Drug interactions
Doxepin + Promethazine
Severity: Major
Doxepin 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 drugs are sedating and strongly anticholinergic, and both can prolong the QT interval. Combination increases the risk of excessive drowsiness, confusion, urinary retention, constipation and ventricular arrhythmia, especially with other risk factors.
What this interaction means in plain words
Doxepin 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.
Doxepin belongs to Dermatology; Promethazine belongs to Respiratory.
Why it happens
Additive H1 and muscarinic blockade with additive QT prolongation via cardiac potassium channel effects.
What to do
Avoid combining where possible, particularly with electrolyte disturbance or other QT-prolonging drugs; if used, obtain an ECG and monitor for sedation and anticholinergic toxicity.
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 Doxepin
- Doxepin + Isocarboxazid Contraindicated
- Doxepin + Phenelzine Contraindicated
- Doxepin + Procarbazine Contraindicated
- Doxepin + Safinamide Contraindicated
- Doxepin + Selegiline Contraindicated
- Doxepin + Tranylcypromine Contraindicated
Frequently asked questions
Can I take Doxepin with Promethazine?
MediHelp rates the interaction as major. Doxepin 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 are sedating and strongly anticholinergic, and both can prolong the QT interval. Combination increases the risk of excessive drowsiness, confusion, urinary retention, constipation and ventricular arrhythmia, especially with other risk factors.
How serious is the interaction between Doxepin 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 combining where possible, particularly with electrolyte disturbance or other QT-prolonging drugs; if used, obtain an ECG and monitor for sedation and anticholinergic toxicity.
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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