Cyclophosphamide and Indomethacin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Indomethacin
Cyclophosphamide
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
Fluid retention
Interaction Deep Dive
In a case report, the concurrent use of cyclophosphamide and indomethacin resulted in fluid retention. Indomethacin inhibits prostaglandins (PgE2 & PgI2) which maintains renal flow, while cyclophosphamide has been demonstrated to increase antidiuretic hormone (ADH)12.
Why it happens (mechanism)
Increase of inappropriate antidiuretic hormone (ADH) secretion
Common questions
Can I take Cyclophosphamide and Indomethacin together?
Fluid retention Always confirm with your pharmacist or prescriber before making any change.
How serious is the Cyclophosphamide and Indomethacin interaction?
It is rated minor. Usually limited clinical impact.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Cyclophosphamide or Indomethacin 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)
- McCarthy JT, Torres VE, Romero JC, et al: Acute intrinsic renal failure induced by indomethacin: role of prostaglandin synthetase inhibition. Mayo Clin Proc 1982; 57:289-296. DOI
- Webberley MJ & Murray JA: Life-threatening acute hyponatraemia induced by low dose cyclophosphamide and indomethacin. Postgrad Med J 1989; 65:950-952. PubMed
Keep reading about Indomethacin
Keep reading about Cyclophosphamide
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