Belumosudil and Rilzabrutinib: 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
Rilzabrutinib
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 medicines can interact. Rilzabrutinib (Wayrilz) can slow down a liver enzyme called CYP3A that helps clear certain drugs from your body. Belumosudil (Rezurock) is broken down partly by that same enzyme. So when you take them together, belumosudil may build up a bit more than usual, which could make its side effects (like nausea, tiredness, or swelling) more likely.
The good news is that this is expected, not something surprising to your care team. This concern is based on how the drugs work in theory, not on lots of real-world reports. Keep taking both exactly as prescribed and let your doctor or pharmacist know how you are feeling. They can watch you more closely and adjust your dose if needed.
Mechanism: Rilzabrutinib is a moderate CYP3A inhibitor; belumosudil is a CYP3A substrate. Inhibition of belumosudil metabolism is predicted to increase its exposure (AUC/Cmax) and the risk of substrate-related adverse effects. Neither drug acts here as a prodrug requiring CYP3A for activation, so the effect is increased belumosudil activity, not reduced.
- Direction: increased belumosudil exposure.
- Magnitude: not specific to belumosudil; with midazolam (sensitive probe), rilzabrutinib raised Cmax/AUC ~2.2-fold, predicted up to 3.0-fold at 400 mg BID.
- Onset: unspecified. Evidence: theoretical.
- Management: monitor for belumosudil adverse reactions more frequently; individualize/adjust dose as clinically indicated.
What happens
Increased CYP3A substrate exposure and an increased risk of CYP3A substrate-related adverse reactions
Interaction Deep Dive
When rilzabrutinib (a moderate CYP3A inhibitor) is given together with CYP3A substrates, the exposure to those substrates can rise, raising the likelihood of adverse reactions tied to them. Watch more closely for adverse reactions caused by the co-administered CYP3A substrate and adjust its dose as needed. A drug interaction study in healthy participants showed that giving a single 400 mg dose of rilzabrutinib alongside midazolam (a sensitive CYP3A substrate) produced a 2.2-fold rise in both midazolam Cmax and AUC. In patients with immune thrombocytopenia, midazolam AUC is projected to climb as much as 3.0-fold when co-administered with rilzabrutinib 400 mg twice daily1.
Why it happens (mechanism)
Inhibition of CYP3A-substrate metabolism by rilzabrutinib
How to manage this interaction
This interaction is usually manageable. Your care team can handle it by watching you and tailoring your dose.
- Keep taking both medicines as prescribed unless your prescriber tells you otherwise.
- Your team may monitor you more closely for belumosudil side effects such as nausea, fatigue, diarrhea, or swelling.
- Your belumosudil dose may need to be adjusted and individualized by your care team if side effects appear.
- Report any new or worsening symptoms to your pharmacist or doctor, and make sure they have your full medication list.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In a drug interaction study conducted in healthy volunteers, administering a single 400 mg dose of rilzabrutinib together with midazolam (a sensitive CYP3A substrate) raised the Cmax and AUC of midazolam by 2.2-fold. In patients with immune thrombocytopenia, midazolam AUC is projected to rise by as much as 3.0-fold when given alongside 400 mg rilzabrutinib twice daily 1.
Common questions
Can I take Belumosudil and Rilzabrutinib together?
Rilzabrutinib can raise belumosudil levels and may increase its side effects, so keep taking both as prescribed and let your care team monitor you and adjust the dose if needed. This is a theoretical, manageable interaction. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Belumosudil and Rilzabrutinib interaction?
It is rated moderate. Can be significant — usually manageable with 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 Rilzabrutinib interaction managed?
This interaction is usually manageable. Your care team can handle it by watching you and tailoring your dose. Keep taking both medicines as prescribed unless your prescriber tells you otherwise. Your team may monitor you more closely for belumosudil side effects such as nausea, fatigue, diarrhea, or swelling. Your belumosudil dose may need to be adjusted and individualized by your care team if sid… Management is individual — always follow your own care team's guidance.
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 Belumosudil or Rilzabrutinib 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: WAYRILZ™ oral tablets, rilzabrutinib oral tablets. Genzyme Corporation (per FDA), Cambridge, MA, 2025. DailyMed
Keep reading about Rilzabrutinib
Keep reading about Belumosudil
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