Warfarin and Antiplatelet Combination Use Among Commercially Insured Patients Enrolled in an Anticoagulation Management Service

Outcomes of direct oral anticoagulants with aspirin vs warfarin with aspirin: a registry-based cohort study

Background

For patients anticoagulated with direct oral anticoagulants (DOACs) or warfarin and on aspirin (ASA) for nonvalvular atrial fibrillation and/or venous thromboembolism, it is unclear if bleeding outcomes differ.

Objectives

To assess bleeding rates for ASA with DOACs vs warfarin and one another.

Methods

Registry-based cohort study of patients followed by a 6-center quality improvement collaborative in Michigan using data from 2009 to 2022. The study included adults on ASA with warfarin or DOACs for atrial fibrillation and/or venous thromboembolism without a recent myocardial infarction or heart valve replacement.

Results

After propensity matching by anticoagulant class, we compared 2 groups of 1467 patients followed for a median of 18.0 months. Any bleeding and nonmajor bleeding was increased with DOACs + ASA compared with warfarin + ASA (32.2 vs 27.8 and 27.1 vs 22.9 events/100 patient-years; relative risks [RRs], 1.1 and 1.2; 95% CIs, 1.1-1.2 and 1.1-1.3, respectively). After matching by drug, patients on apixaban + ASA vs warfarin + ASA had more bleeding (31.2 vs 27.8 events/100 patient-years; RR, 1.1; 95% CI, 1.0-1.2) and nonmajor bleeding but less major bleeding (3.8 vs 4.7 events/100 patient-years; RR, 0.8; 95% CI, 0.6-1.0) and emergency room visits for bleeding. Patients on rivaroxaban + ASA vs warfarin + ASA had more bleeding (39.3 vs 26.3 events/100 patient-years, RR, 1.5; 95% CI, 1.3-1.6), nonmajor bleeding, and thrombosis. Patients on apixaban + ASA vs rivaroxaban + ASA had significantly less bleeding (22.5 vs 39.3/100 patient-years; RR, 0.6; 95% CI, 0.5-0.7), nonmajor bleeding, major bleeding (2.1 vs 5.5 events/100 patient-years; RR, 0.4; 95% CI, 0.2-0.6), emergency room visits for bleeding, and thrombotic events.

Conclusion

Patients on DOAC + ASA without a recent myocardial infarction or heart valve replacement had more nonmajor bleeding but otherwise similar outcomes compared with warfarin + ASA. Patients treated with rivaroxaban + ASA experienced more adverse clinical events compared with warfarin + ASA or apixaban + ASA.

Assessment of an Intervention to Reduce Aspirin Prescribing for Patients Receiving Warfarin for Anticoagulation

IMPORTANCE

For some patients receiving warfarin, adding aspirin (acetylsalicylic acid) increases bleeding risk with unclear treatment benefit. Reducing excess aspirin use could be associated with improved clinical outcomes.

OBJECTIVE

To assess changes in aspirin use, bleeding, and thrombosis event rates among patients treated with warfarin.

DESIGN, SETTING, AND PARTICIPANTS

This pre-post observational quality improvement study was conducted from January 1, 2010, to December 31, 2019, at a 6-center quality improvement collaborative in Michigan among 6738 adults taking warfarin for atrial fibrillation and/or venous thromboembolism without an apparent indication for concomitant aspirin. Statistical analysis was conducted from November 26, 2020, to June 14, 2021.

INTERVENTION

Primary care professionals for patients taking aspirin were asked whether an ongoing combination aspirin and warfarin treatment was indicated. If not, then aspirin was discontinued with the approval of the managing clinician.

MAIN OUTCOMES AND MEASURES

Outcomes were assessed before and after intervention for the primary analysis and before and after 24 months before the intervention (when rates of aspirin use first began to decrease) for the secondary analysis. Outcomes included the rate of aspirin use, bleeding, and thrombotic outcomes. An interrupted time series analysis assessed cumulative monthly event rates over time.

