Abemaciclib and Diltiazem: 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
Diltiazem
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.
You've been prescribed diltiazem (a heart and blood pressure medicine) along with abemaciclib (Verzenio, a cancer medicine). Diltiazem can slow down the liver enzyme that normally breaks abemaciclib down. When that happens, abemaciclib can build up a bit more in your body, which may raise the chance of side effects like diarrhea, low blood counts, tiredness, or nausea.
This concern is based mostly on how these drugs work rather than strong studies, so please don't panic. Keep taking both exactly as prescribed. Your care team knows how to handle this by watching you a little more closely and adjusting your abemaciclib dose if needed. Reach out to your pharmacist or doctor with any questions.
Effect: Diltiazem, a moderate CYP3A4 inhibitor, may reduce CYP3A4-mediated metabolism of abemaciclib (a CYP3A4 substrate), increasing plasma levels of abemaciclib and its active metabolite and raising toxicity risk (diarrhea, neutropenia, hepatotoxicity, fatigue).
- Direction: increased abemaciclib exposure
- Onset: unspecified
- Evidence: theoretical (mechanism-based)
- Management: Monitor for adverse reactions. If dose reduction is needed, reduce abemaciclib in 50-mg increments per labeling (e.g., 150 mg BID to 100 mg BID, then 50 mg BID; 200 mg BID stepping down similarly). Discontinue if 50 mg BID is not tolerated.
Neither agent requires bioactivation in a way that reverses this direction.
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 think about lowering the abemaciclib dose in 50-mg steps. For patients on 150 mg twice daily, reduce first to 100 mg twice daily, then to 50 mg twice daily, and stop the drug 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, then to 50 mg twice daily, and discontinue if 50 mg twice daily is not tolerated1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated abemaciclib metabolism
How to manage this interaction
Good news: this is a manageable situation, and both medicines can often be used together with the right oversight.
- Keep taking both as prescribed unless your care team tells you otherwise.
- Your team may monitor you more closely for abemaciclib side effects such as diarrhea, unusual tiredness, signs of infection, or lab changes in blood counts and liver values.
- Your abemaciclib dose may be reduced in 50-mg steps and individualized by your oncology team if side effects appear.
- Tell your pharmacist or prescriber if you develop frequent diarrhea, fever, or extreme fatigue, and mention every medicine you take.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) According to 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 Diltiazem together?
Diltiazem can raise abemaciclib levels and increase side effect risk, but your care team can manage this by watching you closely and adjusting your abemaciclib dose if needed. 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 Diltiazem 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 Diltiazem interaction managed?
Good news: this is a manageable situation, and both medicines can often be used together with the right oversight. Keep taking both as prescribed unless your care team tells you otherwise. Your team may monitor you more closely for abemaciclib side effects such as diarrhea, unusual tiredness, signs of infection, or lab changes in blood counts and liver values. Your abemaciclib dose may be reduced… 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 Diltiazem 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 Diltiazem
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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