Cyclophosphamide

What is this medication for?

• Combination chemotherapy (lymphoma/CHOP, leukemias, carcinomas, sarcomas); immunosuppression (SLE, pemphigus, rheumatoid arthritis, glomerulonephritis, IMHA — controversial benefit with prednisone)
• Metronomic low-dose + piroxicam — delays local recurrence of incompletely resected soft tissue sarcomas
• Slows FIP progression (2–4 mg/kg 4×/wk)

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

• Hemorrhagic cystitis is the cyclophosphamide signature: acrolein sits in the bladder — push fluids, encourage voiding, never dose at bedtime without a pee break; cystitis risk forces drug holidays or switching to chlorambucil.
• Tablet-core structure: compounding or the whole-tablet weekly-total trick beats inaccurate splitting.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• Myelosuppression (Dose-limiting)
• stomach/intestinal (loss of appetite, vomiting, diarrhea) (Common)
• Sterile hemorrhagic cystitis (Acrolein injury — encourage frequent voiding/urine dilution; more common with chronic by mouth use)
• Alopecia (Poodles, Old English Sheepdogs and similar coats)

Worth a phone call to your veterinarian

• Any new symptom that worries you.

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Trouble breathing, collapse, seizures, severe vomiting or diarrhea, facial swelling, or pale gums

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Prior anaphylaxis; pregnancy
• has or has had: Leukopenia/low platelet counts, prior radiotherapy, hepatic/renal impairment, active infection (dangerous immunosuppression)

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Other myelosuppressives
  • Doxorubicin
  • Allopurinol
  • Barbiturates, chloramphenicol
  • NSAIDs/piroxicam

Storage and handling

Tablets: active drug is inside an inner core tablet — splitting/crushing is inaccurate; compound <25 mg doses or convert to whole-25 mg-tablet weekly totals (Mackin method). Chemo gloves for handling.

Good to know

• Hemorrhagic cystitis is the cyclophosphamide signature: acrolein sits in the bladder — push fluids, encourage voiding, never dose at bedtime without a pee break; cystitis risk forces drug holidays or switching to chlorambucil.
• Prodrug design: hepatic activation required — hepatic dysfunction alters both toxicity and efficacy.
• Metronomic dosing (10 mg/m² daily + piroxicam) is anti-angiogenic low-toxicity chemo — a different philosophy from MTD pulses.
• Tablet-core structure: compounding or the whole-tablet weekly-total trick beats inaccurate splitting.