Drug Interaction Report

Acenocoumarol and Azathioprine: Interaction Details

A pharmacist-reviewed analysis of the Acenocoumarol and Azathioprine interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Acenocoumarol

No brand names on record
+

Azathioprine

Azasan Azasan® Imuran Imuran®
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Jul 11, 2026
Editorial policy · Data sources
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Interaction severity
Moderate
Can be significant — usually manageable with monitoring.
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.

Of 95 documented Acenocoumarol interactions, 25 are rated moderate — including this one.
Onset
delayed
Evidence
probable
Severity
Moderate

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 Acenocoumarol and Azathioprine together?

Reduced acenocoumarol therapeutic efficacy Always confirm with your pharmacist or prescriber before making any change.

How serious is the Acenocoumarol and Azathioprine 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 Acenocoumarol or Azathioprine 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)

  1. Fernandez MA, Regadera A, & Aznar J: Acenocoumarol and 6-mercaptopurine: an important drug interaction (letter). Haematologica 1999; 84:664-665.
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Acenocoumarol

Keep reading about Acenocoumarol

All Acenocoumarol interactions (95)
Also serious with: Defibrotide Injection Bicalutamide Fluorouracil Injection Orlistat
Azathioprine

Keep reading about Azathioprine

All Azathioprine interactions (219) Azathioprine drug information
Also serious with: Febuxostat Atovaquone Peginterferon Alfa-2A Injection Acarbose
Beyond drug–drug

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:

Acenocoumarol + Activated Charcoal Danshen Piracetam Acetyl-l-carnitine Aconite Allspice Aloe Alpha-lipoic Acid + 213 more
Azathioprine + Activated Charcoal Beer Siberian Cocklebur Wine Active Hexose Correlated Compound (ahcc) Alfalfa American Ginseng Andrographis + 98 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.