Abemaciclib and Ribociclib: 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
Ribociclib
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.
These two cancer medicines, ribociclib (Kisqali) and abemaciclib (Verzenio), aren't usually taken together, but here's the concern if they are. Ribociclib slows down a liver enzyme called CYP3A4. That enzyme is also one of the main ways your body breaks down abemaciclib. So ribociclib can cause abemaciclib to build up in your body, which may lead to more side effects, like diarrhea, low blood counts, or tiredness.
The good news is this is something your cancer care team can manage. They may check on you more often and can adjust your dose if needed. Please don't change anything on your own, just talk with your oncologist or pharmacist.
Effect: Ribociclib is a strong CYP3A4 inhibitor. Abemaciclib is a CYP3A4 substrate, so coadministration is predicted to increase abemaciclib exposure (AUC/Cmax) and raise the risk of dose-dependent toxicity (diarrhea, neutropenia, fatigue, hepatotoxicity).
- Mechanism: Inhibition of CYP3A4-mediated abemaciclib metabolism.
- Direction: Increased substrate exposure (neither drug is a prodrug).
- Evidence: Theoretical; extrapolated from a ribociclib/midazolam study showing significant Cmax and AUC increases.
- Onset: Unspecified.
Management: Avoid strong CYP3A4 inhibitors with abemaciclib where possible; if combined, monitor closely for toxicity and consider abemaciclib dose reduction per labeling.
What happens
Increased exposure of CYP3A4 substrate and an increased risk of CYP3A4 substrate-related adverse reactions
Interaction Deep Dive
Taking ribociclib, which is a potent inhibitor of CYP3A4, together with CYP3A4 substrates that have a narrow therapeutic index can raise the exposure to the substrate and can likewise heighten the substrate's adverse reactions. When ribociclib was given alongside midazolam (a sensitive CYP3A4 substrate) in a drug interaction study conducted in healthy subjects, both the Cmax and AUC of midazolam rose significantly. Throughout concurrent administration, watch for an increase in the CYP3A4 substrate's adverse reactions. A reduction in the CYP3A4 substrate dose may be required1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism by ribociclib
How to manage this interaction
This combination is generally avoided, but if your care team does use both, they have clear ways to keep you safe.
- Keep taking both as prescribed unless your oncologist tells you otherwise. Do not stop or change doses on your own.
- Your team may monitor you more closely for side effects like diarrhea, low blood counts, and fatigue.
- The abemaciclib dose may need to be reduced and individualized by your care team.
- Report new or worsening side effects to your pharmacist or oncologist promptly.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In a drug interaction study conducted in healthy subjects, giving ribociclib 400 mg once daily for 8 days together with midazolam raised midazolam Cmax by 2.1-fold and AUC(inf) by 3.8-fold. When ribociclib is given at 600 mg once daily, midazolam Cmax is projected to rise by 2.4-fold and AUC by 5.2-fold 1.
Common questions
Can I take Abemaciclib and Ribociclib together?
Ribociclib can raise abemaciclib levels and increase side effects, so this combination is usually avoided; if used together, your care team will watch you closely and may lower the abemaciclib dose. Never change your medicines on your own. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Abemaciclib and Ribociclib 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 Abemaciclib and Ribociclib interaction managed?
This combination is generally avoided, but if your care team does use both, they have clear ways to keep you safe. Keep taking both as prescribed unless your oncologist tells you otherwise. Do not stop or change doses on your own. Your team may monitor you more closely for side effects like diarrhea, low blood counts, and fatigue. The abemaciclib dose may need to be reduced and individualized by y… 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.
Questions for your pharmacist
- Does my dose of Abemaciclib or Ribociclib 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: KISQALI(R) oral tablets, ribociclib oral tablets. Novartis Pharmaceuticals Corporation (per FDA), East Hanover, NJ, 2025. DailyMed
Keep reading about Ribociclib
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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