Drug interactions
Fosphenytoin + Tolterodine
Severity: Minor
Fosphenytoin and Tolterodine: 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, formed from fosphenytoin, induces CYP3A4 and may lower tolterodine concentrations, potentially reducing efficacy. The effect is limited when CYP2D6 is active.
What this interaction means in plain words
Fosphenytoin and Tolterodine 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; Tolterodine belongs to Genitourinary.
Why it happens
Enzyme induction by phenytoin increases CYP3A4-mediated tolterodine clearance.
What to do
Monitor urinary symptom control and increase tolterodine 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 Tolterodine
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 Tolterodine?
MediHelp rates the interaction as minor. Fosphenytoin and Tolterodine 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, formed from fosphenytoin, induces CYP3A4 and may lower tolterodine concentrations, potentially reducing efficacy. The effect is limited when CYP2D6 is active.
How serious is the interaction between Fosphenytoin and Tolterodine?
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 urinary symptom control and increase tolterodine dose if efficacy is lost.
What other medicines interact with Tolterodine?
MediHelp also lists interactions of Tolterodine with, for example, Clarithromycin, Clozapine, Cobicistat. The full list is on the Tolterodine page.
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