Abemaciclib and Atazanavir: 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
Atazanavir
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.
Let's talk about taking atazanavir (Reyataz) together with your cancer medicine abemaciclib (Verzenio). Your body normally breaks down abemaciclib using a liver enzyme called CYP3A4. Atazanavir slows that enzyme down, so abemaciclib can build up higher than usual in your blood.
Higher levels can mean stronger side effects, like diarrhea, low blood counts, tiredness, or nausea. The good news is this is very manageable. Your care team may watch you a bit more closely and can adjust your abemaciclib dose if needed. Please don't stop or change either medicine on your own. Just check in with your pharmacist or doctor so they can keep you safe.
Effect: Increased abemaciclib exposure. Atazanavir, a moderate-to-strong CYP3A4 inhibitor, inhibits CYP3A4-mediated metabolism of abemaciclib (a CYP3A4 substrate), raising plasma levels of abemaciclib and its active metabolites and increasing toxicity risk. Neither drug's activity depends on being converted by the affected enzyme, so the direction is increased effect.
- Direction: Increased abemaciclib effect/toxicity
- Onset: Unspecified
- Evidence: Theoretical
- Management: Monitor for adverse reactions (diarrhea, hepatotoxicity, myelosuppression). Consider dose reduction in 50-mg increments per labeling (150 mg BID to 100 mg to 50 mg; 200 mg BID to 150 mg to 100 mg to 50 mg; discontinue if 50 mg BID not tolerated).
What happens
Increased abemaciclib plasma concentration
Interaction Deep Dive
Taking abemaciclib, which is metabolized by CYP3A4, together with a moderate CYP3A4 inhibitor can raise plasma concentrations of both abemaciclib and its active metabolite, potentially heightening toxicity. When these agents are given together, watch for adverse reactions and consider lowering the abemaciclib dose in 50-mg steps. Patients on 150 mg twice daily should first be reduced to 100 mg twice daily, then to 50 mg twice daily, with treatment stopped if 50 mg twice daily cannot be tolerated. 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, discontinuing use if 50 mg twice daily is not tolerated1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated abemaciclib metabolism
How to manage this interaction
Both medicines can be used together when your care team manages it. Here is what that usually looks like:
- Keep taking both exactly as prescribed unless your doctor tells you otherwise.
- Closer monitoring for side effects such as diarrhea, unusual tiredness, easy bruising, or signs of infection.
- Dose adjustment: your team may lower the abemaciclib dose in steps (for example, in 50-mg increments) and individualize it for you.
Report any new or worsening side effects to your pharmacist or prescriber promptly so your dose can be tailored.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In drug interaction studies, the combined administration of abemaciclib with verapamil and diltiazem (both moderate CYP3A inhibitors) is projected to raise the AUC of abemaciclib together 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 Atazanavir together?
Atazanavir can raise abemaciclib levels and side effects by slowing its breakdown; keep taking both as prescribed, but let your care team 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 Atazanavir 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 Atazanavir interaction managed?
Both medicines can be used together when your care team manages it. Here is what that usually looks like: Keep taking both exactly as prescribed unless your doctor tells you otherwise. Closer monitoring for side effects such as diarrhea, unusual tiredness, easy bruising, or signs of infection. Dose adjustment: your team may lower the abemaciclib dose in steps (for example, in 50-mg increments) and… 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 Atazanavir 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 Atazanavir
Keep reading about Abemaciclib
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major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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