Warfarin pharmacogenetics

Role of Clinical Pharmacology in Diversity and Inclusion in Global Drug Development: Current Practices and Industry Perspectives: White Paper

The 2022 United States Food and Drug Administration (US FDA) draft guidance on diversity plan (DP), which will be implemented through the Diversity Action Plans by December 2025, under the 21st Century Cures Act, marks a pivotal effort by the FDA to ensure that registrational studies adequately reflect the target patient populations based on diversity in demographics and baseline characteristics. This white paper represents the culminated efforts of the International Consortium of Quality and Innovation (IQ) Diversity and Inclusion (D&I) Working Group (WG) to assess the implementation of the draft FDA guidance by members of the IQ consortium in the discipline of clinical pharmacology (CP). This article describes current practices in the industry and emphasizes the tools and techniques of quantitative pharmacology that can be applied to support the inclusion of a diverse population during global drug development, to support diversity and inclusion of underrepresented patient populations, in multiregional clinical trials (MRCTs). It outlines strategic and technical recommendations to integrate demographics, including age, sex/gender, race/ethnicity, and comorbidities, in multiregional phase III registrational studies, through the application of quantitative pharmacology. Finally, this article discusses the challenges faced during global drug development, which may otherwise limit the enrollment of a broader, potentially diverse population in registrational trials. Based on the outcomes of the IQ survey that provided the current awareness of diversity planning, it is envisioned that in the future, industry efforts in the inclusion of previously underrepresented populations during global drug development will culminate in drug labels that apply to the intended patient populations at the time of new drug application or biologics license application rather than through post-marketing requirements.

Exploring the complex relationship between vitamin K, gut microbiota, and warfarin variability in cardiac surgery patients

BACKGROUND AND OBJECTIVES

Due to the high individual variability of anticoagulant warfarin, this study aimed to investigate the effects of vitamin K concentration and gut microbiota on individual variability of warfarin in 246 cardiac surgery patients.

METHODS

The pharmacokinetics and pharmacodynamics (PKPD) model predicted international normalized ratio (INR) and warfarin concentration. Serum and fecal samples were collected to detect warfarin and vitamin K [VK1 and menaquinone-4 (MK4)] concentrations and gut microbiota diversity, respectively. In addition, the patient's medical records were reviewed for demographic characteristics, drug history, and CYP2C9, VKORC1, and CYP4F2 genotypes.

RESULTS

The PKPD model predicted ideal values of 62.7% for S-warfarin, 70.4% for R-warfarin, and 76.4% for INR. The normal VK1 level was 1.34±1.12 nmol/ml (95% CI: 0.33-4.08 nmol/ml), and the normal MK4 level was 0.22±0.18 nmol/ml (95% CI: 0.07-0.63 nmol/ml). The MK4 to total vitamin K ratio was 16.5±9.8% (95% CI: 4.3-41.5%). The S-warfarin concentration of producing 50% of maximum anticoagulation and the half-life of prothrombin complex activity tended to increase with vitamin K. Further, Prevotella and Eubacterium of gut microbiota identified as the main bacteria associated with individual variability of warfarin. The results suggest that an increase in vitamin K concentration can decrease anticoagulation, and gut microbiota may influence warfarin anticoagulation through vitamin K2 synthesis.

CONCLUSION

This study highlights the importance of considering vitamin K concentration and gut microbiota when prescribing warfarin. The findings may have significant implications for the personalized use of warfarin. Further research is needed to understand better the role of vitamin K and gut microbiota in warfarin anticoagulation.

A Case of Unexplained Warfarin Resistance: A Case Report and Literature Review

Adjusting the exact warfarin dose has always been challenging since it has a narrow therapeutic window. Numerous factors, including poor drug compliance, drug-drug interactions, and malabsorption syndromes, affect the warfarin plasma concentration, leading to oversensitivity or resistance to warfarin. Patients who need more than 15 mg/d of warfarin for maintained anticoagulant effects are considered warfarin resistant. We describe a 62-year-old man referred to our center with bruising on his feet in June 2021. The patient had a history of valve replacement (mechanical prosthetic valves in 2013), hypothyroidism, and atrial fibrillation. He presented with warfarin resistance (first noticed in 2013) and did not reach the desired warfarin therapeutic effect despite receiving 60 mg of warfarin daily. Upon admission, the patient was on warfarin (100 mg/d) with an international normalized ratio (INR) of 1.5. He underwent laboratory and molecular genetic tests, which showed no mutation in the CYP2C9 and VKORC1, the genes associated with warfarin resistance. A stepwise diagnosis is required to identify the underlying cause. Assessing the patient's compliance, drug history, dietary habits, malabsorption diseases, and genetics may be necessary. We evaluated these possible reasons for resistance and found no correlation. The patient's warfarin intake was monitored closely to reach the INR therapeutic target of 3-3.5. He decided to leave the hospital with personal consent. He was discharged with a cardiologist referral and 24 warfarin tablets daily (120 mg/d) with an INR of 1.8. The patient was followed up 6 months and 2 years after discharge and was on the same daily dose of warfarin as at discharge, with no complications.

Association of Genetic Polymorphisms with Complications of Implanted LVAD Devices in Patients with Congestive Heart Failure: A Kazakhstani Study

The left ventricular assist device (LVAD) is one of the alternative treatments for heart failure (HF) patients. However, LVAD support is followed by thrombosis, and bleeding complications which are caused by high non-physiologic shear stress and antithrombotic/anticoagulant therapy. A high risk of complications occurs in the presence of the genotype polymorphisms which are involved in the coagulation system, hemostasis function and in the metabolism of the therapy. The aim of the study was to investigate the influence of single-nucleotide polymorphisms (SNP) in HF patients with LVAD complications. We analyzed 21 SNPs in HF patients (n = 98) with/without complications, and healthy controls (n = 95). SNPs rs9934438; rs9923231 in VKORC1, rs5918 in ITGB3 and rs2070959 in UGT1A6 demonstrated significant association with HF patients’ complications (OR (95% CI): 3.96 (1.42–11.02), p = 0.0057), (OR (95% CI): 3.55 (1.28–9.86), p = 0.011), (OR (95% CI): 5.37 (1.79–16.16), p = 0.0056) and OR (95% CI): 4.40 (1.06–18.20), p = 0.044]. Genotype polymorphisms could help to predict complications at pre- and post-LVAD implantation period, which will reduce mortality rate. Our research showed that patients can receive treatment with warfarin and aspirin with a personalized dosage and LVAD complications can be predicted by reference to their genotype polymorphisms in VKORC1, ITGB3 and UGT1A6 genes.

