Omeprazole and Letermovir: 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
Letermovir
Omeprazole
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.
Here is what is going on. Letermovir (Prevymis) can slow down one of the liver enzymes that helps break down omeprazole (Prilosec). When that enzyme is slowed, more omeprazole may build up in your body, which could make its effects and side effects a bit stronger.
I want to be honest with you: this is based on lab reasoning and a study with a different drug, not direct proof with omeprazole itself, so it is more of a caution than a certainty. The good news is your care team can handle this easily by watching how you feel and adjusting your dose if needed. Please do not stop either medicine on your own. Just check in with your pharmacist or doctor.
Mechanism: Letermovir is a moderate CYP3A inhibitor. Omeprazole is a CYP3A substrate (primarily CYP2C19, secondarily CYP3A4), so inhibition may increase omeprazole exposure. Neither drug is a prodrug here.
- Direction: Likely increased omeprazole AUC/Cmax.
- Magnitude: Not quantified for omeprazole. Surrogate midazolam data showed AUC increases of roughly 47% (IV) and 125% (oral) with letermovir 240 mg PO daily.
- Onset: Unspecified.
- Evidence: Theoretical (extrapolated from a probe substrate).
Management: Monitor clinically; omeprazole dose may need individualized adjustment.
What happens
Altered omeprazole exposure
Interaction Deep Dive
Taking letermovir together with omeprazole (a CYP3A substrate) can change how much omeprazole is present in the body. During a drug interaction study, giving letermovir (240 mg orally once daily) alongside the CYP3A substrate midazolam (a single 1 mg IV dose) produced rises in midazolam AUC, Cmax and C24hr of 47%, 5% and 174%, respectively. Furthermore, administering letermovir (240 mg orally once daily) with midazolam (a single 2 mg oral dose) raised midazolam AUC and Cmax by 125% and 72%, respectively. Clinical monitoring is advised, and adjusting the dose may be required1.
Why it happens (mechanism)
Inhibition of CYP3A-mediated metabolism of omeprazole; unknown
How to manage this interaction
What your care team may do:
- Keep an eye on how you respond, since omeprazole levels may run a little higher.
- Adjust and individualize your omeprazole dose if that becomes appropriate.
- Monitor you more closely while you are on both medicines.
What you can do:
- Keep taking both medicines exactly as prescribed.
- Tell your pharmacist or prescriber about any new or stronger side effects.
- Do not start, stop, or change either medicine on your own.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In a study evaluating drug interactions, giving letermovir (240 mg orally once daily) together with the CYP3A substrate midazolam (a single 1 mg IV dose) raised midazolam's AUC, Cmax, and C24hr by 47%, 5%, and 174%, respectively. In addition, administering letermovir (240 mg orally once daily) alongside midazolam (a single 2 mg oral dose) increased midazolam's AUC and Cmax by 125% and 72%, respectively 1.
Common questions
Can I take Omeprazole and Letermovir together?
Letermovir may raise omeprazole levels by slowing its breakdown, so your care team may watch you more closely and adjust your omeprazole dose if needed. Keep taking both as prescribed and report any new side effects. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Omeprazole and Letermovir 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 Omeprazole and Letermovir interaction managed?
What your care team may do: Keep an eye on how you respond, since omeprazole levels may run a little higher. Adjust and individualize your omeprazole dose if that becomes appropriate. Monitor you more closely while you are on both medicines. What you can do: Keep taking both medicines exactly as prescribed. Tell your pharmacist or prescriber about any new or stronger side effects. Do not start, st… 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 Letermovir 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: PREVYMIS(R) oral tablets, oral pellets, intravenous injection, letermovir oral tablets, oral pellets, intravenous injection. Merck Sharp & Dohme Corp (per FDA), Rahway, NJ, 2024. DailyMed
Keep reading about Letermovir
Keep reading about Omeprazole
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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.
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