The investigation of connection between anticoagulant therapy and vitamin K homologues in human determined by LC-MS/MS

Aim: Differences are existed in the bioactivity among various vitamin K (VK) forms. To investigate the correlation between clinical parameters of initial anticoagulation and plasma levels of VK1 and VK2 (MK-4 and MK-7), it was necessary to establish a quantitative method for simultaneous determination.Materials & methods: Plasma samples in cardiovascular patients were extracted by cyclohexane and analyzed using a C18 column. Baseline concentrations of VK1, MK-4 and MK-7 were 0.98 ± 0.52 ng/ml, 0.45 ± 0.13 ng/ml and 0.65 ± 0.31 ng/ml, respectively. The concentrations of MK-7 and total VKs were significantly relevant to INR0, respectively (p = 0.010 and p = 0.048, respectively).Conclusion: Thus, when adjusting anticoagulation dosage, concentrations of various VK homologues might be considered.

Ascorbic acid-induced warfarin resistance after breast cancer surgery: a case report and literature review

Warfarin is an anticoagulant that requires INR-based dosage adjustment. Ascorbic acid may impair warfarin effectiveness according to limited literature. We report a rare case of a 63-year-old woman with an aortic valve replacement history who developed warfarin resistance after taking ascorbic acid for anemia following breast cancer surgery. Despite increasing the warfarin dose from 6 mg to 10 mg daily, her INR remained below the therapeutic range. After ruling out other causes of warfarin resistance, we discontinued ascorbic acid and observed a rapid increase in INR to target values. The temporal relationship and the absence of other confounding factors confirmed the causality of ascorbic acid in this case. We recommend that patients concomitantly taking vitamin C and warfarin should monitor their INR values closely and discontinue ascorbic acid as soon as possible if they exhibit signs of warfarin resistance.

Approaches to Precision-based Anticoagulation management in the critically Ill

Anticoagulant therapy is commonly associated with a high incidence of avoidable adverse events, especially in the acute care setting. This has led to several initiatives by key national health care stakeholders, including specific attention to The Joint Commission's National Patient Safety Goals, to improve anticoagulation management. The subject of special populations has long been identified as challenging by clinicians with the use of anticoagulants. This is driven in part by numerous variables that can contribute to hard outcomes such as bleeding, thrombosis, length of stay, hospital re-admission, morbidity, and mortality. Despite the notable effort to improve the use of anticoagulants with numerous clinical trials, guidelines, guidance statements, and other sources of published evidence, notable difficulties continue to challenge practitioners in managing this class of medications. This is especially the case with very diverse critically ill populations where countless variables exist, many of which were never explored in trials or have historically been frequently excluded. Trials evaluating anticoagulation therapy often can only account for small portions of variables that may affect thrombosis and hemostasis, and study methods often do not reflect the constantly changing dynamic conditions seen in unique critically ill patients. Clinicians providing care to the numerous critically ill populations are faced with conditions that lead to relatively small therapeutic windows, which makes designing safe optimal anticoagulation management plans difficult when dealing with complex patients and mechanical support devices. The approach to crafting a successful management plan for anticoagulant therapy must incorporate the numerous variables that are continuously assessed and revised during the patient's time in the intensive care unit. We explore considerations and approaches when developing, assessing, and implementing an individualized or precision-based management plan that involves the use of anticoagulants in the critically ill. The skills and thought process provided will assist clinicians in managing this unique, variable, and challenging population.

Association of VKORC1 and CYP2C9 single-nucleotide polymorphisms with warfarin dose adjustment in Saudi patients

OBJECTIVES

Despite its wide usage, warfarin therapy remains challenging due to its narrow therapeutic index, inter-individual response variability, and risk of bleeding. Previous reports have suggested that polymorphisms in VKORC1 and CYP2C9 genes could influence warfarin therapy. Herein, we investigated whether VKORC1 -1173C>T, CYP2C9*2, and CYP2C9*3 gene polymorphisms are associated with warfarin dose adjustment and related bleeding events.

METHODS

This cross-sectional study was conducted on Saudi adults receiving warfarin for more than 1 month. Their demographics and relevant clinical data were obtained. Genotyping for VKORC1 -1173C>T, CYP2C9*2, and CYP2C9*2 genotypes was performed.