Premarket assessment of molecular alterations in drug targets: a case study of 2020 drug approvals

Aim: Molecular alterations in drug targets may result in differential drug activity. Therefore, the authors aimed to characterize how molecular alterations in drug targets were assessed during drug development. Materials & methods: The authors analyzed nonclinical and clinical study reports submitted to the US FDA for novel drugs approved in 2020 to determine if in vitro studies, animal models or clinical studies assessed molecular alterations in the drug target. Results & conclusion: Assessment of the impact of molecular alterations in drug targets on drug activity varies considerably depending on the type of assessment and therapeutic area. Premarket assessment of drug target molecular alterations is common in the oncology setting, less frequent in the genetic disease setting and rare for other diseases.

Warfarin Usage in Patients with Atrial Fibrillation Undergoing Hemodialysis in Indonesian Population

The data about the efficacy and safety of warfarin usage in atrial fibrillation (AF) in hemodialysis patients is still limited, especially in the Asia population. The population of this study was end-stage renal disease patients with AF who underwent hemodialysis. The design of the study was a retrospective observational cohort that collected the patient data from 2016 to 2019. The Cox regression model was applied to assess the effect of warfarin on the outcomes. We conducted a survival analysis by comparing Kaplan-Meier curves using the log-rank test. We also measured the time in therapeutic range as a quality indicator of warfarin usage. Among 444 hemodialysis patients, 126 patients with AF matched the inclusion criteria, 88 patients completely followed up. Half patients used warfarin. The mean age was 52.2 ± 12.97 years, the mean follow-up duration was 11 ± 10 months. We observed all-cause death in 86.4% of patients, ischemic stroke in 10.2%, and hemorrhagic stroke in 2.3% of patients. There were no significant differences in all-cause death, ischemic stroke, and hemorrhagic stroke. Warfarin use was not associated with a lower rate for death (HR 0.782; 95% CI, 0.494-1.237, P = 0.293) or ischemic stroke (HR 0.435; 95% CI, 0.103-1.846, P = 0.259) or hemorrhagic stroke (HR 0.564; 95% CI, 0.034-9.386, P = 0.689). None of the patients reach the time in the therapeutic range >65%. Our findings suggest that warfarin has no association with mortality, ischemic stroke, and hemorrhagic stroke events rate in atrial fibrillation patients who underwent hemodialysis in the Indonesian population.

Functional Assessment of 12 Rare Allelic CYP2C9 Variants Identified in a Population of 4773 Japanese Individuals

Cytochrome P450 2C9 (CYP2C9) is an important drug-metabolizing enzyme that contributes to the metabolism of approximately 15% of clinically used drugs, including warfarin, which is known for its narrow therapeutic window. Interindividual differences in CYP2C9 enzymatic activity caused by CYP2C9 genetic polymorphisms lead to inconsistent treatment responses in patients. Thus, in this study, we characterized the functional differences in CYP2C9 wild-type (CYP2C9.1), CYP2C9.2, CYP2C9.3, and 12 rare novel variants identified in 4773 Japanese individuals. These CYP2C9 variants were heterologously expressed in 293FT cells, and the kinetic parameters (K_m, k_cat, V_max, catalytic efficiency, and CL_int) of (S)-warfarin 7-hydroxylation and tolbutamide 4-hydroxylation were estimated. From this analysis, almost all novel CYP2C9 variants showed significantly reduced or null enzymatic activity compared with that of the CYP2C9 wild-type. A strong correlation was found in catalytic efficiencies between (S)-warfarin 7-hydroxylation and tolbutamide 4-hydroxylation among all studied CYP2C9 variants. The causes of the observed perturbation in enzyme activity were evaluated by three-dimensional structural modeling. Our findings could clarify a part of discrepancies among genotype–phenotype associations based on the novel CYP2C9 rare allelic variants and could, therefore, improve personalized medicine, including the selection of the appropriate warfarin dose.

Pd(II)-Catalyzed oxidative alkenylation of 4-hydroxycoumarin with maleimide via a C-H bond activation strategy

A Pd(ii)-catalyzed oxidative alkenylation of 4-hydroxycoumarins with maleimides for the synthesis of 4-hydroxy-3-maleimidecoumarins has been described. This methodology proceeds via C-H activation and C(sp2)-C(sp2) bond formation providing a series of alkenylated Heck-type products.

Mus musculus populations in Western Australia lack VKORC1 mutations conferring resistance to first generation anticoagulant rodenticides: Implications for conservation and biosecurity

Background

Humans routinely attempt to manage pest rodent populations with anticoagulant rodenticides (ARs). We require information on resistance to ARs within rodent populations to have effective eradication programs that minimise exposure in non-target species. Mutations to the VKORC1 gene have been shown to confer resistance in rodents with high proportions of resistance in mice found in all European populations tested. We screened mutations in Mus musculus within Western Australia, by sampling populations from the capital city (Perth) and a remote island (Browse Island). These are the first Australian mouse populations screened for resistance using this method. Additionally, the mitochondrial D-loop of house mice was sequenced to explore population genetic structure, identify the origin of Western Australian mice, and to elucidate whether resistance was linked to certain haplotypes.

Results

No resistance-related VKORC1 mutations were detected in either house mouse population. A genetic introgression in the intronic sequence of the VKORC1 gene of Browse Island house mouse was detected which is thought to have originated through hybridisation with the Algerian mouse (Mus spretus). Analysis of the mitochondrial D-loop reported two haplotypes in the house mouse population of Perth, and two haplotypes in the population of Browse Island.

Conclusions

Both house mouse populations exhibited no genetic resistance to ARs, in spite of free use of ARs in Western Australia. Therefore weaker anticoagulant rodenticides can be employed in pest control and eradication attempts, which will result in reduced negative impacts on non-target species. Biosecurity measures must be in place to avoid introduction of resistant house mice, and new house mouse subspecies to Western Australia.

