Ensitrelvir 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
Belumosudil
Ensitrelvir
No brand names on record
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 belumosudil (Rezurock) together with ensitrelvir. Your body uses a liver enzyme called CYP3A to break down belumosudil. Ensitrelvir blocks that enzyme, so belumosudil can build up higher than intended in your body. That means the drug's effects and side effects (like nausea, tiredness, or changes in blood counts) could become stronger.
This combination is actually listed as one to avoid, so it matters. The good news is your care team can manage this by carefully planning the timing of these medicines. Please don't stop or change anything on your own. Just talk with your pharmacist or doctor first.
Effect: Ensitrelvir is a strong CYP3A inhibitor; belumosudil is a CYP3A substrate. Coadministration is expected to increase belumosudil exposure (higher AUC/Cmax) and the risk of substrate-related adverse effects.
Magnitude: Not quantified for belumosudil specifically, but ensitrelvir raised midazolam AUC ~6.77-fold and Cmax ~2.80-fold; effect on dexamethasone persisted ~10 days post-dose.
- Direction: increased substrate exposure
- Evidence: probable
- Severity: contraindicated
Management: Avoid concomitant use. Evaluate PK factors before initiating ensitrelvir, and account for prolonged CYP3A inhibition when reinitiating the substrate. Neither agent is a prodrug requiring activation.
What happens
Increased CYP3A substrates exposure and an increased risk of CYP3A substrates-related adverse effects
Interaction Deep Dive
Giving ensitrelvir together with CYP3A substrates is contraindicated because it can raise the exposure of those substrates and lead to adverse effects. Drug interaction studies demonstrated this: when midazolam (a CYP3A substrate) was given as a single 2 mg oral dose alongside ensitrelvir at the clinical dose (375 mg on day 1 followed by 125 mg on days 2 to 5), on Day 5 the midazolam Cmax rose roughly 2.80-fold and its AUC(0 to inf) rose 6.77-fold relative to midazolam given by itself. Similarly, coadministering a single 1 mg dose of dexAMETHasone with ensitrelvir (750 mg on day 1 and 250 mg on days 2 to 5, which is twice the recommended dose) on day 5, and then giving dexAMETHasone alone on day 9 (5 days after the final ensitrelvir dose) and on day 14 (10 days after the final ensitrelvir dose), produced the following changes versus dexAMETHasone given alone: on day 5 an approximately 1.47-fold rise in Cmax and a 3.47-fold rise in AUC(0 to inf); on day 9 a 1.24-fold rise in Cmax and a 2.38-fold rise in AUC(0 to inf); and on day 14 a 1.17-fold rise in Cmax and a 1.58-fold rise in AUC(0 to inf). Ensitrelvir should be started only after the relevant clinical and pharmacokinetic factors associated with the concomitant medication have been carefully weighed. Furthermore, restarting contraindicated CYP3A substrates should be decided based on an evaluation of how long CYP3A inhibition persists together with patient specific considerations1.
Why it happens (mechanism)
Inhibition of CYP3A-mediated metabolism by ensitrelvir
How to manage this interaction
This pairing is flagged as one to avoid because ensitrelvir can raise belumosudil levels significantly. Here is how a care team typically handles it:
- They review your full medication list and timing before starting ensitrelvir.
- Because ensitrelvir's enzyme-blocking effect can last for days after the last dose, they consider that waiting period before restarting belumosudil.
- They may monitor you more closely for side effects.
What you should do: keep taking your medicines exactly as prescribed, and don't stop or adjust either one yourself. Tell your pharmacist or prescriber that you take belumosudil before starting ensitrelvir so they can plan safely.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) Giving midazolam (a CYP3A substrate) as a single 2 mg oral dose together with ensitrelvir at the clinical dose (375 mg on day 1 and 125 mg on days 2 to 5) on Day 5 produced an approximately 2.80-fold rise in Cmax and a 6.77-fold rise in AUC(0 to inf) of midazolam relative to midazolam given by itself. In addition, co-administering dexAMETHasone (1 mg single dose) with ensitrelvir (750 mg on day 1 and 250 mg on days 2 to 5, which is twice the recommended dose) on day 5, and giving it alone on day 9 (5 days after the final ensitrelvir dose) and day 14 (10 days after the final ensitrelvir dose), yielded an approximately 1.47-fold rise in Cmax and a 3.47-fold rise in AUC(0 to inf) of dexAMETHasone on day 5, a 1.24-fold rise in Cmax and a 2.38-fold rise in AUC(0 to inf) on day 9, and a 1.17-fold rise in Cmax and a 1.58-fold rise in AUC(0 to inf) on day 14, compared with dexAMETHasone given alone 1.
Common questions
Can I take Ensitrelvir and Belumosudil together?
Ensitrelvir blocks the enzyme that clears belumosudil, so combining them can raise belumosudil levels and side effects; this combination is one to avoid, so check with your pharmacist or doctor before starting ensitrelvir. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Ensitrelvir and Belumosudil interaction?
It is rated contraindicated. These should generally not be used together.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Ensitrelvir and Belumosudil interaction managed?
This pairing is flagged as one to avoid because ensitrelvir can raise belumosudil levels significantly. Here is how a care team typically handles it: They review your full medication list and timing before starting ensitrelvir. Because ensitrelvir's enzyme-blocking effect can last for days after the last dose, they consider that waiting period before restarting belumosudil. They may monitor you mo… 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 Ensitrelvir 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: XOCOVA® oral tablets, ensitrelvir oral tablets. Shionogi Inc. Florham Park, NJ, 2026. DailyMed
Keep reading about Belumosudil
Keep reading about Ensitrelvir
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