RESULTS

Patients who are homozygous for the mutant T allele VKORC1 T/T required the lowest warfarin daily maintenance dose, compared to VKORC1 C/T and VKORC1 C/C. Similarly, there was a significant reduction in warfarin daily maintenance dose among CYP2C9*1/*3 and CYP2C9*1/*2 groups compared to CYP2C9*1/*1. However, we found no significant correlation between the studied polymorphisms and warfarin-associated bleeding.

CONCLUSIONS

Similar to other populations, the VKORC1 and CYP2C9 gene polymorphisms are significantly associated with warfarin dosage in Saudi patients. The presence of at least one copy of the mutant alleles for VKORC1 -1173C>T, CYP2C9*2, and CYP2C9*3 is associated with a significant reduction in warfarin maintenance dose.

Association of VKORC1 and CYP2C9 single-nucleotide polymorphisms with warfarin dose adjustment in Saudi patients

OBJECTIVES

Despite its wide usage, warfarin therapy remains challenging due to its narrow therapeutic index, inter-individual response variability, and risk of bleeding. Previous reports have suggested that polymorphisms in VKORC1 and CYP2C9 genes could influence warfarin therapy. Herein, we investigated whether VKORC1 -1173C>T, CYP2C9*2, and CYP2C9*3 gene polymorphisms are associated with warfarin dose adjustment and related bleeding events.

METHODS

This cross-sectional study was conducted on Saudi adults receiving warfarin for more than 1 month. Their demographics and relevant clinical data were obtained. Genotyping for VKORC1 -1173C>T, CYP2C9*2, and CYP2C9*2 genotypes was performed.

RESULTS

Patients who are homozygous for the mutant T allele VKORC1 T/T required the lowest warfarin daily maintenance dose, compared to VKORC1 C/T and VKORC1 C/C. Similarly, there was a significant reduction in warfarin daily maintenance dose among CYP2C9*1/*3 and CYP2C9*1/*2 groups compared to CYP2C9*1/*1. However, we found no significant correlation between the studied polymorphisms and warfarin-associated bleeding.

CONCLUSIONS

Similar to other populations, the VKORC1 and CYP2C9 gene polymorphisms are significantly associated with warfarin dosage in Saudi patients. The presence of at least one copy of the mutant alleles for VKORC1 -1173C>T, CYP2C9*2, and CYP2C9*3 is associated with a significant reduction in warfarin maintenance dose.

Variants in CDHR3, CACNAC1, and LTA Genes Predisposing Sensitivity and Response to Warfarin in Patients with Cardiovascular Disease

Introduction

Warfarin has been in use for more than 60 years; however, it has serious side effects including major bleeding. The high interpatient variability in the required dose impacts the sensitivity and responsiveness to warfarin in different patients. This study aims to assess the influence of CDHR3, CACNAC1, and LTA gene polymorphisms on the variability of warfarin dose requirements and susceptibility to coronary heart disease in the Jordanian population.

Methods

This study was conducted in the anti-coagulation clinic in Queen Alia Heart Institute in Amman, with 212 patients in total. Three SNPs were genotyped within CDHR3 (rs10270308), CACNAC1 (rs216013), and LTA (rs1041981) genes.

Results

Our findings revealed that patients with LTA polymorphism are more prone to warfarin sensitivity than others. Furthermore, carriers of the LTA polymorphism needed a lower initial dose of warfarin and are associated with less variation in doses required to achieve target INR.

Conclusion

The current study could help in understanding the role of genetic variability in warfarin dosing and matching patients to different treatment options. Clinical applications of these findings for warfarin treatment may also contribute to improving the efficacy and safety of warfarin treatment in Jordanian patients with cardiovascular disease.

The relative toxicity of brodifacoum enantiomers

Brodifacoum (BDF) is a potent, long-acting anticoagulant rodenticide that can cause fatal poisoning in humans. The chemical structure of BDF includes 2 chiral carbons, resulting in 2 pairs of diastereomers, BDF-cis (R/S and S/R) and BDF-trans (R/R and S/S). However, the relative potency of these molecules is not known. The purpose of this study was to compare the in vitro and in vivo toxic effects of the 2 BDF diastereomer pairs. In adult Sprague-Dawley rats BDF-cis was significantly more toxic than BDF-trans (LD₅₀ values of 219 versus 316 μg/kg, respectively) while racemic BDF had intermediate potency (266 μg/kg). In adult New Zealand white rabbits, BDF-cis had a longer half-life than BDF-trans which could contribute to its observed increased toxicity. Lastly, BDF-cis (10 μM), but not BDF-trans, damaged cultured SH-SY5Y human neuroblastoma cells by attenuating mitochondrial reductive capacity. Taken together, these data suggest that different toxic manifestations of BDF poisoning in mammals could be attributed, in part, to differences in relative enantiomer concentrations present in racemic formulations of this commercially-available toxicant.