Prediction of the impact of CYP2C9 and VKORC1 genotypes on warfarin-sorafenib interactions in whites and Asians

Aim: To predict the impact of the different CYP2C9 and VKORC1 genotypes on warfarin-sorafenib interactions in whites and Asians. Materials & methods: The influences of the CYP2C9*1/*3 and VKORC1 -1639 A/A genotypes on increases in anticoagulation responses (international normalized ratio [INR]) in the presence of sorafenib were predicted using the population pharmacokinetic/pharmacodynamic (PK/PD) model in whites and Asians. Results: INRs were predicted to be 2.0-2.1- versus 1.8-1.9-times higher in the presence of sorafenib in the CYP2C9 (*1/*1 vs *1/*3) groups than those for warfarin alone in both whites and Asians. INRs were also predicted to be 2.1-2.2- versus 1.9-2.1-times higher in the VKORC1 (GG or GA vs AA) groups. Conclusion: Warfarin-sorafenib interactions might be similar irrespective of CYP2C9 and VKORC1 genotypes or ethnicity.

Analysis of Factors That Interrupt With INR Control in the First Anticoagulation Clinic Monitoring Jordanian Patients

Multiple factors such as vitamin K consumption, drug interactions, herbs interactions, disease states, and alcohol intake affect international normalized ratio (INR) values and thus warfarin dosing. These variables have been described in general and for all patients in the literature. In contrast, the factors that affect INR control in a specific population are rarely studied. Being aware of these factors contributes a lot in maintaining an INR control and avoiding the supratherapeutic or subtherapeutic anticoagulation and the associated risks of hemorrhage or thromboembolism. The aim of this study is to recognize the specific population factors in Jordanian patients that interrupt INR control. Such recognition provides clinical pharmacists managing the anti-coagulation clinic (ACC) with necessary tools and predictors of dose adjustment, nontarget INR handling, and points to add on to the educational session. A total of 2788 patients were referred to the first clinical pharmacists managed ACC at Queen Alia Heart Institute—the only official referral hospital for cardiac patients in Jordan—for education and monitoring between November 1, 2013, and November 1, 2016. We evaluated specific population factors that interrupt INR control using a pretested, structured clinical data collection form. The patients were followed up regularly for achieving target INR (TINR). For patients who were not achieving TINR, the possible cause was examined thoroughly by reviewing the patient’s medical file for recent medication intake, comorbidities, and laboratory results. Then the patients or their caregiver were asked direct questions regarding their diet, food supplements, cigarette smoking, shisha smoking, alcohol intake, herbs, and complementary medicine use and compliance, in addition to performing pharmacogenetic testing (polymorphisms of vitamin K–epoxide reductase complex [VKORC1] and cytochrome P450 2C9 [CYP2C9] genes) in special cases. For a total of 2788 patients, 89 488 INR values were included in the study. Of all, 20 365 (22.8%) were non-TINR values, 13 145 (14%) were subtherapeutic, and 7220 (8.1%) were supratherapeutic. All patients included in the study had a non-TINR at least 3 times (n = 65, 2.3%) and as frequent as 50 times (n = 21, 0.8%) during the study period. Non-TINR values ranged from 1 to 11. Serious side effects reported in 7 patients with uncontrolled INR, 6 were bleeding, which required hospitalization (2 upper gastrointestinal [GI] bleeding, 3 nasal bleeding, and 1 eye bleeding), 1 was cerebrovascular accident (CVA thrombolytic). Factors that interrupted INR control in our population, arranged in descending sequence, were concurrent medication use 46.9% (mainly Salicylates and Amiodarone), smoking cigarettes and shisha 17% (represented the most frequent single factor that caused non-TINR in the present study), a nonbalanced dietary vitamin K intake 16.88% caused changes in INR (lower) was related to an increase in the intake of vitamin K-rich food, were noticed to be much more in the spring season in Jordan (end of March and April mainly), herbal supplements 15.02%; Hawthorn (Crataegus, الزعرور) is an herb that lives widely in Jordan, and shockingly we found that it is used very commonly in our ACC patients and corresponded to an elevated INR <8 in 11 patients, and serious bleeding events that required hospitalization in 2 cases), noncompliance 1.49%, comorbid diseases 1%, malabsorption 0.53%, alcohol intake 0.39%, and VKORC1 A/G and CYP2C9 *1*1 genotype 0.15%. The analysis of factors that interrupted with INR control in our patients were both predicted and distinctive; most of these factors were reported previously by other researchers. On the other hand, many of the previously reported factors were not frequently detected in our patients, and the frequency of each of the realized factors was contributed differently to non-TINR in our population. Alarming factors causing non-TINR detected in our study include smoking both cigarettes and shisha, herbal use (Hawthorn and Ginseng), increased intake of vitamin K rich food in the spring season, and concurrent medication use (Salicylates, Amiodarone, Ciprofloxacin, nonsteroidal anti-inflammatory drugs [NSAIDS], Azithromycin, Clarithromycin: although the use of these drugs is mandatory sometimes, it can be replaced by an alternative, eg, antibiotics or monitored closely together with warfarin).

Racial, Ethnic, and Socioeconomic Inequities in the Prescription of Direct Oral Anticoagulants in Patients With Venous Thromboembolism in the United States

BACKGROUND

Beginning in 2012, direct oral anticoagulants (DOACs) were approved for treatment and prevention of venous thromboembolism. Prior investigations have demonstrated slow rates of adoption of novel therapeutics for black patients. We assessed the association of racial/ethnic and socioeconomic factors with DOAC use among commercially insured venous thromboembolism patients.

METHODS AND RESULTS

We performed a retrospective cohort analysis of adult patients with an incident diagnosis of venous thromboembolism between January 2010 and December 2016 using OptumInsight's Clinformatics Data Mart. We identified the first filled oral anticoagulant prescription within 30 days of discharge of an inpatient admission. We performed a multivariable logistic regression, adjusting for age, sex, race/ethnicity, region, zip code-linked household income, and clinical covariates to identify factors associated with the use of DOACs. Race and ethnicity were determined in this database through a combination of public records, self-report, and proprietary ethnicity code tables. There were 14 140 patients included in the analysis. Treatment with DOACs increased from <0.1% in 2010 to 65.6% in 2016. In multivariable analyses, black patients were less likely to receive a DOAC compared with white patients (odds ratio, 0.86; 95% CI, 0.77-0.97; P=0.02). There were no differences in DOAC utilization among Asian (odds ratio, 1.06; 95% CI, 0.75-1.49; P=0.74) or Hispanic patients (odds ratio, 1.04; 95% CI, 0.88-1.22; P=0.66) compared with whites. Patients with a household income over $100 000 per year were more likely to receive DOAC therapy compared with patients with a household income of <$40 000 per year (odds ratio, 1.50; 95% CI, 1.33-1.69; P<0.0001).

