Drug interactions
Fosphenytoin + Solifenacin
Severity: Moderate
Fosphenytoin and Solifenacin: 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
Phenytoin, the active form of fosphenytoin, induces CYP3A4 and may reduce solifenacin concentrations. The therapeutic effect on bladder symptoms could be reduced.
What this interaction means in plain words
Fosphenytoin and Solifenacin 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 belongs to Central Nervous System; Solifenacin belongs to Genitourinary.
Why it happens
CYP3A4 induction by phenytoin increases solifenacin metabolism.
What to do
Monitor for loss of efficacy and titrate solifenacin to response within the maximum labeled dose, or consider an alternative.
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 Solifenacin
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 Solifenacin?
MediHelp rates the interaction as moderate. Fosphenytoin and Solifenacin 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. Phenytoin, the active form of fosphenytoin, induces CYP3A4 and may reduce solifenacin concentrations. The therapeutic effect on bladder symptoms could be reduced.
How serious is the interaction between Fosphenytoin and Solifenacin?
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 efficacy and titrate solifenacin to response within the maximum labeled dose, or consider an alternative.
What other medicines interact with Solifenacin?
MediHelp also lists interactions of Solifenacin with, for example, Adagrasib, Amiodarone, Amisulpride. The full list is on the Solifenacin page.
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