Pharmacogenomics of Novel Direct Oral Anticoagulants: Newly Identified Genes and Genetic Variants

Direct oral anticoagulants (DOAC) have shown an upward prescribing trend in recent years due to favorable pharmacokinetics and pharmacodynamics without requirement for routine coagulation monitoring. However, recent studies have documented inter-individual variability in plasma drug levels of DOACs. Pharmacogenomics of DOACs is a relatively new area of research. There is a need to understand the role of pharmacogenomics in the interpatient variability of the four most commonly prescribed DOACs, namely dabigatran, rivaroxaban, apixaban, and edoxaban. We performed an extensive search of recently published research articles including clinical trials and in-vitro studies in PubMed, particularly those focusing on genetic loci, single nucleotide polymorphisms (SNPs), and DNA polymorphisms, and their effect on inter-individual variation of DOACs. Additionally, we also focused on commonly associated drug-drug interactions of DOACs. CES1 and ABCB1 SNPs are the most common documented genetic variants that contribute to alteration in peak and trough levels of dabigatran with demonstrated clinical impact. ABCB1 SNPs are implicated in alteration of plasma drug levels of rivaroxaban and apixaban. Studies conducted with factor Xa, ABCB1, SLCOB1, CYP2C9, and VKORC1 genetic variants did not reveal any significant association with plasma drug levels of edoxaban. Pharmacokinetic drug-drug interactions of dabigatran are mainly mediated by p-glycoprotein. Strong inhibitors and inducers of CYP3A4 and p-glycoprotein should be avoided in patients treated with rivaroxaban, apixaban, and edoxaban. We conclude that some of the inter-individual variability of DOACs can be attributed to alteration of genetic variants of gene loci and drug-drug interactions. Future research should be focused on exploring new genetic variants, their effect, and molecular mechanisms that contribute to alteration of plasma levels of DOACs.

Advances in anticoagulation therapy

Because atrial fibrillation (AF) is a major risk for thrombotic disease, many patients with AF are managed with anticoagulation for primary or secondary prevention of these events. The emergence of novel oral anticoagulants offers patients and providers options to consider beyond warfarin. Decision making should address safety, tolerability, efficacy, price, and simplicity of use; and decisions should be individualized for each patient.

Potential of a Pharmacogenetic-Guided Algorithm to Predict Optimal Warfarin Dosing in a High-Risk Hispanic Patient: Role of a Novel NQO1*2 Polymorphism

Deep abdominal vein thrombosis is extremely rare among thrombotic events secondary to the use of contraceptives. A case to illustrate the clinical utility of ethno-specific pharmacogenetic testing in warfarin management of a Hispanic patient is reported. A 37-year-old Hispanic Puerto Rican, non-gravid female with past medical history of abnormal uterine bleeding on hormonal contraceptive therapy was evaluated for abdominal pain. Physical exam was remarkable for unspecific diffuse abdominal tenderness, and general initial laboratory results-including coagulation parameters-were unremarkable. A contrast-enhanced computed tomography showed a massive thrombosis of the main portal, splenic, and superior mesenteric veins. On admission the patient was started on oral anticoagulation therapy with warfarin at 5 mg/day and low-molecular-weight heparin. The prediction of an effective warfarin dose of 7.5 mg/day, estimated by using a recently developed pharmacogenetic-guided algorithm for Caribbean Hispanics, coincided with the actual patient's warfarin dose to reach the international normalized ratio target. We speculate that the slow rise in patient's international normalized ratio observed on the initiation of warfarin therapy, the resulting high risk for thromboembolic events, and the required warfarin dose of 7.5 mg/day are attributable in some part to the presence of the NQO1*2 (g.559C>T, p.P187S) polymorphism, which seems to be significantly associated with resistance to warfarin in Hispanics. By adding genotyping results of this novel variant, the predictive model can inform clinicians better about the optimal warfarin dose in Caribbean Hispanics. The results highlight the potential for pharmacogenetic testing of warfarin to improve patient care.