CONCLUSIONS

Although DOAC adoption has increased steadily since 2012, among a commercially insured population, black race and low household income were associated with lower use of DOACs for incident venous thromboembolism despite controlling for other clinical and socioeconomic factors. These findings suggest the possibility of both racial and socioeconomic inequity in access to this novel pharmacotherapy.

Plasma Response to Deuterium-Labeled Vitamin K Intake Varies by TG Response, but Not Age or Vitamin K Status, in Older and Younger Adults

Background

Phylloquinone is the primary form of vitamin K in the diet and circulation. Large intra- and interindividual variances in circulating phylloquinone have been partially attributed to age. However, little is known about the nondietary factors that influence phylloquinone absorption and metabolism. Similarly, it is not known if phylloquinone absorption is altered by the individual's existing vitamin K status.

Objective

The purpose of this secondary substudy was to compare plasma response with deuterium-labeled phylloquinone intake in older and younger adults after dietary phylloquinone depletion and repletion.

Methods

Forty-two older [mean ± SD age: 67.2 ± 8.0 y; body mass index (BMI; in kg/m2): 25.4 ± 4.6; n = 12 men, 9 women] and younger (mean ± SEM age: 31.8 ± 6.6 y; BMI: 25.5 ± 3.3; n = 9 men, 12 women) adults were maintained on sequential 28-d phylloquinone depletion (∼10 µg phylloquinone/d) and 28-d phylloquinone repletion (∼500 µg phylloquinone/d) diets. On the 23rd d of each diet phase, participants consumed deuterated phylloquinone-rich collard greens (2H-phylloquinone). Plasma and urinary outcome measures over 72 h were compared by age group, sex, and dietary phase via 2-factor repeated-measures ANOVA.

Results

The plasma 2H-phylloquinone area under the curve (AUC) did not differ in response to phylloquinone depletion or repletion, but was 34% higher in older than in younger adults (P = 0.02). However, plasma 2H-phylloquinone AUC was highly correlated with the serum triglyceride (TG) AUC (r2 = 0.45). After adjustment for serum TG response, the age effect on the plasma 2H-phylloquinone AUC was no longer significant.

Conclusions

Plasma 2H-phylloquinone response did not differ between phylloquinone depletion and repletion in older and younger adults. The age effect observed was explained by the serum TG response and was completely attenuated after adjustment. Plasma response to phylloquinone intake, therefore, seems to be a predominantly lipid-driven effect and not dependent on existing vitamin K status. More research is required to differentiate the effect of endogenous compared with exogenous lipids on phylloquinone absorption. This trial was registered at clinicaltrials.gov as NCT00336232.

Creating and validating a warfarin pharmacogenetic dosing algorithm for Colombian patients

Purpose

Warfarin is an oral anticoagulant associated with adverse reaction to drugs due to wide inter- and intra-individual dosage variability. Warfarin dosage has been related to non-genetic and genetic factors. CYP2C9 and VKORC1 gene polymorphisms affect warfarin metabolism and dosage. Due to the central role of populations’ ethnical and genetic origin on warfarin dosage variability, novel algorithms for Latin American subgroups are necessary to establish safe anticoagulation therapy.

Patients and methods

We genotyped CYP2C9*2 (c.430C > T), CYP2C9*3 (c.1075A > C), CYP4F2 (c.1297G > A), and VKORC1 (−1639 G > A) polymorphisms in 152 Colombian patients who received warfarin. We evaluated the impact on the variability of patients’ warfarin dose requirements. Multiple linear regression analysis, using genetic and non-genetic variables, was used for creating an algorithm for optimal warfarin maintenance dose.

Results

Median weekly prescribed warfarin dosage was significantly lower in patients having the VKORC1-1639 AA genotype and poor CYP2C9*2/*2,*2/*3 metabolizers than their wild-type counterparts. We found a 2.3-fold increase in mean dose for normal sensitivity patients (wild-type VKORC1/CYP2C9 genotypes) compared to the other groups (moderate and high sensitivity); 31.5% of the patients in our study group had warfarin sensitivity-related genotypes. The estimated regression equation accounted for 44.4% of overall variability in regard to warfarin maintenance dose. The algorithm was validated, giving 45.9% correlation (R²=0.459).

Conclusion

Our results describe and validate the first algorithm for predicting warfarin maintenance in a Colombian mestizo population and have contributed toward the understanding of pharmacogenetics in a Latin American population subgroup.

Development and application of a rapid and sensitive genotyping method for pharmacogene variants using the single-stranded tag hybridization chromatographic printed-array strip (STH-PAS)

Genetic polymorphisms contribute to inter-individual variability in the metabolism of multiple clinical drugs, including warfarin, thiopurines, primaquine, and aminoglycosides. A rapid and sensitive clinical assessment of various genome biomarkers is, therefore, required to predict the individual responsiveness of each patient to these drugs. In this study, we developed a novel genotyping method for the detection of nine pharmacogene variants that are important in the prediction of drug efficiency and toxicity. This genotyping method uses competitive allele-specific PCR and a single-stranded tag hybridization chromatographic printed-array strip (STH-PAS) that can unambiguously determine the presence or absence of the gene variant by displaying visible blue lines on the chromatographic printed-array strip. Notably, the results of our STH-PAS method were in 100% agreement with those obtained using standard Sanger sequencing and KASP assay genotyping methods for CYP4F2 gene deletion. Moreover, the results were obtained within 90 min, including the PCR amplification and signal detection processes. The sensitive and rapid nature of this novel method make it ideal for clinical genetic testing to predict drug efficacy and toxicity, and in doing so will aid in the development of individualized medicine and better patient care.

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

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

A New Approach towards Minimizing the Risk of Misdosing Warfarin Initiation Doses

It is a challenge to be able to prescribe the optimal initial dose of warfarin. There have been many studies focused on an efficient strategy to determine the optimal initial dose. Numerous clinical, genetic, and environmental factors affect the warfarin dose response. In practice, it is common that the initial warfarin dose is substantially different from the stable maintenance dose, which may increase the risk of bleeding or thrombosis prior to achieving the stable maintenance dose. In order to minimize the risk of misdosing, despite popular warfarin dose prediction models in the literature which create dose predictions solely based on patients' attributes, we have taken physicians' opinions towards the initial dose into consideration. The initial doses selected by clinicians, along with other standard clinical factors, are used to determine an estimate of the difference between the initial dose and estimated maintenance dose using shrinkage methods. The selected shrinkage method was LASSO (Least Absolute Shrinkage and Selection Operator). The estimated maintenance dose was more accurate than the original initial dose, the dose predicted by a linear model without involving the clinicians initial dose, and the values predicted by the most commonly used model in the literature, the Gage clinical model.

