Belumosudil and Erythromycin: 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
Erythromycin
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.
Here's what's going on. Your body uses a liver enzyme called CYP3A4 to break down belumosudil (Rezurock). Erythromycin slows that enzyme down. So when you take both together, belumosudil can build up in your body more than usual.
More belumosudil means stronger effects, but it can also mean more side effects, like nausea, tiredness, or changes in your labs. The good news is this is very manageable. Your care team can adjust your dose and keep a closer eye on how you're doing. Don't stop or change either medicine on your own. Just check in with your pharmacist or doctor so they can plan for it.
Mechanism: Erythromycin is a moderate CYP3A4 inhibitor; belumosudil is a CYP3A4 substrate. Coadministration inhibits belumosudil metabolism, increasing its exposure (AUC/Cmax) and the risk of concentration-related adverse effects. Neither drug is a prodrug, so the effect is straightforward accumulation of active belumosudil.
- Direction: increased belumosudil exposure/effect
- Severity: major
- Onset: unspecified
- Evidence: theoretical
Management: Consider belumosudil dose adjustment individualized by the care team. Monitor for CYP3A4-substrate adverse effects (GI intolerance, fatigue, hepatic enzyme changes). Note that strong CYP3A4 inhibitors already carry a labeled belumosudil dose recommendation; apply clinical judgment with this moderate inhibitor.
What happens
Increased CYP3A4 substrate exposure and an increased risk of CYP3A4-substrate-related adverse effects
Interaction Deep Dive
When erythromycin is given together with CYP3A4 substrates, the exposure to those substrates may rise, potentially heightening or extending both their therapeutic and adverse effects. In patients taking erythromycin at the same time, consider adjusting the dose and, where feasible, carefully monitor the concentrations of the CYP3A4 substrates123.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism by erythromycin
How to manage this interaction
The main point: keep taking both medicines exactly as prescribed unless your care team tells you otherwise. This interaction is something they can plan around.
- Your belumosudil dose may need to be adjusted and individualized by your care team while you are on erythromycin.
- Your team may monitor you more closely for side effects and check relevant labs.
- Tell your pharmacist and prescriber that you take both drugs, and report any new nausea, unusual tiredness, or other new symptoms.
If erythromycin is only a short course, mention that too, since timing can matter.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Belumosudil and Erythromycin together?
Erythromycin can raise belumosudil levels and side effects because it slows the enzyme that clears it; keep taking both as prescribed and ask your care team whether your dose needs adjusting or closer monitoring. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Belumosudil and Erythromycin 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 Erythromycin interaction managed?
The main point: keep taking both medicines exactly as prescribed unless your care team tells you otherwise. This interaction is something they can plan around. Your belumosudil dose may need to be adjusted and individualized by your care team while you are on erythromycin. Your team may monitor you more closely for side effects and check relevant labs. Tell your pharmacist and prescriber that you… 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.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Belumosudil or Erythromycin 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 (3)
- Product Information: Erythromycin Lactobionate IV injection lyophilized powder for solution, erythromycin lactobionate IV injection lyophilized powder for solution. Nexus Pharmaceuticals (per DailyMed), Lincolnshire, IL, 2024.
- Product Information: Erythromycin oral delayed-release capsules, erythromycin oral delayed-release capsules. Dr. Reddy's Laboratories Inc. (per DailyMed), Princeton, NJ, 2025. DailyMed
- Product Information: ERYTHROMYCIN ETHYLSUCCINATE oral suspension granule, erythromycin ethylsuccinate oral suspension granule. ANI Pharmaceuticals, Inc (per DailyMed), Baudette, MN, 2025. DailyMed
Keep reading about Erythromycin
Keep reading about Belumosudil
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Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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