Abemaciclib and Fluconazole: 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
Fluconazole
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. Fluconazole (Diflucan) slows that enzyme down. When it's slowed, abemaciclib can build up higher than usual in your blood.
That means you could feel its side effects more strongly, like diarrhea, tiredness, nausea, or a drop in blood counts. This is based on how the drugs work rather than strong studies, so it's a possible concern, not a sure thing. The good news is your care team can manage it easily by watching you a bit more closely and adjusting your dose if needed. Don't stop either medicine on your own, just let your pharmacist or doctor know you take both.
Mechanism: Fluconazole is a moderate CYP3A4 inhibitor; abemaciclib is a CYP3A4 substrate (active parent plus active metabolites). Inhibition reduces abemaciclib clearance, increasing exposure (AUC/Cmax) of abemaciclib and its active metabolites, raising toxicity risk.
Direction: increased abemaciclib effect and toxicity. Evidence: theoretical. Onset: unspecified.
Management:
- Monitor for adverse reactions (diarrhea, neutropenia/leukopenia, fatigue, hepatotoxicity).
- Consider reducing abemaciclib in 50-mg increments per labeling: 150 mg BID to 100 mg BID to 50 mg BID; 200 mg BID down through 150, 100, 50 mg BID.
- Discontinue if 50 mg BID is not tolerated.
- Individualize dose and consider CBC/LFT monitoring per protocol.
What happens
Increased abemaciclib plasma concentration
Interaction Deep Dive
When abemaciclib (a substrate of CYP3A4) is taken together with a moderate CYP3A4 inhibitor, the plasma concentrations of abemaciclib and its active metabolite can rise, potentially heightening toxicity. Should the two be given at the same time, 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 is not tolerated, stop the drug. For patients on 200 mg twice daily, the first reduction is to 150 mg twice daily, the second to 100 mg twice daily, and the third 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
This is manageable with your care team's help. Keep taking both medicines exactly as prescribed unless your prescriber tells you otherwise.
- Your team may watch you more closely for side effects like diarrhea, low blood counts, fatigue, or nausea while you're on both drugs.
- They may adjust your abemaciclib dose, which is typically done in 50-mg steps and individualized to you.
- Report new or worsening side effects promptly, especially significant diarrhea.
What to do: Tell your pharmacist and oncologist that you take fluconazole with abemaciclib so they can plan monitoring or a dose adjustment if needed.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) Drug interaction investigations predict that giving abemaciclib together with verapamil and diltiazem (both moderate CYP3A inhibitors) will 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 Fluconazole together?
Fluconazole can raise abemaciclib levels and its side effects by slowing its breakdown; keep taking both as prescribed and let your oncology team know so 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 Fluconazole 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 Fluconazole interaction managed?
This is manageable with your care team's help. Keep taking both medicines exactly as prescribed unless your prescriber tells you otherwise. Your team may watch you more closely for side effects like diarrhea, low blood counts, fatigue, or nausea while you're on both drugs. They may adjust your abemaciclib dose, which is typically done in 50-mg steps and individualized to you. Report new or worseni… 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 Fluconazole 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 Fluconazole
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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