The pharmacoepigenomics informatics pipeline defines a pathway of novel and known warfarin pharmacogenomics variants

AIM

'Pharmacoepigenomics' methods informed by omics datasets and pre-existing knowledge have yielded discoveries in neuropsychiatric pharmacogenomics. Now we evaluate the generality of these methods by discovering an extended warfarin pharmacogenomics pathway.

MATERIALS & METHODS

We developed the pharmacoepigenomics informatics pipeline, a scalable multi-omics variant screening pipeline for pharmacogenomics, and conducted an experiment in the genomics of warfarin.

RESULTS

We discovered known and novel pharmacogenomics variants and genes, both coding and regulatory, for warfarin response, including adverse events. Such genes and variants cluster in a warfarin response pathway consolidating known and novel warfarin response variants and genes.

CONCLUSION

These results can inform a new warfarin test. The pharmacoepigenomics informatics pipeline may be able to discover new pharmacogenomics markers in other drug-disease systems.

The Rate of Epistaxis Incidence in New-Generation Anticoagulants and Perioperative Approach in Otorhinolaryngological Practices

Nose bleeding is a common situation seen in otorhinolaryngological practices. One of the greatest risk factors in nose bleeding is the use of anticoagulant medicine. With the medicine developed in recent years, the risk of nose bleeding due to the frequent use of anticoagulant and antiagregant is gradually increasing.The purpose of this study is to determine the effects of especially new-generation anticoagulants on nose bleeding. In addition, the use and complications of new-generation anticoagulants and antiagregants have been compiled in light of information obtained from the literature.Three hundred forty patients whose follow-up is conducted by the cardiology department and who use oral antithrombocytic medicine have been included in the study. It has been determined that 15% of these patients use new-generation oral anticoagulants (Rivaroksaban, apiksaban, dabigatran, danaparoid) and the other patients are treated with conventional antithrombocytic treatment (Aspirin, Warfarin, Enoksaparin sodium). The rate of nose bleeding in patients who use classical anticoagulants has been observed to be 28%. In 30 of these patients who had nose bleeding, while cauterization and buffering by otorhinolaryngology specialists, major intervention has not been necessary for any of the patients. While bleeding has been observed in 26% of the patients who use new-generation anticoagulants, bleeding that required operational intervention has taken place in 2 patients. Bleedings have been stopped surgically through a large number of cauterization and buffering.While the new-generation anticoagulants cause lower rate of bleeding, it has been observed that controlling these bleedings is more difficult.

Pharmacogenetics: An Important Part of Drug Development with A Focus on Its Application

Since the human genome project in 2003, the view of personalized medicine to improve diagnosis and cure diseases at the molecular level became more real. Sequencing the human genome brought some benefits in medicine such as early detection of diseases with a genetic predisposition, treating patients with rare diseases, the design of gene therapy and the understanding of pharmacogenetics in the metabolism of drugs. This review explains the concepts of pharmacogenetics, polymorphisms, mutations, variations, and alleles, and how this information has helped us better understand the metabolism of drugs. Multiple resources are presented to promote reducing the gap between scientists, physicians, and patients in understanding the use and benefits of pharmacogenetics. Some of the most common clinical examples of genetic variants and how pharmacogenetics was used to determine treatment options for patients having these variants were discussed. Finally, we evaluated some of the challenges of implementing pharmacogenetics in a clinical setting and proposed actions to be taken to make pharmacogenetics a standard diagnostic tool in personalized medicine.

Warfarin Pharmacogenomics in Diverse Populations

Genotype-guided warfarin dosing algorithms are a rational approach to optimize warfarin dosing and potentially reduce adverse drug events. Diverse populations, such as African Americans and Latinos, have greater variability in warfarin dose requirements and are at greater risk for experiencing warfarin-related adverse events compared with individuals of European ancestry. Although these data suggest that patients of diverse populations may benefit from improved warfarin dose estimation, the vast majority of literature on genotype-guided warfarin dosing, including data from prospective randomized trials, is in populations of European ancestry. Despite differing frequencies of variants by race/ethnicity, most evidence in diverse populations evaluates variants that are most common in populations of European ancestry. Algorithms that do not include variants important across race/ethnic groups are unlikely to benefit diverse populations. In some race/ethnic groups, development of race-specific or admixture-based algorithms may facilitate improved genotype-guided warfarin dosing algorithms above and beyond that seen in individuals of European ancestry. These observations should be considered in the interpretation of literature evaluating the clinical utility of genotype-guided warfarin dosing. Careful consideration of race/ethnicity and additional evidence focused on improving warfarin dosing algorithms across race/ethnic groups will be necessary for successful clinical implementation of warfarin pharmacogenomics. The evidence for warfarin pharmacogenomics has a broad significance for pharmacogenomic testing, emphasizing the consideration of race/ethnicity in discovery of gene-drug pairs and development of clinical recommendations for pharmacogenetic testing.

Genetics and clinical response to warfarin and edoxaban in patients with venous thromboembolism

OBJECTIVE

The aim of this study was to investigate whether genetic variants can identify patients with venous thromboembolism (VTE) at an increased risk of bleeding with warfarin.

METHODS

Hokusai-venous thromboembolism (Hokusai VTE), a randomised, multinational, double-blind, non-inferiority trial, evaluated the safety and efficacy of edoxaban versus warfarin in patients with VTE initially treated with heparin. In this subanalysis of Hokusai VTE, patients genotyped for variants in CYP2C9 and VKORC1 genes were divided into three warfarin sensitivity types (normal, sensitive and highly sensitive) based on their genotypes. An exploratory analysis was also conducted comparing normal responders to pooled sensitive responders (ie, sensitive and highly sensitive responders).

RESULTS

The analysis included 47.7% (3956/8292) of the patients in Hokusai VTE. Among 1978 patients randomised to warfarin, 63.0% (1247) were normal responders, 34.1% (675) were sensitive responders and 2.8% (56) were highly sensitive responders. Compared with normal responders, sensitive and highly sensitive responders had heparin therapy discontinued earlier (p<0.001), had a decreased final weekly warfarin dose (p<0.001), spent more time overanticoagulated (p<0.001) and had an increased bleeding risk with warfarin (sensitive responders HR 1.38 [95% CI 1.11 to 1.71], p=0.0035; highly sensitive responders 1.79 [1.09 to 2.99]; p=0.0252).

