Drug interactions
Diphenhydramine + Flavoxate
Severity: Moderate
Diphenhydramine and Flavoxate: 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. With flavoxate it can cause additive dry mouth, urinary retention, constipation, sedation and confusion, particularly in older adults.
What this interaction means in plain words
Diphenhydramine and Flavoxate 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; Flavoxate belongs to Genitourinary.
Why it happens
Additive antimuscarinic pharmacodynamic effects.
What to do
Monitor for urinary retention and cognitive effects. Use a non-sedating antihistamine where an antihistamine is needed.
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 Flavoxate
- Clozapine + Flavoxate Major
- Abobotulinumtoxina + Flavoxate Moderate
- Aclidinium + Flavoxate Moderate
- Amantadine + Flavoxate Moderate
- Amitriptyline + Flavoxate Moderate
- Amoxapine + Flavoxate Moderate
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Diphenhydramine with Flavoxate?
MediHelp rates the interaction as moderate. Diphenhydramine and Flavoxate 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. With flavoxate it can cause additive dry mouth, urinary retention, constipation, sedation and confusion, particularly in older adults.
How serious is the interaction between Diphenhydramine and Flavoxate?
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 for urinary retention and cognitive effects. Use a non-sedating antihistamine where an antihistamine is needed.
What other medicines interact with Flavoxate?
MediHelp also lists interactions of Flavoxate with, for example, Clozapine, Abobotulinumtoxina, Aclidinium. The full list is on the Flavoxate page.
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