Abemaciclib and Fluvoxamine: 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
Fluvoxamine
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.
Here's what's going on. Your body clears abemaciclib (Verzenio) using a liver enzyme called CYP3A4. Fluvoxamine slows that enzyme down. When the enzyme works slower, more abemaciclib can build up in your blood.
That can mean stronger side effects, like diarrhea, nausea, tiredness, or a drop in your blood counts. This concern is based on how the drugs are expected to behave rather than proven cases, so please don't worry. Keep taking both exactly as prescribed. Your cancer team can manage this easily by watching you a little more closely and adjusting your abemaciclib dose if needed. Just let them know you take both.
Mechanism: Fluvoxamine is a moderate CYP3A4 inhibitor; abemaciclib is a CYP3A4 substrate (active, not a prodrug). Inhibition reduces metabolism, increasing abemaciclib and active-metabolite exposure (AUC/Cmax) and risk of toxicity.
- Direction: increased abemaciclib effect/toxicity
- Evidence: theoretical; onset: unspecified; severity: moderate
- Monitoring: diarrhea, neutropenia/CBC, hepatic function, fatigue, VTE signs
- Management: if coadministered, reduce abemaciclib by 50-mg increments (e.g., 150 mg BID to 100 mg BID, then 50 mg BID; 200 mg BID to 150 to 100 to 50 mg BID); discontinue if 50 mg BID not tolerated.
What happens
Increased abemaciclib plasma concentration
Interaction Deep Dive
When abemaciclib, which is a substrate of CYP3A4, is taken together with a moderate inhibitor of CYP3A4, the plasma concentrations of both abemaciclib and its active metabolite may rise, potentially increasing toxicity. Should the two agents 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 is to 50 mg twice daily; if 50 mg twice daily cannot be tolerated, stop treatment. 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
The good news: this is manageable with a few standard steps from your care team.
- Keep taking both as prescribed unless your prescriber tells you otherwise.
- Your team may watch you more closely for side effects such as diarrhea, nausea, fatigue, or changes in your blood counts.
- They may lower your abemaciclib dose in 50-mg steps if needed, and will tailor the dose to you.
- Tell your pharmacist and oncologist that you take both drugs, and report 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) According to drug interaction studies, taking 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 Fluvoxamine together?
Fluvoxamine can raise abemaciclib levels and side effects by slowing its breakdown; keep taking both as prescribed and let your oncology team know, since they can monitor you and adjust the abemaciclib dose if needed. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Abemaciclib and Fluvoxamine 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 Fluvoxamine interaction managed?
The good news: this is manageable with a few standard steps from your care team. Keep taking both as prescribed unless your prescriber tells you otherwise. Your team may watch you more closely for side effects such as diarrhea, nausea, fatigue, or changes in your blood counts. They may lower your abemaciclib dose in 50-mg steps if needed, and will tailor the dose to you. Tell your pharmacist and o… 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 Fluvoxamine 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 Fluvoxamine
Keep reading about Abemaciclib
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