Drug Interaction Report

Letermovir Injection and Aprepitant: Interaction Details

A pharmacist-reviewed analysis of the Letermovir Injection and Aprepitant interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Aprepitant

Aponvie Cinvanti Emend
+

Letermovir Injection

Prevymis Prevymis®
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
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Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
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 346 documented Letermovir Injection interactions, 332 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
probable
Severity
Major

What happens

Increased aprepitant exposure

Interaction Deep Dive

Avoid coadministration of aprepitant or fosaprepitant (CYP3A4 substrates) and a moderate CYP3A4 inhibitor as this may increase aprepitant plasma concentrations and increase the risk of adverse effects12. In a study in 10 patients with mild to moderate hypertension, administration of 100 mg of fosaprepitant as an intravenous infusion with 120 mg of dilTIAZem, a moderate CYP3A4 inhibitor administered three times daily, resulted in a 1.5-fold increase in the aprepitant AUC and a 1.4-fold increase in the dilTIAZem AUC 2.

Why it happens (mechanism)

Inhibition of CYP3A4-mediated aprepitant metabolism

Literature reports

1 report — tap to read

a) In a study in 10 patients with mild to moderate hypertension, administration of 100 mg of fosaprepitant as an intravenous infusion with 120 mg of dilTIAZem, a moderate CYP3A4 inhibitor administered three times daily, resulted in a 1.5-fold increase in the aprepitant AUC and a 1.4-fold increase in the dilTIAZem AUC 2.

Common questions

Can I take Letermovir Injection and Aprepitant together?

Increased aprepitant exposure Always confirm with your pharmacist or prescriber before making any change.

How serious is the Letermovir Injection and Aprepitant 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 "probable". Good supporting evidence, though not definitively proven.

Questions for your pharmacist

  • Does my dose of Letermovir Injection or Aprepitant 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)

  1. Product Information: EMEND(R) intravenous injection, fosaprepitant intravenous injection. Merck Sharp & Dohme Corp (per FDA), Whitehouse Station, NJ, 2022. DailyMed
  2. Product Information: FOCINVEZ intravenous injection, fosaprepitant intravenous injection. Spes Pharmaceuticals Inc (per FDA), North Brunswick, NJ, 2023. DailyMed
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Aprepitant

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Letermovir Injection

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All Letermovir Injection interactions (346) Letermovir Injection 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:

Aprepitant + Activated Charcoal Grapefruit St. John's Wort Acacia Rigidula Adrafinil African Wild Potato Alkanna Alpine Ragwort + 150 more

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

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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.