Drug interactions
Fosphenytoin + Omeprazole
Severity: Moderate
Fosphenytoin and Omeprazole: 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
Omeprazole can inhibit phenytoin metabolism, raising phenytoin levels and risking nystagmus, ataxia and confusion. Phenytoin is also an enzyme inducer that can lower omeprazole exposure. Phenytoin's narrow therapeutic index makes the first effect more important.
What this interaction means in plain words
Fosphenytoin and Omeprazole 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; Omeprazole belongs to Gastrointestinal Tract.
Why it happens
Omeprazole inhibits CYP2C19/CYP2C9 metabolism of phenytoin, while phenytoin induces omeprazole metabolism.
What to do
Monitor phenytoin levels and signs of toxicity when omeprazole is started or stopped, and adjust dose accordingly. Watch for reduced acid suppression.
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 Omeprazole
- Mavacamten + Omeprazole Contraindicated
- Omeprazole + Rilpivirine Contraindicated
- Acalabrutinib + Omeprazole Major
- Atazanavir + Omeprazole Major
- Citalopram + Omeprazole Major
- Clopidogrel + Omeprazole 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 Omeprazole?
MediHelp rates the interaction as moderate. Fosphenytoin and Omeprazole 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. Omeprazole can inhibit phenytoin metabolism, raising phenytoin levels and risking nystagmus, ataxia and confusion. Phenytoin is also an enzyme inducer that can lower omeprazole exposure. Phenytoin's narrow therapeutic index makes the first effect more important.
How serious is the interaction between Fosphenytoin and Omeprazole?
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 levels and signs of toxicity when omeprazole is started or stopped, and adjust dose accordingly. Watch for reduced acid suppression.
What other medicines interact with Omeprazole?
MediHelp also lists interactions of Omeprazole with, for example, Mavacamten, Rilpivirine, Acalabrutinib. The full list is on the Omeprazole page.
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