Ribavirin and Mercaptopurine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Ribavirin
Mercaptopurine
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
An increased risk of azaTHIOprine-induced myelotoxicity and an increased risk of hepatotoxicity
Interaction Deep Dive
Concomitant use of azaTHIOprine and ribavirin (in combination with pegylated interferon) has been associated with myelotoxicity2. If concomitant use of azaTHIOprine and ribavirin is necessary, weekly monitoring of complete blood counts, including platelets, is recommended for the first month, with twice-monthly monitoring for the second and third months, then monthly or more frequent monitoring with dosage or therapy changes 3. Discontinue ribavirin treatment if pancytopenia occurs and do not reintroduce ribavirin while the patient is on concomitant azaTHIOprine 4. Hepatotoxicity may be increased when mercaptopurine is coadministered with other products that can cause hepatoxicity, such as ribavirin. Hepatic injury can occur with any dosage but seems to occur with greater frequency when the recommended dosage is exceeded. Monitor serum transaminase levels, alkaline phosphatase, and bilirubin levels at weekly intervals when first beginning therapy and at monthly intervals thereafter. Withhold mercaptopurine at onset of hepatotoxicity 1.
Why it happens (mechanism)
Reduced azaTHIOprine clearance; additive hepatotoxic effects
Literature reports
1 report — tap to read
a) A retrospective review of 8 patients demonstrated the development of severe pancytopenia within 3 to 7 weeks after concomitant use of azaTHIOprine and ribavirin. While receiving azaTHIOprine for inflammatory bowel disease, 7 patients experienced bone marrow suppression (mean interval of 4.6 +/- 1.6 weeks) following the addition of ribavirin plus peginterferon alfa for chronic hepatitis C. Mean platelet count at time of pancytopenia was 69.75 +/- 82.8 x 10(-3)/mm(3), with a mean hemoglobin level of 7.75 g/dL +/- 1.3 g/dL, and a mean neutrophil count of 0.45 +/- 0.26 x 10(-3)/mm(3). One patient experienced severe pancytopenia after the introduction of azaTHIOprine while being treated for hepatitis C virus (HCV) with ribavirin and peginterferon alfa. Blood counts returned to normal following withdrawal of azaTHIOprine and HCV therapy (mean duration of 5 +/- 1 weeks). No hematological toxicity occurred following the reinstatement of HCV or azaTHIOprine treatment alone in any of the 8 patients 42.
Common questions
Can I take Ribavirin and Mercaptopurine together?
An increased risk of azaTHIOprine-induced myelotoxicity and an increased risk of hepatotoxicity Always confirm with your pharmacist or prescriber before making any change.
How serious is the Ribavirin and Mercaptopurine interaction?
It is rated major. Potentially serious — often needs a change or close 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 Ribavirin or Mercaptopurine 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 a safer alternative to one of these medications for me?
References (4)
- Product Information: PURIXAN(R) oral suspension, mercaptopurine oral suspension. Rare Disease Therapeutics Inc (per FDA), Franklin, TN, 2024. DailyMed
- Peyrin-Biroulet L, Cadranel JF, Nousbaum JB, et al: Interaction of ribavirin with azathioprine metabolism potentially induces myelosuppression. Aliment Pharmacol Ther 2008; 28(8):984-993. PubMed
- Product Information: IMURAN(R) oral tablets, azathioprine oral tablets. Prometheus Laboratories Inc (per FDA), San Diego, CA, 2011. DailyMed
- Product Information: COPEGUS(R) oral tablets, ribavirin oral tablets. Genentech, Inc, South San Francisco, CA, 2010. DailyMed
Keep reading about Ribavirin
Keep reading about Mercaptopurine
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.
Check another combination
Our instant two-drug interaction checker is almost here.
Still have questions about this combination?
Every question gets a real answer from a licensed pharmacist — free, and usually within a day.
Ask the pharmacist