RESULTS

A total of 6738 patients treated with warfarin (3160 men [46.9%]; mean [SD] age, 62.8 [16.2] years) were followed up for a median of 6.7 months (IQR, 3.2-19.3 months). Aspirin use decreased slightly from a baseline mean use of 29.4% (95% CI, 28.9%-29.9%) to 27.1% (95% CI, 26.1%-28.0%) during the 24 months before the intervention (P < .001 for slope before and after 24 months before the intervention) with an accelerated decrease after the intervention (mean aspirin use, 15.7%; 95% CI, 14.8%-16.8%; P = .001 for slope before and after intervention). In the primary analysis, the intervention was associated with a significant decrease in major bleeding events per month (preintervention, 0.31%; 95% CI, 0.27%-0.34%; postintervention, 0.21%; 95% CI, 0.14%-0.28%; P = .03 for difference in slope before and after intervention). No change was observed in mean percentage of patients having a thrombotic event from before to after the intervention (0.21% vs 0.24%; P = .34 for difference in slope). In the secondary analysis, reducing aspirin use (starting 24 months before the intervention) was associated with decreases in mean percentage of patients having any bleeding event (2.3% vs 1.5%; P = .02 for change in slope before and after 24 months before the intervention), mean percentage of patients having a major bleeding event (0.31% vs 0.25%; P = .001 for change in slope before and after 24 months before the intervention), and mean percentage of patients with an emergency department visit for bleeding (0.99% vs 0.67%; P = .04 for change in slope before and after 24 months before the intervention), with no change in mean percentage of patients with a thrombotic event (0.20% vs 0.23%; P = .36 for change in slope before and after 24 months before the intervention).

CONCLUSIONS AND RELEVANCE

This quality improvement intervention was associated with an acceleration of a preexisting decrease in aspirin use among patients taking warfarin for atrial fibrillation and/or venous thromboembolism without a clear indication for aspirin therapy. Reductions in aspirin use were associated with reduced bleeding. This study suggests that an anticoagulation clinic-based aspirin deimplementation intervention can improve guideline-concordant aspirin use.

A descriptive study of antithrombotic medication patterns in adult patients with recent venous thromboembolism

Objectives:

The objective of this study is to describe the most common self-reported antithrombotic therapy utilization patterns in a national cohort of patients with recent venous thromboembolism (VTE).

Methods:

Extant data from a national online survey administered to 907 patients 18 years of age or older with VTE in the last two years were analyzed. Patients’ self-reported antithrombotic usage patterns used during three phases of treatment for the most recent VTE episode were summarized using descriptive statistics.

Results:

The following overall antithrombotic usage patterns were identified: warfarin (38.7%), direct oral anticoagulants (DOACs) (26.1%), switching between warfarin and DOACs (13.3%), aspirin only (8.7%), switching between different DOACs (4.5%), injectable anticoagulants only (3.9%), and no treatment (4.7%). Extended antithrombotic therapy beyond 90 days was reported by 65.7% of patients. Aspirin coadministration with anticoagulant therapy occurred for 33.7%.

Conclusions:

In this national sample of recent VTE sufferers warfarin therapy remains the most used anticoagulant followed closely by DOAC therapy. Switching between warfarin and DOACs and between different DOACs was common which could indicate adverse events or affordability issues. Aspirin coadministration with anticoagulant therapy was present in 1 of 3 patients and is a potential medication safety intervention for anticoagulation providers.

The Prevalence and Risks of Inappropriate Combination of Aspirin and Warfarin in Clinical Practice: Results From WARFARIN-TR Study

Background

The use of warfarin and aspirin in combination is restricted to limited patients under relevant guidelines.

Aims

To evaluate the prevalence of the inappropriate combination of aspirin and warfarin therapy in daily practice and its risks.

Study Design

Cross-sectional study.

Methods

The awareness, efficacy, safety, and time in the therapeutic range of warfarin in the Turkish population study is a multi-center observational study that includes 4987 patients using warfarin for any reason between January 1, 2014, and December 31, 2014. To determine the prevalence of inappropriate combination use in daily practice, all patients who had a history of atherosclerotic disease (ischemic heart disease, peripheral artery disease) or cerebrovascular disease (n=1498) were excluded. The data of 3489 patients were analyzed. We defined inappropriate combination as all patients who received aspirin and warfarin regardless of the indication for warfarin use, under the direction of the European Society of Cardiology guideline recommendation.

