Drug interactions
Darifenacin + Promethazine
Severity: Moderate
Darifenacin 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 anticholinergic effects such as dry mouth, constipation, urinary retention, blurred vision, tachycardia and confusion. Older patients are at particular risk of cognitive impairment, and promethazine adds sedation.
What this interaction means in plain words
Darifenacin 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.
Darifenacin belongs to Genitourinary; Promethazine belongs to Respiratory.
Why it happens
Additive muscarinic receptor antagonism; promethazine is also a CYP2D6 substrate and darifenacin is a modest CYP2D6 inhibitor.
What to do
Monitor for anticholinergic adverse effects, constipation and urinary retention, and consider a non-anticholinergic antiemetic or antihistamine alternative in elderly patients. Reduce doses if effects emerge.
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?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Darifenacin and Promethazine, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 7 days on the web. No card needed.
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 Darifenacin
Frequently asked questions
Can I take Darifenacin with Promethazine?
MediHelp rates the interaction as moderate. Darifenacin 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 anticholinergic effects such as dry mouth, constipation, urinary retention, blurred vision, tachycardia and confusion. Older patients are at particular risk of cognitive impairment, and promethazine adds sedation.
How serious is the interaction between Darifenacin 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, constipation and urinary retention, and consider a non-anticholinergic antiemetic or antihistamine alternative in elderly patients. Reduce doses if effects emerge.
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.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
