Nafcillin Injection and Larotrectinib: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Larotrectinib
No brand names on recordNafcillin 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
Reduced larotrectinib exposure
Interaction Deep Dive
Concomitant use of larotrectinib with a moderate CYP3A4 inducer may decrease larotrectinib plasma concentrations, which may decrease the efficacy of larotrectinib. For coadministration with a moderate CYP3A4 inducer, double the dose of larotrectinib. After the moderate CYP3A4 inducer has been discontinued for 3 to 5 elimination half-lives, resume the dose of larotrectinib that was used prior to initiating the inducer1.
Why it happens (mechanism)
Induction of CYP3A4-mediated metabolism of larotrectinib
Literature reports
1 report — tap to read
a) Coadministration of larotrectinib with efavirenz (a moderate CYP3A4 inducer) is predicted to decrease steady state AUC and Cmax of larotrectinib by 72% and 60%, respectively, compared to administration of larotrectinib alone 1.
Common questions
Can I take Nafcillin Injection and Larotrectinib together?
Reduced larotrectinib exposure Always confirm with your pharmacist or prescriber before making any change.
How serious is the Nafcillin Injection and Larotrectinib 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 Nafcillin Injection or Larotrectinib 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: VITRAKVI(R) oral capsules, oral solution, larotrectinib oral capsules, oral solution. Bayer HealthCare Pharmaceuticals Inc (per FDA), Whippany, NJ, 2022. DailyMed
Keep reading about Larotrectinib
Keep reading about Nafcillin Injection
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