Warfarin with Fish Oil Interaction Details
Brand Names Associated with Warfarin
- Coumadin®
- Jantoven®
- Warfarin
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Nov 07, 2023
Interaction Effect
Increased risk of bleeding
Interaction Summary
Concomitant use of fish oil and warfarin may result in an elevated INR and an increased risk of bleeding. A case report demonstrated a probable association between fish oil use and elevated INR in a patient who was stabilized on warfarin therapy. One potential mechanism for this interaction is thought to be the inhibitory effect of fish oil on thromboxane A2 due to eicosapentaenoic acid (EPA) from the fish oil replacing and decreasing the availability of the thromboxane precursor in the phospholipids of the cell membrane . Therefore, it is recommended that the patient be educated and closely monitored when a fish oil supplement is initiated or the fish oil dose is adjusted in a patient stable on warfarin therapy. It is also important to inquire about all medications, including over-the-counter drugs and supplements, that the patient is taking .
Severity
Major
Onset
Delayed
Evidence
Probable
How To Manage Interaction
Concomitant use of fish oil and warfarin may result in an elevated INR and an increased risk of bleeding. Therefore, educating and closely monitoring the patient is warranted when a fish oil supplement is initiated or the fish oil dose is adjusted in a patient stable on warfarin. It is also important to inquire about all medications, including over-the-counter drugs and supplements, that the patient is taking.
Mechanism Of Interaction
Decreased platelet aggregation due to inhibitory effect of fish oil on thromboxane A2 levels
Literature Reports
A) A 67-year-old woman taking warfarin 1.5 mg/day alternating with 1 mg/day with stable, therapeutic INRs began taking fish oil 1000 mg/day. After coadministration began, the warfarin dose was adjusted to 1.5 mg/day and INRs remained in the therapeutic range for 5 months. Six months after coadministration began, the INR was 4.3. One week before the supratherapeutic INR result, the patient had increased her fish oil dose to 2000 mg/day. The fish oil dose was reduced to 1000 mg/day and the warfarin dose was held for 1 day, then reduced and titrated until a therapeutic INR was maintained. No bleeding complications occurred. According to the Naranjo scale, there was a probable relationship between the supratherapeutic INR and the fish oil .
Warfarin Overview
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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.
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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:
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.