Drug interactions
Perphenazine + Promethazine
Severity: Major
Perphenazine 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 phenothiazines with QT-prolonging, sedative and anticholinergic properties. Combined use increases the risk of arrhythmia and CNS depression, and perphenazine is itself a CYP2D6 substrate.
What this interaction means in plain words
Perphenazine 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.
Perphenazine 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; otherwise obtain an ECG, correct electrolytes and monitor sedation and QTc.
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 Perphenazine
- Ibutilide + Perphenazine Contraindicated
- Perphenazine + Pimozide Contraindicated
- Perphenazine + Thioridazine Contraindicated
- Adagrasib + Perphenazine Major
- Alfentanil + Perphenazine Major
- Amiodarone + Perphenazine Major
Frequently asked questions
Can I take Perphenazine with Promethazine?
MediHelp rates the interaction as major. Perphenazine 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 phenothiazines with QT-prolonging, sedative and anticholinergic properties. Combined use increases the risk of arrhythmia and CNS depression, and perphenazine is itself a CYP2D6 substrate.
How serious is the interaction between Perphenazine 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; otherwise obtain an ECG, correct electrolytes and monitor sedation and QTc.
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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