Drug interactions
Diphenhydramine + Fesoterodine
Severity: Moderate
Diphenhydramine and Fesoterodine: 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
Diphenhydramine is a strongly anticholinergic first-generation antihistamine. Combined with fesoterodine it increases the risk of dry mouth, constipation, urinary retention, blurred vision, sedation and delirium, particularly in older adults.
What this interaction means in plain words
Diphenhydramine and Fesoterodine 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.
Diphenhydramine belongs to Respiratory; Fesoterodine belongs to Genitourinary.
Why it happens
Additive antimuscarinic effects at central and peripheral muscarinic receptors.
What to do
Avoid or minimize diphenhydramine in older patients and use a non-sedating second-generation antihistamine instead; monitor for anticholinergic effects.
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 Fesoterodine
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Diphenhydramine with Fesoterodine?
MediHelp rates the interaction as moderate. Diphenhydramine and Fesoterodine 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. Diphenhydramine is a strongly anticholinergic first-generation antihistamine. Combined with fesoterodine it increases the risk of dry mouth, constipation, urinary retention, blurred vision, sedation and delirium, particularly in older adults.
How serious is the interaction between Diphenhydramine and Fesoterodine?
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 or minimize diphenhydramine in older patients and use a non-sedating second-generation antihistamine instead; monitor for anticholinergic effects.
What other medicines interact with Fesoterodine?
MediHelp also lists interactions of Fesoterodine with, for example, Bethanechol, Clozapine, Levoketoconazole. The full list is on the Fesoterodine page.
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