Drug interactions
Grapefruit + Quinidine
Severity: Minor
Grapefruit and Quinidine: minor 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
Grapefruit juice inhibits intestinal CYP3A4, which can slow quinidine absorption and metabolism, though studies show only modest and variable changes in quinidine exposure. The practical effect is usually small.
What this interaction means in plain words
Grapefruit and Quinidine have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Why it happens
Furanocoumarins in grapefruit inhibit intestinal CYP3A4 metabolism of quinidine.
What to do
Advise keeping grapefruit intake consistent or avoiding large quantities. Monitor ECG if the patient has a high intake and there are signs of quinidine toxicity.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
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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 Grapefruit with Quinidine?
MediHelp rates the interaction as minor. Grapefruit and Quinidine have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Grapefruit juice inhibits intestinal CYP3A4, which can slow quinidine absorption and metabolism, though studies show only modest and variable changes in quinidine exposure. The practical effect is usually small.
How serious is the interaction between Grapefruit and Quinidine?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Advise keeping grapefruit intake consistent or avoiding large quantities. Monitor ECG if the patient has a high intake and there are signs of quinidine toxicity.
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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