Drug Interaction Report

Doxifluridine and Allopurinol: Interaction Details

A pharmacist-reviewed analysis of the Doxifluridine and Allopurinol interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Allopurinol

Aloprim Lopurin® Zyloprim Zyloprim®
+

Doxifluridine

No brand names on record
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Jul 11, 2026
Editorial policy · Data sources
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Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
How we grade severity & evidence

Severity levels

  • Contraindicated: These should generally not be used together.
  • Major: Potentially serious — often needs a change or close monitoring.
  • Moderate: Can be significant — usually manageable with monitoring.
  • Minor: Usually limited clinical impact.

Evidence grades

  • Established: Well documented — supported by controlled studies or strong clinical data.
  • Probable: Good supporting evidence, though not definitively proven.
  • Suspected: Some evidence suggests this interaction, but it is not well established.
  • Possible: Limited or conflicting evidence; the interaction may occur.
  • Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.

Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.

Of 36 documented Doxifluridine interactions, 34 are rated major — including this one.
Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.
Onset
unspecified
Evidence
probable
Severity
Major

What happens

Reduced capecitabine or doxifluridine or fluorouracil (prodrugs of capecitabine) or tegafur (prodrug of fluorouracil) exposure and reduced efficacy of capecitabine or doxifluridine or fluorouracil or tegafur

Interaction Deep Dive

Avoid concomitant use of allopurinol or oxypurinol (prodrug of allopurinol) and capecitabine or doxifluridine or fluorouracil (prodrugs of capecitabine) or tegafur (prodrug of fluorouracil) as it may reduce conversion of capecitabine to the active metabolites, 5-fluoro-2-deoxyuridine monophosphate (FdUMP) and 5-fluorouridine triphosphate (FUTP), which may reduce capecitabine efficacy2 and may also reduce the anti-tumor activity of fluorouracil 13.

Why it happens (mechanism)

Reduced capecitabine active metabolites exposure

Common questions

Can I take Doxifluridine and Allopurinol together?

Reduced capecitabine or doxifluridine or fluorouracil (prodrugs of capecitabine) or tegafur (prodrug of fluorouracil) exposure and reduced efficacy of capecitabine or doxifluridine or fluorouracil or tegafur Always confirm with your pharmacist or prescriber before making any change.

How serious is the Doxifluridine and Allopurinol interaction?

It is rated major. Potentially serious — often needs a change or close monitoring.

How quickly could this interaction happen?

The documented onset is "unspecified". The timing of this interaction is not well characterized.

How strong is the evidence for this interaction?

The evidence is graded "probable". Good supporting evidence, though not definitively proven.

Questions for your pharmacist

  • Does my dose of Doxifluridine or Allopurinol need adjusting while I take them together?
  • What symptoms should prompt me to call you or my prescriber right away?
  • Does the timing of my doses matter for this combination?
  • Is there a safer alternative to one of these medications for me?

References (3)

  1. Product Information: ALOPRIM(R) intravenous injection, allopurinol sodium intravenous injection. Mylan Institutional LLC (per FDA), Rockford, IL, 2022. DailyMed
  2. Product Information: XELODA(R) oral tablets, capecitabine oral tablets. Genentech USA Inc (per FDA), South San Francisco, CA, 2022. DailyMed
  3. Product Information: Teysuno oral capsules, tegafur, gimeracil, oteracil oral capsules. Nordic Group (per EMA), Hoofddorp, Netherlands, 2016.
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Allopurinol

Keep reading about Allopurinol

All Allopurinol interactions (32) Allopurinol drug information
Also serious with: Fezolinetant Didanosine Acenocoumarol Pegloticase Injection
Doxifluridine

Keep reading about Doxifluridine

All Doxifluridine interactions (36)
Also serious with: Leucovorin Injection Nateglinide Erdafitinib Flurbiprofen Ophthalmic
Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

Allopurinol + Activated Charcoal Asarabacca Beer Siberian Cocklebur Wine Aristolochia Ashwagandha Black Cohosh + 52 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.