The nature and frequency of potential warfarin drug interactions that increase the risk of bleeding in patients with atrial fibrillation

New Perspectives on Risk Assessment and Anticoagulation in Elective Spine Surgery Patients: The Impact of Ultra-Minimally Invasive Endoscopic Surgery Techniques on Patients with Cardiac Disease

The advent of ultra-minimally invasive endoscopic spine surgery, characterized by significantly reduced surgery times, minimal blood loss, and minimal tissue trauma, has precipitated a paradigm shift in the preoperative management of patients with cardiac disease undergoing elective spine procedures. This perspective article explores how these advancements have influenced the requirements for preoperative cardiac workups and the protocols surrounding the cessation of anticoagulation and antiplatelet therapies. Traditionally, extensive cardiac evaluations and the need to stop anticoagulation and antiplatelet agents have posed challenges, increasing the risk of cardiac events and delaying surgical interventions. However, the reduced invasiveness of endoscopic spine surgery presents a safer profile for patients with cardiac comorbidities, potentially minimizing the necessity for rigorous cardiac clearance and allowing for more flexible anticoagulation management. This perspective article synthesizes current research and clinical practices to provide a comprehensive overview of these evolving protocols. It also discusses the implications of these changes for patient safety, surgical outcomes, and overall healthcare efficiency. Finally, the article suggests directions for future research, emphasizing the need for updated guidelines that reflect the reduced perioperative risk associated with these innovative surgical techniques. This discussion is pivotal for primary care physicians, surgeons, cardiologists, and the broader medical community in optimizing care for this high-risk patient population.

Anticoagulant and antiplatelet combined therapy in patients 75 years and over with atrial fibrillation: a prospective observational study assessing adherence to clinical guidelines

Objective

According to current guidelines on atrial fibrillation (AF), the addition of an antiplatelet therapy to an anticoagulant for a stable vascular disease does not decrease the ischaemic hazard but increases the risk of bleeding. The aim of the study was to assess compliance of practices with existing clinical guidelines concerning the use of anticoagulant-antiplatelet combined therapy in patients 75 years and over with AF.

Methods

This prospective observational study was carried out at the University Hospital of Strasbourg (France) between August 2016 and January 2017 with data collection on 1 day of every month. To be included, the patient had to be 75 years and over with AF and treated with anticoagulant-antiplatelet therapy. The population included all the patients admitted at the hospital excluding those from the Gynaecology-Obstetrics and Paediatrics departments. With regard to clinical ongoing guidelines (French, European, American and Canadian), the patients were sorted into three groups. Group 1: combined therapy in compliance with recommendations; Group 2: combined therapy debatable as to benefit-risk ratio; and Group 3: combined therapy not compliant with recommendations.

Result

Ninety-three out of 3307 patients 75 years and over received anticoagulant-antiplatelet combined therapy prior to their hospital admission. Thirty-two patients (34.4% - Group 1) had experienced an acute event and/or revascularisation within the past year. Twenty-four patients (25.8% - Group 2) had not experienced recent revascularisation and had stable coronary disease but were suffering from peripheral artery disease. Group 3 consisted of 37 patients (39.8%), none of which had experienced recent revascularisation or had unstable coronary disease. For all groups, the main dual therapy was acetylsalicylic acid + fluindione (59.1%).

Conclusion

In our study, 37 antiplatelet (39.8%) treatments could have been stopped. These results should spur prescribers into regular reassessment of combination antithrombotic therapy since it contributes to polypharmacy and increases the risk of adverse events.

Predictors of Major Bleeding Among Working-Age Adults with Atrial Fibrillation: Evaluating the Effects of Potential Drug-drug Interactions and Switching from Warfarin to Non-vitamin K Oral Anticoagulants

PURPOSE

This study aims to evaluate the associations between switching from warfarin to non-vitamin K oral anticoagulants (NOACs), exposure to potential drug-drug interactions (DDIs), and major bleeding events in working-age adults with atrial fibrillation (AF).

METHODS

We conducted a retrospective cohort study using the claims database of commercially insured working-age adults with AF from 2010 to 2015. Switchers were defined as patients who switched from warfarin to NOAC; non-switchers were defined as those who remained on warfarin. We developed novel methods to calculate the number and proportion of days with potential DDIs with NOAC/warfarin. Multivariate logistic regressions were utilized to evaluate the associations between switching to NOACs, exposure to potential DDIs, and major bleeding events.

RESULTS

Among a total of 4126 patients with AF, we found a significantly lower number of potential DDIs and the average proportion of days with potential DDIs in switchers than non-switchers. The number of potential DDIs (AOR 1.14, 95% CI 1.02-1.27) and the HAS-BLED score (AOR 1.64, 95% CI 1.48-1.82) were significantly and positively associated with the likelihood of a major bleeding event. The proportion of days with potential DDIs was also significantly and positively associated with risk for bleeding (AOR 1.42, 95% CI 1.03, 1.96). We did not find significant associations between switching to NOACs and major bleeding events.

CONCLUSIONS

The number and duration of potential DDIs and patients' comorbidity burden are important factors to consider in the management of bleeding risk in working-age AF adults who take oral anticoagulants.

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.

