Drug interactions
Doxepin + Quinidine
Severity: Major
Doxepin and Quinidine: 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 can prolong the QT interval, and quinidine also raises doxepin exposure by inhibiting CYP2D6. Together they increase the risk of torsades de pointes and other ventricular arrhythmias.
What this interaction means in plain words
Doxepin and Quinidine 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; Quinidine belongs to Anti Parasitic.
Why it happens
Additive QT prolongation plus quinidine inhibition of CYP2D6-mediated doxepin metabolism.
What to do
Avoid the combination where possible and choose a non-QT-prolonging antidepressant. If unavoidable, obtain a baseline and follow-up ECG, correct potassium and magnesium, and lower the doxepin dose.
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 Quinidine
- Adagrasib + Quinidine Contraindicated
- Arsenic trioxide + Quinidine Contraindicated
- Artemether / lumefantrine + Quinidine Contraindicated
- Chloroquine + Quinidine Contraindicated
- Dofetilide + Quinidine Contraindicated
- Dronedarone + Quinidine Contraindicated
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 Quinidine?
MediHelp rates the interaction as major. Doxepin and Quinidine 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 quinidine also raises doxepin exposure by inhibiting CYP2D6. Together they increase the risk of torsades de pointes and other ventricular arrhythmias.
How serious is the interaction between Doxepin and Quinidine?
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 and choose a non-QT-prolonging antidepressant. If unavoidable, obtain a baseline and follow-up ECG, correct potassium and magnesium, and lower the doxepin dose.
What other medicines interact with Quinidine?
MediHelp also lists interactions of Quinidine with, for example, Adagrasib, Arsenic trioxide, Artemether / lumefantrine. The full list is on the Quinidine page.
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