Drug interactions
Finasteride + Fosphenytoin
Severity: Minor
Finasteride and Fosphenytoin: 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 finasteride concentrations. Reduced efficacy is possible with prolonged use, though evidence is limited.
What this interaction means in plain words
Finasteride and Fosphenytoin have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Finasteride belongs to Genitourinary; Fosphenytoin belongs to Central Nervous System.
Why it happens
Induction of CYP3A4 increasing finasteride clearance.
What to do
No empirical dose change; reassess finasteride response if long-term anticonvulsant therapy is needed.
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 Finasteride
- Finasteride + Levoketoconazole Moderate
- Finasteride + Nefazodone Moderate
- Finasteride + Rifampin Moderate
- Finasteride + St john's wort Moderate
- Amobarbital + Finasteride Minor
- Aprepitant + Finasteride Minor
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 Finasteride with Fosphenytoin?
MediHelp rates the interaction as minor. Finasteride and Fosphenytoin 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 finasteride concentrations. Reduced efficacy is possible with prolonged use, though evidence is limited.
How serious is the interaction between Finasteride and Fosphenytoin?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: No empirical dose change; reassess finasteride response if long-term anticonvulsant therapy is needed.
What other medicines interact with Finasteride?
MediHelp also lists interactions of Finasteride with, for example, Levoketoconazole, Nefazodone, Rifampin. The full list is on the Finasteride page.
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