Omeprazole and Fosnetupitant: 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
Fosnetupitant
No brand names on recordOmeprazole
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.
Let me explain this one simply. Fosnetupitant is a drug used to prevent nausea and vomiting from chemotherapy. Once it's in your body, it turns into netupitant, which gently slows down a liver enzyme called CYP3A4. That enzyme helps break down many other medicines.
Your acid-reducing medicine, omeprazole, is partly handled by that same enzyme. So when the two are used together, omeprazole may build up a bit more than usual and its effects could be stronger for a while. The good news is this is a known, manageable situation. Your care team can adjust doses and keep an eye on you, so just make sure they know you're taking both.
Mechanism: Fosnetupitant is a prodrug of netupitant, a moderate CYP3A4 inhibitor. Omeprazole is a partial CYP3A4 substrate, so inhibition may increase omeprazole exposure (elevated AUC/Cmax) with a rapid onset. Enzyme inhibition can persist up to ~1 week after a single netupitant dose.
- Direction: increased omeprazole exposure and effect.
- Evidence: theoretical for this pair; supported by observed AUC/Cmax increases in erythromycin and dexamethasone probe studies.
- Management: avoid concomitant CYP3A4 substrates for 1 week after netupitant/fosnetupitant; if unavoidable, consider reducing the substrate dose. Individualize and monitor for exaggerated substrate effects.
What happens
Increased exposure of CYP3A4 substrate
Interaction Deep Dive
For a period of 1 week, do not use CYP3A4 substrates together with netupitant or fosnetupitant (the prodrug form of netupitant), which acts as a moderate CYP3A4 inhibitor. When netupitant or fosnetupitant is taken alongside CYP3A4 substrates, the exposure to those substrates can rise. In a pharmacokinetic study, coadministration of netupitant led to higher mean AUC and Cmax values for erythromycin, a CYP3A4 substrate. For the CYP3A4 probe substrate dexAMETHasone, elevated AUC persisted for as long as 8 days after a single netupitant dose. Concurrent administration of CYP3A4 substrates with netupitant is to be avoided for 1 week. Should a CYP3A4 substrate need to be given within 1 week of netupitant, a reduction in the dose of that CYP3A4 substrate should be considered1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism by netupitant
How to manage this interaction
Here's how a care team typically handles this:
- They may avoid giving CYP3A4 substrates during the roughly 1-week window after fosnetupitant, or, if the medicine is needed, reduce the dose and individualize it.
- They may watch you a bit more closely for stronger-than-usual effects.
What you should do: keep taking both medicines exactly as prescribed, and don't stop or change anything on your own. Just tell your pharmacist or prescriber that you're using fosnetupitant and omeprazole together so they can confirm the timing and dosing are right for you.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
2 reports — tap to read
a) In a study that evaluated how long CYP3A4 inhibition lasted by using dexAMETHasone as a CYP3A4 probe substrate, the mean AUC of dexAMETHasone rose by 1.6-fold on day 1, 2.4-fold on day 4, 1.5-fold on day 6, and 1.2-fold on day 8 following a single dose of the netupitant 300 mg/palonosetron 0.5 mg combination given to participants on day 1. These participants had received a dexAMETHasone regimen consisting of 12 mg on day 1 and then 8 mg on days 2, 3, 4, 6, 8, and 10 1.
b) A pharmacokinetic study showed that coadministration of erythromycin 500 mg with netupitant 300 mg produced a 56% increase in the mean AUC of erythromycin and a 92% increase in the Cmax 1.
Common questions
Can I take Omeprazole and Fosnetupitant together?
Netupitant (from fosnetupitant) can raise omeprazole levels for about a week, so let your care team confirm the timing and dose; keep taking both as prescribed unless they tell you otherwise. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Omeprazole and Fosnetupitant interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How is the Omeprazole and Fosnetupitant interaction managed?
Here's how a care team typically handles this: They may avoid giving CYP3A4 substrates during the roughly 1-week window after fosnetupitant, or, if the medicine is needed, reduce the dose and individualize it. They may watch you a bit more closely for stronger-than-usual effects. What you should do: keep taking both medicines exactly as prescribed, and don't stop or change anything on your own. Ju… 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.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Omeprazole or Fosnetupitant 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: AKYNZEO(R) oral capsules, netupitant palonosetron oral capsules. Helsinn Therapeutics (US), Inc (per FDA), Iselin, NJ, 2018. DailyMed
Keep reading about Fosnetupitant
Keep reading about Omeprazole
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