Drug interactions
Darifenacin + Fosphenytoin
Severity: Moderate
Darifenacin and Fosphenytoin: 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
Fosphenytoin, which is converted to phenytoin, is a CYP3A4 inducer and can lower darifenacin exposure. This may reduce control of overactive bladder symptoms.
What this interaction means in plain words
Darifenacin and Fosphenytoin 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.
Darifenacin belongs to Genitourinary; Fosphenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces hepatic and intestinal CYP3A4, increasing darifenacin metabolism.
What to do
Monitor for loss of antimuscarinic efficacy and increase the darifenacin dose within labeled limits if needed. Reassess if the anticonvulsant is stopped, as darifenacin levels will rise.
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 Darifenacin
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 Darifenacin with Fosphenytoin?
MediHelp rates the interaction as moderate. Darifenacin and Fosphenytoin 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, which is converted to phenytoin, is a CYP3A4 inducer and can lower darifenacin exposure. This may reduce control of overactive bladder symptoms.
How serious is the interaction between Darifenacin and Fosphenytoin?
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 for loss of antimuscarinic efficacy and increase the darifenacin dose within labeled limits if needed. Reassess if the anticonvulsant is stopped, as darifenacin levels will rise.
What other medicines interact with Darifenacin?
MediHelp also lists interactions of Darifenacin with, for example, Atazanavir, Bethanechol, Clarithromycin. The full list is on the Darifenacin page.
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