Prevalence of Drug Combinations Increasing Bleeding Risk Among Warfarin Users With and Without Alzheimer's Disease

PURPOSE

The aim of this study was to analyse the prevalence and predictors of drug combinations increasing bleeding risk among warfarin users with and without Alzheimer's disease (AD).

METHODS

This retrospective observational study utilised data from the Finnish MEDALZ-2005 cohort. The MEDALZ-2005 study included all community-dwelling persons with a clinically verified diagnosis of AD at the end of 2005, and one comparison person without AD for each case. Data on drug use was collected from the Prescription Register. We included persons who were warfarin users during the study period 2006-2009. Drug combinations increasing bleeding risk with warfarin included selective serotonin reuptake inhibitors (SSRIs), non-steroidal anti-inflammatory agents (NSAIDs), other antithrombotic drugs and tramadol. Factors associated with combination use were investigated with logistic regression.

RESULTS

During the follow-up, 3385 persons with AD and 4830 persons without AD used warfarin. Drug combinations increasing bleeding risk were more common in warfarin users with AD than without AD [35.9 and 30.5%, respectively (p < 0.0001)]. The most common combination was SSRIs and warfarin, which was more common among persons with AD (23.8%) than among persons without AD (10.9%). NSAIDs and warfarin combination was more common among persons without AD. Combination use was associated with AD, female gender, younger age, diabetes mellitus, rheumatoid arthritis and asthma/chronic obstructive pulmonary disease (COPD).

CONCLUSIONS

Use of drug combinations increasing bleeding risk was more common among warfarin users with AD. Special attention should be paid to minimise the duration of concomitant use and to find safer alternatives without increased bleeding risk.

Warfarin-drug interactions: An emphasis on influence of polypharmacy and high doses of amoxicillin/clavulanate

The objective of this study was to investigate the effect of polypharmacy and high doses of amoxicillin/clavulanate on warfarin response in hospitalized patients. This was a prospective cross-sectional observational study on 120 patients from July 2013 to January 2014. Potentially interacting drugs were classified according to their tendency of increasing international normalized ratio (INR) or bleeding risk. The 87.5% of patients prescribed high-dose amoxicillin/clavulanate (10-12 g daily) compared with 28.9% of patients prescribed a normal dose (up to 3.6 g daily) had INR values ≥ 4 during the hospital stay (P ≤ .001). Increased number of potentially interacting drugs that are known to increase INR was a significant predictor of having INR values ≥ 4 (OR, 2.5; 95%CI, 1.3-4.7), and increased number of potentially interacting drugs that are known to increase bleeding risk was a significant predictor of experiencing bleeding episodes (OR, 3.1; 95%CI, 1.3-7.3). High doses of amoxicillin/clavulanate were associated with a higher risk of over-anticoagulation when combined with warfarin than were normal doses. Increased risk of having INR ≥ 4 and bleeding events was associated with increased numbers of potentially interacting drugs prescribed, indicating that polypharmacy is a problem of concern. Frequent monitoring of warfarin therapy along with patients' medications is necessary to avoid complications.

Comparison of warfarin therapy clinical outcomes following implementation of an automated mobile phone-based critical laboratory value text alert system

BACKGROUND

Computerized alert and reminder systems have been widely accepted and applied to various patient care settings, with increasing numbers of clinical laboratories communicating critical laboratory test values to professionals via either manual notification or automated alerting systems/computerized reminders. Warfarin, an oral anticoagulant, exhibits narrow therapeutic range between treatment response and adverse events. It requires close monitoring of prothrombin time (PT)/international normalized ratio (INR) to ensure patient safety. This study was aimed to evaluate clinical outcomes of patients on warfarin therapy following implementation of a Personal Handy-phone System-based (PHS) alert system capable of generating and delivering text messages to communicate critical PT/INR laboratory results to practitioners' mobile phones in a large tertiary teaching hospital.

METHODS

A retrospective analysis was performed comparing patient clinical outcomes and physician prescribing behavior following conversion from a manual laboratory result alert system to an automated system. Clinical outcomes and practitioner responses to both alert systems were compared. Complications to warfarin therapy, warfarin utilization, and PT/INR results were evaluated for both systems, as well as clinician time to read alert messages, time to warfarin therapy modification, and monitoring frequency.

RESULTS

No significant differences were detected in major hemorrhage and thromboembolism, warfarin prescribing patterns, PT/INR results, warfarin therapy modification, or monitoring frequency following implementation of the PHS text alert system. In both study periods, approximately 80% of critical results led to warfarin discontinuation or dose reduction. Senior physicians' follow-up response time to critical results was significantly decreased in the PHS alert study period (46.3% responded within 1 day) compared to the manual notification study period (24.7%; P = 0.015). No difference in follow-up response time was detected for junior physicians.

CONCLUSIONS

Implementation of an automated PHS-based text alert system did not adversely impact clinical or safety outcomes of patients on warfarin therapy. Approximately 80% immediate recognition of text alerts was achieved. The potential benefits of an automated PHS alert for senior physicians were demonstrated.

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.

