Sirolimus 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
Sirolimus
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. Belumosudil (Rezurock) slows down a natural 'pump' in your body called P-gp that normally helps move sirolimus (Rapamune) out. When that pump is blocked, more sirolimus can build up in your blood.
Sirolimus is a narrow therapeutic index drug, which means the gap between the right amount and too much is small. Higher levels can raise the risk of side effects like low blood counts, infections, mouth sores, or kidney and lung problems. The good news: your care team can manage this by checking your sirolimus blood levels and adjusting your dose. Keep taking both exactly as prescribed and talk with your pharmacist or doctor before changing anything.
Mechanism: Belumosudil inhibits P-glycoprotein (P-gp)-mediated efflux. Sirolimus is a P-gp substrate (and CYP3A4 substrate), so P-gp inhibition can increase sirolimus systemic exposure.
- Direction: Increased sirolimus exposure (Cmax/AUC), higher toxicity risk.
- Magnitude: Not established for sirolimus; belumosudil roughly doubled dabigatran Cmax and AUC.
- Evidence: Probable. Severity: Major (sirolimus is NTI). Onset: Unspecified.
- Management: Avoid combination if possible. If coadministered, reduce sirolimus dose as needed and monitor whole-blood trough concentrations, CBC, renal function, and toxicity signs.
What happens
Increased P-gp substrate exposure
Interaction Deep Dive
Do not give belumosudil (a P-gp inhibitor) together with a P-gp substrate that has a narrow therapeutic index (NTI), since even small shifts in concentration could produce serious toxicities. When such coadministration is unavoidable, reduce the dose of the P-gp substrate as required. A drug interaction study found that adding belumosudil raised both the Cmax and AUC of dabigatran (a P-gp substrate) by 2-fold1.
Why it happens (mechanism)
Inhibition of P-gp-mediated efflux transport by belumosudil
How to manage this interaction
What your care team may do:
- Prefer to avoid using these two together when possible.
- If you do need both, they may lower your sirolimus dose and individualize it to you.
- They may check your sirolimus blood levels more closely, along with blood counts and kidney function.
What you should do: Keep taking both medicines exactly as prescribed. Do not stop or change either one on your own. Ask your pharmacist or prescriber whether your sirolimus level should be checked, and report side effects like unusual bruising, infections, mouth sores, or swelling.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) A drug interaction study showed that giving belumosudil together with dabigatran (a P-gp substrate) raised the Cmax and AUC of dabigatran by 2-fold 1.
Common questions
Can I take Sirolimus and Belumosudil together?
Belumosudil can raise sirolimus levels by blocking the P-gp pump, and since sirolimus has a narrow safety margin this is a major interaction. Your team will avoid the combo when possible or lower the sirolimus dose and monitor blood levels closely. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Sirolimus 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 Sirolimus and Belumosudil interaction managed?
What your care team may do: Prefer to avoid using these two together when possible. If you do need both, they may lower your sirolimus dose and individualize it to you. They may check your sirolimus blood levels more closely, along with blood counts and kidney function. What you should do: Keep taking both medicines exactly as prescribed. Do not stop or change either one on your own. Ask your phar… 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 Sirolimus 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: REZUROCK(R) oral tablets, belumosudil oral tablets. Kadmon Pharmaceuticals LLC (per FDA), Bridgewater, NJ, 2024. DailyMed
Keep reading about Sirolimus
Keep reading about Belumosudil
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