Thioguanine and Mesalamine Rectal: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Mesalamine Rectal
Thioguanine
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 myelosuppression
Interaction Deep Dive
Thioguanine is metabolized by thiopurine methyltransferase (TPMT). Decreased TPMT activity causes an accumulation of active metabolites of thioguanine, which has been associated with an increased risk of life-threatening myelosuppression. Mesalamine is a relatively potent inhibitor of TPMT activity. Therefore, careful monitoring of blood counts is recommended in patients receiving concomitant therapy with 6-mercaptopurine and mesalamine1.
Why it happens (mechanism)
Inhibition by mesalamine of thiopurine methyltransferase
Common questions
Can I take Thioguanine and Mesalamine Rectal together?
An increased risk of myelosuppression Always confirm with your pharmacist or prescriber before making any change.
How serious is the Thioguanine and Mesalamine Rectal 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 "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Thioguanine or Mesalamine Rectal 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)
- Product Information: Tabloid(R), thioguanine. GlaxoSmithKline, Research Triangle Park, NC, 2004. DailyMed
Keep reading about Mesalamine Rectal
Keep reading about Thioguanine
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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