Selumetinib and Abametapir: 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 recordSelumetinib
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 it is only applied to the scalp, some of it gets into your body and can briefly block a liver enzyme (called CYP3A4) that helps break down other medicines. Selumetinib (Koselugo) is one of those medicines. If the enzyme is slowed down, selumetinib can build up to higher levels than expected, which may raise the chance of side effects.
This concern is based on how the drugs work rather than on real cases, but it is taken seriously. The good news is that your care team can plan the timing so this does not become a problem. Please talk with your doctor or pharmacist before using both.
Mechanism: Abametapir is a potent CYP3A4 inhibitor; even topical application produces systemic exposure sufficient to reduce CYP3A4-mediated clearance of substrates such as selumetinib. Neither drug is a prodrug, so inhibition increases selumetinib exposure (AUC/Cmax), raising toxicity risk.
- Direction: increased selumetinib exposure
- Onset: rapid
- Severity: major
- Evidence: theoretical (mechanism-based)
Management: Avoid CYP3A4 substrates, including selumetinib, within 2 weeks of abametapir application. If concurrent use is unavoidable, avoid abametapir and select an alternative lice treatment. Coordinate timing and any monitoring through the care team.
What happens
Increased exposure of CYP3A4 substrate
Interaction Deep Dive
For a period of 2 weeks following the application of abametapir, refrain from using CYP3A4 substrates. Where that cannot be done, 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 usually be handled safely by planning around the timing.
- Keep taking selumetinib (Koselugo) as prescribed unless your care team tells you otherwise.
- Abametapir's enzyme-blocking effect can last a while, so the usual advice is to avoid CYP3A4 medicines like selumetinib for about 2 weeks after applying abametapir.
- If you cannot separate them that way, your team may recommend a different lice treatment instead of abametapir.
Before using abametapir, let your pharmacist or prescriber know you take selumetinib so they can choose the safest option and monitor you more closely if needed.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Selumetinib and Abametapir together?
Abametapir can raise selumetinib levels and side-effect risk, so avoid selumetinib for about 2 weeks after applying abametapir; if that is not possible, use a different lice treatment. Check with your pharmacist or doctor first. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Selumetinib and Abametapir 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 Selumetinib and Abametapir interaction managed?
Both of these can usually be handled safely by planning around the timing. Keep taking selumetinib (Koselugo) as prescribed unless your care team tells you otherwise. Abametapir's enzyme-blocking effect can last a while, so the usual advice is to avoid CYP3A4 medicines like selumetinib for about 2 weeks after applying abametapir. If you cannot separate them that way, your team may recommend a diff… 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 Selumetinib or Abametapir 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 Selumetinib
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