Fosfomycin and Buprenorphine: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Buprenorphine
Fosfomycin
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.
Both of these medicines can affect your heart's rhythm. Buprenorphine (a pain or opioid-treatment medicine) and fosfomycin (an antibiotic, often taken as a single dose for a bladder infection) can each slightly stretch out part of your heartbeat, called the QT interval. Taken together, that effect could add up and, in rare cases, lead to an irregular heartbeat.
This is a theoretical concern, not something proven to happen often. Still, it's worth a quick word with your pharmacist or doctor. They can check your other medicines and your electrolyte levels (like potassium and magnesium) and manage this safely. Don't stop either medicine on your own.
Interaction: Additive QT-interval prolongation from concurrent buprenorphine and fosfomycin, raising theoretical risk of ventricular arrhythmias (including torsades de pointes).
- Mechanism: Pharmacodynamic (additive), not metabolic. Neither is a prodrug relevant here.
- Direction: Enhanced cardiac (QT) effect.
- Evidence: Theoretical; onset unspecified.
- Severity: Major.
- Management: Manufacturer advises avoiding coadministration with QT-prolonging agents. If used together, correct and monitor electrolytes (K+, Mg2+), assess baseline/interval ECG, and review other QT-prolonging drugs and risk factors (bradycardia, hepatic impairment, higher buprenorphine doses).
What happens
An increased risk of QT interval prolongation
Interaction Deep Dive
Because it may heighten the likelihood of ventricular arrhythmias, fosfomycin should not be given together with other agents recognized for prolonging the QT interval. Electrolyte levels should be monitored throughout fosfomycin therapy1.
Why it happens (mechanism)
Additive QT interval prolongation
How to manage this interaction
The goal is to keep your heart rhythm safe while treating your infection.
- Keep taking both medicines exactly as prescribed unless your care team tells you otherwise.
- Tell your pharmacist and prescriber you take buprenorphine before starting fosfomycin, and list any other medicines, since some can add to this effect.
- Your team may check your electrolytes (potassium and magnesium) and, in some cases, your heart rhythm with an ECG.
- Because fosfomycin for a bladder infection is often just a single dose, your care team may decide an alternative antibiotic, closer monitoring, or timing works best for you.
- Get urgent help for fainting, palpitations, or a racing/irregular heartbeat.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Fosfomycin and Buprenorphine together?
Combining buprenorphine and fosfomycin may add up to prolong the QT interval, a mostly theoretical but potentially serious heart-rhythm concern. Ask your pharmacist or doctor to review it; they may check electrolytes, monitor your heart, or pick a different antibiotic. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Fosfomycin and Buprenorphine 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 is the Fosfomycin and Buprenorphine interaction managed?
The goal is to keep your heart rhythm safe while treating your infection. Keep taking both medicines exactly as prescribed unless your care team tells you otherwise. Tell your pharmacist and prescriber you take buprenorphine before starting fosfomycin, and list any other medicines, since some can add to this effect. Your team may check your electrolytes (potassium and magnesium) and, in some cases… Management is individual — always follow your own care team's guidance.
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 Fosfomycin or Buprenorphine 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
Keep reading about Buprenorphine
Keep reading about Fosfomycin
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:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
Check another combination
Our instant two-drug interaction checker is almost here.
Still have questions about this combination?
Every question gets a real answer from a licensed pharmacist — free, and usually within a day.
Ask the pharmacist