Ifosfamide 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 recordIfosfamide
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, but it can slow down a liver enzyme (called CYP3A4) for a couple of weeks after you use it. Ifosfamide is a chemotherapy medicine that actually needs that same enzyme to switch it into its active form.
So the concern here is a bit different from a typical interaction. Slowing the enzyme could change how much active chemo your body makes, and it could also let other byproducts build up. This is based on theory, not real cases, but because chemo is powerful, it is taken seriously. The good news is your cancer care team can plan around it and time things safely.
Mechanism: Abametapir inhibits CYP3A4 for up to ~2 weeks post-application. Ifosfamide is a prodrug requiring CYP3A4-mediated 4-hydroxylation for activation, so this interaction is not a simple parent-drug accumulation.
- Direction: CYP3A4 inhibition may reduce bioactivation to the active alkylating species while increasing exposure to the parent and potentially altering the chloroacetaldehyde/neurotoxic metabolite balance.
- Evidence: Theoretical; onset rapid.
- Severity: Major.
- Management: Avoid CYP3A4 substrates within 2 weeks of abametapir; if unavoidable, avoid abametapir. Coordinate with oncology; monitor efficacy and toxicity closely if co-exposure occurs.
What happens
Increased exposure of CYP3A4 substrate
Interaction Deep Dive
For a period of 2 weeks following abametapir application, refrain from administering CYP3A4 substrates. Where such avoidance cannot be achieved, do not use abametapir1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism by abametapir
How to manage this interaction
The documented guidance is to keep these two apart in time:
- Avoid overlap: CYP3A4 substrates like ifosfamide are generally avoided within 2 weeks after abametapir is applied. If that timing cannot be arranged, the abametapir may be avoided instead.
- Do not change anything on your own. Keep taking your medicines as prescribed and let your care team make the plan.
- Tell your team about any lice treatment (even over-the-counter or one you used recently) before a chemotherapy cycle.
- Your oncology team can time treatment and monitor you more closely to keep this safe.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Ifosfamide and Abametapir together?
Abametapir can block the enzyme that activates and clears ifosfamide for about two weeks, so avoid using them close together and tell your oncology team about any recent lice treatment. They will time your chemo safely. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Ifosfamide 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 Ifosfamide and Abametapir interaction managed?
The documented guidance is to keep these two apart in time: Avoid overlap: CYP3A4 substrates like ifosfamide are generally avoided within 2 weeks after abametapir is applied. If that timing cannot be arranged, the abametapir may be avoided instead. Do not change anything on your own. Keep taking your medicines as prescribed and let your care team make the plan. Tell your team about any lice treatm… 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 Ifosfamide 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 Ifosfamide
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