Abametapir and Efavirenz: 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 recordEfavirenz
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 to treat head lice. Even though you put it on your scalp, a little 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 efavirenz, an HIV medicine.
With that enzyme slowed down, efavirenz could build up higher than usual, which may raise the chance of side effects like dizziness, sleep problems, or vivid dreams. This is a theoretical concern based on how the drug works, not on real-world reports, but it is taken seriously. The good news is your care team can plan the timing of these medicines so you stay safe.
Mechanism: Abametapir is a CYP3A4 inhibitor. Efavirenz is a CYP3A4 substrate (and neither is a prodrug requiring 3A4 activation), so inhibition is expected to increase efavirenz exposure (AUC/Cmax).
- Direction: increased efavirenz levels, greater risk of CNS effects (dizziness, abnormal dreams, insomnia).
- Onset: rapid.
- Evidence: theoretical, based on the known inhibitory profile of topical abametapir.
- Magnitude: not quantified.
Management: Avoid CYP3A4 substrates, including efavirenz, for 2 weeks after a single abametapir application. If concurrent use cannot be avoided, avoid abametapir and consider an alternative lice treatment.
What happens
Increased exposure of CYP3A4 substrate
Interaction Deep Dive
For a period of 2 weeks following abametapir application, refrain from using CYP3A4 substrates. Should this be impractical, then abametapir itself should not be used 1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism by abametapir
How to manage this interaction
This is a manageable situation, and your care team has clear options.
- Timing matters: The guidance is to avoid CYP3A4-metabolized medicines like efavirenz for about 2 weeks after applying abametapir lotion.
- Do not stop your HIV medicine on your own. Efavirenz is important therapy, so keep taking it as prescribed.
- Before using abametapir for lice, tell your pharmacist or prescriber that you take efavirenz. They may recommend a different lice treatment instead.
- Watch for increased dizziness, drowsiness, or vivid dreams and report these.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Abametapir and Efavirenz together?
Abametapir lice lotion can briefly raise efavirenz levels by blocking the enzyme that clears it, so tell your care team before using it; they will likely pick a different lice treatment or adjust timing. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Abametapir and Efavirenz 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 Efavirenz interaction managed?
This is a manageable situation, and your care team has clear options. Timing matters: The guidance is to avoid CYP3A4-metabolized medicines like efavirenz for about 2 weeks after applying abametapir lotion. Do not stop your HIV medicine on your own. Efavirenz is important therapy, so keep taking it as prescribed. Before using abametapir for lice, tell your pharmacist or prescriber that you take ef… 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 Efavirenz 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 Efavirenz
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