CONCLUSION

In this study, CYP2C9 and VKORC1 genotypes identified patients with VTE at increased bleeding risk with warfarin.

TRIAL REGISTRATION NUMBER

NCT00986154.

Clinical effect of CYP2C9*5/*6 genotype on a patient's warfarin dose requirement

We describe a 38-year-old African-American female treated with warfarin for acute bilateral pulmonary emboli who is a carrier of two rare CYP2C9 variant alleles, *5 and *6, along with VKORC1 -1639GG and CYP4F2 433Val/Val genotypes. Warfarin was dosed according to the hospital's Personalized Medicine Program recommendations of 5-6 mg/day for the first 6 days, and reduced to 2.5 mg/day starting on day 8 and continued for the following 3 weeks. This case sheds further light on the cumulative clinical impact of the CYP2C9 variant alleles, *5 and *6, on warfarin dose requirements and practical considerations for warfarin genotyping in a racially and ethnically diverse population.

Impact of Body Mass Index and Genetics on Warfarin Major Bleeding Outcomes in a Community Setting

BACKGROUND

Several studies have demonstrated an association between body mass index (BMI) and warfarin therapeutic dose, but none evaluated the association of BMI with the clinically important outcome of major bleeding in a community setting. To address this evidence gap, we conducted a case-control study to evaluate the association between BMI and major bleeding risk among patients receiving warfarin.

METHODS

We used a case-control study design to evaluate the association between obesity (BMI >30.0 kg/m²) and major bleeding risk among 265 cases and 305 controls receiving warfarin at Group Health, an integrated healthcare system in Washington State. Multivariate logistic regression was used to adjust for potential confounders derived from health plan records and a self-report survey. In exploratory analyses we evaluated the interaction between genetic variants potentially associated with warfarin bleeding (CYP2C9, VKORC1, and CYP4F2) and obesity on the risk of major bleeding.

RESULTS

Overall, the sample was 55% male, 94% Caucasian, and mean age was 70 years. Cases and controls had an average of 3.4 and 3.7 years of warfarin use, respectively. Obese patients had significantly lower major bleeding risk relative to non-obese patients (odds ratio [OR] 0.60, 95% confidence interval [CI] 0.39-0.92). The OR was 0.56 (95% CI 0.35-0.90) in patients with ≥1 year of warfarin use, and 0.78 (95% CI 0.40-1.54) in patients with <1 year of warfarin use. An exploratory analysis indicated a statistically significant interaction between CYP4F2*3 genetic status and obesity (P = .049), suggesting a protective effect of obesity on the risk of major bleeding among those wild type for CYP4F2*3, but not among variants.

CONCLUSIONS

Our findings suggest that BMI is an important clinical factor in assessing and managing warfarin therapy. Future studies should confirm the major bleeding associations, including the interaction between obesity and CYP4F2*3 status identified in this study, and evaluate potential mechanisms.

Theory-based pharmacokinetics and pharmacodynamics of S- and R-warfarin and effects on international normalized ratio: influence of body size, composition and genotype in cardiac surgery patients

AIMS

The aims of this study are to apply a theory-based mechanistic model to describe the pharmacokinetics (PK) and pharmacodynamics (PD) of S- and R-warfarin.

METHODS

Clinical data were obtained from 264 patients. Total concentrations for S- and R-warfarin were measured by ultra-high performance liquid tandem mass spectrometry. Genotypes were measured using pyrosequencing. A sequential population PK parameter with data method was used to describe the international normalized ratio (INR) time course. Data were analyzed with NONMEM. Model evaluation was based on parameter plausibility and prediction-corrected visual predictive checks.

RESULTS

Warfarin PK was described using a one-compartment model. CYP2C9 *1/*3 genotype had reduced clearance for S-warfarin, but increased clearance for R-warfarin. The in vitro parameters for the relationship between prothrombin complex activity (PCA) and INR were markedly different (A = 0.560, B = 0.386) from the theory-based values (A = 1, B = 0). There was a small difference between healthy subjects and patients. A sigmoid E_max PD model inhibiting PCA synthesis as a function of S-warfarin concentration predicted INR. Small R-warfarin effects was described by competitive antagonism of S-warfarin inhibition. Patients with VKORC1 AA and CYP4F2 CC or CT genotypes had lower C50 for S-warfarin.

CONCLUSION

A theory-based PKPD model describes warfarin concentrations and clinical response. Expected PK and PD genotype effects were confirmed. The role of predicted fat free mass with theory-based allometric scaling of PK parameters was identified. R-warfarin had a minor effect compared with S-warfarin on PCA synthesis. INR is predictable from 1/PCA in vivo.

Comparison of Dabigatran vs. Warfarin in Acute Vnous Thromboemboly: Systematic Review

Acute Venous Thromboembolism (VTE) is a common disease associated with the significant morbidity and mortality. We reviewed clinical outcomes systematically with Dabigatran as a direct oral anticoagulants (DOAC) for treatment of acute VTE. We used Ovide, PubMed, Cochrane (CENTRAL), EMBASE, Scopus, Science Direct, LILAC(for article written not English) and also Iranian database; Magiran, Isc, Iran Medex, Iran DOC, Doaj up to May 2014 to identify randomized clinical trials of Dabigatran compared with conventional treatment for VTE. Two investigators extracted data independently. Number of 5107 patients including two trails were selected. The risk of recurrent VTE was similar with the Dabigatran and standard treatment (Hazard Ratio, 95% confidence interval 1.09 (0.76-1.57). Dabigatran reduced the risk of minor bleeding in comparison with standard treatment; Warfarin (0.62) (0.50-0.76). Finally-in minor bleeding-the Dabigatran seemed as effective as, and probably safer than standard treatment of acute VTE. But in some aspects such as adherence to treatment, pregnant patient, impact on quality of life, new researches are needed to be clarified.

The potential drug-drug interaction between proton pump inhibitors and warfarin

BACKGROUND

Proton pump inhibitors (PPIs) have been suggested to increase the effect of warfarin, and clinical guidelines recommend careful monitoring of international normalized ratio (INR) when initiating PPI among warfarin users. However, this drug-drug interaction is sparsely investigated in a clinical setting. The aim was to assess whether initiation of PPI treatment among users of warfarin leads to increased INR values.