Effect of novel limited-spectrum MMP inhibitor XL784 in abdominal aortic aneurysms

BACKGROUND

Inhibiting the growth of small abdominal aortic aneurysms (AAAs) is a clinically valuable goal and fills an important therapeutic void. Based on studies in animals and humans, inhibition of the activity of elastolytic matrix metalloproteinases (MMPs) has the potential to slow AAA expansion and limit morbidity and the need for surgery. Previous attempts to make use of the synthetic MMP inhibitors in the treatment of chronic conditions have been limited by intolerable side effects. The limited-spectrum synthetic MMP inhibitor, XL784, was well tolerated and devoid of side-effects associated with other nonspecific MMP inhibitors in phase I studies. We hypothesized that clinically relevant doses of XL784 would be effective at inhibiting aneurysm development in a mouse model.

METHODS

The 14-day elastase-perfusion model of AAA in mice was used. An initial screening study of XL784 (50 [n = 17], 125 [n = 17], and 250 mg/kg [n = 18]) administered via gavage daily until harvest. Controls received diluent alone (n = 18) or doxycycline in drinking water (n = 19). Aortic diameter was measured pre-perfusion (AD(pre)) and at harvest (AD(har)). A second study used XL784 (250 [n = 9]; 375 [n = 9], and 500 mg/kg [n = 14]) and diluent alone (n = 9) administered via gavage. The percentage dilatation [%ΔAD = [(AD(har) - AD(pre))/AD(pre)] ×100] was calculated and elastin and inflammatory content was scored.

RESULTS

All mice tolerated the treatments similarly. Control mice all developed aneurysms with a mean %ΔAD of 158.5% ± 4.3%. Treatment with all doses of XL784 and doxycycline were effective in inhibiting aortic dilatation. There was a clear dose-response relationship between XL784 and reductions in aortic dilatation at harvest (50 mg/kg 140.4% ± 3.2%; 125 mg/kg 129.3% ± 5.1%; 250 mg/kg 119.2% ± 3.5%; all Ps < .01 compared to control). This continued with the higher doses (375 mg/kg 88.6% ± 4.4%; 500 mg/kg 76.0% ± 3.5%). The highest 2 doses of XL784 tested were more effective than doxycycline (112.2% ± 2.0%, P < .05) in inhibiting maximal dilatation of the aorta after elastase perfusion.

Risk of hemorrhage and treatment costs associated with warfarin drug interactions in patients with atrial fibrillation

BACKGROUND

Drug interactions with warfarin are common and may be responsible for increased patient morbidity and treatment costs.

OBJECTIVES

To assess the usage patterns of drugs that potentiate warfarin's anticoagulant activity and discuss their associated relationship with both risk of hemorrhage and treatment costs among warfarin users with atrial fibrillation (AF).

METHODS

A nested case-control study of long-term warfarin-treated AF patients was conducted using a health insurance claims database. Patients with a hemorrhagic event (cases) were matched to control patients using the incidence density sampling method. Drug-potentiating warfarin effects were identified within 30 days before the hemorrhagic event. Conditional logistic regression was used to calculate the association between use of potentiating drugs and hemorrhage risk. Mean treatment costs and CIs were calculated using the bootstrap method and tested using the t-test. Factors associated with treatment costs were determined using generalized linear models with the log-link function and γ distribution.

RESULTS

Approximately 80% of AF patients were prescribed at least 1 warfarin-potentiating medication while taking warfarin. Patients who used these medications had a 26% higher risk of hemorrhage compared with those who did not use these drugs. Likelihood of hemorrhagic events was significantly increased with the use of potentiating drugs from the following therapeutic classes: anticoagulants (odds ratio [OR] = 1.91), anti-infectives (OR = 1.76), antiplatelets (OR = 1.56), and analgesics (OR = 1.33). The risk also increased when patients took ≥3 therapeutic classes of interacting medications (OR = 1.62-1.85). Among patients with a hemorrhagic event, patients who were prescribed potentiating drugs had higher hemorrhage-related treatment costs ($1359) compared with those patients without prescriptions for warfarin-potentiating drugs ($691; P < 0.001).

CONCLUSIONS

Warfarin-potentiating drugs were commonly used among AF patients on warfarin. The use of potentiating drugs increased the risk of a hemorrhage, leading to higher treatment costs. More frequent monitoring or alternative anticoagulant therapies are needed to avoid frequent warfarin drug interactions.

Stroke prevention in elderly patients with atrial fibrillation: challenges for anticoagulation

Elderly patients with atrial fibrillation (AF), who constitute almost half of all AF patients, are at increased risk of stroke. Anticoagulant therapies, especially vitamin K antagonists (VKA), reduce the risk of stroke in all patients including the elderly but are frequently under-used in older patients. Failure to initiate VKA in elderly AF patients is related to a number of factors, including the limitations of current therapies and the increased risk for major haemorrhage associated with advanced age and anticoagulation therapy. Of particular concern is the risk of intracranial haemorrhages (ICH), which is associated with high rates of mortality and morbidity. Novel oral anticoagulant agents that are easier to use and might offer similar or better levels of stroke prevention with a similar or reduced risk of bleeding should increase the use of antithrombotic therapy in the management of elderly AF patients. Amongst these new agents, the recently approved direct thrombin inhibitor dabigatran provides effective stroke prevention with a significant reduction of ICH, and enables clinicians to tailor the dose according to age and haemorrhagic risk.

Evaluation of warfarin drug interaction listings in US product information for warfarin and interacting drugs

BACKGROUND

Because interactions with warfarin represent a serious risk to patients, drug information sources used by clinicians should contain accurate, timely, and practical drug interaction information.

