Drug interactions
Armodafinil + Fosphenytoin
Severity: Moderate
Armodafinil and Fosphenytoin: 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, a strong inducer of CYP3A4, and may lower armodafinil exposure, potentially reducing wakefulness-promoting effect. Armodafinil may also modestly raise phenytoin levels by inhibiting CYP2C19.
What this interaction means in plain words
Armodafinil and Fosphenytoin 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.
Armodafinil belongs to Central Nervous System; Fosphenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4 (and possibly P-gp), increasing armodafinil clearance, while armodafinil weakly inhibits CYP2C19, which metabolizes phenytoin.
What to do
Monitor clinical response to armodafinil and consider a dose increase if efficacy is lost. Monitor phenytoin concentrations and signs of toxicity when armodafinil is started or stopped.
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 Armodafinil
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 Armodafinil with Fosphenytoin?
MediHelp rates the interaction as moderate. Armodafinil and Fosphenytoin 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, a strong inducer of CYP3A4, and may lower armodafinil exposure, potentially reducing wakefulness-promoting effect. Armodafinil may also modestly raise phenytoin levels by inhibiting CYP2C19.
How serious is the interaction between Armodafinil and Fosphenytoin?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor clinical response to armodafinil and consider a dose increase if efficacy is lost. Monitor phenytoin concentrations and signs of toxicity when armodafinil is started or stopped.
What other medicines interact with Armodafinil?
MediHelp also lists interactions of Armodafinil with, for example, Avapritinib, Elacestrant, Elbasvir / grazoprevir. The full list is on the Armodafinil page.
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