METHODS

The study was an observational self-controlled study from 1998 to 2012 leveraging data on INR measurements on patients treated with warfarin from primary care and outpatient clinics and their use of prescription drugs. Data were analyzed in 2015. We assessed INR, warfarin dose, and dose/INR ratio before and after initiating PPI treatment using the paired student's t-test.

RESULTS

We identified 305 warfarin users initiating treatment with PPIs. The median age was 71 years (interquartile range 63-78 years), and 64% were men. The mean INR in the 70 days prior to PPI initiation was 2.6 (95%CI 2.5-2.8) and 2.6 (95%CI 2.5-2.7) in the period 1-3 weeks after PPI initiation (p = 0.67). Further, neither mean warfarin dose nor the dose/INR ratios were significantly different before and after PPI initiation. Sensitivity analyses revealed no differences among individual PPIs.

CONCLUSIONS

We found no evidence of a clinically meaningful drug-drug interaction between PPIs and warfarin in a Northern European patient population of unselected patients from an everyday outpatient and primary care clinical setting. Thus, we do not support the recommendation to "cautiously monitor" users of warfarin initiating PPI treatment.

Pharmacokinetic and pharmacodynamic drug interactions with ethanol (alcohol)

Ethanol (alcohol) is one of the most widely used legal drugs in the world. Ethanol is metabolized by alcohol dehydrogenase (ADH) and the cytochrome P450 (CYP) 2E1 drug-metabolizing enzyme that is also responsible for the biotransformation of xenobiotics and fatty acids. Drugs that inhibit ADH or CYP2E1 are the most likely theoretical compounds that would lead to a clinically significant pharmacokinetic interaction with ethanol, which include only a limited number of drugs. Acute ethanol primarily alters the pharmacokinetics of other drugs by changing the rate and extent of absorption, with more limited effects on clearance. Both acute and chronic ethanol use can cause transient changes to many physiologic responses in different organ systems such as hypotension and impairment of motor and cognitive functions, resulting in both pharmacokinetic and pharmacodynamic interactions. Evaluating drug interactions with long-term use of ethanol is uniquely challenging. Specifically, it is difficult to distinguish between the effects of long-term ethanol use on liver pathology and chronic malnutrition. Ethanol-induced liver disease results in decreased activity of hepatic metabolic enzymes and changes in protein binding. Clinical studies that include patients with chronic alcohol use may be evaluating the effects of mild cirrhosis on liver metabolism, and not just ethanol itself. The definition of chronic alcohol use is very inconsistent, which greatly affects the quality of the data and clinical application of the results. Our study of the literature has shown that a significantly higher volume of clinical studies have focused on the pharmacokinetic interactions of ethanol and other drugs. The data on pharmacodynamic interactions are more limited and future research addressing pharmacodynamic interactions with ethanol, especially regarding the non-central nervous system effects, is much needed.

Revisiting Warfarin Dosing Using Machine Learning Techniques

Determining the appropriate dosage of warfarin is an important yet challenging task. Several prediction models have been proposed to estimate a therapeutic dose for patients. The models are either clinical models which contain clinical and demographic variables or pharmacogenetic models which additionally contain the genetic variables. In this paper, a new methodology for warfarin dosing is proposed. The patients are initially classified into two classes. The first class contains patients who require doses of >30 mg/wk and the second class contains patients who require doses of ≤30 mg/wk. This phase is performed using relevance vector machines. In the second phase, the optimal dose for each patient is predicted by two clinical regression models that are customized for each class of patients. The prediction accuracy of the model was 11.6 in terms of root mean squared error (RMSE) and 8.4 in terms of mean absolute error (MAE). This was 15% and 5% lower than IWPC and Gage models (which are the most widely used models in practice), respectively, in terms of RMSE. In addition, the proposed model was compared with fixed-dose approach of 35 mg/wk, and the model proposed by Sharabiani et al. and its outperformance were proved in terms of both MAE and RMSE.

Effects of Pregnane X Receptor Genetic Polymorphisms on Stable Warfarin Doses

Objective:

Pregnane X receptor (PXR) is a transcriptional regulator of many drug-metabolizing enzymes including cytochrome P450 (CYP) 2C9. The objective of this study was to assess the possible association between PXR single-nucleotide polymorphisms (SNPs) and stable warfarin doses.

Methods:

A total of 201 patients with stable warfarin doses from the EwhA-Severance Treatment (EAST) Group of Warfarin were included in this study. The influence of genetic polymorphisms on stable warfarin doses was investigated by genotyping 11 SNPs, that is, vitamin K epoxide reductase complex 1 (VKORC1) rs9934438, CYP2C9 rs1057910, CYP4F2 rs2108622, constitutive androstane receptor (CAR) rs2501873, hepatocyte nuclear factor 4α (HNF4α) rs3212198, and PXR (rs3814055, rs1403526, rs3732357, rs3732360, rs2276707 and rs2472682). Subgroup analysis was conducted on CYP2C9 wild-type homozygote allele (AA) carriers.

Results:

One PXR SNP of rs2472682 (A>C) exhibited significant association with stable warfarin doses in study population and the subgroup; variant homozygote carriers required significantly lower daily doses of warfarin than those carrying wild allele by about 0.8 mg. Approximate 43.7% of overall interindividual variability in warfarin dose requirement was explained by multivariate regression model. VKORC1, CYP2C9, age, CYP4F2, PXR rs2472682, and CAR/HNF4α rs2501873/rs3212198 accounted for 29.6%, 5.9%, 3.7%, 2.3%, 1.3%, and 0.9% of the variability, respectively. PXR SNP of rs2472682 remained a significant factor in CYP2C9 wild-type homozygote carriers based on univariate and multivariate analyses. The combination of CAR/HNF4α/PXR SNPs of rs2501873/rs3212198/rs2472682 showed about 1 mg dose difference between grouped genotypes in study population and subgroup.

Conclusion:

Our results revealed that PXR could be a determinant of stable warfarin doses.

