Pralsetinib and Letermovir Injection: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Letermovir Injection
Pralsetinib
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 pralsetinib exposure and an increased risk of pralsetinib-related adverse events
Interaction Deep Dive
Concomitant use of pralsetinib (a CYP3A substrate) and a moderate CYP3A inhibitor may increase pralsetinib exposure, which may increase the incidence and severity of adverse reactions. Avoid concomitant use of pralsetinib with moderate CYP3A inhibitors. If coadministration cannot be avoided, reduce the pralsetinib dose in patients taking 400 mg, 300 mg and 200 mg orally once daily to 300 mg, 200 mg and 100 mg orally once daily respectively. After the inhibitor has been discontinued for 3 to 5 elimination half-lives of the inhibitor, resume pralsetinib at the dose taken prior to initiating the inhibitor1.
Why it happens (mechanism)
Inhibition of CYP3A-mediated metabolism of pralsetinib
Literature reports
2 reports — tap to read
a) In a model-informed approach, coadministration of verapamil (a combined P-gp and moderate CYP3A inhibitor) 80 mg thrice daily with pralsetinib is predicted to increase pralsetinib Cmax by 60% and AUC by 108% 1.
b) In a model-informed approach, coadministration of fluconazole (a moderate CYP3A inhibitor) 400 mg once daily with pralsetinib is predicted to increase pralsetinib Cmax by 15% and AUC by 71% 1.
Common questions
Can I take Pralsetinib and Letermovir Injection together?
Increased pralsetinib exposure and an increased risk of pralsetinib-related adverse events Always confirm with your pharmacist or prescriber before making any change.
How serious is the Pralsetinib 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 Pralsetinib 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: GAVRETO(TM) oral capsules, pralsetinib oral capsules. Genentech USA Inc (per FDA), South San Fransisco, CA, 2023. DailyMed
Keep reading about Letermovir Injection
Keep reading about Pralsetinib
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