Azathioprine and Acenocoumarol: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Acenocoumarol
No brand names on recordAzathioprine
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Reduced acenocoumarol therapeutic efficacy
Interaction Deep Dive
A female stabilized on acenocoumarol experienced a significant decrease in her international normalized ratio (INR) when mercaptopurine therapy was initiated for leukemia. The acenocoumarol dose was increased 3.5-fold to maintain her INR. When mercaptopurine was discontinued, her INR quadrupled, necessitating an acenocoumarol dose decrease back to its previous level. Acenocoumarol efficacy should be evaluated within one week of initiating or discontinuing mercaptopurine1.
Why it happens (mechanism)
Induction of hepatic microenzyme activity responsible for acenocoumarol metabolism
Literature reports
1 report — tap to read
a) A 53-year-old female with an aortic prosthetic valve was stabilized for three years on acenocoumarol 21 mg weekly with a corresponding mean international normalized ratio (INR) of 3.3. Therapy with mercaptopurine was started following a diagnosis of acute promyelocytic leukemia. Her acenocoumarol dose was progressively increased to 71 mg weekly to maintain an INR of 3.4. Within one week of discontinuing mercaptopurine, her INR increased to 12. Acenocoumarol was temporarily discontinued and reintroduced at 21 mg weekly. She did not experience any hemorrhagic complications 1.
Common questions
Can I take Azathioprine and Acenocoumarol together?
Reduced acenocoumarol therapeutic efficacy Always confirm with your pharmacist or prescriber before making any change.
How serious is the Azathioprine and Acenocoumarol interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Azathioprine or Acenocoumarol need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (1)
- Fernandez MA, Regadera A, & Aznar J: Acenocoumarol and 6-mercaptopurine: an important drug interaction (letter). Haematologica 1999; 84:664-665.
Keep reading about Acenocoumarol
Keep reading about Azathioprine
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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