Drug interactions
Promazine + Thioridazine
Severity: Major
Promazine and Thioridazine: major interaction.
Last updated Sources: UK SmPC
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 phenothiazines that prolong the QTc interval, so concurrent use adds to the risk of torsades de pointes and sudden death. There is also additive sedation and anticholinergic burden.
What this interaction means in plain words
Promazine and Thioridazine 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.
Why it happens
Additive QT prolongation via hERG potassium channel blockade.
What to do
Avoid combining two phenothiazines; use a single agent. Check ECG and electrolytes if both have been given.
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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References
Other interactions of Thioridazine
- Abiraterone + Thioridazine Contraindicated
- Adagrasib + Thioridazine Contraindicated
- Amiodarone + Thioridazine Contraindicated
- Amisulpride + Thioridazine Contraindicated
- Amitriptyline + Thioridazine Contraindicated
- Amoxapine + Thioridazine Contraindicated
Frequently asked questions
Can I take Promazine with Thioridazine?
MediHelp rates the interaction as major. Promazine and Thioridazine 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 phenothiazines that prolong the QTc interval, so concurrent use adds to the risk of torsades de pointes and sudden death. There is also additive sedation and anticholinergic burden.
How serious is the interaction between Promazine and Thioridazine?
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 combining two phenothiazines; use a single agent. Check ECG and electrolytes if both have been given.
What other medicines interact with Thioridazine?
MediHelp also lists interactions of Thioridazine with, for example, Abiraterone, Adagrasib, Amiodarone. The full list is on the Thioridazine page.
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