OBJECTIVE

The aim of this study was to assess the information regarding warfarin interactions that is included in the official labeling of prescription products that interact with warfarin.

METHODS

We examined the official labeling information approved by the US Food and Drug Administration for the 50 drugs, biologics, and drug classes that were commonly identified by 3 drug information compendia--Clinical Pharmacology, ePocrates(®), and Micromedex(®)--and the warfarin US prescribing information (PI) as having an interaction with warfarin. The PI of each product was assessed for possible mention of an interaction with warfarin. The data were collected and tabulated by 1 investigator. A clinical investigator evaluated the data for accuracy and consistency. Unresolved issues were discussed with a third investigator and decided by consensus. The interaction listings were compared to determine similarities, differences, and inconsistencies and analyzed by 5 investigators.

RESULTS

Of the labeling for 73 products evaluated, 62 (85%) included mention of an interaction with warfarin. Those failing to mention the warfarin interaction were for older generic drugs or influenza vaccine. Among the labels listing an interaction with warfarin, the location of the information, the terminology used, and the inclusion of evidence for the interaction was inconsistent . When considering the PI for all 73 products, Fleiss' kappa coefficient (κ = 0.467) suggested moderate concordance according to the method of Landis and Koch.

CONCLUSION

This assessment of official US product labeling for 50 drugs, biologics, and drug classes known to interact with warfarin, comprising 73 distinct agents, found that 15% failed to mention the interaction, even though the interaction was mentioned in the warfarin labeling.

Warfarin-associated bleeding events and concomitant use of potentially interacting medicines reported to the Norwegian spontaneous reporting system

AIMS

To study warfarin associated bleeding events reported to the Norwegian spontaneous reporting system and evaluate the differences in assessment of potentially interacting medicines between reporters and evaluators.

METHODS

Data on bleeding events on warfarin were retrieved from the Norwegian spontaneous reporting system database. Key measurements were time to bleeding, use of concomitant medications and the evaluation done by reporters.

RESULTS

In 289 case reports a total of 1261 medicines (median 4.0 per patient, range 1-17) was used. The evaluators (authors of this article) identified 546 medicines including warfarin (median 2.0 per patient, range 1-7) that could possibly cause bleeding alone or in combination. Reporters assessed 349 medicines (median 1.0 per patient, range 1-4) as suspect. Evaluators identified 156 pharmacokinetic and 101 pharmacodynamic interactions, compared with 19 pharmacokinetic and 56 pharmacodynamic interactions reported as suspected by the reporters. Time to bleeding was stated in 224 reports. Among the early bleeding events, the reports on warfarin without interacting medicines showed the highest INR (international normalized ratio). Heparin was used in 17/21 reported bleeding events during the first week on warfarin. Among the late bleeding events, reports with pharmacokinetic interacting medicines had the highest INR.

CONCLUSIONS

Concomitant use of potentially interacting medicines was involved in the majority of the warfarin-associated bleeding events reported to the Norwegian spontaneous reporting system. Reporters assessed mostly warfarin as the only contributor to bleeding. In particular, pharmacokinetically interacting medicines were not suspected as contributing to bleeding.

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.

Drug-drug interactions in a geriatric outpatient cohort: prevalence and relevance

BACKGROUND

The prevalence of drug-drug interactions (DDIs) in a geriatric population may be high because of polypharmacy. However, wide variance in the clinical relevance of these interactions has been shown.

OBJECTIVES

To explore whether adverse drug reactions (ADRs) as a result of DDIs can be identified by clinical evaluation, to describe the prevalence of ADRs and diminished drug effectiveness as a result of DDIs and to verify whether the top ten most frequent potential DDIs known to public pharmacies are of primary importance in geriatric outpatients in the Netherlands.

METHOD

All adverse events classified by the Naranjo algorithm as being a possible ADR and drug combinations resulting in diminished drug effectiveness were identified prospectively in 807 geriatric outpatients (mean age 81 years) at their first visit. The setting was a diagnostic day clinic. The Medication Appropriateness Index (MAI) and Beers criteria were used to evaluate drug use and identify possible DDIs. The ten most frequent potential interactions, according to a 1997 national database of public pharmacies ('Top Ten') in the Netherlands, and possible adverse events as a result of other interactions, were described. The effects of changes in medication regimen were recorded by checking the medical records.

RESULTS

In 300 patients (44.5% of the 674 patients taking more than one drug), 398 potential DDIs were identified. In 172 (25.5%) of patients taking more than one drug, drug combinations were identified that were responsible for at least one ADR or which possibly resulted in reduced effectiveness of therapy. Eighty-four of the 158 possible ADRs resulting from enhanced action of drugs forming combinations listed in the 'Top Ten' were seen in 73 patients. Only four DDIs resulting in less effective therapy that involved drug combinations in the 'Top Ten' were identified. Changes in drug regimens pertaining to possible interactions were proposed or put into effect in 111 of the 172 (65%) patients with possible DDIs. Sixty-one (55%) of these patients returned for follow-up. Of these, 49 (80%) were shown to have improved after changes were made to their medication regimen.

