Drug interactions
Promethazine + Trifluoperazine
Severity: Major
Promethazine and Trifluoperazine: major interaction.
Last updated Sources: US FDA label
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 can prolong the QT interval and cause sedation. Together they increase the risk of torsades de pointes, extrapyramidal symptoms, hypotension and CNS depression.
What this interaction means in plain words
Promethazine and Trifluoperazine 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 from potassium channel blockade, with additive dopaminergic, anticholinergic and sedative effects.
What to do
Avoid concurrent use where possible and select a non-QT-prolonging alternative. If needed, monitor ECG and electrolytes and watch for oversedation.
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 Promethazine
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
- Amiodarone + Promethazine Major
- Amisulpride + Promethazine Major
Frequently asked questions
Can I take Promethazine with Trifluoperazine?
MediHelp rates the interaction as major. Promethazine and Trifluoperazine 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 can prolong the QT interval and cause sedation. Together they increase the risk of torsades de pointes, extrapyramidal symptoms, hypotension and CNS depression.
How serious is the interaction between Promethazine and Trifluoperazine?
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 concurrent use where possible and select a non-QT-prolonging alternative. If needed, monitor ECG and electrolytes and watch for oversedation.
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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