Drug interactions
Benztropine + Promethazine
Severity: Moderate
Benztropine 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 strong antimuscarinic activity, so combined use adds to anticholinergic effects such as dry mouth, constipation, urinary retention, blurred vision, tachycardia and confusion. Older patients and those with glaucoma or prostatic hypertrophy are at particular risk.
What this interaction means in plain words
Benztropine 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.
Benztropine belongs to Central Nervous System; Promethazine belongs to Respiratory.
Why it happens
Additive pharmacodynamic blockade of muscarinic receptors.
What to do
Monitor for anticholinergic toxicity, especially delirium, urinary retention and constipation, and use the lowest effective doses. Consider an alternative antiemetic or antihistamine in elderly patients.
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 Benztropine
- Benztropine + Memantine-donepezil Major
- Abobotulinumtoxina + Benztropine Moderate
- Amantadine + Benztropine Moderate
- Amitriptyline + Benztropine Moderate
- Amoxapine + Benztropine Moderate
- Atropine iv / + Benztropine Moderate
Frequently asked questions
Can I take Benztropine with Promethazine?
MediHelp rates the interaction as moderate. Benztropine 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 strong antimuscarinic activity, so combined use adds to anticholinergic effects such as dry mouth, constipation, urinary retention, blurred vision, tachycardia and confusion. Older patients and those with glaucoma or prostatic hypertrophy are at particular risk.
How serious is the interaction between Benztropine 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 toxicity, especially delirium, urinary retention and constipation, and use the lowest effective doses. Consider an alternative antiemetic or antihistamine in elderly patients.
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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