Drug interactions
Fosphenytoin + Tamsulosin
Severity: Moderate
Fosphenytoin and Tamsulosin: 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 is converted to phenytoin, an enzyme inducer that may lower tamsulosin concentrations. Reduced exposure may weaken relief of urinary symptoms.
What this interaction means in plain words
Fosphenytoin and Tamsulosin 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; Tamsulosin belongs to Genitourinary.
Why it happens
Phenytoin induces CYP3A4, increasing tamsulosin metabolism.
What to do
Assess urinary symptom control after starting or stopping fosphenytoin. Increase the tamsulosin dose or choose another agent if the response is inadequate.
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 Tamsulosin
- Alfuzosin + Tamsulosin Major
- Avanafil + Tamsulosin Major
- Ceritinib + Tamsulosin Major
- Clarithromycin + Tamsulosin Major
- Cobicistat + Tamsulosin Major
- Doxazosin + Tamsulosin Major
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 Tamsulosin?
MediHelp rates the interaction as moderate. Fosphenytoin and Tamsulosin 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 is converted to phenytoin, an enzyme inducer that may lower tamsulosin concentrations. Reduced exposure may weaken relief of urinary symptoms.
How serious is the interaction between Fosphenytoin and Tamsulosin?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Assess urinary symptom control after starting or stopping fosphenytoin. Increase the tamsulosin dose or choose another agent if the response is inadequate.
What other medicines interact with Tamsulosin?
MediHelp also lists interactions of Tamsulosin with, for example, Alfuzosin, Avanafil, Ceritinib. The full list is on the Tamsulosin page.
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