Drug interactions
Fosphenytoin + Vitamin d
Severity: Moderate
Fosphenytoin 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
Chronic phenytoin therapy, which fosphenytoin delivers, lowers vitamin D activity and can lead to osteomalacia and reduced bone density. Patients on long-term treatment may need extra vitamin D.
What this interaction means in plain words
Fosphenytoin 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.
Fosphenytoin belongs to Central Nervous System; Vitamin d belongs to Gastrointestinal Tract.
Why it happens
Phenytoin induces hepatic CYP enzymes, accelerating the catabolism of vitamin D and its metabolites.
What to do
Monitor 25-hydroxyvitamin D, calcium and bone health during long-term therapy. Supplement vitamin D and increase the dose if levels are low.
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 d
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 d?
MediHelp rates the interaction as moderate. Fosphenytoin 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. Chronic phenytoin therapy, which fosphenytoin delivers, lowers vitamin D activity and can lead to osteomalacia and reduced bone density. Patients on long-term treatment may need extra vitamin D.
How serious is the interaction between Fosphenytoin 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, calcium and bone health during long-term therapy. Supplement vitamin D and increase the dose if levels are low.
What other medicines interact with Vitamin d?
MediHelp also lists interactions of Vitamin d with, for example, Aluminum hydroxide, Amlodipine-hydrochlorothiazide-valsartan, Amlodipine-olmesartan-hydrochlorothiazide. The full list is on the Vitamin d page.
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