic tests are focused on drugs used in oncology and psychiatry fields and for antiviral drugs. However, the scientific evidence is also high for other drugs used in other medical areas, for example, in cardiology. In this article, we discuss the evidence and guidelines currently available on pharmacogenetics for clopidogrel, warfarin, acenocoumarol, and simvastatin and its implementation in daily clinical practice.

Warfarin Dose and CYP2C Gene Cluster: An African Ancestral-Specific Variant Is a Strong Predictor of Dose in Black South African Patients

Warfarin is a widely prescribed anticoagulant with a narrow therapeutic index. The rs12777823G>A single-nucleotide polymorphism (SNP) in the CYP2C gene cluster has been shown to influence optimal warfarin doses in African Americans. We report here effects of rs12777823G>A SNP on warfarin dose requirements in two South African population groups, black Africans (BA) and mixed ancestry (MA). A total of 425 participants on warfarin treatment were enrolled in the study. The age group of the studied population ranged between 44 and 66 years, with 69% females enrolled. Genetic characterization of the rs12777823G>A was done using the TaqMan SNP genotyping assay. To further compare effects of rs12777823G>A to those of other SNPs, VKORC1 g.-1639G>A and 4 SNPs in CYP2C9 gene (i.e., CYP2C9 c.430C>T, c.1075A>C, c.449G>A, and c.1003C>T) were analyzed. The rs12777823A variant allele frequencies were 0.28 and 0.25 in the BA and MA, respectively. The rs12777823A/A genotype was associated with significantly (p = 0.002) reduced mean warfarin dosage (27 ± 5.3 mg/week) compared with the G/G genotype (45 ± 16.1 mg/week) among BA, but not among the MA. The rs12777823G>A is located in a nongenomic region, suggesting that this SNP might be in linkage disequilibrium with another, likely causal SNP that is present in BA only. Given ongoing worldwide efforts to identify clinically relevant human genetic variation impacting on optimal warfarin dose selection, the African ancestry-specific genetic variant in the CYP2C cluster and others warrant further research and consideration in development of future warfarin dosing algorithms for precision medicine guidelines.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Warfarin: The End or the End of One Size Fits All Therapy?

Oral anticoagulants are required for both treatment and prophylaxis in many different diseases. Clinicians and patients now have a choice of oral anticoagulants, including the vitamin K antagonists (of which warfarin is the most widely used and is used as the exemplar in this paper), and direct oral anticoagulants (DOACs: dabigatran, apixaban, rivaroxaban, and edoxaban). This paper explores the recent advances and controversies in oral anticoagulation. While some commentators may favour a complete switchover to DOACs, this paper argues that warfarin still has a place in therapy, and a stratified approach that enables the correct choice of both drug and dose would improve both patient outcomes and affordability.

Pharmacogenetic studies with oral anticoagulants. Genome-wide association studies in vitamin K antagonist and direct oral anticoagulants

Oral anticoagulants (OAs) are the recommended drugs to prevent cardiovascular events and recurrence in patients with atrial fibrillation (AF) and cardioembolic stroke. We conducted a literature search to review the current state of OAs pharmacogenomics, focusing on Genome Wide Association Studies (GWAs) in patients treated with vitamin K antagonists (VKAs) and direct oral anticoagulants (DOACs).

VKAs: Warfarin, acenocoumarol, fluindione and phenprocoumon have long been used, but their interindividual variability and narrow therapeutic/safety ratio makes their dosage difficult. GWAs have been useful in finding genetic variants associated with VKAs response. The main genes involved in VKAs pharmacogenetics are: VKORC1, CYP2C19 and CYP4F2. Variants in these genes have been included in pharmacogenetic algorithms to predict the VKAs dose individually in each patient depending on their genotype and clinical variables.

DOACs: Dabigatran, apixaban, rivaroxaban and edoxaban have been approved for patients with AF. They have stable pharmacokinetics and do not require routine blood checks, thus avoiding most of the drawbacks of VKAs. Except for a GWAs performed in patients treated with dabigatran, there is no Genome Wide pharmacogenomics data for DOACs. Pharmacogenomics could be useful to predict the better clinical response and avoid adverse events in patients treated with anticoagulants, identifying the most appropriate anticoagulant drug for each patient. Current pharmacogenomics data show that the polymorphisms affecting VKAs or DOACs are different, concluding that personalized medicine based on pharmacogenomics could be possible. However, more studies are required to implement personalized medicine in clinical practice with OA and based on pharmacogenetics of DOACs.

Nuclear receptor gene polymorphisms and warfarin dose requirements in the Quebec Warfarin Cohort

Warfarin is primarily metabolized by cytochrome 2C9, encoded by gene CYP2C9. Here, we investigated whether variants in nuclear receptor genes which regulate the expression of CYP2C9 are associated with warfarin response. We used data from 906 warfarin users from the Quebec Warfarin Cohort (QWC) and tested the association of warfarin dose requirement at 3 months following the initiation of therapy in nine nuclear receptor genes: NR1I3, NR1I2, NR3C1, ESR1, GATA4, RXRA, VDR, CEBPA, and HNF4A. Three correlated SNPs in the VDR gene (rs4760658, rs11168292, and rs11168293) were associated with dose requirements of warfarin (P = 2.68 × 10^-5, P = 5.81 × 10^-4, and P = 5.94 × 10^-4, respectively). Required doses of warfarin were the highest for homozygotes of the minor allele at the VDR variants (P < 0.0026). Variants in the VDR gene were associated with the variability in response to warfarin, emphasizing the possible clinical relevance of nuclear receptor gene variants on the inter-individual variability in drug metabolism.

Pharmacogenetics of Adverse Drug Reactions

Adverse drug reactions (ADRs) are an important cause of morbidity and mortality. Genetic factors predispose to many ADRs, affecting susceptibility to both type A and type B reactions. The overall contribution of genetics will vary according to drug and ADR, and should be considered when attempting to predict and prevent ADRs. Genetic risk factors are considered in detail for a number of type A ADRs, especially those relating to warfarin and thiopurines, and type B ADRs affecting skin, the liver, and the heart. As the availability of whole genome sequencing increases, it is likely that prospective genotype for particular ADRs prior to drug prescription will become more common in the future. Current examples of genetic testing to prevent ADRs which have already been implemented and future prospects for developments in the field are discussed in detail.