A Novel Admixture-Based Pharmacogenetic Approach to Refine Warfarin Dosing in Caribbean Hispanics

AIM

This study is aimed at developing a novel admixture-adjusted pharmacogenomic approach to individually refine warfarin dosing in Caribbean Hispanic patients.

PATIENTS & METHODS

A multiple linear regression analysis of effective warfarin doses versus relevant genotypes, admixture, clinical and demographic factors was performed in 255 patients and further validated externally in another cohort of 55 individuals.

RESULTS

The admixture-adjusted, genotype-guided warfarin dosing refinement algorithm developed in Caribbean Hispanics showed better predictability (R2 = 0.70, MAE = 0.72mg/day) than a clinical algorithm that excluded genotypes and admixture (R2 = 0.60, MAE = 0.99mg/day), and outperformed two prior pharmacogenetic algorithms in predicting effective dose in this population. For patients at the highest risk of adverse events, 45.5% of the dose predictions using the developed pharmacogenetic model resulted in ideal dose as compared with only 29% when using the clinical non-genetic algorithm (p<0.001). The admixture-driven pharmacogenetic algorithm predicted 58% of warfarin dose variance when externally validated in 55 individuals from an independent validation cohort (MAE = 0.89 mg/day, 24% mean bias).

CONCLUSIONS

Results supported our rationale to incorporate individual's genotypes and unique admixture metrics into pharmacogenetic refinement models in order to increase predictability when expanding them to admixed populations like Caribbean Hispanics.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01318057.

New oral anticoagulants in practice: pharmacological and practical considerations

Although highly effective, warfarin use is complicated by its unpredictable narrow therapeutic window, genetic heterogeneity in pharmacokinetic response, numerous food and drug interactions, and the need for regular international normalized ratio (INR) monitoring. Currently, several novel oral anticoagulant (NOAC) drugs (dabigatran, rivaroxaban, apixaban) are available on the market as alternatives to warfarin. These agents all feature more predictable pharmacodynamic and pharmacokinetic properties than warfarin. Additionally, the NOACs do not require routine monitoring of coagulation parameters, and have a relatively lower potential for interactions with drug, herb, and dietary constituents, which enhances the convenience of management for both patients and health professionals alike. However, there are other considerations regarding the use of NOACs that must be taken into account during management of therapy. In contrast to warfarin, most NOACs need dosage adjustments in renal impairment and are contraindicated in severe liver impairment, and there are no specific antidotes for treating NOAC-related over-anticoagulation. The more frequent dosing needed for NOACs may reduce adherence, especially in elderly patients with polypharmacy. Furthermore, NOACs, especially dabigatran, are not as well tolerated as warfarin in patients with gastrointestinal diseases. Overall, the availability of the NOACs has expanded the treatment armamentarium, but they are not without risk. Given the limited experience with the NOACs, their limited range of indications, and their cost, the characteristics of each anticoagulant must be carefully considered to carefully select the agent that will provide the optimal risk/benefit profile in the individual patient.

Warfarin anticoagulant therapy: a Southern Italy pharmacogenetics-based dosing model

Background and Aim

Warfarin is the most frequently prescribed anticoagulant worldwide. However, warfarin therapy is associated with a high risk of bleeding and thromboembolic events because of a large interindividual dose-response variability. We investigated the effect of genetic and non genetic factors on warfarin dosage in a South Italian population in the attempt to setup an algorithm easily applicable in the clinical practice.

Materials and Methods

A total of 266 patients from Southern Italy affected by cardiovascular diseases were enrolled and their clinical and anamnestic data recorded. All patients were genotyped for CYP2C9*2,*3, CYP4F2*3, VKORC1 -1639 G>A by the TaqMan assay and for variants VKORC1 1173 C>T and VKORC1 3730 G>A by denaturing high performance liquid chromatography and direct sequencing. The effect of genetic and not genetic factors on warfarin dose variability was tested by multiple linear regression analysis, and an algorithm based on our data was established and then validated by the Jackknife procedure.

Results

Warfarin dose variability was influenced, in decreasing order, by VKORC1-1639 G>A (29.7%), CYP2C9*3 (11.8%), age (8.5%), CYP2C9*2 (3.5%), gender (2.0%) and lastly CYP4F2*3 (1.7%); VKORC1 1173 C>T and VKORC1 3730 G>A exerted a slight effect (<1% each). Taken together, these factors accounted for 58.4% of the warfarin dose variability in our population. Data obtained with our algorithm significantly correlated with those predicted by the two online algorithms: Warfarin dosing and Pharmgkb (p<0.001; R² = 0.805 and p<0.001; R² = 0.773, respectively).

