Drug interactions
Donepezil + Promethazine
Severity: Moderate
Donepezil and Promethazine: 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
Donepezil can prolong the QT interval and cause bradycardia, and promethazine has a smaller potential for QT prolongation. Their pharmacological actions also oppose each other, since promethazine's anticholinergic effect can reduce the cognitive benefit of donepezil.
What this interaction means in plain words
Donepezil and Promethazine 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.
Donepezil belongs to Central Nervous System; Promethazine belongs to Respiratory.
Why it happens
Pharmacodynamic antagonism of cholinesterase inhibition by antimuscarinic action, plus possible additive QT prolongation.
What to do
Avoid promethazine in patients taking donepezil for dementia where possible and use a non-anticholinergic antiemetic. If combined, monitor ECG in patients with cardiac risk factors.
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 Promethazine
- Cabergoline + Promethazine Contraindicated
- Dopamine + Promethazine Contraindicated
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
Other interactions of Donepezil
- Donepezil + Dronedarone Contraindicated
- Donepezil + Pimozide Contraindicated
- Donepezil + Thioridazine Contraindicated
- Donepezil + Vandetanib Contraindicated
- Amiodarone + Donepezil Major
- Amisulpride + Donepezil Major
Frequently asked questions
Can I take Donepezil with Promethazine?
MediHelp rates the interaction as moderate. Donepezil and Promethazine 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. Donepezil can prolong the QT interval and cause bradycardia, and promethazine has a smaller potential for QT prolongation. Their pharmacological actions also oppose each other, since promethazine's anticholinergic effect can reduce the cognitive benefit of donepezil.
How serious is the interaction between Donepezil and Promethazine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid promethazine in patients taking donepezil for dementia where possible and use a non-anticholinergic antiemetic. If combined, monitor ECG in patients with cardiac risk factors.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Cabergoline, Dopamine, Ibutilide. The full list is on the Promethazine page.
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