CONCLUSION

In this study, nearly half of the geriatric outpatients attending a diagnostic day clinic who were taking more than one drug were candidates for DDIs. One-quarter of these patients were found to have possible adverse events or diminished treatment effectiveness that may have been at least partly caused by these DDIs. These potential interactions can be identified through clinical evaluation. In the majority of patients (99 of 172) the potential interactions resulting in possible ADRs or diminished effectiveness were not present in the 'Top Ten' interactions described by a national database of public pharmacies, a finding that emphasizes that the particular characteristics of geriatric patients (e.g. frequent psychiatric co-morbidities) need to be considered when evaluating their drug use. At least 7% of all patients taking more than one drug, and 80% of those with possible drug interactions whose drug regimen was adjusted, benefited from changes made to their drug regimens.

Risk of major bleeding during concomitant use of antibiotic drugs and coumarin anticoagulants

BACKGROUND

Coumarin anticoagulants are prone to drug-drug interactions. For example, antibiotic drugs may enhance the anticoagulant effect of coumarins. However, whether such interactions are associated with an increased risk of bleeding, and if so, how frequently this occurs remains unknown.

OBJECTIVE

To assess the risk of major bleeding associated with the concomitant use of antibiotic drugs and coumarin anticoagulant therapy.

METHODS

We analyzed a retrospective cohort study including all users of acenocoumarol or phenprocoumon in the PHARMO Record Linkage System (age range: 40-80 years). All patients were followed up until end of last coumarin treatment, hospitalization for bleeding, death, or end of study period. For each patient, the number of days on either coumarins alone, or on coumarins in combination with antibiotic drugs was determined. From these data, the relative risks of major bleeding were calculated.

RESULTS

A total of 52,102 users of acenocoumarol and 7885 users of phenprocoumon met the inclusion criteria of our study cohort and contributed 139,159 person-years of follow-up. During follow-up, 838 patients (1.4%) were hospitalized for a bleeding while taking coumarins. Of the 62 different antibiotics taken by study members, 19 were associated with a bleeding episode. Of these, 10 were associated with a statistically significant increased bleeding risk. The relative risk of bleeding was three to five for doxycycline, amoxicillin, amoxicillin/clavulanic acid, ciprofloxacin, cotrimoxazole, azithromycin and pheneticillin, nine for tetracycline and 43 for cefradine and neomycin.

CONCLUSION

Based on relative risks and incidence of use, amoxicillin (alone or with clavulanic acid) and doxycycline are the main antibiotic drugs associated with major bleeding when used in combination with coumarin.

Quantity and quality of potential drug interactions with coumarin anticoagulants in the Netherlands

OBJECTIVE

Coumarin anticoagulants are prone to potentially life-threatening drug-drug interactions due to a combination of unfavorable properties. However, real life data on the actual occurrence are scarce. The aim of this study was to quantify and qualify potential drug interactions with coumarin anticoagulants in daily practice.

METHODS

A cohort study including all users of phenprocoumon or acenocoumarol during the period 1991-2003 in the PHARMO Record Linkage System. All 24 individual drugs and 11 drug groups interacting with coumarins according to central database used in the Dutch pharmacies were considered.

MAIN OUTCOME MEASURE

Frequency and type of potential drug interactions during anticoagulant therapy with coumarins.

RESULTS

48,627 out of 76,455 mainly acenocoumarol-users (64%) were dispensed at least one potentially interacting drug (PID) during anticoagulant therapy. About 35% of these cases were dispensed a (very) strongly interacting drug, whereas 3% were dispensed a contraindicated drug. Antibacterial drugs and NSAIDs (39% and 37% of all users, respectively) were the most frequently dispensed PIDs.

CONCLUSION

Potential drug interactions with coumarins frequently occur in daily practice, confronting two-thirds of patients with an increased risk of bleeding. To a large part, this is attributable to commonly prescribed medication like antibacterial drugs and NSAIDs. This situation substantiates the need for proper monitoring or new anticoagulants with less drug-drug interactions.

Utilization review of concomitant use of potentially interacting drugs in Thai patients using warfarin therapy

PURPOSE

In Thailand, there has been no study determining the concomitant use of medications, known to potentially interact with warfarin, in patients receiving warfarin therapy. This paper examined the frequency of which specific interacting drugs were concomitantly used in warfarin users.

METHODS

We retrospectively examined the database of warfarin outpatient medical records from a regional 756-bed hospital located in the north of Thailand. All patients receiving warfarin from 10 June 1999 to 4 August 2004 were reviewed to identify all drugs possessing interaction potential with warfarin. The potential of significant interactions were divided into high, moderate and low, according to the extent of evidence documented in textbooks and literature.

RESULTS

Among 1093 patients receiving warfarin therapy, 914 (84%) patients received at least one potentially interacting drug and half of them (457 patients) received at least one drug with high potential for interaction. The most frequently concomitant drug that increased INR was acetaminophen (63%, 316/457). Propylthiouracil was the most frequently concomitant drug that decreased INR response (4%, 19/457), while diclofenac was the most frequently concomitant drug that increased bleeding risk (16%, 73/457).

CONCLUSIONS

About a half of patients receiving warfarin therapy was prescribed concomitant drug(s) that has a high potential of interactions with warfarin. These patients should be closely monitored and counselled to watch for signs and symptoms of bleeding and thrombosis to avoid adverse events associated with drug interactions.

