Ifosfamide Injection and Thiotepa: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Ifosfamide Injection
Thiotepa
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.
What happens
Increased CYP2B6 substrates exposure
Interaction Deep Dive
Concomitant use of thiotepa and CYP2B6 substrates may increase the exposure of CYP2B6 substrates1. Coadministration of thiotepa (a potent CYP2B6 inhibitor) may result in increased plasma concentrations of CYP2B6 substrates. In a pharmacokinetic study, CYP2B6 activity was inhibited by 78.1% +/- 0.2% when thiotepa was used with S-mephenytoin (CYP2B6 substrate probe) in human liver microsomes. Due to the potential for higher levels of the CYP2B6 substrate, coadministration should be done cautiously 2.
Why it happens (mechanism)
Inhibition of CYP2B6-substrate metabolism by thiotepa
Literature reports
1 report — tap to read
a) In a pharmacokinetic study using S-mephenytoin as a CYP2B6 substrate probe with thiotepa in human liver microsomes, CYP2B6 activity was inhibited by 78.1% +/- 0.2%. Thiotepa in the range of 50 to 100 mcmol inhibited the activity of CYP2B6 by 78% and 83%, respectively, with a plateau effect seen around 50 mcmol 2.
Common questions
Can I take Ifosfamide Injection and Thiotepa together?
Increased CYP2B6 substrates exposure Always confirm with your pharmacist or prescriber before making any change.
How serious is the Ifosfamide Injection and Thiotepa interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
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 Injection or Thiotepa 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 anything you'd monitor while I'm on both?
References (2)
- Product Information: TEPYLUTE intravenous injection, thiotepa intravenous injection. Shorla Oncology Inc (per FDA), Cambridge, MA, 2024. DailyMed
- Rae JM, Soukhova NV, Flockhart DA, et al: Triethylenethiophosphoramide is a specific inhibitor of cytochrome P450 2B6: implications for cyclophosphamide metabolism. Drug Metab Dispos 2002; 30(5):525-530. PubMed
Keep reading about Ifosfamide Injection
Keep reading about Thiotepa
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