Fosaprepitant 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
Fosaprepitant
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.
You've been prescribed buprenorphine (a pain or opioid-treatment medicine) and fosaprepitant, an anti-nausea drug often given with chemotherapy. Fosaprepitant can slow down the liver enzyme (called CYP3A4) that normally breaks down buprenorphine. When that happens, more buprenorphine can build up in your body.
That extra buildup can make the opioid effects stronger and last longer, which may cause more sedation (drowsiness) and slowed breathing. The good news is this is very manageable. Your care team can adjust your buprenorphine dose and keep a closer eye on you. Keep taking both medicines as prescribed, and tell your doctor or pharmacist right away if you feel unusually sleepy or short of breath.
Effect: Fosaprepitant, a moderate CYP3A4 inhibitor, inhibits CYP3A4-mediated metabolism of buprenorphine, increasing buprenorphine exposure (AUC/Cmax) and the risk of opioid-related adverse events including sedation and respiratory depression.
- Direction: Increased buprenorphine effect (buprenorphine is the affected substrate; not a prodrug in this context).
- Severity/Evidence: Major; probable substantiation. Onset unspecified.
- Management: If starting the inhibitor, consider reducing the buprenorphine dose until stable and monitor frequently for sedation/respiratory depression. On inhibitor discontinuation, consider a dose increase and monitor for withdrawal. For fixed formulations (subQ depot, patch), monitor closely for over-medication; transition to a titratable formulation if precise adjustment is needed.
What happens
Increased buprenorphine exposure and an increased risk of buprenorphine-related adverse events
Interaction Deep Dive
Because plasma buprenorphine concentrations rise when buprenorphine is taken together with a CYP3A4 inhibitor, opioid effects such as respiratory depression may be extended. When a patient on buprenorphine requires a CYP3A4 inhibitor, it may be appropriate to lower the buprenorphine dose until drug effects stabilize, with frequent monitoring for sedation and respiratory depression. Conversely, when the CYP3A4 inhibitor is stopped in a patient who is receiving buprenorphine, consider raising the buprenorphine dose until stable effects are reached, watching for signs of opioid withdrawal2. Should dose adjustment prove impossible once the CYP3A4 inhibitor is removed, switch the patient back to a buprenorphine formulation that allows finer dose titration. For patients being converted from transmucosal buprenorphine given alongside CYP3A4 inhibitors, monitor to confirm that the plasma buprenorphine concentration delivered by subQ buprenorphine is sufficient. For those already established on subQ buprenorphine who then need a CYP3A4 inhibitor, watch for indications of over-medication. If features of buprenorphine toxicity or overdose develop and the co-administered drug cannot be lowered or stopped, decrease the buprenorphine dose. When the available doses cannot deliver the intended dose, halt treatment and manage the patient using a buprenorphine formulation that supports more precise dose adjustments 1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism of buprenorphine
How to manage this interaction
Both medications can be used together safely with the right precautions. Your care team manages this by tailoring your buprenorphine dose and watching you more closely.
- Keep taking both as prescribed unless your prescriber tells you otherwise.
- Your buprenorphine dose may be adjusted and individualized while you are on fosaprepitant, and adjusted again when it is stopped.
- Your team may monitor you more frequently for excess drowsiness and slowed breathing.
- Contact your care team promptly if you notice heavy sedation, confusion, or shortness of breath. If you use a long-acting form (patch or injection), ask how they will monitor you.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) Studies have not examined how coadministered CYP3A4 inhibitors influence buprenorphine exposure in individuals receiving subQ buprenorphine; nevertheless, these interactions have been documented in studies employing transmucosal buprenorphine. Buprenorphine's effects may vary according to the route of administration 1.
Common questions
Can I take Fosaprepitant and Buprenorphine together?
Fosaprepitant can raise buprenorphine levels and increase drowsiness and slowed breathing, so your care team may adjust your buprenorphine dose and monitor you more closely. Keep taking both as prescribed and report any unusual sleepiness or breathing trouble. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Fosaprepitant 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 Fosaprepitant and Buprenorphine interaction managed?
Both medications can be used together safely with the right precautions. Your care team manages this by tailoring your buprenorphine dose and watching you more closely. Keep taking both as prescribed unless your prescriber tells you otherwise. Your buprenorphine dose may be adjusted and individualized while you are on fosaprepitant, and adjusted again when it is stopped. Your team may monitor you… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Fosaprepitant 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 (2)
- Product Information: BRIXADI(TM) subcutaneous extended-release injection, buprenorphine subcutaneous extended-release injection. Braeburn Inc (per FDA), Plymouth Meeting, PA, 2023. DailyMed
- Product Information: ZUBSOLV(R) sublingual tablets, buprenorphine naloxone sublingual tablets. Orexo US Inc (per FDA), Morristown, NJ, 2023. DailyMed
Keep reading about Buprenorphine
Keep reading about Fosaprepitant
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