Abametapir and Lapatinib: 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 recordLapatinib
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 to treat head lice. Even though you only put it on your scalp, a little gets into your body and can briefly block a liver enzyme called CYP3A4. That enzyme is one of the main ways your body breaks down lapatinib (Tykerb), a cancer medicine.
If the enzyme is blocked, lapatinib can build up in your blood and cause stronger side effects, like diarrhea or heart rhythm changes. This is a caution based on how the drugs work, not something proven in studies. The good news is your care team can manage the timing of these two medicines, so please check with your pharmacist or doctor before using both.
Mechanism: Abametapir inhibits CYP3A4. Lapatinib is a CYP3A4 substrate, so its metabolism is reduced, increasing lapatinib exposure (AUC/Cmax).
- Direction: Increased lapatinib effect and toxicity risk (diarrhea, hepatotoxicity, QT prolongation).
- Onset: Rapid; enzyme inhibition can persist, so caution extends ~2 weeks post-application.
- Evidence: Theoretical, based on abametapir's known CYP3A4 inhibition.
- Severity: Major.
Management: Avoid CYP3A4 substrates such as lapatinib within 2 weeks after abametapir application. If concurrent therapy cannot be avoided, avoid using abametapir. Consider alternative lice treatments and monitor for lapatinib-related toxicity if exposure occurred.
What happens
Increased exposure of CYP3A4 substrate
Interaction Deep Dive
Refrain from administering CYP3A4 substrates for a period of 2 weeks following the application of abametapir. When avoiding these substrates is not practical, do not use abametapir instead1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism by abametapir
How to manage this interaction
Both of these can be used safely with the right plan, so keep taking your prescribed lapatinib and talk to your care team before starting abametapir lice treatment.
- The label advises avoiding CYP3A4 substrates like lapatinib for 2 weeks after applying abametapir. If that separation is not possible, the guidance is to avoid the abametapir instead.
- Your team may suggest a different lice treatment that does not cause this interaction.
- Ask your pharmacist or oncologist how to time these medicines, and report any new diarrhea, unusual tiredness, or heartbeat changes.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Abametapir and Lapatinib together?
Abametapir can raise lapatinib levels by blocking its breakdown, so avoid lapatinib for 2 weeks after using abametapir; if you cannot separate them, avoid the abametapir and ask your care team about a different lice treatment. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Abametapir and Lapatinib 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 Lapatinib interaction managed?
Both of these can be used safely with the right plan, so keep taking your prescribed lapatinib and talk to your care team before starting abametapir lice treatment. The label advises avoiding CYP3A4 substrates like lapatinib for 2 weeks after applying abametapir. If that separation is not possible, the guidance is to avoid the abametapir instead. Your team may suggest a different lice treatment th… 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 Lapatinib 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 Lapatinib
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.
Check another combination
Our instant two-drug interaction checker is almost here.
Still have questions about this combination?
Every question gets a real answer from a licensed pharmacist — free, and usually within a day.
Ask the pharmacist