Drug interactions
Fesoterodine + Promethazine
Severity: Moderate
Fesoterodine 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
Both drugs have antimuscarinic activity, so combined use increases dry mouth, constipation, urinary retention, blurred vision and cognitive impairment. Promethazine's antimuscarinic effect may also oppose the therapeutic benefit of a bladder antimuscarinic in some contexts and adds sedation.
What this interaction means in plain words
Fesoterodine 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.
Fesoterodine belongs to Genitourinary; Promethazine belongs to Respiratory.
Why it happens
Additive muscarinic receptor antagonism; promethazine is also a CYP2D6 substrate and fesoterodine's active metabolite is handled by CYP2D6 and CYP3A4.
What to do
Monitor for anticholinergic adverse effects, especially urinary retention and confusion in older adults, and consider a non-anticholinergic alternative to promethazine.
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 Fesoterodine
Frequently asked questions
Can I take Fesoterodine with Promethazine?
MediHelp rates the interaction as moderate. Fesoterodine 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. Both drugs have antimuscarinic activity, so combined use increases dry mouth, constipation, urinary retention, blurred vision and cognitive impairment. Promethazine's antimuscarinic effect may also oppose the therapeutic benefit of a bladder antimuscarinic in some contexts and adds sedation.
How serious is the interaction between Fesoterodine 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, especially urinary retention and confusion in older adults, and consider a non-anticholinergic alternative to promethazine.
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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