Intracerebral haemorrhage: an often neglected medical emergency

Intracerebral haemorrhage (ICH) is the deadliest form of stroke, carrying a mortality rate between 30% and 55%, increasing to 67% in patients on oral anticoagulant therapy (OAT). Despite its relevant incidence, the treatment of ICH has been until recently a largely neglected item, addressed by only a few trials. Early treatment of ICH in non-anticoagulated patients with recombinant activated factor VII (rFVII) has been demonstrated to be able to limit the growth of the haematoma, but such a promising result requires further confirmations. In ICH patients receiving OAT a prompt reversal of the anticoagulant effect should be warranted in order to reduce the consequences of this dreadful adverse event. In clinical practice, however, just a small proportion of anticoagulated patients receive this treatment, probably because of the fear of thromboembolic complications. It is now time to check our way of thinking about ICH, regarding and treating it as a compelling medical emergency.

Development of a Contemporary Bleeding Risk Model for Elderly Warfarin Recipients

BACKGROUND AND PURPOSE

Develop and validate a contemporary bleeding risk model to guide the clinical use of warfarin in the elderly atrial fibrillation (AF) population.

METHODS

Chart-abstracted data from the National Registry of Atrial Fibrillation was combined with Medicare part A claims to identify major bleeding events requiring hospitalization. Using a split-sample technique, candidate variables that provided statistically stable relationships with major bleeding events were selected for model development. Three risk categories were created and validated. The new model was compared to existing bleeding risk models using c-statistics and Kaplan-Meier curves.

RESULTS

Model development and validation was conducted on 26,345 AF patients who were > 65 years of age and had been discharged from the hospital while receiving warfarin therapy. The following eight variables were included in the final risk score model: age > or = 70 years; gender; remote bleeding; recent (ie, during index hospitalization) bleeding; alcohol/drug abuse; diabetes; anemia; and antiplatelet use. Bleeding rates were 0.9%, 2.0%, and 5.4%, respectively, for the groups with low, moderate, and high risk, compared to the bleeding rates for groups with moderate risk (1.5% and 1.0%) and high risk (1.8% and 2.5%) from other models.

CONCLUSIONS

Using a nationally derived data set, we developed a model based on contemporary practice standards for determining major bleeding risk among AF patients receiving warfarin therapy. The larger sample size afforded the opportunity to incorporate additional risk factors. In addition, since the majority of our population was > 65 years of age, we had greater ability to stratify risk among the elderly.

Consultation de pharmacie et niveau de connaissance des patients hospitalisés traits par des médicaments anti-vitamine K

The report published by the French Agency for the Medical Safety of Health Products in 2001 estimated the number of hospital admissions in France for hemorrhagic accidents caused by oral anticoagulants (OA) to be 17,000. For this reason, we have set up pharmaceutical counselling for hospitalized patients treated with OA. The object of this article is to describe this therapeutic education program and to present the level of knowledge that patients have of their OA treatment. Among 68 patients treated prior to their admission, 87% knew the name of the OA, 86% the role of this treatment, 80% the dosing schedule, 57% what to do if a dose had been forgotten, 34% the signs of overdose, 48% the signs of and risks associated with not following the treatment schedule, 94% the advantage of biological follow-up and 68% the principal combinations of drugs that should be avoided. Among 118 patients whose treatment was begun during hospitalization, the level of knowledge for each item were respectively: 41%, 61%, 38%, 37%, 19%, 23%, 34% and 24% at the time of counselling. Newly treated patients acquired their knowledge from contact with nurses. The least known items were the symptoms and risks associated with overdosing or underdosing. This knowledge is therefore fragmentary and does not guarantee the patients' safety, which justifies the proposition of this type of counselling to such hospitalized patients.

Interaction of warfarin with drugs, natural substances, and foods

Variability in the anticoagulant response to warfarin is an ongoing clinical dilemma. Fluctuations in dietary vitamin K are an important source of variance, and the need for constancy in vitamin K intake is routinely emphasized for warfarin-treated patients. Anticoagulant response is also influenced by a number of drugs that induce or inhibit warfarin metabolism, as well as by genetic polymorphisms that may modulate expression or activity of CYP2C9, the isoform mediating clearance of S-warfarin. The possible role of dietary factors other than vitamin K, as well as of herbal medicines or supplements as contributors to the instability of anticoagulation in warfarin-treated patients, has received recent attention. St. John's wort and possibly some ginseng formulations may have the potential to diminish warfarin anticoagulation, apparently by inducing CYP2C9 activity. Otherwise, there is no reliable evidence to indicate that any dietary component (other than vitamin K) or any herbal product has an effect on the anticoagulant response to warfarin. Scientific conclusions on this important therapeutic issue should be based on valid scientific data rather than unvalidated case reports.

Differential associations of beta-blockers with hemorrhagic events for chronic heart failure patients on warfarin

PURPOSE

Beta-blockers have many different physiologic effects that could potentially influence the risk of hemorrhagic events in chronic heart failure patients (CHF) on warfarin. We examined how different beta-blockers vary in their associated risk of a hemorrhagic event.

