Drug Interaction Report

Arsenic Trioxide and Fosfomycin: Interaction Details

Name: Arsenic Trioxide and Fosfomycin Interaction
Creator: Dr. Brian Staiger, PharmD, BCPS

A pharmacist-reviewed analysis of the Arsenic Trioxide and Fosfomycin 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

Fosfomycin

Contepo Monurol® Sachet

Arsenic Trioxide

Trisenox

Medically reviewed by

Dr. Brian Staiger, PharmD, BCPS

Updated Jul 11, 2026

Editorial policy · Data sources

Interaction severity

Major

Potentially serious — often needs a change or close monitoring.

Minor

Moderate

Major

Contraindicated

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 310 documented Arsenic Trioxide interactions, 286 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

An increased risk of QT interval prolongation

Interaction Deep Dive

Avoid coadministration of fosfomycin with other drugs known to prolong the QT interval as it may increase the risk for ventricular arrhythmias. Monitor electrolytes during treatment with fosfomycin¹.

Why it happens (mechanism)

Additive QT interval prolongation

Common questions

Can I take Arsenic Trioxide and Fosfomycin together?

An increased risk of QT interval prolongation Always confirm with your pharmacist or prescriber before making any change.

How serious is the Arsenic Trioxide and Fosfomycin 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.

Questions for your pharmacist

Does my dose of Arsenic Trioxide or Fosfomycin 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 (1)

Product Information: CONTEPO intravenous injection, fosfomycin intravenous injection. Meitheal Pharmaceuticals Inc (per FDA), Chicago, IL, 2025. DailyMed

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Fosfomycin

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All Fosfomycin interactions (63) Fosfomycin drug information

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Arsenic Trioxide

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All Arsenic Trioxide interactions (310) Arsenic Trioxide 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:

Fosfomycin + Activated Charcoal Bacillus Coagulans Bacillus Subtilis Bifidobacterium Animalis Subsp. Lactis Bifidobacterium Bifidum Bifidobacterium Breve Bifidobacterium Longum Coffee Charcoal + 36 more

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

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A message from HelloPharmacist

About our interaction database: depth, not breadth

HelloPharmacist doesn't license one of the big commercial interaction databases, so what you'll find here is not a complete list of every known drug interaction. Instead, each entry is researched, analyzed, and written up individually — documented from the published literature, reviewed by a pharmacist, and cited so you can check every source yourself.

If a combination isn't listed here, it means we haven't documented it yet — never that it's safe. For screening a full medication list, we recommend pairing this site with a comprehensive tool like the Drugs.com Interaction Checker and, most importantly, a review by your own pharmacist. For a deep, plain-English, fully sourced explanation of a specific documented interaction — that's exactly what we built this for.

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.