Abametapir and Larotrectinib: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jun 30, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Abametapir
No brand names on recordLarotrectinib
No brand names on record
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.
Abametapir is a lotion used on the scalp to treat head lice. Even though it's applied to the skin, some of it can get into your body and briefly block a liver enzyme called CYP3A4. That enzyme is one of the main ways your body breaks down larotrectinib, your cancer medicine.
When that enzyme is slowed down, larotrectinib can build up higher than expected, which may increase the chance of side effects. This is based on how the drugs are expected to behave, so it's a caution rather than something proven. The good news is your care team can plan around this by spacing out the medicines or choosing a different lice treatment. Don't change anything yourself, just check with your pharmacist or doctor.
Mechanism: Abametapir is a potent CYP3A4 inhibitor; larotrectinib is a CYP3A4 substrate. Inhibition reduces larotrectinib metabolism, increasing its exposure (AUC/Cmax) and raising the risk of concentration-dependent toxicity. Neither agent is a prodrug requiring CYP3A4 activation, so the effect is a straightforward exposure increase.
- Direction: increased larotrectinib effect/toxicity
- Onset: rapid
- Evidence: theoretical
- Magnitude: not quantified; inhibition can persist for up to ~2 weeks after a single abametapir application
Management: Avoid CYP3A4 substrates, including larotrectinib, within 2 weeks of abametapir application. If concomitant use is unavoidable, avoid abametapir. Consider larotrectinib dose adjustment and closer monitoring if co-use cannot be prevented.
What happens
Increased exposure of CYP3A4 substrate
Interaction Deep Dive
Refrain from administering CYP3A4 substrates for a period of 2 weeks following abametapir application. Should this prove impractical, abametapir itself should not be used 1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism by abametapir
How to manage this interaction
What your care team may do:
- Try to avoid using abametapir while you are on larotrectinib, since its effect on the liver enzyme can last up to about 2 weeks.
- Consider a different head lice treatment that doesn't cause this interaction.
- If both must be used, they may adjust and individualize your larotrectinib dose and watch you more closely for side effects.
What you should do:
- Keep taking your larotrectinib as prescribed, don't stop on your own.
- Before using any lice treatment, tell your pharmacist or prescriber you take larotrectinib so they can pick the safest option.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Abametapir and Larotrectinib together?
Abametapir can block the enzyme that clears larotrectinib, letting it build up, so avoid using them together within 2 weeks; ask your pharmacist about a safer lice treatment. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Abametapir 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 "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How is the Abametapir and Larotrectinib interaction managed?
What your care team may do: Try to avoid using abametapir while you are on larotrectinib, since its effect on the liver enzyme can last up to about 2 weeks. Consider a different head lice treatment that doesn't cause this interaction. If both must be used, they may adjust and individualize your larotrectinib dose and watch you more closely for side effects. What you should do: Keep taking your lar… Management is individual — always follow your own care team's guidance.
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 Abametapir 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: XEGLYZE(TM) topical lotion, abametapir topical lotion. Dr Reddy’s Laboratories Inc (per FDA), Princeton, NJ, 2020. DailyMed
Keep reading about Abametapir
Keep reading about Larotrectinib
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