Drug interactions
Fluphenazine + Promethazine
Severity: Major
Fluphenazine and Promethazine: 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 agents are phenothiazines that can prolong the QT interval and cause sedation and anticholinergic effects. Together they increase the risk of arrhythmia, CNS depression and extrapyramidal or anticholinergic toxicity.
What this interaction means in plain words
Fluphenazine 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.
Fluphenazine belongs to Central Nervous System; Promethazine belongs to Respiratory.
Why it happens
Additive QT prolongation and additive CNS depressant and anticholinergic effects.
What to do
Avoid combined use where possible; if needed, obtain a baseline ECG, correct electrolytes and monitor QTc 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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References
Other interactions of Promethazine
- Cabergoline + Promethazine Contraindicated
- Dopamine + Promethazine Contraindicated
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
Other interactions of Fluphenazine
- Arsenic trioxide + Fluphenazine Contraindicated
- Dofetilide + Fluphenazine Contraindicated
- Fluphenazine + Ibutilide Contraindicated
- Fluphenazine + Pimozide Contraindicated
- Adagrasib + Fluphenazine Major
- Alfentanil + Fluphenazine Major
Frequently asked questions
Can I take Fluphenazine with Promethazine?
MediHelp rates the interaction as major. Fluphenazine 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 agents are phenothiazines that can prolong the QT interval and cause sedation and anticholinergic effects. Together they increase the risk of arrhythmia, CNS depression and extrapyramidal or anticholinergic toxicity.
How serious is the interaction between Fluphenazine 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 combined use where possible; if needed, obtain a baseline ECG, correct electrolytes and monitor QTc and sedation.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Cabergoline, Dopamine, Ibutilide. The full list is on the Promethazine page.
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