Drug interactions
Fosphenytoin + Vitamin B6
Severity: Moderate
Fosphenytoin 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, which are the active form of fosphenytoin. This could reduce seizure control in susceptible patients.
What this interaction means in plain words
Fosphenytoin 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.
Fosphenytoin belongs to Central Nervous System; Vitamin B6 belongs to Gastrointestinal Tract.
Why it happens
Pyridoxine may increase phenytoin metabolism, although the mechanism is not firmly established.
What to do
Avoid routine high-dose pyridoxine supplementation in patients on fosphenytoin or phenytoin. If it is needed, monitor free and total phenytoin levels and seizure control.
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
- Isoniazid + Vitamin B6 Moderate
- Levodopa + Vitamin B6 Moderate
- Penicillamine + Vitamin B6 Moderate
- Phenobarbital + Vitamin B6 Moderate
- Phenytoin + Vitamin B6 Moderate
Other interactions of Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Fosphenytoin with Vitamin B6?
MediHelp rates the interaction as moderate. Fosphenytoin 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, which are the active form of fosphenytoin. This could reduce seizure control in susceptible patients.
How serious is the interaction between Fosphenytoin 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 routine high-dose pyridoxine supplementation in patients on fosphenytoin or phenytoin. If it is needed, monitor free and total phenytoin levels and seizure control.
What other medicines interact with Vitamin B6?
MediHelp also lists interactions of Vitamin B6 with, for example, Ethotoin, Isoniazid, Levodopa. The full list is on the Vitamin B6 page.
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