Drug interactions
Phenobarbital + Valproic acid
Severity: Moderate
Phenobarbital and Valproic acid: 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
Valproate raises phenobarbital concentrations, which can cause excess sedation and cognitive slowing. Phenobarbital in turn can lower valproate levels through enzyme induction.
What this interaction means in plain words
Phenobarbital and Valproic acid 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
Valproate inhibits hepatic metabolism of phenobarbital, while phenobarbital induces valproate clearance.
What to do
Monitor for sedation and check phenobarbital and valproate levels, reducing the phenobarbital dose if needed.
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 Valproic acid
- Ertapenem + Valproic acid Contraindicated
- Imipenem / cilastatin / relebactam + Valproic acid Contraindicated
- Imipenem / cilastatin + Valproic acid Contraindicated
- Meropenem / vaborbactam + Valproic acid Contraindicated
- Meropenem + Valproic acid Contraindicated
- Calcium / magnesium / potassium / sodium oxybates + Valproic acid Major
Frequently asked questions
Can I take Phenobarbital with Valproic acid?
MediHelp rates the interaction as moderate. Phenobarbital and Valproic acid 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. Valproate raises phenobarbital concentrations, which can cause excess sedation and cognitive slowing. Phenobarbital in turn can lower valproate levels through enzyme induction.
How serious is the interaction between Phenobarbital and Valproic acid?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for sedation and check phenobarbital and valproate levels, reducing the phenobarbital dose if needed.
What other medicines interact with Valproic acid?
MediHelp also lists interactions of Valproic acid with, for example, Ertapenem, Imipenem / cilastatin / relebactam, Imipenem / cilastatin. The full list is on the Valproic acid page.
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