Rilzabrutinib and Letermovir Injection: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Rilzabrutinib
Letermovir Injection
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 rilzabrutinib exposure and an increased risk of rilzabrutinib-related adverse reactions
Interaction Deep Dive
Avoid concomitant use of rilzabrutinib (CYP3A substrate) with moderate CYP3A inhibitors as it may increase rilzabrutinib exposure, which may increase rilzabrutinib-related side effects than usual. If a moderate CYP3A inhibitor cannot be avoided, and these inhibitors will be used short term (such as anti-infectives for seven days or less), interrupt treatment with rilzabrutinib. In a drug interaction study, concomitant use of rilzabrutinib with moderate CYP3A inhibitors (fluconazole, erythromycin and verapamil) is predicted to increase rilzabrutinib Cmax and AUC by approximately 3-fold at steady state1.
Why it happens (mechanism)
Inhibition of CYP3A-mediated metabolism of rilzabrutinib
Literature reports
1 report — tap to read
a) In a drug interaction study, concomitant use of rilzabrutinib with moderate CYP3A inhibitors (fluconazole, erythromycin and verapamil) is predicted to increase rilzabrutinib Cmax and AUC by approximately 3-fold at steady state 1.
Common questions
Can I take Rilzabrutinib and Letermovir Injection together?
Increased rilzabrutinib exposure and an increased risk of rilzabrutinib-related adverse reactions Always confirm with your pharmacist or prescriber before making any change.
How serious is the Rilzabrutinib 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 "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Rilzabrutinib 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)
- Product Information: WAYRILZ™ oral tablets, rilzabrutinib oral tablets. Genzyme Corporation (per FDA), Cambridge, MA, 2025. DailyMed
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