Fedratinib and Belumosudil: 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
Fedratinib
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.
Let's talk about taking fedratinib (Inrebic) together with belumosudil (Rezurock). Fedratinib slows down a liver enzyme called CYP3A4, which is one of the main ways your body breaks down belumosudil. When that breakdown slows, more belumosudil can build up in your blood than expected.
That doesn't mean something bad will happen, but it does mean there's a higher chance of side effects from belumosudil. The good news is this is very manageable. Your care team can keep an eye on how you're feeling and adjust your doses so both medicines stay safe and effective. Keep taking both as prescribed, and check in with your pharmacist or doctor with any questions.
Effect: Fedratinib is a moderate CYP3A4 inhibitor; belumosudil is a CYP3A4 substrate. Coadministration is expected to increase belumosudil exposure (AUC/Cmax), raising the risk of substrate-related adverse effects.
Mechanism: Inhibition of CYP3A4-mediated metabolism of belumosudil by fedratinib. As a reference, fedratinib increased midazolam AUC ~4-fold in single-dose PK studies.
- Direction: increased substrate (belumosudil) concentrations
- Onset: unspecified
- Evidence: probable; severity major
- Management: if coadministration is necessary, monitor for belumosudil adverse reactions and adjust/individualize the belumosudil dose per response.
What happens
Increased CYP3A4 substrate exposure
Interaction Deep Dive
When fedratinib, which inhibits CYP3A4, is taken alongside CYP3A4 substrates, the concentrations of those substrates may rise, raising the likelihood of adverse reactions from them. Single-dose pharmacokinetic investigations demonstrated that fedratinib produced a 4-fold increase in the AUC of midazolam, a CYP3A4 substrate. Should combined use be required, watch for adverse reactions and modify the dosing of CYP3A4 substrate drugs1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated substrate metabolism by fedratinib
How to manage this interaction
If your team prescribes both, here is what usually happens and what you can do:
- Keep taking both as prescribed unless your prescriber tells you otherwise. Do not stop or change doses on your own.
- Expect closer monitoring. Your care team may watch you more closely for belumosudil side effects.
- Dose tailoring: the belumosudil dose may need to be adjusted and individualized by your care team.
- Speak up: report any new or worsening symptoms to your pharmacist or doctor.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) When a single 2 mg dose of midazolam (a CYP3A4 substrate) was given together with fedratinib, the AUC of midazolam rose by 4-fold 1.
Common questions
Can I take Fedratinib and Belumosudil together?
Fedratinib can raise belumosudil levels by blocking the CYP3A4 enzyme that clears it, increasing the chance of side effects. Keep taking both as prescribed and let your care team monitor you and adjust the belumosudil dose as needed. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Fedratinib and Belumosudil 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 Fedratinib and Belumosudil interaction managed?
If your team prescribes both, here is what usually happens and what you can do: Keep taking both as prescribed unless your prescriber tells you otherwise. Do not stop or change doses on your own. Expect closer monitoring. Your care team may watch you more closely for belumosudil side effects. Dose tailoring: the belumosudil dose may need to be adjusted and individualized by your care team. Speak u… 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 Fedratinib or Belumosudil 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: INREBIC(R) oral capsules, fedratinib oral capsules. Bristol-Myers Squibb Company (per FDA), Princeton, NJ, 2023. DailyMed
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