Drug interactions
Memantine-donepezil + Phenytoin
Severity: Moderate
Memantine-donepezil and Phenytoin: 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
Phenytoin is an inducer of CYP3A4 and other enzymes and can lower donepezil concentrations, potentially reducing its effect. Donepezil labeling lists enzyme inducers such as phenytoin as able to increase donepezil clearance.
What this interaction means in plain words
Memantine-donepezil and Phenytoin 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.
Memantine-donepezil belongs to Central Nervous System; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4 (and CYP2D6), increasing hepatic clearance of donepezil.
What to do
Monitor cognitive and functional response and consider titrating donepezil upward if benefit declines; reassess if phenytoin is 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 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 Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Memantine-donepezil with Phenytoin?
MediHelp rates the interaction as moderate. Memantine-donepezil and Phenytoin 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. Phenytoin is an inducer of CYP3A4 and other enzymes and can lower donepezil concentrations, potentially reducing its effect. Donepezil labeling lists enzyme inducers such as phenytoin as able to increase donepezil clearance.
How serious is the interaction between Memantine-donepezil and Phenytoin?
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 and consider titrating donepezil upward if benefit declines; reassess if phenytoin is stopped.
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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