Drug interactions
Fosphenytoin + Memantine-donepezil
Severity: Moderate
Fosphenytoin and Memantine-donepezil: 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 known inducer of CYP3A4, and may lower donepezil concentrations. The cognitive benefit of donepezil could be reduced during long-term co-therapy.
What this interaction means in plain words
Fosphenytoin and Memantine-donepezil 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; Memantine-donepezil belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4, accelerating donepezil metabolism.
What to do
Monitor cognitive and functional response when fosphenytoin is started or stopped. Consider adjusting the donepezil dose if response is lost.
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 Memantine-donepezil
- Dronedarone + Memantine-donepezil Contraindicated
- Memantine-donepezil + Thioridazine Contraindicated
- Amantadine + Memantine-donepezil Major
- Amiodarone + Memantine-donepezil Major
- Amisulpride + Memantine-donepezil Major
- Amitriptyline + Memantine-donepezil 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 Memantine-donepezil?
MediHelp rates the interaction as moderate. Fosphenytoin and Memantine-donepezil 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 known inducer of CYP3A4, and may lower donepezil concentrations. The cognitive benefit of donepezil could be reduced during long-term co-therapy.
How serious is the interaction between Fosphenytoin and Memantine-donepezil?
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 cognitive and functional response when fosphenytoin is started or stopped. Consider adjusting the donepezil dose if response is lost.
What other medicines interact with Memantine-donepezil?
MediHelp also lists interactions of Memantine-donepezil with, for example, Dronedarone, Thioridazine, Amantadine. The full list is on the Memantine-donepezil page.
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