Warfarin with Aspirin Interaction Details

Brand Names Associated with Warfarin

Brand Names Associated with Aspirin

Medical Content Editor Dr. Brian Staiger, PharmD
Last updated Mar 04, 2024

Interaction Effect

Increased risk of bleeding

Interaction Summary

Because bleeding risk is increased when antiplatelet agents are used concomitantly with warfarin, closely monitor patients receiving such combination therapy[1]. In patients with DVT and/or pulmonary embolism (PE) and stable cardiovascular disease receiving aspirin for cardiovascular risk modification, suspending aspirin for the duration of anticoagulation therapy for DVT and/or PE is suggested (conditional recommendation based on very low certainty in the evidence of effects); however, this suggestion does not apply to patients with a recent acute coronary event or coronary intervention [2]. In patients receiving warfarin, treatment with aspirin (mainly 100 mg or less per day) without a clear therapeutic indication significantly increased 1-year cumulative incidence of overall bleeding, major bleeding, emergency department visits for bleeding, and hospitalizations for bleeding compared with no aspirin in a propensity score-matched study; the incidence of thrombosis, rate of CNS bleeding, and mortality rates were similar between groups [3].

Severity

Major

Onset

Unspecified

Evidence

Established

How To Manage Interaction

Because bleeding risk is increased when antiplatelet agents, such as aspirin, are used concomitantly with warfarin, closely monitor patients receiving such combination therapy[1]. In patients with DVT and/or pulmonary embolism (PE) and stable cardiovascular disease receiving aspirin for cardiovascular risk modification, suspending aspirin for the duration of anticoagulation therapy for DVT and/or PE is suggested (conditional recommendation based on very low certainty in the evidence of effects); however, this suggestion does not apply to patients with a recent acute coronary event or coronary intervention [2].

Mechanism Of Interaction

Additive effects on hemostasis

Literature Reports

A) In patients receiving warfarin for atrial fibrillation or VTE, treatment with aspirin without a clear therapeutic indication compared with no aspirin significantly increased 1-year cumulative incidence of overall bleeding (26% vs 20.3%), major bleeding (5.7% vs 3.3%), emergency department (ED) visits for bleeding (13.3% vs 9.8%), and hospitalizations for bleeding (8.1% vs 5.2%) in a propensity score-matched study (n=3688, 1844 patients per group); these results persisted for at least 3 years of follow up. There were no significant differences with aspirin versus no aspirin in the 1-year rates of mortality (4.4% vs 3.7%) and thrombosis (2.3% vs 2.7%; ischemic stroke, TIA , VTE, acute coronary syndrome or myocardial infarction, ED visits, hospitalizations for thrombosis); the type of thrombotic event and rate of CNS bleeding were similar between groups. Low-dose aspirin (100 mg or less per day) was used by 84% of patients receiving aspirin [3].

B) In a meta-analysis of six randomized clinical trials, the use of aspirin with warfarin was associated with more than double the frequency of intracranial hemorrhage. The trials included 3874 patients with 31 diagnosed intracranial hemorrhages. The frequency of intracranial hemorrhage was not dependent on the dose of aspirin used or on the range of anticoagulation. These data suggest that even low doses of aspirin should be used cautiously in anticoagulated patients with a high risk of intracranial hemorrhage, such as the elderly [4].

References

1 ) Product Information: COUMADIN(R) oral tablets, warfarin sodium oral tablets. Bristol-Myers Squibb Company (per manufacturer), Princeton, NJ, 2019.

2 ) Ortel TL, Neumann I, Ageno W, et al: American Society of Hematology 2020 guidelines for management of venous thromboembolism: treatment of deep vein thrombosis and pulmonary embolism. Blood Adv 2020; 4(19):4693-4738.PubMed Abstract: http://www.ncbi.nlm.nih.gov/...

3 ) Schaefer JK , Li Y , Gu X , et al: Association of adding aspirin to warfarin therapy without an apparent indication with bleeding and other adverse events. JAMA Intern Med 2019; 179(4):533-541.PubMed Abstract: http://www.ncbi.nlm.nih.gov/...

4 ) Hart RG, Benavente O, & Pearce LA: Increased risk of intracranial hemorrhage when aspirin is combined with warfarin: a meta-analysis and hypothesis. Cerebrovasc Dis 1999; 9:215-217.

Warfarin Overview

• Warfarin is used to prevent blood clots from forming or growing larger in your blood and blood vessels. It is prescribed for people with certain types of irregular heartbeat, people with prosthetic (replacement or mechanical) heart valves, and people who have suffered a heart attack. Warfarin is also used to treat or prevent venous thrombosis (swelling and blood clot in a vein) and pulmonary embolism (a blood clot in the lung). Warfarin is in a class of medications called anticoagulants ('blood thinners'). It works by decreasing the clotting ability of the blood.

Aspirin Overview

• Prescription aspirin is used to relieve the symptoms of rheumatoid arthritis (arthritis caused by swelling of the lining of the joints), osteoarthritis (arthritis caused by breakdown of the lining of the joints), systemic lupus erythematosus (condition in which the immune system attacks the joints and organs and causes pain and swelling) and certain other rheumatologic conditions (conditions in which the immune system attacks parts of the body). Nonprescription aspirin is used to reduce fever and to relieve mild to moderate pain from headaches, menstrual periods, arthritis, toothaches, and muscle aches. Nonprescription aspirin is also used to prevent heart attacks in people who have had a heart attack in the past or who have angina (chest pain that occurs when the heart does not get enough oxygen). Nonprescription aspirin is also used to reduce the risk of death in people who are experiencing or who have recently experienced a heart attack. Nonprescription aspirin is also used to prevent ischemic strokes (strokes that occur when a blood clot blocks the flow of blood to the brain) or mini-strokes (strokes that occur when the flow of blood to the brain is blocked for a short time) in people who have had this type of stroke or mini-stroke in the past. Aspirin will not prevent hemorrhagic strokes (strokes caused by bleeding in the brain). Aspirin is in a group of medications called salicylates. It works by stopping the production of certain natural substances that cause fever, pain, swelling, and blood clots.

• Aspirin is also available in combination with other medications such as antacids, pain relievers, and cough and cold medications. This monograph only includes information about the use of aspirin alone. If you are taking a combination product, read the information on the package or prescription label or ask your doctor or pharmacist for more information.

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Definitions

Severity Categories

Contraindicated

These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.

Major

This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.

Moderate

This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.

Minor

While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.

Onset

Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.

Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.

Evidence

Level of documentation of the interaction.

Established: The interaction is documented and substantiated in peer-reviewed medical literature.

Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.

How To Manage The Interaction

Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.

It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.

Mechanism Of Interaction

The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.

Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.

Where Does Our Information Come From?

Information for our drug interactions is compiled from several drug compendia, including:

• Gold Standard Drug Database
• Micromedex
• Lexicomp
• DrugBank

The prescribing information for each drug, as published on DailyMED, is also used. 

Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.

The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.