Drug Interaction Report

Fostemsavir and Itraconazole: Interaction Details

A pharmacist-reviewed analysis of the Fostemsavir and Itraconazole 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

Itraconazole

Sporanox Tolsura
+

Fostemsavir

Rukobia Rukobia®
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
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 240 documented Fostemsavir interactions, 208 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
theoretical
Severity
Major

What happens

Increased fostemsavir exposure and an increased risk of QT interval prolongation

Interaction Deep Dive

Coadministration of fostemsavir with a drug with a known risk of torsade de pointes may increase the risk of torsade de pointes. Use fostemsavir with caution when coadministered with drugs with a known risk of torsade de pointes1. Also, concomitant administration of itraconazole (a potent CYP3A4 inhibitor) with fostemsavir (a CYP3A4 substrate) may increase the plasma concentrations of these substrates resulting in increased adverse reactions of these substrates. Monitor for adverse reactions. Dose reduction of fostemsavir may be necessary 23.

Why it happens (mechanism)

Inhibition of CYP3A4-mediated metabolism of fostemsavir; additive QT interval prolongation

Common questions

Can I take Fostemsavir and Itraconazole together?

Increased fostemsavir exposure and an increased risk of QT interval prolongation Always confirm with your pharmacist or prescriber before making any change.

How serious is the Fostemsavir and Itraconazole 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 "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.

From our Q&A

Real reader questions about these medications, each personally answered by our pharmacist:

Questions for your pharmacist

  • Does my dose of Fostemsavir or Itraconazole 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: RUKOBIA oral extended-release tablets, fostemsavir oral extended-release tablets. ViiV Healthcare (per FDA), Research Triangle Park, NC, 2020. DailyMed
  2. Product Information: SPORANOX(R) oral solution, itraconazole oral solution. Janssen Pharmaceuticals Inc (per FDA), Titusville, NJ, 2024. DailyMed
  3. Product Information: SPORANOX(R) oral capsules, itraconazole oral capsules. Janssen Pharmaceuticals Inc (per FDA), Titusville, NJ, 2024. DailyMed
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Itraconazole

Keep reading about Itraconazole

All Itraconazole interactions (206)
Also serious with: Dihydroergotamine Injection Disopyramide Lovastatin Finerenone
Fostemsavir

Keep reading about Fostemsavir

All Fostemsavir interactions (240) Fostemsavir drug information
Also serious with: Fosphenytoin Ivosidenib Grazoprevir Lumacaftor
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:

Itraconazole + Activated Charcoal Beer Grapefruit Siberian Cocklebur St. John's Wort Wine Acacia Rigidula Adrafinil + 174 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.