Drug interactions
Oxybutynin + Phenytoin
Severity: Minor
Oxybutynin 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 is an inducer of CYP3A4 and may lower oxybutynin concentrations, reducing its antimuscarinic effect.
What this interaction means in plain words
Oxybutynin 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.
Oxybutynin belongs to Genitourinary; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4, increasing oxybutynin clearance.
What to do
Monitor clinical response and increase the oxybutynin dose if efficacy is lost.
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 Oxybutynin
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
Frequently asked questions
Can I take Oxybutynin with Phenytoin?
MediHelp rates the interaction as minor. Oxybutynin 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 is an inducer of CYP3A4 and may lower oxybutynin concentrations, reducing its antimuscarinic effect.
How serious is the interaction between Oxybutynin 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 clinical response and increase the oxybutynin dose if efficacy is lost.
What other medicines interact with Oxybutynin?
MediHelp also lists interactions of Oxybutynin with, for example, Bethanechol, Clozapine, Potassium chloride. The full list is on the Oxybutynin page.
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