METHODS

We used databases from the Department of Veterans Affairs (VA) that contain information on medications prescribed, diagnoses, and hospitalizations. We identified patients with CHF on warfarin and either metoprolol, carvedilol, atenolol, or no beta-blocker during 1999-2001. We modeled time to first hemorrhagic event using a Cox proportional hazards model, adjusting for age, ethnicity, comorbidities, and other factors. INR levels were examined in a subsample of 3546 patients.

RESULTS

We identified 66,988 CHF patients on warfarin. Hemorrhagic events occurred in 15.3% of the sample and, in 3.8% of the sample, the hemorrhage was considered severe. Compared to patients on carvedilol, the hazards ratio for a new hemorrhagic event was 1.25 (1.17, 1.34) for no beta-blocker, 1.27 (1.18, 1.38) for atenolol, and 1.38 (1.28, 1.48) for metoprolol. No differences in INR levels were evident among the four groups.

CONCLUSIONS

The risk for a hemorrhagic event among CHF patients on warfarin may be affected by beta-blocker use and varies depending on which beta-blocker is prescribed.

Search for Predictors of Nontherapeutic INR Results with Warfarin Therapy

BACKGROUND

The effectiveness and safety of warfarin require maintaining an international normalized ratio (INR) within the therapeutic range.

OBJECTIVE

To identify predictors of nontherapeutic INR results in patients receiving warfarin.

METHODS

A retrospective study was conducted using 350 ambulatory care patients from a broad geographic region, all receiving long-term warfarin therapy and followed in a tertiary-care cardiology clinic. Possible predictors of nontherapeutic INR results (gender, age, body weight, body mass index, height, race, tobacco use, alcohol use, warfarin dose, therapeutic indication, regimen intensity, INR monitoring frequency/category, interacting medications, adverse events) were assessed with logistic regression models. Subset analysis involved 146 patients concurrently monitored with capillary whole blood INR (CoaguChek).

RESULTS

As measured on venous specimens, 52% (182/350) of the patients had subtherapeutic INR results and 13% (44/350) had supratherapeutic INR results despite frequent (≤4 wk) monitoring in 75% of the patients. Due to the small sample size, supratherapeutic INR results could not be further analyzed. Of 19 predictors tested, only daily warfarin dose (p < 0.02) and regimen intensity (p < 0.03) were significant independent and additive predictors of subtherapeutic results. Patients on the high-intensity regimen (INR 2.5–3.5) and receiving warfarin ≤6 mg/day had >50% risk of having subtherapeutic INR results. Subtherapeutic CoaguChek results were independent predictors of subtherapeutic venipuncture INR results in the subset (p = 0.001).

CONCLUSIONS

In the absence of readily identifiable predictors, only higher warfarin dosing and/or more frequent monitoring (possibly with point-of-care/home monitoring devices) may minimize the time that INRs are subtherapeutic, especially in patients receiving low-dose and/or high-intensity anticoagulation therapy.

Treatment patterns and real-world effectiveness of warfarin in nonvalvular atrial fibrillation within a managed care system

OBJECTIVE

To examine warfarin utilization and clinical effectiveness among patients with nonvalvular atrial fibrillation within usual clinical care in a managed care system.

RESEARCH DESIGN AND METHODS

A retrospective analysis of health care claims for an approximately four million member managed care organization was performed. Health plan members with a diagnosis of nonvalvular atrial fibrillation in calendar year 2000 were identified and stratified into two cohorts: Warfarin Therapy (newly initiating warfarin) or Warfarin Candidates (eligible for warfarin therapy according to the ACC/AHA/ESC Guidelines for the Management of Patients with Atrial Fibrillation, but did not receive warfarin).

MEASUREMENTS

The occurrence of thromboembolism, ischemic stroke, and hemorrhage during a maximum 720-day follow-up were compared between cohorts, adjusting for age, gender, and other risk factors, using Cox regression.

RESULTS

Among 12 539 subjects (mean age 78.0 +/- 8.8 years) with nonvalvular atrial fibrillation, 4895 (39.0%) initiated Warfarin Therapy and 7644 (61.0%) were Warfarin Candidates. Event occurrences among Warfarin Therapy vs. Warfarin Candidates were: ischemic stroke, 3.7% vs. 4.5%; any thromboembolism, 7.8% vs. 10.8%; and hemorrhage, 4.4% vs. 4.9%, respectively. Warfarin therapy was not associated with an increased risk for hemorrhage (hazard ratio [HR] = 0.97, 95% confidence interval [CI] = 0.82-1.15), while risks for ischemic stroke and any thromboembolism were significantly reduced, by 22% (HR = 0.78, 95% CI = 0.65-0.93) and 34% (HR = 0.66, 95% CI = 0.59-0.75), respectively.

CONCLUSIONS

Within usual clinical care for the managed care population examined, warfarin remains underused despite current guidelines recommending its use in nearly all patients with nonvalvular atrial fibrillation. Although utilization of anticoagulation clinics and INR values attained were unknown in this study, the observed risk reductions for ischemic stroke and thromboembolism were lower than those achieved in clinical trials, while no increased risk for hemorrhage was observed. These findings suggest that warfarin is used conservatively, and dosed cautiously, diminishing the full potential benefit of anticoagulant therapy in patients with nonvalvular atrial fibrillation.

