Belumosudil and Tazemetostat: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 15, 2026 · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Tazemetostat
Belumosudil
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.
These two cancer and transplant-related medicines can affect each other. Tazemetostat (Tazverik) can speed up the way your body breaks down belumosudil (Rezurock). When that happens, there can be less belumosudil in your bloodstream, which may make it work less well.
The good news is that your care team knows how to handle this. They may adjust your dose or keep a closer eye on how well your treatment is working. Please keep taking both medicines exactly as prescribed, and talk with your pharmacist or doctor before making any changes.
Effect: Tazemetostat is a CYP3A inducer; belumosudil is a CYP3A substrate. Coadministration is expected to increase belumosudil clearance, lowering its exposure (AUC/Cmax) and potentially reducing efficacy.
Magnitude: In a PK study, tazemetostat 800 mg BID reduced midazolam (sensitive CYP3A substrate) AUC by 40% and Cmax by 21%. Belumosudil effect is inferred from this induction potential.
Evidence: Probable. Onset: unspecified (induction typically develops over days).
- Monitor for reduced belumosudil efficacy (chronic GVHD control).
- Dose may need to be individualized by the care team.
- Consider a non-inducing alternative where clinically appropriate.
What happens
Reduced CYP3A substrate exposure and reduced efficacy of CYP3A substrate
Interaction Deep Dive
When tazemetostat is taken alongside CYP3A substrates, the exposure to those substrates may fall, which can diminish their effectiveness. A drug interaction study in patients showed that giving tazemetostat 800 mg twice daily together with oral midazolam (a sensitive CYP3A substrate) lowered the AUC of midazolam by 40% and its Cmax by 21%1.
Why it happens (mechanism)
Induction of CYP3A-substrate metabolism by tazemetostat
How to manage this interaction
Your care team can manage this combination. Because tazemetostat may lower the amount of belumosudil in your body, here is what they typically do:
- Keep taking both medicines as prescribed unless your team tells you otherwise.
- Your belumosudil dose may need to be adjusted and individualized by your care team.
- Your team may monitor you more closely to make sure your belumosudil is still working well.
- In some cases they may consider a different medicine option.
Let your pharmacist or prescriber know you are on both, and report any worsening of the symptoms belumosudil is meant to control.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In a study evaluating drug interactions, giving tazemetostat 800 mg twice daily together with oral midazolam (a sensitive CYP3A substrate) to patients reduced midazolam AUC by 40% and Cmax by 21% 1.
Common questions
Can I take Belumosudil and Tazemetostat together?
Tazemetostat can speed up the breakdown of belumosudil, which may make belumosudil less effective. Keep taking both as prescribed and let your care team adjust the dose or monitor you more closely. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Belumosudil and Tazemetostat interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Belumosudil and Tazemetostat interaction managed?
Your care team can manage this combination. Because tazemetostat may lower the amount of belumosudil in your body, here is what they typically do: Keep taking both medicines as prescribed unless your team tells you otherwise. Your belumosudil dose may need to be adjusted and individualized by your care team. Your team may monitor you more closely to make sure your belumosudil is still working well… Management is individual — always follow your own care team's guidance.
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 Belumosudil or Tazemetostat 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 (1)
- Product Information: TAZVERIK(R) oral tablets, tazemetostat oral tablets. Epizyme Inc (per FDA), Cambridge, MA, 2024. DailyMed
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