Results

The mean age of patients was 59.2±13.8 years (41.8% male). The prevalence of the inappropriate use of warfarin and aspirin combination was 20.0%. The prevalence of combination therapy in patients with a primary indication for mechanical heart valve, non-valvular atrial fibrillation, and other reasons was 20.5%, 18.7%, and 21.0%, respectively. Multivariate logistic regression analysis revealed that age (odds ratio, 1.009; 95% confidence interval, 1.002-1.015; p=0.010), heart failure (odds ratio, 1.765; 95% confidence interval, 1.448-2.151; p<0.001), smoking (odds ratio, 1.762; 95% confidence interval, 1.441-1.153; p<0.010), chronic kidney disease (odds ratio, 2.057; 95% confidence interval, 1.494-2.833; p<0.001), and deep vein thrombosis (odds ratio, 0.463; 95% confidence interval, 0.229-0.718; p=0.001) were independent predictors of combination therapy (r2=0.66). The mean time in therapeutic range of patients receiving combination therapy was significantly lower than in those on warfarin monotherapy (51.6±27.05 vs. 54.7±23.93; p=0.006). Overall, 19.4% (n=677) of patients had a bleeding event (major bleeding 13.0%, n=88) within a year. Percentages of patients with combination therapy were significantly higher in patients with major bleeding than in patients without major bleeding (29.5% vs. 19.7%; p=0.023).

Conclusion

Our study demonstrated that 20.0% of patients taking warfarin use concomitant aspirin inappropriately in daily practice. Patients receiving aspirin with warfarin were demonstrated to have more comorbidities, lower time in therapeutic range levels, and higher bleeding rates.

A rolling-horizon pharmacokinetic pharmacodynamic model for warfarin inpatients in transient clinical states

Aim: To design a pharmacokinetic pharmacodynamic model to make individualized and adaptive international normalized ratio (INR) predictions for warfarin inpatients in changing clinical status. Methods: We tested a new model on 60 inpatients at Columbia University. The model personalizes four submodels and minimizes the number of parameters to be estimated. Prediction accuracy was assessed by prediction error, absolute prediction error and percentage absolute prediction error. Results: The INRs were accurately predicted 5 days into the future. Median prediction error: 0.01–0.12; median absolute prediction error: 0.17–0.5 and median percentage absolute prediction error: 9.85–26.06%. Conclusion: Patients exhibit interindividual and intertemporal variability. The model captures the variability and provides accurate and personalized INR predictions.

Pharmacokinetic and pharmacodynamic interactions of aspirin with warfarin in beagle dogs

1. Warfarin and aspirin are widely used in a wide spectrum of thromboembolic and atherothrombotic diseases. Despite the potential efficacy of warfarin-aspirin therapy, the safety and side effect of combined therapy remains unclear. 2. The aim of this study was to investigate the pharmacokinetic and pharmacodynamic interactions between warfarin and aspirin in beagles after single and multiple doses. 3. Coadministration of aspirin had no significant effects on the area under the plasma concentration time curve (AUC(0-t)) and maximum plasma concentration (Cmax) of R- and S-warfarin after a single dose of warfarin, but significantly increase the AUC(0-t) and Cmax and dramatically decrease the clearance (CL) of R- and S-warfarin after multiple dose of warfarin. Accordingly, there was a slight increase in the AUEC(0-t) and Emax of activated partial thromboplastin time (aPTT), prothrombin time (PT) and international normalized ratio (INR) after multiple dose of warfarin. 4. Coadministration of warfarin had no markedly effects on the AUC(0-t) and Cmax of aspirin and its metabolite salicylic acid after single or multiple dose of aspirin. Meanwhile, the AUEC(0-t) and Emax of inhibition of platelet aggregation (IPA) were not significantly affected by warfarin. 5. Our animal study indicated that coadministration of aspirin with warfarin can cause significant pharmacokinetic and pharmacodynamic drug-drug interactions in beagles. However, more studies are urgently needed to assess related information of warfarin-aspirin drug interactions in healthy volunteers or patients.

Inappropriate combination of warfarin and aspirin

Objective:

A combination of warfarin and aspirin is associated with increased bleeding compared with warfarin monotherapy. The aim of the study was to investigate the incidence and appropriateness of the combination of warfarin and aspirin in patients with atrial fibrillation (AF) or mechanical heart valve (MHV).

Methods:

This cross-sectional study included consecutive patients with AF or MHV on chronic warfarin therapy (>3 months) without acute coronary syndrome or have not undergone a revascularization procedure in the preceding year. Medical history, concomitant diseases, and treatment data were acquired through patient interviews and from hospital records.