Concomitant drug, dietary, and lifestyle issues in patients with atrial fibrillation receiving anticoagulation therapy for stroke prophylaxis

Atrial fibrillation is a common cardiac arrhythmia and the leading risk factor for stroke. In those at moderate to high risk of stroke, oral anticoagulation therapy with warfarin (a vitamin K antagonist) significantly reduces not only the frequency of such events but also their severity and the associated risk of death. However, achieving optimal anticoagulation with this agent is clinically challenging in view of its complex pharmacokinetic and pharmacodynamic profile. In this regard, concomitant drug therapy (both prescription and over-the-counter medications, including herbal products, vitamins, and various nutritional supplements), along with alcohol intake, dietary factors, and changes in lifestyle, can significantly affect anticoagulation control and thereby expose patients to the risk of bleeding or thromboembolic complications (due to over- and underanticoagulation, respectively). Therefore, it is recommended that intensified monitoring of anticoagulation be performed at initiation and discontinuation of concomitant drug therapy, and in the case of significant dietary and lifestyle changes. Moreover, many patients receive inadequate education and are unaware of such risks and their implications, highlighting the need for better awareness and education on this important aspect of anticoagulation therapy.

Deadly drug interactions in emergency medicine

Many life-threatening drug interactions are predictable, avoidable events. Emergency medicine physicians have a responsibility to recognize and prevent drug interactions. Keeping current on the many pharmaceutical therapies,their pharmacology, and potential drug interactions currently represents one of the biggest challenges for emergency medicine practitioners. Using current drug interaction resources and knowing the limited number of medications that are responsible for the most serious drug interactions can ease this seemingly overwhelming burden greatly. Clinicians need to be particularly vigilant when prescribing drugs for patients who are taking medications with potential for drug interactions leading to serious consequences.

Frequency of Concurrent Use of Warfarin with Potentially Interacting Drugs

STUDY OBJECTIVE

To determine the rates of concomitant use of drugs known to interact with warfarin by increasing the prothrombin time expressed as the international normalized ratio (INR), decreasing the INR, or increasing bleeding risk without apparent changes in INR in a cohort of patients receiving long-term warfarin therapy.

DESIGN

Retrospective, longitudinal cohort study.

SETTING

Large pharmacy benefits manager database.

PATIENTS

A total of 134,833 patients who were prescribed long-term warfarin from June 1, 1999-May 31, 2000.

MEASUREMENTS AND MAIN RESULTS

Longitudinal pharmacy claims from the pharmacy benefits manager database were reviewed to identify coprescription of warfarin and drugs associated with significant interactions with warfarin. Of the 134,833 patients receiving long-term warfarin therapy, 109,998 (81.6%) were prescribed a concurrent prescription for at least one potentially interacting drug, including 87,346 (64.8%) who were prescribed one or more concomitant drugs associated with interactions known to increase the INR. Acetaminophen-containing products, prescribed for 22.7% of patients receiving concomitant prescriptions, and thyroid hormones, prescribed for 17.5%, were the most commonly prescribed concurrent drugs associated with an increased INR response. The most frequently prescribed interacting agents associated with a decreased INR response were trazodone (2.2%) and carbamazepine (1.1%). The most commonly prescribed agents independently associated with increased bleeding risk were cyclooxygenase-2 inhibitors.

CONCLUSION

Many patients receiving warfarin therapy are treated with concomitant drugs that may interact with the warfarin. The high percentage of patients taking drugs that may increase INR or bleeding risk is a reminder that bleeding events are a likely adverse outcome of combining drugs that interact with warfarin. Careful warfarin management is necessary to avoid adverse events associated with drug interactions.

Combined Anticoagulant–Antiplatelet Use and Major Bleeding Events in Elderly Atrial Fibrillation Patients

Background and Purpose— Bleeding risks from combined antiplatelet-warfarin therapy have not been well-described in clinical practice. We examined antiplatelet therapy among warfarin users and the impact on major bleeding rates.

Methods— Retrospective cohort analysis of persons discharged on warfarin after an atrial fibrillation admission using data from Medicare’s National Stroke Project. Data included Medicare claims, enrollment information, and medical record abstracted data. Logistic regression and Cox proportional hazards models were used to predict concurrent antiplatelet use and hospitalization with a major acute bleed within 90 days after discharge from the index AF admission.

Results— 10 093 warfarin patients met inclusion criteria with a mean age of 77 years; 19.4% received antiplatelet therapy. Antiplatelet use was less common among women, older persons, and persons with cancer, terminal diagnoses, dementia, and bleeding history. Persons with coronary disease were more likely to receive an antiplatelet agent. Antiplatelets increased major bleeding rates from 1.3% to 1.9% ( P =0.052). In the multivariate analysis, factors associated with bleeding events included age (OR, 1.03; 95% CI, 1.002 to 1.05), anemia (OR, 2.52; 95% CI, 1.64 to 3.88), a history of bleeding (OR, 2.40; 95% CI, 1.71 to 3.38), and concurrent antiplatelet therapy (OR, 1.53; 95% CI, 1.05 to 2.22).

Conclusions— Although concerns about increased bleeding risk with combined warfarin-antiplatelet therapy are not unfounded, the risk of bleeding is moderately increased. The decision to use concurrent antiplatelet therapy appears to be tempered by cardiac and bleeding risk factors.