Drug interactions
Loperamide + Quinidine
Severity: Major
Loperamide and Quinidine: 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
Quinidine inhibits P-glycoprotein, which normally limits loperamide absorption and its entry into the central nervous system. Loperamide exposure rises several-fold, potentially causing central opioid effects such as respiratory depression. Both drugs also prolong the QT interval, adding cardiac risk.
What this interaction means in plain words
Loperamide 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.
Loperamide belongs to Gastrointestinal Tract; Quinidine belongs to Anti Parasitic.
Why it happens
Quinidine inhibits P-glycoprotein (and CYP2D6/3A4 contribution) increasing loperamide absorption and CNS penetration, plus additive QT prolongation.
What to do
Avoid the combination where possible and use an alternative antidiarrheal. If unavoidable, use the lowest loperamide dose and monitor ECG and for CNS or respiratory depression.
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 Loperamide
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 Loperamide with Quinidine?
MediHelp rates the interaction as major. Loperamide 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. Quinidine inhibits P-glycoprotein, which normally limits loperamide absorption and its entry into the central nervous system. Loperamide exposure rises several-fold, potentially causing central opioid effects such as respiratory depression. Both drugs also prolong the QT interval, adding cardiac risk.
How serious is the interaction between Loperamide 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 use an alternative antidiarrheal. If unavoidable, use the lowest loperamide dose and monitor ECG and for CNS or respiratory depression.
What other medicines interact with Loperamide?
MediHelp also lists interactions of Loperamide with, for example, Amiodarone, Amisulpride, Anagrelide. The full list is on the Loperamide page.
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