Letermovir Injection and Zanubrutinib: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Letermovir Injection
Zanubrutinib
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.
What happens
Increased zanubrutinib exposure and an increased risk of zanubrutinib-related toxicity
Interaction Deep Dive
Zanubrutinib is primarily metabolized by CYP3A, and concomitant use of zanubrutinib with a CYP3A inhibitor increases zanubrutinib exposure, which may increase the risk of zanubrutinib toxicities. Coadministration of zanubrutinib with erythromycin 500 mg 4 times daily (a moderate CYP3A inhibitor) is predicted to increase zanubrutinib Cmax by 284% and AUC by 317%. When zanubrutinib and a moderate CYP3A inhibitor are coadministered, reduce zanubrutinib to 80 mg twice daily and further modify the dosage as required for adverse reactions. After discontinuation of a CYP3A inhibitor, resume previous dosage of zanubrutinib1.
Why it happens (mechanism)
Inhibition of CYP3A-mediated metabolism of zanubrutinib
Literature reports
2 reports — tap to read
a) The predicted increase in zanubrutinib exposure when coadministered with dilTIAZem 180 mg once daily, is a 62% increase in zanubrutinib Cmax and a 62% increase in AUC. The assessment was conducted in patients with B-cell lymphoma administered multiple doses of zanubrutinib 1.
b) The predicted increases in zanubrutinib exposure when coadministered with fluconazole 400 mg/day is a 157% increase in zanubrutinib Cmax and a 278% increase in AUC. The assessment was conducted in patients with B-cell lymphoma administered multiple doses of zanubrutinib 1.
Common questions
Can I take Letermovir Injection and Zanubrutinib together?
Increased zanubrutinib exposure and an increased risk of zanubrutinib-related toxicity Always confirm with your pharmacist or prescriber before making any change.
How serious is the Letermovir Injection and Zanubrutinib 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 "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Letermovir Injection or Zanubrutinib 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: BRUKINSA(R) oral capsules, oral tablets, zanubrutinib oral capsules, oral tablets. BeOne Medicines USA, Inc. (per FDA), Pennington, NJ, 2025. DailyMed
Keep reading about Letermovir Injection
Keep reading about Zanubrutinib
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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:
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