Abemaciclib and Idelalisib: 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
Idelalisib
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 idelalisib (Zydelig) together with abemaciclib (Verzenio). Your body uses a liver enzyme called CYP3A4 to break down abemaciclib. Idelalisib blocks that enzyme, so abemaciclib can build up in your blood to higher levels than expected.
Higher levels can mean more side effects, like diarrhea, tiredness, or a drop in your blood counts. The good news is that this is very manageable. Your care team can simply lower your abemaciclib dose while you're on idelalisib and watch you a little more closely. Please don't change anything on your own, just check in with your oncology team or pharmacist.
Effect: Idelalisib is a strong CYP3A4 inhibitor; abemaciclib is a CYP3A4 substrate. Coadministration reduces abemaciclib metabolism, increasing plasma concentrations of abemaciclib and its active metabolites, raising toxicity risk.
- Direction: Increased abemaciclib exposure (AUC/Cmax).
- Onset: Unspecified; evidence is theoretical/label-based.
- Management: If starting dose was 200 mg or 150 mg BID, reduce abemaciclib to 100 mg BID. If already reduced to 100 mg BID for AEs, reduce to 50 mg BID. On idelalisib discontinuation, resume prior dose after 3 to 5 inhibitor half-lives.
- Monitor: Diarrhea, myelosuppression, hepatotoxicity, fatigue.
What happens
Increased abemaciclib plasma concentration
Interaction Deep Dive
Taking abemaciclib together with a potent CYP3A4 inhibitor can raise plasma concentrations of abemaciclib and its active metabolite, potentially heightening toxicity. When these agents are given together and the initial abemaciclib dose was either 200 mg or 150 mg twice daily, the abemaciclib dose should be lowered to 100 mg twice daily. For patients whose dose was already cut to 100 mg twice daily because of adverse reactions, abemaciclib should be reduced further to 50 mg twice daily. Once the strong CYP3A inhibitor is stopped, the abemaciclib dose can be raised again (after 3-5 half-lives of the inhibitor have elapsed) back to the dose that had been in use prior to starting the strong inhibitor1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated abemaciclib metabolism
How to manage this interaction
This combination is manageable with a planned dose adjustment and closer monitoring by your oncology team.
- Keep taking both exactly as prescribed unless your team tells you otherwise.
- Your team may lower your abemaciclib dose while you are on idelalisib, and raise it back up after idelalisib is stopped.
- Report side effects promptly, especially diarrhea, unusual tiredness, fever, or signs of infection.
- Ask your pharmacist or prescriber before starting or stopping either medicine.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
2 reports — tap to read
a) In drug interaction studies, taking abemaciclib together with itraconazole (a strong CYP3A inhibitor) is projected to raise the AUC of abemaciclib along with its active metabolites (M2, M18 and M20) by 2.2-fold 1.
b) In drug interaction studies conducted in cancer patients, giving a single 50 mg dose of abemaciclib (0.3 times the approved 150 mg dosage) with clarithromycin 500 mg twice daily (a strong CYP3A inhibitor) raised the AUC(0 to infinity) of abemaciclib plus its active metabolites (M2, M18, and M20) by 1.7-fold relative to abemaciclib given alone 1.
Common questions
Can I take Abemaciclib and Idelalisib together?
Idelalisib can raise abemaciclib levels and side effects by blocking its breakdown, but your oncology team can manage this by lowering the abemaciclib dose and monitoring you more closely. Keep taking both as prescribed and report new side effects. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Abemaciclib and Idelalisib 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 Idelalisib interaction managed?
This combination is manageable with a planned dose adjustment and closer monitoring by your oncology team. Keep taking both exactly as prescribed unless your team tells you otherwise. Your team may lower your abemaciclib dose while you are on idelalisib, and raise it back up after idelalisib is stopped. Report side effects promptly, especially diarrhea, unusual tiredness, fever, or signs of infect… 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 Idelalisib 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, 2017. DailyMed
Keep reading about Idelalisib
Keep reading about Abemaciclib
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