Drug interactions
Metformin + Phenytoin
Severity: Minor
Metformin 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
Phenytoin can raise blood glucose and may offset the effect of metformin. Glycemic control may worsen, and hypoglycemia may occur if phenytoin is later withdrawn.
What this interaction means in plain words
Metformin 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.
Metformin belongs to Endocrine; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin inhibits insulin secretion, producing pharmacodynamic antagonism of glucose lowering.
What to do
Monitor blood glucose when phenytoin is started, changed or stopped, and adjust the antidiabetic dose as needed.
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 Metformin
Frequently asked questions
Can I take Metformin with Phenytoin?
MediHelp rates the interaction as minor. Metformin 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. Phenytoin can raise blood glucose and may offset the effect of metformin. Glycemic control may worsen, and hypoglycemia may occur if phenytoin is later withdrawn.
How serious is the interaction between Metformin 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: Monitor blood glucose when phenytoin is started, changed or stopped, and adjust the antidiabetic dose 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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