Abemaciclib and Primidone: 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
Primidone
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. Primidone (Mysoline) can speed up a liver enzyme called CYP3A. Your cancer medicine abemaciclib (Verzenio) is broken down by that same enzyme. So when you take them together, your body may clear the abemaciclib faster than usual. That can leave less of it in your system, which may make it work less well against your cancer.
This concern is based mostly on how these drugs behave in theory, not on strong studies. Still, it's worth taking seriously because keeping your cancer treatment effective matters. Please don't change anything on your own. Your care team can manage this by adjusting your dose or watching you more closely.
Mechanism: Primidone (and its active metabolite phenobarbital) is a CYP3A4 inducer. Abemaciclib is a CYP3A4 substrate, so co-administration may increase its metabolism.
- Direction: Reduced abemaciclib exposure (decreased AUC/Cmax), risking loss of antineoplastic efficacy.
- Onset: Unspecified; enzyme induction typically develops over days to weeks.
- Evidence: Theoretical.
- Magnitude: Not quantified.
- Management: Avoid concurrent use where feasible; prefer a non-inducing anticonvulsant. If unavoidable, dose may need individualization by oncology and monitor clinical/radiographic response closely.
What happens
Reduced CYP3A substrate exposure and reduced efficacy of CYP3A substrate
Interaction Deep Dive
When PHENobarbital, which induces CYP3A, is taken together with a CYP3A substrate, the substrate's exposure can be lowered, potentially diminishing the CYP3A substrate's efficacy. In cases where such combined use is unavoidable, monitor neonates carefully and think about raising the CYP3A substrate's dose as needed1.
Why it happens (mechanism)
Induction of CYP3A-mediated metabolism of CYP3A substrates
How to manage this interaction
Keep taking both medicines as prescribed unless your care team tells you otherwise. This interaction can usually be managed.
- Your oncology and neurology teams may decide whether these two can be used together or whether an alternative seizure medicine that does not speed up drug metabolism is a better fit.
- If they are used together, your abemaciclib dose may need to be adjusted and individualized by your care team.
- Your team may monitor your response to treatment more closely.
Ask your pharmacist or prescriber before starting, stopping, or changing either drug, and mention any new medicines.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Abemaciclib and Primidone together?
Primidone can speed up how your body clears abemaciclib, possibly making the cancer drug less effective, so let your oncology and neurology teams coordinate on dosing or an alternative. Do not change anything on your own. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Abemaciclib and Primidone interaction?
It is rated major. Potentially serious — often needs a change or close 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 Primidone interaction managed?
Keep taking both medicines as prescribed unless your care team tells you otherwise. This interaction can usually be managed. Your oncology and neurology teams may decide whether these two can be used together or whether an alternative seizure medicine that does not speed up drug metabolism is a better fit. If they are used together, your abemaciclib dose may need to be adjusted and individualized… 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 Primidone 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 a safer alternative to one of these medications for me?
References (1)
- Product Information: SEZABY(TM) intravenous injection, phenobarbital sodium intravenous injection. Sun Pharmaceutical Industries Inc (per manufacturer), Cranbury, NJ, 2022. DailyMed
Keep reading about Primidone
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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