Warfarin pharmacology, clinical management, and evaluation of hemorrhagic risk for the elderly

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.

Functionally Significant Coumarin-Related Variant Alleles and Time to Therapeutic Range in Chilean Cardiovascular Patients

Despite the development of new oral agents over the last decade, vitamin K antagonists (VKAs) remain the most widely used anticoagulants for treating and preventing thromboembolism worldwide. In Chile, the Ministry of Health indicates that acenocoumarol should be used in preference to any other coumarin. Complications of inappropriate dosing are among the most frequently reported adverse events associated with this medication. It is well known that polymorphisms in pharmacokinetic and pharmacodynamic proteins related to coumarins (especially warfarin) influence response to these drugs. This work analyzed the impact of CYP2C19*2 (rs4244285), CYP1A2*1F (rs762551), GGCx (rs11676382), CYP2C9*2 (rs1799853), CYP2C9*3 (rs1057910), CYP4F2 (rs2108622), VKORC1 (rs9923231), VKORC1 (rs7294), CYP3A4*1B (rs2740574), and ABCB1 (rs1045642) polymorphisms on time to therapeutic range for oral anticoagulants in 304 Chilean patients. CYP2C9*3 polymorphisms were associated with time to therapeutic range for acenocoumarol in Chilean patients, and the CYP4F2 TT genotype, MDR1 A allele, CYP1A2 A allele, and CYP3A4T allele are promising variants that merit further analysis. The presence of polymorphisms explained only 4.1% of time to therapeutic range for acenocoumarol in a multivariate linear model. These results improve our understanding of the basis of ethnic variations in drug metabolism and response to oral anticoagulant therapy. We hope that these findings will contribute to developing an algorithm for VKA dose adjustment in the Chilean population in the near future, decreasing the frequency of stroke, systemic embolism, and bleeding-related adverse events.

Anticoagulation Management With Coumarinic Drugs in Chilean Patients

Warfarin and acenocoumarol are used in various cardiovascular disorders to improve the prognosis of patients with thromboembolic disease. However, there is a lack of substantial efficacy and safety data on antithrombotic prophylaxis in several countries, particularly in Latin America. The aim of this study was to provide information about the efficacy of anticoagulants in Chilean patients. Data were collected from databases of the Western Metropolitan Health Service, Santiago, Chile. We identified 6280 records of patients receiving anticoagulant treatment. The three most common diagnoses were rhythm disorder (43.7%), venous thrombosis (22%), and valvular prosthesis (10.7%). The majority of patients (98.5%) received acenocoumarol while 1.5% of patients received warfarin, at weekly therapeutic doses of 13.6 mg and 30.4 mg, respectively. For total diagnoses, the median time in the therapeutic range was 50%. However, better results, 66.7%, were observed when a telemedicine strategy was used only in Santiago Province. Our findings emphasize that in Chile, where the number of patients receiving anticoagulant treatment increases every year, telemedicine, by committed teams, improves the use of oral anticoagulants and is able to increase quality indicators of anticoagulant treatment care.

Pharmacokinetic drug interactions of the non-vitamin K antagonist oral anticoagulants (NOACs)

The use of warfarin, the most commonly prescribed oral anticoagulant, is being questioned by clinicians worldwide due to warfarin several limitations (a limited therapeutic window and significant variability in dose-response among individuals, in addition to a potential for drug-drug interactions). Therefore, the need for non-vitamin K antagonist oral anticoagulants (NOACs) with a rapid onset of antithrombotic effects and a predictable pharmacokinetic (PK) and pharmacodynamic (PD) profile led to the approval of five new drugs: the direct factor Xa (F-Xa) inhibitors rivaroxaban, apixaban, edoxaban and betrixaban (newly approved by FDA) and the direct thrombin (factor-IIa) inhibitor dabigatran etexilate. The advantages of NOACs over warfarin are a fixed-dosage, the absence of the need for drug monitoring for changes in anti-coagulation and fewer clinically significant PK and PD drug-drug interactions. NOACs exposure will likely be increased by the administration of strong P-glycoprotein (P-gp) and cytochrome P450 (CYP) 3A4-inhibitors and may increase the risk of bleeds. On the contrary, P-gp inducers could significantly decrease the NOACs plasma concentration with an associated reduction in their anticoagulant effects. This manuscript gives an overview of NOACs PK profiles and their drug-drug interactions potential. This is meant to be of help to physicians in choosing the best therapeutic approach for their patients.