Conclusions

Our algorithm, which is based on six polymorphisms, age and gender, is user-friendly and its application in clinical practice could improve the personalized management of patients undergoing warfarin therapy.

Development of a pharmacogenetic-guided warfarin dosing algorithm for Puerto Rican patients

AIM

This study was aimed at developing a pharmacogenetic-driven warfarin-dosing algorithm in 163 admixed Puerto Rican patients on stable warfarin therapy.

PATIENTS & METHODS

A multiple linear-regression analysis was performed using log-transformed effective warfarin dose as the dependent variable, and combining CYP2C9 and VKORC1 genotyping with other relevant nongenetic clinical and demographic factors as independent predictors.

RESULTS

The model explained more than two-thirds of the observed variance in the warfarin dose among Puerto Ricans, and also produced significantly better 'ideal dose' estimates than two pharmacogenetic models and clinical algorithms published previously, with the greatest benefit seen in patients ultimately requiring <7 mg/day. We also assessed the clinical validity of the model using an independent validation cohort of 55 Puerto Rican patients from Hartford, CT, USA (R(2) = 51%).

CONCLUSION

Our findings provide the basis for planning prospective pharmacogenetic studies to demonstrate the clinical utility of genotyping warfarin-treated Puerto Rican patients.

Essential nursing competencies for genetics and genomics: implications for critical care

The implications of genetics and genomics for critical care nurses are becoming more evident, not only in the care provided but also in the numerous medications administered. Genetic causes are being discovered for an increasing number of chronic illnesses and diseases, such as Huntington disease. Because of the scientific and pharmacological advances, leading nursing organizations, such as the American Nurses Association, have established competencies in genetic knowledge for nurses. Such competencies help ensure quality care. Recent advances in the pharmacogenomics of therapy for human immunodeficiency virus disease, cancer, cardiovascular disease, and malignant hyperthermia have indicated a genetic linkage; therefore treatments are targeted toward the genetic aspect of the abnormality. Critical care nurses need knowledge of these genetic conditions and of medications affected by genetic factors.

Prediction of warfarin dose reductions in Puerto Rican patients, based on combinatorial CYP2C9 and VKORC1 genotypes

BACKGROUND

The influence of CYP2C9 and VKORC1 polymorphisms on warfarin dose has been investigated in white, Asian, and African American populations but not in Puerto Rican Hispanic patients.

OBJECTIVE

To test the associations between genotypes, international normalized ratio (INR) measurements, and warfarin dosing and gauge the impact of these polymorphisms on warfarin dose, using a published algorithm.

METHODS

A retrospective warfarin pharmacogenetic association study in 106 Puerto Rican patients was performed. DNA samples from patients were assayed for 12 variants in both CYP2C9 and VKORC1 loci by HILOmet PhyzioType assay. Demographic and clinical nongenetic data were retrospectively collected from medical records. Allele and genotype frequencies were determined and Hardy-Weinberg equilibrium (HWE) was tested.

RESULTS

Sixty-nine percent of patients were carriers of at least one polymorphism in either the CYP2C9 or the VKORC1 gene. Double, triple, and quadruple carriers accounted for 22%, 5%, and 1%, respectively. No significant departure from HWE was found. Among patients with a given CYP2C9 genotype, warfarin dose requirements declined from GG to AA haplotypes; whereas, within each VKORC1 haplotype, the dose decreased as the number of CYP2C9 variants increased. The presence of these loss-of-function alleles was associated with more out-of-range INR measurements (OR = 1.38) but not with significant INR >4 during the initiation phase. Analyses based on a published pharmacogenetic algorithm predicted dose reductions of up to 4.9 mg/day in carriers and provided better dose prediction in an extreme subgroup of highly sensitive patients, but also suggested the need to improve predictability by developing a customized model for use in Puerto Rican patients.

CONCLUSIONS

This study laid important groundwork for supporting a prospective pharmacogenetic trial in Puerto Ricans to detect the benefits of incorporating relevant genomic information into a customized DNA-guided warfarin dosing algorithm.