Results:

Three hundred and sixty patients (213 with AF, 147 with MHV) were included. In those with AF, a significantly higher warfarin-aspirin combination was observed with concomitant vascular disease (38.8% vs. 14.6%), diabetes (36.6% vs. 16.3%), statin therapy (40% vs. 16.9%), left ventricular systolic dysfunction (33.3% vs. 17.5%) (p<0.05 for all). The use of combination therapy was similar between different CHADS-VASc scores. In patients with MHV, higher combination therapy was observed in males (41% vs. 26.7% in females; p=0.070), concomitant vascular disease (47.8% vs. 29.8%; p=0.091), and AF (56.3% vs. 29.8%; p=0.033). Independent predictors of warfarin-aspirin combination were concomitant vascular disease, diabetes, and (younger) age in patients with AF and were concomitant AF and male sex in patients with MHV. Interestingly, the incidence of combination therapy was found to increase with a higher HAS-BLED score in both patients with AF and MHV (p<0.001).

Conclusion:

The combination of warfarin and aspirin was found to be prescribed to patients with AF mainly for the prevention of cardiovascular events, for which warfarin monotherapy usually suffices. On the other hand, co-treatment with aspirin appeared to be underused in patients with MHV. (Anatol J Cardiol 2016; 16: 189-96)

Use and associated risks of concomitant aspirin therapy with oral anticoagulation in patients with atrial fibrillation: insights from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) Registry

BACKGROUND

The role of concomitant aspirin (ASA) therapy in patients with atrial fibrillation (AF) receiving oral anticoagulation (OAC) is unclear. We assessed concomitant ASA use and its association with clinical outcomes among AF patients treated with OAC.

METHODS AND RESULTS

The Outcomes Registry for Better Informed Treatment of Atrial Fibrillation (ORBIT-AF) registry enrolled 10 126 AF patients from 176 US practices from June 2010 through August 2011. The study population was limited to those on OAC (n=7347). Hierarchical multivariable logistic regression models were used to assess factors associated with concomitant ASA therapy. Primary outcomes were 6-month bleeding, hospitalization, ischemic events, and mortality. Overall, 35% of AF patients (n=2543) on OAC also received ASA (OAC+ASA). Patients receiving OAC+ASA were more likely to be male (66% versus 53%; P<0.0001) and had more comorbid illness than those on OAC alone. More than one third of patients (39%) receiving OAC+ASA did not have a history of atherosclerotic disease, yet 17% had elevated Anticoagulation and Risk Factors in Atrial Fibrillation (ATRIA) bleeding risk scores (≥5). Major bleeding (adjusted hazard ratio, 1.53; 95% confidence interval, 1.20-1.96) and bleeding hospitalizations (adjusted hazard ratio, 1.52; 95% confidence interval, 1.17-1.97) were significantly higher in those on OAC+ASA compared with those on OAC alone. Rates of ischemic events were low.

CONCLUSIONS

Patients with AF receiving OAC are often treated with concomitant ASA, even when they do not have cardiovascular disease. Use of OAC+ASA was associated with significantly increased risk for bleeding, emphasizing the need to carefully determine if and when the benefits of concomitant ASA outweigh the risks in AF patients already on OAC.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. UNIQUE IDENTIFIER: NCT01165710.

Major bleeding risk in anticoagulated patients receiving concomitant antiplatelet therapy: a prospective study

INTRODUCTION

Current literature suggesting a higher bleeding risk during combination therapy compared to oral anticoagulation alone is primarily based on retrospective studies or specific populations. We aimed to prospectively evaluate whether unselected medical patients on oral anticoagulation have an increased risk of bleeding when on concomitant antiplatelet therapy.

MATERIAL AND METHODS

We prospectively studied consecutive adult medical patients who were discharged on oral anticoagulants between 01/2008 and 03/2009 from a Swiss university hospital. The primary outcome was the time to a first major bleed on oral anticoagulation within 12 months, adjusted for age, international normalized ratio target, number of medications, and history of myocardial infarction and major bleeding.