Review of antimicrobial use and considerations in the elderly population

Pharmacologic management of infections in elderly patients presents multiple challenges to health care professionals due to variable pharmacokinetics, pharmacodynamics, and immune function. Age is a well-established risk factor for infection, but furthermore is a risk factor for prolonged length of hospital stay, increased incidence of complications, and significant and sustained decline in baseline functional status. In 2014, 46.2 million Americans were aged ≥65 years, accounting for 14.5% of the total population. By 2033, for the first time, the population of persons aged ≥65 years is projected to outnumber the people <18 years of age. According to the National Ambulatory Medical Care Survey and the National Hospital Ambulatory Medical Care Survey, 154 million prescriptions for antimicrobials were estimated to have been written in doctors’ offices and emergency departments during a 1-year time period. In 2014, 266.1 million courses of antimicrobials were dispensed to outpatients by US community pharmacies. A study that evaluated 2007–2009 Medicare Part D data found that patients aged ≥65 years used more antimicrobials, at 1.10 per person per year, compared to 0.88 antimicrobials used per person per year in patients aged 0–64 years. With the abundance of antimicrobial prescriptions and the current growth in the number and proportion of older adults in the US, it is essential that health care providers understand appropriate antimicrobial pharmacotherapy in the elderly patient. This review focuses on the use and implications of antimicrobial agents in the elderly population.

Clinical Pharmacogenetic Testing and Application: Laboratory Medicine Clinical Practice Guidelines

Pharmacogenetic testing for clinical applications is steadily increasing. Correct and adequate use of pharmacogenetic tests is important to reduce unnecessary medical costs and adverse patient outcomes. This document contains recommended pharmacogenetic testing guidelines for clinical application, interpretation, and result reporting through a literature review and evidence-based expert opinions for the clinical pharmacogenetic testing covered by public medical insurance in Korea. This document aims to improve the utility of pharmacogenetic testing in routine clinical settings.

Old and new oral anticoagulants: Food, herbal medicines and drug interactions

The most commonly prescribed oral anticoagulants worldwide are the vitamin K antagonists (VKAs) such as warfarin. Factors affecting the pharmacokinetics of VKAs are important because deviations from their narrow therapeutic window can result in bleedings due to over-anticoagulation or thrombosis because of under-anticoagulation. In addition to pharmacodynamic interactions (e.g., augmented bleeding risk for concomitant use of NSAIDs), interactions with drugs, foods, herbs, and over-the-counter medications may affect the risk/benefit ratio of VKAs. Direct oral anticoagulants (DOACs) including Factor Xa inhibitors (rivaroxaban, apixaban and edoxaban) and thrombin inhibitor (dabigatran) are poised to replace warfarin. Phase-3 studies and real-world evaluations have established that the safety profile of DOACs is superior to those of VKAs. However, some pharmacokinetic and pharmacodynamic interactions are expected. Herein we present a critical review of VKAs and DOACs with focus on their potential for interactions with drugs, foods, herbs and over-the-counter medications.

Challenges of development and implementation of point of care pharmacogenetic testing

INTRODUCTION

Just as technology was the underlying driver of the sequencing of the human genome and subsequent generation of volumes of genome sequence data from healthy and affected individuals, animal, plant, and microbial species alike, so too will technology revolutionize diagnostic testing. One area of intense interest is the use of genetic data to inform decisions regarding drug selection and drug dosing, known as pharmacogenetic (PGx) testing, to improve likelihood of successful treatment outcomes with minimal risks.

AREAS COVERED

This commentary will provide an overview of implementation research of PGx testing, the benefits of point-of-care (POC) testing and overview of POC testing platforms, available PGx tests, and barriers and facilitators to the development and integration of POC-PGx testing into clinical settings. Sources include the published literature, and databases from the Centers for Medicaid and Medicare Services, Food and Drug Administration. Expert commentary: The utilization of POC PGx testing may enable more routine test use, but the development and implementation of such tests will face some barriers before personalized medicine is available to every patient. In particular, provider training, availability of clinical decision supports, and connectivity will be key areas to facilitate routine use.

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.

Acute warfarin toxicity: An unanticipated consequence of amoxicillin/clavulanate administration

PATIENT

Male, 53 FINAL DIAGNOSIS: Acute Warfarin toxicity Symptoms: -

MEDICATION

Warfarin Clinical Procedure: - Specialty: Hematology.

OBJECTIVE

Unusual clinical course.

