Drug interactions
Fosphenytoin + Modafinil
Severity: Moderate
Fosphenytoin and Modafinil: 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 CYP3A4 inducer, which can lower modafinil concentrations and reduce its effect. Modafinil may also inhibit CYP2C19 and raise phenytoin levels, which has a narrow therapeutic index.
What this interaction means in plain words
Fosphenytoin and Modafinil 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; Modafinil belongs to Central Nervous System.
Why it happens
Phenytoin induction of CYP3A4 reduces modafinil exposure; modafinil inhibition of CYP2C19 may reduce phenytoin clearance.
What to do
Monitor phenytoin concentrations and signs of toxicity such as nystagmus or ataxia, and titrate modafinil to clinical response.
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 Modafinil
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 Modafinil?
MediHelp rates the interaction as moderate. Fosphenytoin and Modafinil 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 CYP3A4 inducer, which can lower modafinil concentrations and reduce its effect. Modafinil may also inhibit CYP2C19 and raise phenytoin levels, which has a narrow therapeutic index.
How serious is the interaction between Fosphenytoin and Modafinil?
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 phenytoin concentrations and signs of toxicity such as nystagmus or ataxia, and titrate modafinil to clinical response.
What other medicines interact with Modafinil?
MediHelp also lists interactions of Modafinil with, for example, Lenacapavir, Leniolisib, Lorlatinib. The full list is on the Modafinil page.
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