Drug interactions
Homatropine + Promethazine
Severity: Moderate
Homatropine 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
Homatropine is an antimuscarinic and promethazine has marked anticholinergic properties, so combined use can increase dry mouth, blurred vision, urinary retention, constipation and confusion. Systemic exposure matters most with oral or combination cough products.
What this interaction means in plain words
Homatropine 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.
Homatropine belongs to Genitourinary; Promethazine belongs to Respiratory.
Why it happens
Additive antimuscarinic effects at peripheral and central muscarinic receptors.
What to do
Monitor for anticholinergic adverse effects and avoid in patients with narrow-angle glaucoma, urinary retention or ileus. Use the lowest effective doses, especially in the elderly.
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 Homatropine 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 14 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 Homatropine
- Amantadine + Homatropine Moderate
- Amitriptyline + Homatropine Moderate
- Atropine + Homatropine Moderate
- Benztropine + Homatropine Moderate
- Bethanechol + Homatropine Moderate
- Chlorpromazine + Homatropine Moderate
Frequently asked questions
Can I take Homatropine with Promethazine?
MediHelp rates the interaction as moderate. Homatropine 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. Homatropine is an antimuscarinic and promethazine has marked anticholinergic properties, so combined use can increase dry mouth, blurred vision, urinary retention, constipation and confusion. Systemic exposure matters most with oral or combination cough products.
How serious is the interaction between Homatropine 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 avoid in patients with narrow-angle glaucoma, urinary retention or ileus. Use the lowest effective doses, especially in the elderly.
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.