Genetic polymorphisms are associated with variations in warfarin maintenance dose in Han Chinese patients with venous thromboembolism

AIM

Warfarin is a clinical anticoagulant that requires periodic monitoring because it is associated with adverse outcomes. Personalized medicine, which is based on pharmacogenetics, holds great promise in solving these types of problems. It aims to provide the tools and knowledge to tailor drug therapy to an individual patient, with the potential of increasing safety and efficacy of medications.

MATERIALS & METHODS

In the present study we analyzed genotypes of 14 SNPs for seven genes using DNA from 297 Han Chinese venous thromboembolism patients treated with warfarin.

RESULTS

Multiple regression analyses revealed that CYP2C9 genotype (p = 0.001), VKORC1 genotype (p < 0.001), age (p < 0.01) and weight (p < 0.001) were all associated with warfarin dose requirements, which can explain 37.4% of the variability of warfarin dose among Han Chinese patients. Meanwhile, in the validation cohort, the predicted warfarin daily dose was calculated using the best model with a 64.5% predicted dose being acceptable (-1 mg/day ≤Δwarfarin dose ≤1 mg/day).

CONCLUSION

We developed a pharmacogenetic dose algorithm for warfarin treatment that uses genotypes from two genes (VKORC1 and CYP2C9) and clinical variables to predict therapeutic maintenance doses in Chinese patients with venous thromboembolism. The validity of the dosing algorithm was confirmed in a cohort of venous thromboembolism patients on warfarin therapy.

Warfarin for Venous Thromboembolism Prophylaxis After Elective Hip or Knee Arthroplasty: Exploring the Evidence, Guidelines, and Challenges Remaining

BACKGROUND:

Guidelines for the prevention of venous thromboembolism (VTE) after elective total hip or knee arthroplasty (THA/TKA) have been developed separately by the American Academy of Orthopaedic Surgeons (AAOS) and the American College of Chest Physicians (ACCP). Differences exist in approaches to preventing postoperative VTE through prophylaxis.

OBJECTIVE:

To compare trials using vitamin K antagonists (VKAs) and differences in guidelines to determine the benefits and drawbacks of warfarin for VTE prophylaxis following THA/TKA.

DATA SOURCES:

Guidelines from the AAOS published in 2009 and revised in 2011 and from the ACCP published in 2008 were compared for recommendations on the use of VKAs. A MEDLINE search from 1960 to November 2009 was conducted to identify pertinent articles on the use of warfarin or VKAs for VTE prophylaxis following THA/TKA. Search terms included warfarin, vitamin K antagonist, total hip or total knee replacement, and total hip or total knee arthroplasty.

STUDY SELECTION AND DATA EXTRACTION:

Only clinical trials in which warfarin was the primary agent for prophylaxis compared to other anticoagulants were included.

DATA SYNTHESIS:

Data on differences between guideline recommendations for the use of VKAs and the importance of a deep vein thrombosis or asymptomatic events were extracted. Thirteen comparative trials using VKAs for VTE prophylaxis and international normalized ratio (INR) targets were assessed. Overall, the incidence of bleeding tended to be lower with the use of VKAs, but thrombosis when including asymptomatic events was numerically higher when comparing INR targets. However, INR targets varied, with no comparative trials assessing the AAOS 2009 recommended INR target of 1.5-2.0. The AAOS guidelines initially recommended a longer duration of therapy and expressed stronger support for the use of aspirin for prophylaxis; however, in 2011, its guidelines were revised, with no specific recommendations as to agent, dose, or INR target goal.

CONCLUSIONS:

Warfarin is an effective agent to prevent VTE after elective THA/TKA. The most effective approach, including extended warfarin use up to 4 weeks or longer, has not been determined.

Genetic and nongenetic factors associated with warfarin dose requirements in Egyptian patients

BACKGROUND AND OBJECTIVE

Warfarin is a commonly used oral anticoagulant with a narrow therapeutic index and various genetic and clinical factors that influence interpatient variability in dose requirements. This study investigated the impact of genetic and nongenetic factors on warfarin dose requirements in Egyptians.

METHODS

DNA was extracted from 207 patients taking warfarin for more than 2 months and genotyped for VKORC1 (3673 G>A), CYP2C9 *2*3*4*5*8, CYP4F2 (V33M; rs2108622), APOE (rs429358, rs7412), and CALU(rs339097) gene polymorphisms. Linear regression modeling was conducted to identify the genetic and nongenetic factors that independently influence warfarin dose requirements.

