Drug interactions
Fostemsavir + Phenytoin
Severity: Contraindicated
Fostemsavir and Phenytoin: contraindicated 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 substantially lowers temsavir, the active moiety of fostemsavir, risking loss of virologic response and resistance.
What this interaction means in plain words
Fostemsavir and Phenytoin are not normally used together. Taking them at the same time is expected to cause harm or make one of them unsafe, so a different medicine is usually chosen for one of the two.
Fostemsavir belongs to Anti Virals; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4, which metabolizes temsavir.
What to do
Do not co-administer; use a non-inducing antiepileptic such as levetiracetam.
What to ask your pharmacist
- Is there an alternative to one of these two medicines for me?
- If both are essential, who is monitoring me and how often?
- Which symptoms mean I should stop and seek help straight away?
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Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Other interactions of Fostemsavir
- Apalutamide + Fostemsavir Contraindicated
- Carbamazepine + Fostemsavir Contraindicated
- Enzalutamide + Fostemsavir Contraindicated
- Fostemsavir + Mitotane Contraindicated
- Fostemsavir + Rifampicin Contraindicated
- Efavirenz + Fostemsavir Major
Frequently asked questions
Can I take Fostemsavir with Phenytoin?
MediHelp rates the interaction as contraindicated. Fostemsavir and Phenytoin are not normally used together. Taking them at the same time is expected to cause harm or make one of them unsafe, so a different medicine is usually chosen for one of the two. Phenytoin substantially lowers temsavir, the active moiety of fostemsavir, risking loss of virologic response and resistance.
How serious is the interaction between Fostemsavir and Phenytoin?
MediHelp rates it contraindicated, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Do not co-administer; use a non-inducing antiepileptic such as levetiracetam.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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