Drug interactions
Phenobarbital + Zonisamide
Severity: Moderate
Phenobarbital and Zonisamide: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phenobarbital and other enzyme-inducing antiepileptics shorten the half-life of zonisamide, lowering its concentrations. This may reduce seizure control, and the two drugs also have additive sedative effects.
What this interaction means in plain words
Phenobarbital and Zonisamide can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
Phenobarbital induces CYP3A4, increasing the metabolic clearance of zonisamide.
What to do
Titrate zonisamide to clinical response, as higher doses may be needed with phenobarbital. Re-evaluate the dose if phenobarbital is stopped, because levels will rise.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Zonisamide
- Zonisamide + Zuranolone Major
- Acetazolamide + Zonisamide Moderate
- Amisulpride + Zonisamide Moderate
- Amobarbital + Zonisamide Moderate
- Apalutamide + Zonisamide Moderate
- Asenapine transdermal + Zonisamide Moderate
Frequently asked questions
Can I take Phenobarbital with Zonisamide?
MediHelp rates the interaction as moderate. Phenobarbital and Zonisamide can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Phenobarbital and other enzyme-inducing antiepileptics shorten the half-life of zonisamide, lowering its concentrations. This may reduce seizure control, and the two drugs also have additive sedative effects.
How serious is the interaction between Phenobarbital and Zonisamide?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Titrate zonisamide to clinical response, as higher doses may be needed with phenobarbital. Re-evaluate the dose if phenobarbital is stopped, because levels will rise.
What other medicines interact with Zonisamide?
MediHelp also lists interactions of Zonisamide with, for example, Zuranolone, Acetazolamide, Amisulpride. The full list is on the Zonisamide page.
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