Drug interactions
Diltiazem + Quinidine
Severity: Major
Diltiazem 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
Diltiazem inhibits CYP3A4 and may raise quinidine concentrations, while quinidine may increase diltiazem levels. This can cause hypotension, bradycardia, AV block and QT prolongation.
What this interaction means in plain words
Diltiazem 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.
Diltiazem belongs to Cardiovascular; Quinidine belongs to Anti Parasitic.
Why it happens
Diltiazem inhibits CYP3A4 metabolism of quinidine, and quinidine may reduce diltiazem clearance; additive effects on conduction.
What to do
Monitor ECG, heart rate, blood pressure and quinidine levels, and reduce the quinidine dose as needed.
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 Diltiazem
- Diltiazem + Flibanserin Contraindicated
- Diltiazem + Ivabradine Contraindicated
- Diltiazem + Lomitapide Contraindicated
- Diltiazem + Lonafarnib Contraindicated
- Acebutolol + Diltiazem Major
- Alfentanil + Diltiazem Major
Frequently asked questions
Can I take Diltiazem with Quinidine?
MediHelp rates the interaction as major. Diltiazem 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. Diltiazem inhibits CYP3A4 and may raise quinidine concentrations, while quinidine may increase diltiazem levels. This can cause hypotension, bradycardia, AV block and QT prolongation.
How serious is the interaction between Diltiazem 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: Monitor ECG, heart rate, blood pressure and quinidine levels, and reduce the quinidine dose as needed.
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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