Drug interactions
Flavoxate + Promethazine
Severity: Moderate
Flavoxate 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
Flavoxate has antimuscarinic and smooth-muscle relaxant effects and promethazine is strongly anticholinergic and sedating. Combined use raises the risk of dry mouth, constipation, urinary retention, blurred vision, drowsiness and confusion.
What this interaction means in plain words
Flavoxate 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.
Flavoxate belongs to Genitourinary; Promethazine belongs to Respiratory.
Why it happens
Additive anticholinergic and sedative pharmacodynamic effects.
What to do
Monitor for anticholinergic adverse effects and sedation, particularly in older patients, and reduce doses or choose a non-anticholinergic alternative if they develop.
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
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
- Amiodarone + Promethazine Major
- Amisulpride + Promethazine Major
Other interactions of Flavoxate
- Clozapine + Flavoxate Major
- Abobotulinumtoxina + Flavoxate Moderate
- Aclidinium + Flavoxate Moderate
- Amantadine + Flavoxate Moderate
- Amitriptyline + Flavoxate Moderate
- Amoxapine + Flavoxate Moderate
Frequently asked questions
Can I take Flavoxate with Promethazine?
MediHelp rates the interaction as moderate. Flavoxate 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. Flavoxate has antimuscarinic and smooth-muscle relaxant effects and promethazine is strongly anticholinergic and sedating. Combined use raises the risk of dry mouth, constipation, urinary retention, blurred vision, drowsiness and confusion.
How serious is the interaction between Flavoxate 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: Monitor for anticholinergic adverse effects and sedation, particularly in older patients, and reduce doses or choose a non-anticholinergic alternative if they develop.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Ibutilide, Pimozide, Thioridazine. The full list is on the Promethazine page.
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