Cytarabine and Flucytosine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Cytarabine
Flucytosine
No brand names on record
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.
What happens
Decreased flucytosine efficacy
Interaction Deep Dive
Cytarabine has been reported to inactivate the antifungal activity of flucytosine1. However, this effect has not been clearly supported by in vitro or in vivo studies 2. One patient had variations in flucytosine concentrations when the drug was given with cytarabine. However, the patient's unstable renal function may have caused the fluctuation.
Why it happens (mechanism)
Unknown
Common questions
Can I take Cytarabine and Flucytosine together?
Decreased flucytosine efficacy Always confirm with your pharmacist or prescriber before making any change.
How serious is the Cytarabine and Flucytosine interaction?
It is rated minor. Usually limited clinical impact.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Cytarabine or Flucytosine 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 anything you'd monitor while I'm on both?
References (2)
- Product Information: Ancobon(R), flucytosine. Roche Laboratories Inc. Nutley, NJ, 1994. DailyMed
- Wingfield HJ: Absence of fungistatic antagonism between flucytosine and cytarabine in vitro and in vivo. J Antimicrob Chemother 1987; 20:523-527.
Keep reading about Cytarabine
Keep reading about Flucytosine
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Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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