Drug interactions
Cyanocobalamin + Phenytoin
Severity: Minor
Cyanocobalamin and Phenytoin: minor 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 therapy may be associated with lower vitamin B12 levels. Clinically significant deficiency is uncommon but can contribute to anemia or neuropathy.
What this interaction means in plain words
Cyanocobalamin and Phenytoin have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Cyanocobalamin belongs to Miscellaneous; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin may impair intestinal absorption of vitamin B12; the mechanism is not well defined.
What to do
Check vitamin B12 levels if macrocytosis, anemia or neuropathy develops during long-term phenytoin treatment. Replace B12 if deficient.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
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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 Cyanocobalamin
Frequently asked questions
Can I take Cyanocobalamin with Phenytoin?
MediHelp rates the interaction as minor. Cyanocobalamin and Phenytoin have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Long-term phenytoin therapy may be associated with lower vitamin B12 levels. Clinically significant deficiency is uncommon but can contribute to anemia or neuropathy.
How serious is the interaction between Cyanocobalamin and Phenytoin?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Check vitamin B12 levels if macrocytosis, anemia or neuropathy develops during long-term phenytoin treatment. Replace B12 if deficient.
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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