RESULTS

VKORC1 3673 AA or GA genotype (P<0.0001), one or two variant alleles of CYP2C9 gene (P=0.0004), APOE ε2 haplotype (P=0.01), and increasing age (P<0.0001) were all associated with lower warfarin dose, whereas smoking (P=0.025) and pulmonary embolism (P=0.0059) showed association with higher warfarin doses. These factors explained 31% of the warfarin dose variability. This is the first independent confirmation of the association of the CALU rs339097 variant with higher warfarin dose requirement, although inclusion of this single nucleotide polymorphism in the multiple regression model failed to achieve significance (P=0.066). CYP4F2 (V33M) polymorphism was not significant (P=0.314), despite its high frequency in the studied population (42%).

CONCLUSION

The study shows that VKORC1, CYP2C9 polymorphisms, APOE ε2 variant, and several clinical/demographic variables are important determinants of warfarin dose requirements in Egyptian patients. The percentage of variability explained by these factors is lower than in those of European ancestry, but similar to the variability explained in Asians and African ancestry.

Clinical applications of pharmacogenomics guided warfarin dosing

AIM OF THE REVIEW

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

METHOD

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

RESULTS

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

CONCLUSION

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

Drug interactions with antiretrovirals and warfarin

IMPORTANCE OF THE FIELD

Antiretroviral therapy exhibits significant potential to alter the metabolism of other medications. Warfarin is widely used for the management of clotting disorders and is prone to drug-drug interactions that can result in subtherapeutic anticoagulation or over-anticoagulation.

AREAS COVERED IN THIS REVIEW

The mechanism and clinical significance of drug-drug interactions between warfarin and individual antiretrovirals are discussed. Literature searches were conducted in August of 2009 using multiple databases including Medline (1950 - 2009), EMBASE (1980 - 2009), International Pharmaceutical Abstracts (1970 - 2009) and the Cochrane Database of Systematic Reviews. The following search terms were utilized: warfarin, HIV, antiretroviral, drug interaction, protease inhibitor (PI), non-nucleoside reverse-transcriptase inhibitor (NNRTI), cytochrome P450 (CYP450), CYP2C9 and individual antiretrovirals by name. The manufacturers of PIs and NNRTIs were also contacted regarding unpublished data.

WHAT THE READER WILL GAIN

Clinicians will gain an understanding of the antiretrovirals that are prone to alter warfarin metabolism and the implications for warfarin dose modification.

TAKE HOME MESSAGE

Metabolic interaction between warfarin and antiretrovirals is likely, particularly if NNRTIs or PIs are included in the antiretroviral regimen. Titration of warfarin dose should be conducted on the basis of close monitoring of the international normalized ratio. Empiric warfarin dose modifications should be considered for individual antiretrovirals.

Patient Factors That Influence Warfarin Dose Response

Warfarin has long been the mainstay of oral anticoagulation therapy for the treatment and prevention of venous and arterial thrombosis. The narrow therapeutic index of warfarin, and the complex number of factors that influence international normalized ratio (INR) response, makes optimization of warfarin therapy challenging. Determination of the appropriate warfarin dose during initiation and maintenance therapy requires an understanding of patient factors that influence dose response: age, body weight, nutritional status, acute and chronic disease states, and changes in concomitant drug therapy and diet. This review will examine specific clinical factors that can affect the pharmacokinetics and pharmacodynamics of warfarin, as well as the role of pharmacogenetics in optimizing warfarin therapy.

SNP analysis of Rac1 For personalized ligand interaction

This paper addresses mutational events that give rise to differing response to drugs focusing on Rac1, a protein that has been recognized as a target for drug design for cardiovascular disease due its regulatory role of angiogenesis. Rac1 has been considered with reference to Single Nucleotide Polymorphism (SNP), which has become of great value for personalized medicine. We have considered four variation of Rac1 registered in UNIPROTKB. Two of these variations are due to the environmental or population factors and two are mutation that we have selected because they are located near the binding sites of Rac1. Rac1 has been modelled by Rosetta software and by i-Tasser web server. We have chosen i-Tasser based modelling because the Rac1 structure obtained was more closely resembling crystallography data. In silico model have been used as receptors for docking with a set of 20 morpholines. The results that have been obtained on SNPs shows that a single ligand can react very differently with a mutated structure. Our analysis shows that all mutations that have been considered change Rac1 conformation and increase the accessible surface of Rac1. Our analysis highlights the effect of two sources of genetic variability: single base variation and alternative splicing.