Drug interactions
Phenytoin + Vitamin d
Severity: Moderate
Phenytoin and Vitamin d: 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
Long-term phenytoin accelerates vitamin D catabolism and can lead to low vitamin D status, osteomalacia and reduced bone density.
What this interaction means in plain words
Phenytoin and Vitamin d 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 d belongs to Gastrointestinal Tract.
Why it happens
Phenytoin induces hepatic CYP enzymes, increasing the breakdown of vitamin D and its metabolites.
What to do
Monitor 25-hydroxyvitamin D and bone health in long-term users, and supplement vitamin D and calcium as 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 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
Other interactions of Vitamin d
Frequently asked questions
Can I take Phenytoin with Vitamin d?
MediHelp rates the interaction as moderate. Phenytoin and Vitamin d 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. Long-term phenytoin accelerates vitamin D catabolism and can lead to low vitamin D status, osteomalacia and reduced bone density.
How serious is the interaction between Phenytoin and Vitamin d?
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 25-hydroxyvitamin D and bone health in long-term users, and supplement vitamin D and calcium as needed.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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