Drug interactions
Dextromethorphan + Quinidine
Severity: Moderate
Dextromethorphan and Quinidine: moderate 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
Quinidine potently inhibits CYP2D6 and markedly raises dextromethorphan concentrations. This is used therapeutically in the fixed combination for pseudobulbar affect, but at higher exposures it may cause dizziness, sedation, confusion and, rarely, serotonin toxicity.
What this interaction means in plain words
Dextromethorphan and Quinidine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Dextromethorphan belongs to Respiratory; Quinidine belongs to Anti Parasitic.
Why it happens
Quinidine is a potent CYP2D6 inhibitor that blocks first-pass and systemic metabolism of dextromethorphan.
What to do
Avoid unsupervised use of additional dextromethorphan with quinidine; if combined, use low doses and monitor for CNS adverse effects and QTc prolongation.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Dextromethorphan
- Dextromethorphan + Isocarboxazid Contraindicated
- Dextromethorphan + Linezolid Contraindicated
- Dextromethorphan + Phenelzine Contraindicated
- Dextromethorphan + Rasagiline Contraindicated
- Dextromethorphan + Safinamide Contraindicated
- Dextromethorphan + Selegiline Contraindicated
Other interactions of Quinidine
- Adagrasib + Quinidine Contraindicated
- Arsenic trioxide + Quinidine Contraindicated
- Artemether / lumefantrine + Quinidine Contraindicated
- Chloroquine + Quinidine Contraindicated
- Dofetilide + Quinidine Contraindicated
- Dronedarone + Quinidine Contraindicated
Frequently asked questions
Can I take Dextromethorphan with Quinidine?
MediHelp rates the interaction as moderate. Dextromethorphan and Quinidine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Quinidine potently inhibits CYP2D6 and markedly raises dextromethorphan concentrations. This is used therapeutically in the fixed combination for pseudobulbar affect, but at higher exposures it may cause dizziness, sedation, confusion and, rarely, serotonin toxicity.
How serious is the interaction between Dextromethorphan and Quinidine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid unsupervised use of additional dextromethorphan with quinidine; if combined, use low doses and monitor for CNS adverse effects and QTc prolongation.
What other medicines interact with Dextromethorphan?
MediHelp also lists interactions of Dextromethorphan with, for example, Isocarboxazid, Linezolid, Phenelzine. The full list is on the Dextromethorphan page.
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