Mercaptopurine with Warfarin Interaction Details
Brand Names Associated with Mercaptopurine
- 6-MP
- Mercaptopurine
- Purinethol®
- Purixan®
Brand Names Associated with Warfarin
- Coumadin®
- Jantoven®
- Warfarin
Medical Content Editor Dr. Brian Staiger, PharmD
Last updated
Dec 29, 2023
Interaction Effect
Decreased anticoagulant effectiveness
Interaction Summary
There have been case reports published that indicate a reduction in the anticoagulant activity of warfarin when mercaptopurine is used concurrently. Monitor INR or prothrombin time if used concomitantly. Warfarin dose adjustments may be required to maintain desired levels of anticoagulation .
Severity
Major
Onset
Unspecified
Evidence
Probable
How To Manage Interaction
Use caution with coadministration of mercaptopurine and warfarin, as decreased anticoagulant effects may occur. Monitor INR or prothrombin time when coadministered. Warfarin dose adjustments may be required to maintain desired levels of anticoagulation.
Mechanism Of Interaction
Unknown
Literature Reports
A) In a case report, an 81-year-old man whose INR was stable required multiple re-titrations of his warfarin dosage while receiving 3 separate 12-week cycles of mercaptopurine for acute promyelocytic leukemia. At the start of chemotherapy, a 25% increase in the warfarin maintenance dosage was required. In between the chemotherapy cycles, the patient's warfarin dosage was difficult to stabilize, but he did require decreases in the warfarin dosage while not receiving mercaptopurine .
B) Anticoagulant effects of warfarin are reduced when concurrently used with mercaptopurine. A 62-year-old man previously stabilized on 4 to 10 mg warfarin daily for venous thrombosis for a period of 3 years, was treated with mercaptopurine. The Thrombotest suddenly rose above the therapeutic range with the addition of mercaptopurine. This effect was abolished by increasing the dose of warfarin. However, when the dose of mercaptopurine was increased, the Thrombotest again began to rise. Mercaptopurine was discontinued and the Thrombotest fell sharply. The patient was continued to be treated satisfactorily with original warfarin doses and no further mercaptopurine administration. It is possible that mercaptopurine may inhibit the gastrointestinal absorption of warfarin. However, it is more likely that mercaptopurine stimulates microsomal enzymes to increase the rate of metabolism of warfarin. More data is required to evaluate the significance of this interaction .
Mercaptopurine Overview
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Mercaptopurine is used alone or with other chemotherapy drugs to treat acute lymphocytic leukemia (ALL; also called acute lymphoblastic leukemia and acute lymphatic leukemia; a type of cancer that begins in the white blood cells). Mercaptopurine is in a class of medications called purine antagonists. It works by stopping the growth of cancer cells.
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.