Abemaciclib and Palbociclib: 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
Palbociclib
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.
You've been prescribed two cancer medicines here, palbociclib (Ibrance) and abemaciclib (Verzenio). Palbociclib can gently slow down one of the liver enzymes (called CYP3A) that helps break down certain other drugs. When that enzyme is slowed, some medicines can build up a bit more in your body, which can mean stronger effects and more side effects.
The good news is this concern is mostly theoretical, meaning it's based on how the drug works rather than lots of real-world reports. Your care team knows how to handle this by adjusting doses when needed and keeping a closer eye on you. Keep taking both exactly as prescribed, and check with your pharmacist or oncologist if you have questions.
Mechanism: Palbociclib is a weak, time-dependent CYP3A inhibitor. Coadministration with a CYP3A substrate having a narrow therapeutic index may increase substrate exposure (AUC/Cmax) and toxicity. In DDI studies, multiple-dose palbociclib raised midazolam AUC and Cmax.
- Direction: increased exposure to the CYP3A substrate (neither drug here is a prodrug).
- Severity/Evidence: major severity, theoretical substantiation.
- Onset: unspecified.
- Management: consider dose reduction of the NTI CYP3A substrate; monitor for substrate-specific toxicity. Individualize per care team.
What happens
Increased exposure to CYP3A substrates with a narrow therapeutic index
Interaction Deep Dive
When palbociclib (which acts as a weak, time-dependent inhibitor of CYP3A) is taken together with a CYP3A substrate that has a narrow therapeutic index (NTI), the substrate's exposure and adverse effects may be heightened. In drug interaction studies, giving midazolam alongside repeated doses of palbociclib produced higher midazolam AUC and Cmax. If these agents are used together, consider lowering the dose of the CYP3A substrate and watch patients for signs of toxicity1.
Why it happens (mechanism)
Inhibition of CYP3A substrate metabolism by palbociclib
How to manage this interaction
Your care team can manage this by tailoring your treatment. Typical steps include:
- Adjusting the dose of the affected (CYP3A) medicine, which may need to be individualized by your team.
- Closer monitoring for signs of too much drug effect or side effects.
What you can do:
- Keep taking both medicines exactly as prescribed unless your prescriber tells you otherwise.
- Report any new or worsening side effects to your pharmacist or oncologist.
- Ask before adding new prescriptions, over-the-counter products, or supplements.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) When midazolam (a CYP3A substrate) was given together with repeated doses of palbociclib 125 mg/day to healthy participants (N=26), the AUC and Cmax of midazolam rose by 61% and 37%, respectively 1.
Common questions
Can I take Abemaciclib and Palbociclib together?
Palbociclib can raise levels of certain narrow-margin drugs broken down by CYP3A, so your team may lower that drug's dose and watch you more closely. Keep taking both as prescribed and report any new side effects. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Abemaciclib and Palbociclib 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 Palbociclib interaction managed?
Your care team can manage this by tailoring your treatment. Typical steps include: Adjusting the dose of the affected (CYP3A) medicine, which may need to be individualized by your team. Closer monitoring for signs of too much drug effect or side effects. What you can do: Keep taking both medicines exactly as prescribed unless your prescriber tells you otherwise. Report any new or worsening side ef… 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 Palbociclib 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: IBRANCE(R) oral capsules, palbociclib oral capsules. Pfizer Labs (per FDA), New York, NY, 2019. DailyMed
Keep reading about Palbociclib
Keep reading about Abemaciclib
These medications also interact with supplements
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.
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