Asenapine Transdermal Patch and Primidone: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Primidone
Asenapine Transdermal Patch
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.
What happens
An increased risk of QT interval prolongation and an increased risk of CNS depression
Interaction Deep Dive
Concomitant use of PHENobarbital (a CNS depressant and a QTc interval prolongation agent) with other CNS depressants which are also QTc interval prolongation agents may result in sedation, respiratory depression and may result in a greater increase in the QTc interval and adverse reactions associated with QTc interval prolongation. If concomitant use cannot be avoided, monitor patients for increased risk of QTc interval prolongation. Also, closely monitor patients for signs and symptoms of respiratory depression and sedation1.
Why it happens (mechanism)
Additive QT interval prolongation; additive CNS depression
Common questions
Can I take Asenapine Transdermal Patch and Primidone together?
An increased risk of QT interval prolongation and an increased risk of CNS depression Always confirm with your pharmacist or prescriber before making any change.
How serious is the Asenapine Transdermal Patch 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 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 Asenapine Transdermal Patch 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 Asenapine Transdermal Patch
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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