BACKGROUND

Warfarin remains the most common anticoagulant in the management of thromboembolic diseases. However, its extensive drug interaction requires frequent monitoring and dose adjustments. Almost all antibiotics, including penicillins, have the potential to interact with warfarin causing either under or over anticoagulation which increases the risk for thrombus formation and significant bleeding respectively.

CASE REPORT

A 53-year-old Caucasian male with a history of protein C deficiency and recurrent intravascular thrombosis developed a dental abscess. He was treated with amoxicillin/clavulanate 500/125 mg twice daily and referred to a dentist. He developed significant bleeding after tooth extraction. INR was 20.4. He received fresh frozen plasma and vitamin K with resolution of bleeding.

CONCLUSIONS

While rare, clinically significant prolonged prothrombin time and potentially life threatening bleeding can occur when amoxicillin/clavulanate is concomitantly administered with warfarin. Prompt recognition and intervention is necessary to avoid life threatening complications from warfarin-amoxicillin/clavulanate interaction.

Clinical applications of whole-genome association studies: future applications at the bedside

Until now, performing whole-genome association studies has been an unattainable, but highly desirable, goal for geneticists. With the recent advent of high-throughput genotyping platforms, this goal is now a reality for geneticists today and for clinicians in the not-so-distant future. This review will cover a broad range of topics to provide an overview of this emerging branch of genetics, and will provide references to more specific sources. Specifically, this review will cover the technologies available today and in the near future, the specific types of whole-genome association studies, the benefits and limitations of these studies, the applications to complex disease-gene interactions, diagnostic devices, therapeutics, and finally, we will describe the 5-year perspective and key issues.

A population-based assessment of the drug interaction between levothyroxine and warfarin

Most drug interaction resources suggest that levothyroxine can dramatically potentiate the effect of warfarin. However, the mechanistic basis of the interaction is speculative, and little evidence supports a meaningful drug interaction. We conducted a population-based nested case-control study to examine the risk of hospitalization for hemorrhage following the initiation of levothyroxine in a cohort of 260,076 older patients receiving warfarin. In this group, we identified 10,532 case subjects hospitalized for hemorrhage and 40,595 controls. In the primary analysis, we found no association between hospitalization for hemorrhage during warfarin therapy and initiation of levothyroxine in the preceding 30 days (adjusted odds ratio 1.11, 95% confidence interval 0.67-1.86). Secondary analyses using more remote initiation of levothyroxine also found no association. These findings suggest that concerns about a clinically meaningful levothyroxine-warfarin drug interaction are not justified. Drug interaction resources that presently characterize this interaction as important should reevaluate this classification.

[Upper gastrointestinal haemorrhage in patients over 80 years-old]

OBJECTIVES

To evaluate the patient characteristics, outcome, and prognosis of upper gastrointestinal haemorrhage in the elderly.

MATERIAL AND METHODS

A prospective study was conducted on 103 patients aged 80 years and over, admitted to a Gastrointestinal Bleeding Unit after an episode of upper gastrointestinal bleeding. We analysed the personal history, the characteristics of the bleeding event, and whether an urgent diagnostic or therapeutic endoscopy was performed, in order to identify clinical data and endoscopic findings that may have an influence on the outcome of the haemorrhage.

RESULTS

The major cause of the haemorrhage was peptic ulcer in 65.1%, and 60.2% of patients were on chronic treatment with non-steroidal anti-inflammatory drugs. An urgent diagnostic endoscopy was performed in all of them, identifying the source of bleeding in 94.2%, and treatment was carried out on 28.2%. The likelihood of rebleeding was 8%, and 4.9% of patients underwent emergency surgery, with an overall mortality rate of 5.8%.

CONCLUSIONS

The performance of urgent endoscopy and the application of endoscopic haemostasis are safe and effective in stopping upper gastrointestinal bleeding in the elderly. This has significantly reduced the need for emergency surgery, improving the survival of the bleeding elderly patient and preventing recurrent bleeding.

Concurrent use of warfarin and antibiotics and the risk of bleeding in older adults

BACKGROUND

Antibiotic medications are associated with an increased risk of bleeding among patients receiving warfarin. The recent availability of data from the Medicare Part D prescription drug program provides an opportunity to assess the association of antibiotic medications and the risk of bleeding in a national population of older adults receiving warfarin.