RESULTS

Among the 515 included anticoagulated patients, the incidence rate of a first major bleed was 8.2 per 100 patient-years. Overall, 161 patients (31.3%) were on both anticoagulant and antiplatelet therapy, and these patients had a similar incidence rate of major bleeding compared to patients on oral anticoagulation alone (7.6 vs. 8.4 per 100 patient-years, P=0.81). In a multivariate analysis, the association of concomitant antiplatelet therapy with the risk of major bleeding was not statistically significant (hazard ratio 0.89, 95% confidence interval, 0.37-2.10).

CONCLUSIONS

The risk of bleeding in patients receiving oral anticoagulants combined with antiplatelet therapy was similar to patients receiving oral anticoagulants alone, suggesting that the incremental bleeding risk of combination therapy might not be clinically significant.

Concomitant use of antiplatelet therapy with dabigatran or warfarin in the Randomized Evaluation of Long-Term Anticoagulation Therapy (RE-LY) trial

BACKGROUND

The Randomized Evaluation of Long-term Anticoagulation Therapy (RE-LY) trial showed that dabigatran etexilate 150 mg BID was superior and dabigatran etexilate 110 mg BID was noninferior to warfarin in preventing stroke and systemic embolism in patients with atrial fibrillation. In this subgroup analysis, we assess the efficacy and safety of dabigatran in patients who did and did not receive concomitant antiplatelets.

METHODS AND RESULTS

All comparisons used a Cox proportional hazards model with adjustments made for risk factors for bleeding. A time-dependent analysis was performed when comparing patients with concomitant antiplatelets with those without. Of 18 113 patients, 6952 (38.4%) received concomitant aspirin or clopidogrel at some time during the study. Dabigatran etexilate 110 mg BID was noninferior to warfarin in reducing stroke and systemic embolism, whether patients received antiplatelets (hazard ratio [HR], 0.93; 95% confidence interval [95% CI], 0.70-1.25) or not (HR, 0.87; 95% CI, 0.66-1.15; interaction P=0.738). There were fewer major bleeds than warfarin in both subgroups (HR, 0.82; 95% CI, 0.67-1.00 for patients who used antiplatelets; HR, 0.79; 95% CI, 0.64-0.96 for patients who did not; interaction P=0.794). Dabigatran etexilate 150 mg BID reduced the primary outcome of stroke and systemic embolism in comparison with warfarin. This effect seemed attenuated among patients who used antiplatelets (HR, 0.80; 95% CI, 0.59-1.08) in comparison with those who did not (HR, 0.52; 95% CI, 0.38-0.72; P for interaction=0.058). Major bleeding was similar to warfarin regardless of antiplatelet use (HR, 0.93; 95% CI, 0.76-1.12 for patients who used antiplatelets; HR, 0.94; 95% CI, 0.78-1.15 for patients who did not; P for interaction=0.875). In the time-dependent analysis, concomitant use of a single antiplatelet seemed to increase the risk of major bleeding (HR, 1.60; 95% CI, 1.42-1.82). Dual antiplatelet seemed to increased this even more (HR, 2.31; 95% CI, 1.79-2.98). The absolute risks were lowest on dabigatran etexilate 110 mg BID in comparison with dabigatran etexilate 150 mg BID or warfarin.

CONCLUSIONS

Concomitant antiplatelet drugs appeared to increase the risk for major bleeding in RE-LY without affecting the advantages of dabigatran over warfarin. Choosing between dabigatran etexilate 110 mg BID and dabigatran etexilate 150 mg BID requires a careful assessment of characteristics that influence the balance between benefit and harm.

CLINICAL TRIAL REGISTRATION

URL: http://clinicaltrials.gov. Unique identifier: NCT00262600.

The effects of combined oral anticoagulant-aspirin therapy in patients undergoing tooth extractions: a prospective study

BACKGROUND

The authors conducted a study to evaluate the effect of combined oral anticoagulant-aspirin therapy on postoperative bleeding in patients undergoing tooth extractions.

METHODS

A total of 213 patients were divided into three groups of 71 participants each. Patients in group A received combined anticoagulant-aspirin (100-milligram prophylactic dose) therapy. Patients in group B received oral anticoagulant therapy. Patients in group C received aspirin therapy (100-mg prophylactic dose). Bleeding was marked as an "event" if it met the following criteria: the bleeding continued beyond 12 hours, patient had to call the surgeon or return to dental practice or emergency department, bleeding resolved with large hematoma or ecchymosis within the oral soft tissues, or required a blood transfusion.