Warfarin overdose: a 25-year experience

Warfarin, a vitamin K antagonist, is widely used for the prophylaxis and treatment of thromboembolic disease. While guidelines exist for management of a supratherapeutic international normalized ratio following therapeutic warfarin use, these guidelines are not designed for management of the acute warfarin overdose. There is a paucity of literature describing the latter. The primary objective of this manuscript is to characterize the coagulopathy and describe the bleeding events that occur after a warfarin overdose. A secondary goal is to describe the amount of vitamin K administered to patients presenting with warfarin overdoses. A retrospective chart review of patients admitted with an acute warfarin overdose at two tertiary care medical centers in the USA was conducted. Clinical characteristics were abstracted, and bleeding categories (major, minor, trivial) were defined a priori. Twenty-three patients were admitted during the time period; males accounted for 15/23 (62.5 %) subjects. The median (interquartile range (IQR)) age was 43 (32-48.5) years. Seventeen subjects received vitamin K, with a median (IQR) dose of 15 (10-50) mg. The maximal total amount of vitamin K administered to a single patient during the index hospitalization was 110 mg. Three bleeding events occurred; one classified as major, and two as minor. All patients made a full recovery. In this case series of acute warfarin overdose, nearly all patients developed a coagulopathy, and nearly three-quarters of patients received vitamin K. Bleeding events occurred in a minority of patients.

The Optimal Treatment For Atrial Fibrillation In Less Developed Countries

Atrial fibrillation (AF) is the most common arrhythmia and is a major cardiovascular challenge due to its close association with increased morbidity and mortality. Although the incidence and prevalence of AF is slightly lower in developing countries than in developed countries, the AF-associated risk of stroke is similar. Treatment of AF is far from satisfactory in developing countries, which may be due to limited health-care resources and social and racial characteristics that differ from Western populations. Chronic rate control is still the main treatment strategy of persistent AF because anti-arrhythmic drugs have only a modest long-term effect on maintenance of sinus rhythm, and no superior impact in terms of cardiovascular outcomes. With the development of ablation techniques and strategies, more AF patients received catheter ablation, although the benefit, complications, and high recurrence rate associated with AF ablation remain under investigation. Improvement in antithrombotic therapy of AF has been observed, although still fewer patients receive oral anticoagulants in developing countries than in Western countries. Novel treatment for the prevention of thromboembolism, such as new oral anticoagulants with different mechanisms of action or the percutaneous transcatheter closure of the left atrial appendage, has recently been introduced in developing countries as an alternative option for the prevention of AF-associated strokes. More data are needed regarding upstream therapy.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

CYP4F2 1347 G > A & GGCX 12970 C > G polymorphisms: frequency in north Indians & their effect on dosing of acenocoumarol oral anticoagulant

BACKGROUND & OBJECTIVES

CYP4F2 and γ-glutamyl carboxylase (GGCX) have small but significant roles in the maintenance dose of coumarinic oral anticoagulants (COAs). CYP4F2 1347 G > A and GGCX 12970 C > G polymorphisms have been used in the pharmacogenetic dosing algorithms of warfarin for Caucasians and Chinese populations. India has a large population with multiple ethnic groups but there are no reports about the frequencies of these polymorphisms in north Indians. In the present study, we aimed to find out the allelic frequencies of CYP4F2 1347 G > A and GGCX 12970 C > G polymorphisms in a north Indian population and relate these to daily maintenance drug dose requirements of COA.

METHODS

CYP4F2 1347 G > A and GGCX 12970 C > G polymorphisms were genotyped by polymerase chain reaction - restriction fragment length polymorphism (PCR-RFLP) protocols and Taqman SNP discrimination assays in healthy volunteers (n=102) and patients (n=225) receiving acenocoumarol, an oral anticoagulant, after cardiac valve replacement surgery.

RESULTS

In healthy volunteers, the allele frequencies for CYP4F2 1347 G > A and GGCX 12970 C > G were 43.14 and 1.43 per cent, respectively. No significant differences in mean weight normalized doses of acenocoumarol were found for these CYP4F2 and GGCX genotypes. Binary logistic regression analysis revealed no significant association of any of the genotypes or alleles with the dosing phenotypes for both the SNPs.

INTERPRETATION & CONCLUSIONS

We report distinct frequencies of CYP4F2 1347 G > A and GGCX 12970 C > G polymorphisms in north Indians but these polymorphisms did not have significant bearing on maintenance dose of acenocoumarol oral anticoagulant in cardiac valve replacement patients.

Cytochrome P450 pharmacogenetics in African populations: implications for public health

INTRODUCTION

Africa harbors a disproportionate burden of disease when taking into account the triple challenge caused by HIV/AIDS, tuberculosis (TB) and malaria, against a backdrop of an increasing burden of noncommunicable diseases. More than 80% of therapeutic drugs used in the management of these diseases/conditions are metabolized by CYP enzymes that exhibit genetic polymorphisms.

AREAS COVERED

There is variability in the expression and activities of CYPs resulting in interindividual differences in the response to standard doses of therapeutic drugs, due to genetic polymorphisms, which exhibit both quantitative and qualitative differences between racial and between ethnic groups. The review aims to evaluate the implications of the genetic variation in CYPs on the public health of Africans. The CYPs reviewed here metabolize most of the commonly used therapeutic drugs and include CYP1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 3A4 and 3A5. Allele frequencies are compared between African ethnic groups and among populations of African, Asian and European origin. Data are obtained from our own studies and literature.

EXPERT OPINION

The variability in the pattern of genetic variation between populations translates into differences in drug response. Understanding CYP variability improves rational drug use and has public health significance.

Pharmacogenomics of anti-platelet and anti-coagulation therapy

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

Clopidogrel and warfarin pharmacogenetic tests: what is the evidence for use in clinical practice?

PURPOSE OF REVIEW

To review the most promising genetic markers associated with the variability in the safety or efficacy of warfarin and clopidogrel and highlight the verification and validation initiatives for translating clopidogrel and warfarin pharmacogenetic tests to clinical practice.

RECENT FINDINGS

Rapid advances in pharmacogenetics, continuous decrease in genotyping cost, development of point-of-care devices and the newly established clinical genotyping programs at several institutions hold the promise of individualizing clopidogrel and warfarin based on genotype. Guidelines have been established to assist clinicians in prescribing clopidogrel or warfarin dose based on genotype. However, the clinical utility of clopidogrel and warfarin is still limited. Accordingly, large randomized clinical trials are underway to define the role of clopidogrel and warfarin pharmacogenetics in clinical practice.

SUMMARY

Pharmacogenetics has offered compelling evidence toward the individualization of clopidogrel and warfarin therapies. The rapid advances in technology make the clinical implementation of clopidogrel and warfarin pharmacogenetics possible. The clinical genotyping programs and the ongoing clinical trials will help in overcoming some of the barriers facing the clinical implementation of clopidogrel and warfarin pharmacogenetics.

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.