METHODS

We conducted a case-control study nested within a cohort of 38,762 patients aged 65 years and older who were continuous warfarin users, using enrollment and claims data for a 5% national sample of Medicare beneficiaries with Part D benefits. Cases were defined as patients hospitalized for a primary diagnosis of bleeding and were matched with 3 control subjects on age, race, sex, and indication for warfarin. Logistic regression analysis was used to calculate adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for the risk of bleeding associated with prior exposure to antibiotic medications.

RESULTS

Exposure to any antibiotic agent within the 15 days of the event/index date was associated with an increased risk of bleeding (aOR 2.01; 95% CI, 1.62-2.50). All 6 specific antibiotic drug classes examined (azole antifungals [aOR, 4.57; 95% CI, 1.90-11.03], macrolides [aOR, 1.86; 95% CI, 1.08-3.21], quinolones [aOR, 1.69; 95% CI, 1.09-2.62], cotrimoxazole [aOR, 2.70; 95% CI, 1.46-5.05], penicillins [aOR, 1.92; 95% CI, 1.21-2.07], and cephalosporins [aOR, 2.45; 95% CI, 1.52-3.95]) were associated with an increased risk of bleeding.

CONCLUSION

Among older continuous warfarin users, exposure to antibiotic agents-particularly azole antifungals-was associated with an increased risk of bleeding.

Clinical Pharmacogenetics Implementation Consortium Guidelines for CYP2C9 and VKORC1 genotypes and warfarin dosing

Warfarin is a widely used anticoagulant with a narrow therapeutic index and large interpatient variability in the dose required to achieve target anticoagulation. Common genetic variants in the cytochrome P450-2C9 (CYP2C9) and vitamin K-epoxide reductase complex (VKORC1) enzymes, in addition to known nongenetic factors, account for ~50% of warfarin dose variability. The purpose of this article is to assist in the interpretation and use of CYP2C9 and VKORC1 genotype data for estimating therapeutic warfarin dose to achieve an INR of 2-3, should genotype results be available to the clinician. The Clinical Pharmacogenetics Implementation Consortium (CPIC) of the National Institutes of Health Pharmacogenomics Research Network develops peer-reviewed gene-drug guidelines that are published and updated periodically on http://www.pharmgkb.org based on new developments in the field.(1).

Quality of management of oral anticoagulation as assessed by time in therapeutic INR range in elderly and younger patients with low mean years of formal education: a prospective cohort study

BACKGROUND

despite the overwhelming evidence of its effectiveness, oral anticoagulation continues to be underused in the elderly, presumably due to physicians' misconceptions when estimating bleeding risk and ability to comply with treatment.

OBJECTIVE

to investigate the quality of anticoagulation control among deprived elderly and younger patients.

DESIGN

prospective observational study.

SETTING

a public anticoagulation clinic in a developing country.

SUBJECTS

all adult patients on intended long-term (>90 days) oral anticoagulation. We studied 171 patients (79 elderly and 92 non-elderly) with a mean follow-up of 273 ± 84.9 days.

METHODS

the main outcome measure was the quality of anticoagulation management as measured by the time in therapeutic (TTR) international normalised ratio (INR) range. Elderly patients (≥60 years) were compared with younger patients with respect to the educational level and co-morbidities.

RESULTS

the mean number of years of formal education was 4.37 ± 3.2 years. The mean TTR was 62.50 ± 17.9% in non-elderly and 62.10 ± 16.6% in elderly (P = 0.862) subjects, despite the higher prevalence of co-morbidities in the latter group: heart failure (46.3 versus 28.6%, P = 0.042), diabetes mellitus (22.8 versus 8.7%, P = 0.011), renal failure (estimated glomerular filtration rate <50 ml/min: 38.0 versus 7.1%, P < 0.001) and polypharmacy (84.8 versus 58.7%, P < 0.001). Fifty elderly and 84 non-elderly subjects require little or no assistance in taking medications. Among them, the elderly had lower educational levels (3.42 ± 2.5 versus 5.55 ± 3.4 years of formal education, P < 0.001) and higher rates of cognitive impairment (34.0 versus 13.1%, P = 0.004), but a similar mean TTR (62.46 ± 16.1 versus 63.02 ± 17.8%, P = 0.856). The oldest (≥75 years) patients did as well as those aged ≤50 years (mean TTR: 62.54 ± 16.0 versus 62.23 ± 16.4%, respectively, P = 0.98).

CONCLUSIONS

good-quality management of oral anticoagulation is achievable in deprived populations attending an anticoagulation clinic. Elderly patients may experience similar quality of anticoagulation despite having higher levels of co-morbidities and polypharmacy. These results add evidence to the safety of such therapeutic interventions in the elderly.