RESULTS

Mean international normalized ratio (INR) (standard deviation) was 2.43 (0.61) in group A, and 2.45 (0.60) in group B. Postoperative bleeding occurred in three (4.2 percent) participants in group A, two (2.8 percent) participants in group B and no (0.0 percent) participants in group C. The authors found no statistical significance in postoperative bleeding between these three groups (χ(2) = 2.867, P = .238). All cases of hemorrhage were controlled easily by using local hemostatic measures.

CONCLUSION

Tooth extractions can be performed safely while patients continue to receive combined anticoagulant-aspirin therapy.

CLINICAL IMPLICATIONS

In patients receiving combined anticoagulant-aspirin therapy, simple tooth extractions can be performed safely without discontinuing either oral anticoagulant or antiplatelet therapy if their INRs are within therapeutic range and appropriate local hemostasis measures are provided.

Pharmacokinetic and pharmacodynamic effects of comedication of clopidogrel and dabigatran etexilate in healthy male volunteers

Purpose

To evaluate the pharmacokinetic and pharmacodynamic effects of concomitant administration of single loading doses of clopidogrel or multiple doses of clopidogrel with multiple doses of dabigatran etexilate.

Methods

This was an open-label trial in healthy male subjects. In part 1 (pilot, n = 8) and part 3 (n = 12), a single dose of clopidogrel (300 or 600 mg, respectively) was given concomitantly with dabigatran etexilate at steady state; part 2 was a randomized, multiple-dose, crossover study with the test treatment being clopidogrel at steady state [300 mg loading dose on day 1, then 75 mg once daily (qd)] with concomitant dabigatran.

Results

Bioavailability was moderately increased when a loading dose of clopidogrel (300 mg in part 1 and 600 mg in part 3) was administered concomitantly with dabigatran etexilate 150 mg twice daily (bid). Test/reference ratios for AUC_τ,ss were 135% (90% CI 107–169%) and 132% (90% CI 112–156%), respectively. Steady-state dosing of clopidogrel 75 mg qd and dabigatran etexilate 150 mg bid (part 2) demonstrated minor effects on dabigatran pharmacokinetics (AUC_τ,ss ratio test/reference: 91.9%, 90% CI 78.7–107%) or its pharmacokinetic/pharmacodynamic relationships (activated partial thromboplastin time, ecarin clotting time, thrombin time). Similarly, clopidogrel bioavailability remained unchanged by chronic administration of dabigatran etexilate (part 3: ratio test/reference for AUC₀₋₂₄ was 103%; 90% CI 80.3–131%), as did its pharmacodynamic effects on the inhibition of platelet aggregation.

Conclusions

When given concomitantly, dabigatran etexilate and clopidogrel at clinically relevant doses did not appear to have significant effects on the pharmacokinetic and pharmacodynamic profiles of either agent.

Electronic supplementary material

The online version of this article (doi:10.1007/s00228-012-1304-8) contains supplementary material, which is available to authorized users.

Major bleeding risk associated with warfarin and co-medications in the elderly population

PURPOSE

Warfarin management in the elderly population is complex as medicines prescribed for concomitant diseases may further increase the risk of major bleeding associated with warfarin use. We aimed to quantify the excess risk of bleeding-related hospitalisation when warfarin was co-dispensed with potentially interacting medicines.

METHODS

A retrospective cohort study was undertaken over a 4-year period from July 2002 to June 2006 to examine bleeding risk associated with medications co-administered in patients taking warfarin using an administrative claims database from the Australian Department of Veterans' Affairs. All veterans aged 65 years and over who were new users of warfarin were followed until death or study end. Risk of bleeding was assessed using a Poisson GEE model adjusting for age, gender, socioeconomic status, co-morbidity index, previous bleeding related hospitalisations and indicators of health service use.

RESULTS

Overall, 17661 veterans who used warfarin at any time during the study period were included. The overall incidence rate of bleeding-related hospitalisations was 4.1 (95% CI 3.7-4.6) per 100 person-years in veterans who were not receiving potentially interacting medicines. Bleeding-related hospitalisation rates were significantly increased when warfarin was co-prescribed with low-dose aspirin (Adjusted rate ratio (AdjRR) 1.44, 95% CI 1.00-2.07), clopidogrel (AdjRR 2.23, 95% CI 1.48–3.36), clopidogrel with aspirin (AdjRR 3.44, 95% CI 1.28-9.23), amiodarone (AdjRR 3.33, 95% CI 1.38–8.00) and antibiotics (AdjRR 2.34, 95% CI 1.55-3.54).

