Drug interactions
Hydroxyzine + Promethazine
Severity: Major
Hydroxyzine and Promethazine: major 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 are sedating antihistamines with anticholinergic effects and both can prolong the QT interval. Combining them increases sedation, confusion and anticholinergic effects and adds to the risk of arrhythmia, especially in older patients and those with cardiac risk factors.
What this interaction means in plain words
Hydroxyzine and Promethazine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Hydroxyzine belongs to Respiratory; Promethazine belongs to Respiratory.
Why it happens
Additive H1 antagonism, muscarinic blockade and cardiac potassium channel inhibition causing QT prolongation.
What to do
Avoid using both agents together; choose a single antihistamine. If unavoidable, use low doses, correct electrolytes and monitor ECG and sedation.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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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 Hydroxyzine
- Droperidol + Hydroxyzine Contraindicated
- Hydroxyzine + Pimozide Contraindicated
- Hydroxyzine + Thioridazine Contraindicated
- Hydroxyzine + Vandetanib Contraindicated
- Alfentanil + Hydroxyzine Major
- Amiodarone + Hydroxyzine Major
Frequently asked questions
Can I take Hydroxyzine with Promethazine?
MediHelp rates the interaction as major. Hydroxyzine and Promethazine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Both are sedating antihistamines with anticholinergic effects and both can prolong the QT interval. Combining them increases sedation, confusion and anticholinergic effects and adds to the risk of arrhythmia, especially in older patients and those with cardiac risk factors.
How serious is the interaction between Hydroxyzine and Promethazine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid using both agents together; choose a single antihistamine. If unavoidable, use low doses, correct electrolytes and monitor ECG and sedation.
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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