A team-based approach to warfarin management in long term care: a feasibility study of the MEDeINR electronic decision support system

Background

Previous studies in long-term care (LTC) have demonstrated that warfarin management is suboptimal with preventable adverse events often occurring as a result of poor International Normalized Ratio (INR) control. To assist LTC teams with the challenge of maintaining residents on warfarin in the therapeutic range (INR of 2.0 to 3.0), we developed an electronic decision support system that was based on a validated algorithm for warfarin dosing. We evaluated the MEDeINR system in a pre-post implementation design by examining the impact on INR control, testing frequency, and experiences of staff in using the system.

Methods

For this feasibility study, we piloted the MEDeINR system in six LTC homes in Ontario, Canada. All128 residents (without a prosthetic valve) who were taking warfarin were included. Three-months of INR data prior to MEDeINR was collected via a retrospective chart audit, and three-months of INR data after implementation of MEDeINR was captured in the central computer database. The primary outcomes compared in a pre-post design were time in therapeutic range (TTR) and time in sub/supratherapeutic ranges based on all INR measures for every resident on warfarin. Secondary measures included the number of monthly INR tests/resident and survey/focus-group feedback from the LTC teams.

Results

LTC homes in our study had TTR's that were higher than past reports prior to the intervention. Overall, the TTR increased during the MEDeINR phase (65 to 69%), but was only significantly increased for one home (62% to 71%, p < 0.05). The percentage of time in supratherapeutic decreased from 14% to 11%, p = 0.08); there was little change for the subtherapeutic range (21% to 20%, p = 0.66). Overall, the average number of INR tests/30 days decreased from 4.2 to 3.1 (p < 0.0001) per resident after implementation of MEDeINR. Feedback received from LTC clinicians and staff was that the program decreased the work-load, improved confidence in management and decisions, and was generally easy to use.

Conclusion

Although LTC homes in our sample had TTR's that were relatively high prior to the intervention, the MEDeINR program represented a useful tool to promote optimal TTR, decrease INR venipunctures, streamline processes, and increase nurse and physician confidence around warfarin management. We have demonstrated that MEDeINR was a practical, usable clinical information system that can be incorporated into the LTC environment.

Vitamin K antagonist use in the elderly: special considerations

As the population ages, the number of patients aged 75 years and over treated with vitamin K antagonists (VKAs) is steadily increasing. In this age group, the two main indications for oral anticoagulant therapy are the treatment of venous thromboembolic disease and the prevention of systemic embolism in patients with nonvalvular atrial fibrillation. In both indications, a target international normalized ratio of 2.5 (range: 2.0-3.0) is recommended. Although VKAs are beneficial in thromboembolic disorders, they are still underused. In this review, we will focus on two crucial topics in elderly patients, the specific management of VKAs in these patients and the hemorrhagic risk. Current recommendations concerning the management at the start of treatment, education and adequate monitoring may help to minimize the hemorrhagic risk in these frail patients.

Examining warfarin underutilization rates in patients with atrial fibrillation: Detailed chart review essential to capture contraindications to warfarin therapy

Introduction

Atrial fibrillation affects an estimated 2.5 million Americans and incurs an average annual stroke risk of 4.5% per year. Despite warfarin reducing stroke risk by approximately 66%, prior studies show warfarin usage rates to be about 50%. However, the methods that define warfarin as "inappropriate underutilization" might not be sensitive enough to pick up relative contraindications. We assessed the inappropriate underutilization of warfarin in atrial fibrillation patients at our hospital by abstracting individual patient charts.

Methods

Medical records were reviewed to determine stroke risk factors, warfarin use, and documented contraindications to warfarin use in 364 consecutive patients with atrial fibrillation.

Results

Amongst 364 atrial fibrillation patients, 54.6% received warfarin anticoagulation. Overall, 29.5 % of patients had documented reasons for not prescribing warfarin. Primary reasons listed by treating physicians included: gastrointestinal bleed 10.7%, secondary/transient atrial fibrillation 8.2%, and fall risk 6.3%. Only 7.1% of the patients had no documented reasons for the lack of warfarin use.

Conclusion

Consistent with previous reports, 45.4% of patients in this atrial fibrillation cohort were not prescribed warfarin. However, after reviewing medical charts for documented reasons why warfarin was not used, the inappropriate underutilization rate was only 7.1%. These findings suggest that studies utilizing administrative database and ICD-9 CM coding might overestimate warfarin underutilization.