Drug interactions
Fosphenytoin + Oxybutynin
Severity: Minor
Fosphenytoin and Oxybutynin: 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
Fosphenytoin is converted to phenytoin, a CYP3A4 inducer that may reduce oxybutynin levels and efficacy. Both agents can also contribute to CNS effects.
What this interaction means in plain words
Fosphenytoin and Oxybutynin have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Fosphenytoin belongs to Central Nervous System; Oxybutynin belongs to Genitourinary.
Why it happens
Phenytoin induces CYP3A4, increasing oxybutynin clearance.
What to do
Monitor bladder symptom control and increase the oxybutynin dose if the response is inadequate.
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 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 Oxybutynin?
MediHelp rates the interaction as minor. Fosphenytoin and Oxybutynin have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Fosphenytoin is converted to phenytoin, a CYP3A4 inducer that may reduce oxybutynin levels and efficacy. Both agents can also contribute to CNS effects.
How serious is the interaction between Fosphenytoin and Oxybutynin?
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 bladder symptom control and increase the oxybutynin dose if the response is inadequate.
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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