Drug Interaction Report

Vanzacaftor and Letermovir Injection: Interaction Details

A pharmacist-reviewed analysis of the Vanzacaftor and Letermovir Injection 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

Letermovir Injection

Prevymis Prevymis®
+

Vanzacaftor

No brand names on record
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 9 documented Vanzacaftor interactions, 9 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 vanzacaftor exposure and an increased risk of vanzacaftor-related adverse reactions

Interaction Deep Dive

Coadministration of vanzacaftor and a moderate CYP3A inhibitor may increase the exposure of vanzacaftor, which may increase the risk of vanzacaftor-associated adverse reactions. In a drug interaction study, coadministration of vanzacaftor 20 mg, tezacaftor 100 mg and deutivacaftor 250 mg once daily with moderate CYP3A inhibitor fluconazole 200 mg daily resulted in increased vanzacaftor AUC by 2.55-fold and Cmax by 2.48-fold, it also increased deutivacaftor AUC by 3.13-fold and Cmax by 2.27-fold. Reduce the vanzacaftor dosage with concomitant use of moderate CYP3A inhibitors. For 6 to less than 12 years old, patients weighing less than 40 kg adjust the dose to two tablets of vanzacaftor 4 mg/tezacaftor 20 mg/deutivacaftor 50 mg every other day and for patients greater than or equal to 40 kg adjust the dose to one tablet of vanzacaftor 10 mg/tezacaftor 50 mg/deutivacaftor 125 mg every other day. For 12 years and older patients adjust the dose to one tablet of vanzacaftor 10 mg/tezacaftor 50 mg/deutivacaftor 125 mg every other day1.

Why it happens (mechanism)

Inhibition of CYP3A-mediated metabolism of vanzacaftor

Literature reports

1 report — tap to read

a) In a drug interaction study, coadministration of vanzacaftor 20 mg, tezacaftor 100 mg and deutivacaftor 250 mg once daily with moderate CYP3A inhibitor fluconazole 200 mg daily resulted in increased vanzacaftor AUC by 2.55-fold and Cmax by 2.48-fold, it also increased deutivacaftor AUC by 3.13-fold and Cmax by 2.27-fold 1.

Common questions

Can I take Vanzacaftor and Letermovir Injection together?

Increased vanzacaftor exposure and an increased risk of vanzacaftor-related adverse reactions Always confirm with your pharmacist or prescriber before making any change.

How serious is the Vanzacaftor and Letermovir Injection 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 Vanzacaftor or Letermovir Injection 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)

  1. Product Information: ALYFTREK(R) oral tablets, vanzacaftor, tezacaftor, and deutivacaftor oral tablets. Vertex Pharmaceuticals Incorporated (per FDA), Boston, MA, 2024. DailyMed
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Letermovir Injection

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