Abemaciclib and Fosnetupitant: 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
Fosnetupitant
No brand names on recordAbemaciclib
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 me explain this one simply. Abemaciclib (Verzenio) is a cancer medicine your body breaks down using an enzyme called CYP3A4. Fosnetupitant (which turns into netupitant, used to prevent nausea from chemo) slows that enzyme down a bit. When the enzyme is slowed, abemaciclib can build up in your blood, which may make side effects like diarrhea, low blood counts, tiredness, or nausea more likely.
This concern is mostly theoretical, so please don't worry. Your care team already knows how to handle it, often by spacing the medicines out or adjusting your abemaciclib dose. Keep taking both exactly as prescribed and let your doctor or pharmacist know how you're feeling.
Effect: Increased abemaciclib plasma concentration (including its active metabolite) with potential for increased toxicity.
Mechanism: Netupitant (active moiety of fosnetupitant) is a moderate CYP3A4 inhibitor; abemaciclib is a CYP3A4 substrate. Inhibition reduces abemaciclib clearance, raising exposure (AUC/Cmax). Neither agent is a prodrug in a way that reverses this direction; the parent drug effect is increased.
Evidence: Theoretical. Onset: unspecified.
- Avoid coadministration with netupitant for 1 week where feasible.
- If needed within 1 week, consider dose reduction in 50 mg increments per label.
- Monitor for adverse reactions (diarrhea, myelosuppression, hepatotoxicity, fatigue).
What happens
Increased abemaciclib plasma concentration
Interaction Deep Dive
When abemaciclib (a substrate of CYP3A4) is given together with netupitant (a moderate inhibitor of CYP3A4), plasma concentrations of abemaciclib and its active metabolite may rise, which could heighten toxicity1. For a period of 1 week, coadministration of abemaciclib with netupitant should be avoided; should dosing be required within 1 week of netupitant, a reduction in the abemaciclib dose should be considered2. Where the two agents are used together, watch for adverse reactions and consider lowering the abemaciclib dose in 50-mg steps. For patients on 150 mg twice daily, reduce first to 100 mg twice daily and then to 50 mg twice daily, discontinuing if 50 mg twice daily cannot be tolerated. 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, discontinuing if 50 mg twice daily is not tolerated1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated abemaciclib metabolism
How to manage this interaction
Here is how your care team typically handles this combination:
- Timing: They may try to avoid giving abemaciclib within about 1 week of netupitant when possible.
- Dose adjustment: If both are needed together, your abemaciclib dose may be adjusted and individualized, often reduced in 50 mg steps.
- Monitoring: Your team may watch you more closely for side effects like diarrhea, low blood counts, or fatigue.
Keep taking both exactly as prescribed. Don't stop or change anything on your own. Tell your pharmacist or oncologist promptly if you notice new or worsening side effects so they can tailor your plan.
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 (both moderate CYP3A inhibitors) is projected to raise the AUC of abemaciclib along with 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 Fosnetupitant together?
Netupitant can raise abemaciclib levels and side effects, so your care team may space the drugs out or lower your abemaciclib 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 Fosnetupitant 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 Fosnetupitant interaction managed?
Here is how your care team typically handles this combination: Timing: They may try to avoid giving abemaciclib within about 1 week of netupitant when possible. Dose adjustment: If both are needed together, your abemaciclib dose may be adjusted and individualized, often reduced in 50 mg steps. Monitoring: Your team may watch you more closely for side effects like diarrhea, low blood counts, or fat… 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 Fosnetupitant 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 (2)
Keep reading about Fosnetupitant
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.
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