Drug interactions
Pimavanserin + Promethazine
Severity: Major
Pimavanserin and Promethazine: 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 drugs can prolong the QT interval, and promethazine adds sedation and anticholinergic effects. Pimavanserin labeling advises avoiding other QT-prolonging agents.
What this interaction means in plain words
Pimavanserin 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.
Pimavanserin belongs to Central Nervous System; Promethazine belongs to Respiratory.
Why it happens
Additive QT prolongation and CNS effects via serotonin 5-HT2A inverse agonism and dopamine/histamine antagonism.
What to do
Avoid the combination where possible; if used, obtain ECG, correct electrolytes and monitor for arrhythmia symptoms 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
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
- Amiodarone + Promethazine Major
- Amisulpride + Promethazine Major
Other interactions of Pimavanserin
- Lefamulin + Pimavanserin Contraindicated
- Pimavanserin + Pimozide Contraindicated
- Pimavanserin + Vandetanib Contraindicated
- Adagrasib + Pimavanserin Major
- Amiodarone + Pimavanserin Major
- Amisulpride + Pimavanserin Major
Frequently asked questions
Can I take Pimavanserin with Promethazine?
MediHelp rates the interaction as major. Pimavanserin 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 drugs can prolong the QT interval, and promethazine adds sedation and anticholinergic effects. Pimavanserin labeling advises avoiding other QT-prolonging agents.
How serious is the interaction between Pimavanserin 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 the combination where possible; if used, obtain ECG, correct electrolytes and monitor for arrhythmia symptoms 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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