CONCLUSIONS

Models assessing bleeding risk with warfarin should take account of the range of potentially harmful medicine combinations used in elderly people with comorbid conditions.

Newer antithrombotic drugs

Thromboembolic disorders are one of the disorders for which we are still on the look out for a safe and efficient drug. Despite the widespread use of antithrombotic drugs for the prevention and treatment of arterial and venous thrombosis, thromboembolic diseases continue to be a major cause of death and disability worldwide. This shows our inefficiency in searching efficacious and safe antithrombotic drugs. We have reached the basic mechanism of thrombus formation and by interrupting various steps of this mechanism, we can prevent as well as treat thromboembolic disorders. In continuation of Aspirin, now, we are using Clopidogrel, Ticlopidine and GpIIb/IIIa inhibitors (Abciximab, Tirofiban and Eptifibatide). Warfarin is an old antithrombotic drug which is still being used; but due to various side effects and drug interactions, we are bound to use newer drugs. Newer antiplatelet drugs include Prasugrel, Ticagrelor and Cangrelor, whereas newer thrombin inhibitors are Ximelgatran and Dabigatran. Apixaban is also a newer entry in this category as factor Xa inhibitor. Idrabiotaparinux is an indirect inhibitor of Xa as it accelerates the activity of antithrombin. Moreover, researches and trials for better and safe drugs are ongoing.

Optimizing use of current anticoagulants

Although warfarin has been the mainstay of oral anticoagulation therapy for decades, evidence-based methods for improving the quality of warfarin therapy remain underused. The arrival of new anticoagulants that do not require routine laboratory monitoring and lack the significant dietary and drug interaction potential that are seen with warfarin is an important evolutionary step in the management of thromboembolic disease. However, it will be years before the efficacy and long-term safety of these new agents are defined. Newer oral anticoagulants will be more expensive than generic warfarin. This article examines various approaches to optimize the clinical use of warfarin. For patients able to achieve stable anticoagulation control, warfarin remains an important therapeutic option, delivering similar clinical outcomes at a fraction of the cost to the health care system.

Combined warfarin-aspirin therapy: what is the evidence for benefit and harm and which patients should (and should not) receive it?

Combined warfarin-aspirin therapy is currently used in about 1 million patients in North America for the long-term primary and secondary prevention of atherothrombotic and thromboembolic diseases. Despite a potentially complementary action of anticoagulant and antiplatelet drugs on different components of the thrombotic pathway, their combined use, typically with warfarin and aspirin, is not based in many cases on compelling evidence of a net therapeutic benefit. In the real-world management of patients, clinicians should combine the best available evidence with clinical judgment, considering also that, in most clinical scenarios, clinical practice guidelines may not provide strong or prescriptive recommendations for patients who should (and should not) receive combined aspirin-warfarin therapy. The objectives of this review are to describe the characteristics of patients who are receiving combined warfarin-aspirin therapy, to summarize the evidence for the therapeutic benefit and harm of combined warfarin-aspirin, and to provide practical guidelines as to which patients should (or should not) receive such treatment.

Use of antiplatelet agents for prevention of ischemic stroke

Overall management to lower risk for ischemic stroke is multifaceted. Management includes measures to treat risk factors for accelerated atherosclerosis and stroke, antithrombotic therapies to lower the risk for thromboembolism, and surgery to treat a defined arterial or cardiac lesion. Treatment decisions are made on a case-by-case basis, with most patients receiving some combination of medication and recommendations for lifestyle modification. Some patients will also undergo surgical or endovascular interventions. This article discusses antithrombotic treatment for ischemic stroke prevention, placing major emphasis on the indications for and administration of antiplatelet therapy.

Known knowns and known unknowns: risks associated with combination antithrombotic therapy

BACKGROUND

Use of antiplatelet therapy in combination with oral anticoagulants remains controversial. The purpose of this article is to review current consensus recommendations for antithrombotic therapy, to evaluate risks for bleeding among patients taking combination antithrombotic therapy, and lastly to review single-center data from Kaiser Permanente Colorado detailing clinical outcomes associated with combination therapy.

