Drug Interaction Report

Atazanavir and Irinotecan: Interaction Details

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

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Atazanavir

Reyataz
+

Irinotecan

Camptosar
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
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Interaction severity
Contraindicated
These should generally not be used together.
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 179 documented Atazanavir interactions, 18 are rated contraindicated — 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
theoretical
Severity
Contraindicated

What happens

Increased irinotecan and its active metabolite, SN-38 exposure

Interaction Deep Dive

Concomitant use of atazanavir and irinotecan is contraindicated2. Avoid coadministration of atazanavir (a strong CYP3A4 and UGT1A1 inhibitor) and irinotecan (a CYP3A4 and UGT1A1 substrate) unless there are no therapeutic alternatives, as it may result in increased plasma concentrations of irinotecan and its active metabolite, SN-38. Atazanavir should be discontinued at least 1 week prior to initiating with irinotecan 13.

Why it happens (mechanism)

Inhibition of UGT1A1-mediated irinotecan metabolism; inhibition of CYP3A4-mediated irinotecan metabolism

Common questions

Can I take Atazanavir and Irinotecan together?

Increased irinotecan and its active metabolite, SN-38 exposure Always confirm with your pharmacist or prescriber before making any change.

How serious is the Atazanavir and Irinotecan interaction?

It is rated contraindicated. These should generally not be used together.

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 "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.

Questions for your pharmacist

  • Does my dose of Atazanavir or Irinotecan 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: CAMPTOSAR(R) intravenous injection, irinotecan intravenous injection. Pharmacia & Upjohn Co (per Manufacturer), New York, NY, 2014. DailyMed
  2. Product Information: REYATAZ(R) oral capsules, oral powder, atazanavir oral capsules, oral powder. Bristol-Myers Squibb Company (per FDA), Princeton, NJ, 2020. DailyMed
  3. Product Information: ONIVYDE(R) intravenous injection, irinotecan liposome intravenous injection. Ipsen Biopharmaceuticals Inc (per FDA), Cambridge, MA, 2024. DailyMed
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Atazanavir

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All Atazanavir interactions (179)
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Irinotecan

Keep reading about Irinotecan

All Irinotecan interactions (98) Irinotecan drug information
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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:

Atazanavir + Activated Charcoal Grapefruit St. John's Wort Acacia Rigidula Adrafinil African Wild Potato American Elder Astaxanthin + 144 more
Irinotecan + Activated Charcoal Apple Grapefruit St. John's Wort Sweet Orange Acacia Rigidula Adrafinil African Wild Potato + 145 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.