Letermovir Injection and Pemigatinib: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Letermovir Injection
Pemigatinib
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 pemigatinib exposure and increased risk and severity of adverse reactions
Interaction Deep Dive
Concomitant use of pemigatinib and a strong or moderate CYP3A inhibitor increases pemigatinib exposure, which may increase the incidence and severity of adverse reactions. Concomitant use of pemigatinib and itraconazole, a strong CYP3A inhibitor, increased pemigatinib Cmax by 17% and increased AUC by 88%. Concomitant use of pemigatinib and moderate CYP3A inhibitors is predicted to increase pemigatinib exposure by approximately 50% to 80%. Avoid concomitant use. If concomitant use with a strong or moderate CYP3A inhibitor cannot be avoided reduce the pemigatinib dose from 13.5 mg to 9 mg or from 9 mg to 4.5 mg. If concomitant use of a strong or moderate CYP3A inhibitor is discontinued, increase the pemigatinib dose (after 3 plasma half-lives of the CYP3A inhibitor) to the dose that was used before starting the inhibitor1.
Why it happens (mechanism)
Inhibition of CYP3A-mediated pemigatinib metabolism
Literature reports
2 reports — tap to read
a) Concomitant use of pemigatinib and itraconazole, a strong CYP3A inhibitor, increased pemigatinib Cmax by 17% and increased AUC by 88% following a single oral pemigatinib 4.5 mg dose 1
b) Concomitant use of pemigatinib and moderate CYP3A inhibitors is predicted to increase pemigatinib exposure by approximately 50% to 80% 1.
Common questions
Can I take Letermovir Injection and Pemigatinib together?
Increased pemigatinib exposure and increased risk and severity of adverse reactions Always confirm with your pharmacist or prescriber before making any change.
How serious is the Letermovir Injection and Pemigatinib 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 Pemigatinib 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: PEMAZYRE(TM) oral tablets, pemigatinib oral tablets. Incyte Corporation (per FDA), Wilmington, DE, 2020. DailyMed
Keep reading about Letermovir Injection
Keep reading about Pemigatinib
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:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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