Abemaciclib and Erythromycin: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 10, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Erythromycin
Abemaciclib
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 abemaciclib (Verzenio), your cancer medicine. Erythromycin slows that enzyme down. When the cleanup slows, more abemaciclib can build up in your blood. That can mean stronger side effects, like diarrhea, nausea, tiredness, or a drop in blood cell counts.
The good news is this is very manageable. This concern is based on how these drugs work rather than lots of real-world reports, so please don't stop anything on your own. Your care team can watch you a little more closely and adjust your abemaciclib dose if needed. Let them know if new or worsening side effects show up.
Mechanism: Erythromycin is a moderate CYP3A4 inhibitor; abemaciclib is a CYP3A4 substrate (not a prodrug). Inhibition reduces metabolism, increasing plasma levels of abemaciclib and its active metabolites.
Direction/effect: Increased abemaciclib exposure, raising risk of toxicity (diarrhea, neutropenia, hepatotoxicity, fatigue).
Evidence: Theoretical; onset unspecified; severity moderate.
Management:
- Monitor for adverse reactions if coadministered.
- Consider reducing abemaciclib in 50-mg increments per labeling (150 mg BID to 100, then 50; 200 mg BID to 150, then 100, then 50; discontinue if 50 mg BID not tolerated).
- An alternative non-inhibiting antibiotic may be preferred where clinically feasible.
What happens
Increased abemaciclib plasma concentration
Interaction Deep Dive
When abemaciclib (a substrate of CYP3A4) is taken together with a moderate CYP3A4 inhibitor, plasma concentrations of both abemaciclib and its active metabolite may rise, potentially increasing toxicity. Should the two be given together, watch for adverse reactions and consider lowering the abemaciclib dose in 50-mg steps. For patients on 150 mg twice daily, the first reduction is to 100 mg twice daily and the second to 50 mg twice daily; if 50 mg twice daily cannot be tolerated, discontinue the drug. For patients on 200 mg twice daily, reduce first to 150 mg twice daily, then to 100 mg twice daily, and then to 50 mg twice daily; discontinue if 50 mg twice daily is not tolerated1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated abemaciclib metabolism
How to manage this interaction
Keep taking both exactly as prescribed unless your care team tells you otherwise. This interaction can usually be handled with a few simple steps.
- Your team may monitor you more closely for side effects such as diarrhea, nausea, fatigue, or signs of low blood counts or liver issues.
- The abemaciclib dose may need to be adjusted and individualized by your care team, typically lowered in steps if needed.
- Sometimes a different antibiotic that doesn't affect this enzyme may be chosen instead.
Tell your pharmacist or prescriber that you take Verzenio before starting erythromycin, and report any new or worsening side effects promptly.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In drug interaction studies, giving abemaciclib together with verapamil and diltiazem (moderate CYP3A inhibitors) is expected to raise the AUC of abemaciclib and its active metabolites (M2, M18, and M20) by roughly 1.6-fold and 2.4-fold, respectively 1.
Common questions
Can I take Abemaciclib and Erythromycin together?
Erythromycin can raise abemaciclib (Verzenio) levels and increase side effects; your care team can manage this by monitoring you and adjusting the dose or choosing a different antibiotic. Do not change anything on your own. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Abemaciclib and Erythromycin 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 Abemaciclib and Erythromycin interaction managed?
Keep taking both exactly as prescribed unless your care team tells you otherwise. This interaction can usually be handled with a few simple steps. Your team may monitor you more closely for side effects such as diarrhea, nausea, fatigue, or signs of low blood counts or liver issues. The abemaciclib dose may need to be adjusted and individualized by your care team, typically lowered in steps if nee… 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 Abemaciclib 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 anything you'd monitor while I'm on both?
References (1)
- Product Information: VERZENIO(TM) oral tablets, abemaciclib oral tablets. Lilly USA LLC (per FDA), Indianapolis, IN, 2018. DailyMed
Keep reading about Erythromycin
Keep reading about Abemaciclib
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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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