Drug interactions
Phenytoin + Vitamin B6
Severity: Moderate
Phenytoin and Vitamin B6: 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
High-dose pyridoxine has been reported to lower serum phenytoin concentrations, potentially reducing seizure control. The effect appears mainly with large supplemental doses and is not consistently seen.
What this interaction means in plain words
Phenytoin and Vitamin B6 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.
Phenytoin belongs to Central Nervous System; Vitamin B6 belongs to Gastrointestinal Tract.
Why it happens
Proposed increased phenytoin metabolism by pyridoxine; the mechanism is not firmly established.
What to do
Avoid high-dose pyridoxine supplements in patients on phenytoin where possible. If used, monitor phenytoin serum levels and seizure control and adjust the dose accordingly.
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 Vitamin B6
- Ethotoin + Vitamin B6 Moderate
- Fosphenytoin + Vitamin B6 Moderate
- Isoniazid + Vitamin B6 Moderate
- Levodopa + Vitamin B6 Moderate
- Penicillamine + Vitamin B6 Moderate
- Phenobarbital + Vitamin B6 Moderate
Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Phenytoin with Vitamin B6?
MediHelp rates the interaction as moderate. Phenytoin and Vitamin B6 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. High-dose pyridoxine has been reported to lower serum phenytoin concentrations, potentially reducing seizure control. The effect appears mainly with large supplemental doses and is not consistently seen.
How serious is the interaction between Phenytoin and Vitamin B6?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid high-dose pyridoxine supplements in patients on phenytoin where possible. If used, monitor phenytoin serum levels and seizure control and adjust the dose accordingly.
What other medicines interact with Vitamin B6?
MediHelp also lists interactions of Vitamin B6 with, for example, Ethotoin, Fosphenytoin, Isoniazid. The full list is on the Vitamin B6 page.
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