Drug interactions
Apalutamide + Fosphenytoin
Severity: Major
Apalutamide and Fosphenytoin: major interaction.
Last updated Sources: US FDA label
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
Apalutamide may reduce phenytoin exposure, risking breakthrough seizures. Phenytoin is also itself an enzyme inducer and may reduce apalutamide exposure.
What this interaction means in plain words
Apalutamide and Fosphenytoin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Apalutamide belongs to Endocrine; Fosphenytoin belongs to Central Nervous System.
Why it happens
Apalutamide induces CYP2C19, CYP2C9 and CYP3A4, which metabolize phenytoin; phenytoin in turn induces CYP3A4 and lowers apalutamide levels.
What to do
Monitor phenytoin serum concentrations and seizure control, and adjust the dose accordingly; consider a non-interacting anticonvulsant.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Apalutamide
- Apalutamide + Cabotegravir Contraindicated
- Apalutamide + Cobicistat Contraindicated
- Apalutamide + Doravirine Contraindicated
- Apalutamide + Elbasvir / grazoprevir Contraindicated
- Apalutamide + Ensitrelvir Contraindicated
- Apalutamide + Fostemsavir Contraindicated
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 Apalutamide with Fosphenytoin?
MediHelp rates the interaction as major. Apalutamide and Fosphenytoin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Apalutamide may reduce phenytoin exposure, risking breakthrough seizures. Phenytoin is also itself an enzyme inducer and may reduce apalutamide exposure.
How serious is the interaction between Apalutamide and Fosphenytoin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor phenytoin serum concentrations and seizure control, and adjust the dose accordingly; consider a non-interacting anticonvulsant.
What other medicines interact with Apalutamide?
MediHelp also lists interactions of Apalutamide with, for example, Cabotegravir, Cobicistat, Doravirine. The full list is on the Apalutamide page.
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