METHODS

This was a retrospective, longitudinal pharmacoepidemiologic review. Adult patients receiving warfarin managed by a clinical pharmacy service who had documented antiplatelet (aspirin, clopidogrel, and/or dipyridamole) use (combination therapy cohort) or non-use (monotherapy cohort) were identified as of September 30, 2005. Utilizing integrated, electronic medical records, anticoagulation-related adverse events (death, hemorrhage, thrombosis) and coronary events were identified during a six-month follow-up (October 2005 through March 2006). Proportions of events were compared between cohorts. Independent associations between the cohorts and the outcomes were assessed with adjustment for potential confounding factors.

RESULTS

Data from 2,560 monotherapy and 1,623 combination therapy patients were analyzed. Patients in the combination therapy cohort were more likely to have had anticoagulation-related hemorrhages (4.2% vs. 2.0%, unadjusted p<0.001). With adjustment, combined warfarin and antiplatelet use was independently associated with hemorrhagic (OR=2.75; 95% CI 1.44, 5.28) but not coronary (OR=0.99; 95% CI 0.37, 2.62) events.

CONCLUSIONS

At the population level, the hemorrhagic risk associated with warfarin therapy combined with antiplatelet therapy appears to outweigh the benefits. These findings suggest that clinicians carefully consider risks and benefits when prescribing antiplatelet therapy for patients taking warfarin who do not meet evidence-based criteria for that approach.

Concomitant antiplatelet and anticoagulation therapy: indications, controversies and practical advice

The use of combination antiplatelet and anticoagulant therapy is commonly encountered in clinical practice and is often a source of clinical controversy in regards to the efficacy versus the safety of this regimen. The benefit of combination therapy relates to the probable additive effect of suppressing both platelet and coagulation factor activities. The risk of dual therapy is the potential for increased hemorrhagic events which may outweigh the clinical benefit. This review will focus on the clinical evidence that has demonstrated greater efficacy with combination therapy over either antiplatelet or anticoagulant therapy alone. Clinicians should consider the importance of documentation of combination therapy use in their patients in an effort to target those patients with the greatest benefit, and to avoid unnecessary complications.

Delivery of Optimized Anticoagulant Therapy: Consensus Statement from the Anticoagulation Forum

Objective:

To provide recommendations, policies, and procedures pertaining to the provision of optimized anticoagulation therapy designed to achieve desired clinical endpoints while minimizing the risk of anticoagulant-related adverse outcomes (principally bleeding and thrombosis).

Study Selection and Data Extraction:

Due to this document's scope, the medical literature was searched using a variety of strategies. When possible, recommendations are supported by available evidence; however, because this paper deals with processes and systems of care, high-quality evidence (eg, controlled trials) is unavailable. In these cases, recommendations represent the consensus opinion of all authors who constitute the Board of Directors of The Anticoagulation Forum, an organization dedicated to optimizing anticoagulation care. The Board is composed of physicians, pharmacists, and nurses with demonstrated expertise and significant collective experience in the management of patients receiving anticoagulation therapy.

Data Synthesis:

Recommendations for delivering optimized anticoagulation therapy were developed collaboratively by the authors and are summarized in 9 key areas: (I) Qualifications of Personnel, (II) Supervision, (III) Care Management and Coordination, (IV) Documentation. (V) Patient Education, (VI) Patient Selection and Assessment, (VII) Laboratory Monitoring, (VIII) Initiation and Stabilization of Warfarin Therapy, and (IX) Maintenance of Therapy. Recommendations are intended to inform the development of care systems containing elements with demonstrated benefit in improvement of anticoagulation therapy outcomes. Recommendations for delivering optimized anticoagulation therapy are intended to apply to all clinicians involved in the care of outpatients receiving anticoagulation therapy, regardless of the structure and setting in which that care is delivered.

Conclusions:

Anticoagulation therapy, although potentially life-saving, has inherent risks. Whether a patient is managed in a solo practice or a specialized anticoagulation management service, a systematic approach to the key elements outlined herein will reduce the likelihood of adverse events. The need for continued research to validate optimal practices for managing anticoagulation therapy is acknowledged.

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