Drug interactions
Fluorouracil + Leucovorin
Severity: Major
Fluorouracil and Leucovorin: major 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
Leucovorin is deliberately combined with fluorouracil to enhance its cytotoxic effect, but it also increases fluorouracil toxicity, particularly diarrhea, mucositis and myelosuppression. Severe gastrointestinal toxicity can be dangerous, especially in older patients.
What this interaction means in plain words
Fluorouracil and Leucovorin 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.
Fluorouracil belongs to Oncology; Leucovorin belongs to Miscellaneous.
Why it happens
Leucovorin supplies reduced folate that stabilizes the binding of fluorodeoxyuridylate to thymidylate synthase, enhancing both efficacy and toxicity.
What to do
Use established regimen doses of fluorouracil when combined with leucovorin and monitor blood counts and for diarrhea and mucositis. Interrupt therapy and reduce the dose for significant toxicity.
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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Other interactions of Fluorouracil
Other interactions of Leucovorin
- Capecitabine + Leucovorin Major
- Glucarpidase + Leucovorin Major
- Leucovorin + Phenobarbitone Moderate
- Leucovorin + Phenytoin Moderate
Frequently asked questions
Can I take Fluorouracil with Leucovorin?
MediHelp rates the interaction as major. Fluorouracil and Leucovorin 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. Leucovorin is deliberately combined with fluorouracil to enhance its cytotoxic effect, but it also increases fluorouracil toxicity, particularly diarrhea, mucositis and myelosuppression. Severe gastrointestinal toxicity can be dangerous, especially in older patients.
How serious is the interaction between Fluorouracil and Leucovorin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Use established regimen doses of fluorouracil when combined with leucovorin and monitor blood counts and for diarrhea and mucositis. Interrupt therapy and reduce the dose for significant toxicity.
What other medicines interact with Fluorouracil?
MediHelp also lists interactions of Fluorouracil with, for example, Adenovirus types 4 and 7 live, Axicabtagene ciloleucel, Belatacept. The full list is on the Fluorouracil page.
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