Major Uses

Cyclophosphamide is a powerful immunosuppressant used in conjunction with other drugs to treat serious illnesses that have not responded to other methods of treatment. These illnesses include lymphoma, feline infectious peritonitis, and polyarthritis glomerulephritis.

On a short-term basis, it may also be used to treat severe rheumatoid arthritis, pemphigus complex, and vasculitis. Cyclophosphamide is useful in treating immune related diseases because it suppresses white blood cell production and inhibits newly formed unhealthy cells from developing properly. Although the medication inhibits unhealthy cells from forming properly, it also inhibits healthy cells as well, making it a potent drug that should always be used with caution.

Common Precautions

Leukopenia (lowered white blood cell count) and thrombocytopenia (lowered platelets in blood) can be exacerbated by this medication and animals already suffering from these conditions should be treated with caution. Animals with a greater risk of infection, along with those that have decreased liver or kidney function, should also be monitored closely while taking cyclophosphamide.

Cyclophosphamide causes the suppression of bone marrow production, a condition called myelosuppression. Myelosuppression is the dose-limiting side effect. Allopurinal and thiazide diuretics may increase myelosuppression when taken at the same time as cyclophosphamide. This medication may also cause ulcers in the bladder's lining, which leads to painful and bloody urination.

Nausea, vomiting, diarrhea, and anorexia are common gastrointestinal side effects. Cats are more likely to develop anorexia, while dogs with continuously growing hair like poodles and bichon frises, are more susceptible to alopecia (hair loss).

This medication crosses the placenta and is found in breast milk, so pregnant or nursing animals should not be given cyclophosphamide unless the positive benefits outweigh the negative risks.

If the patient displays signs of weakness, lack of energy, lethargy, infection, bruising, or bleeding, their veterinarian should be contacted immediately. Overdose should be aggressively responded to with gut-emptying techniques.


Cyclophosphamide in tablet form should be stored at room temperature (59 to 86 degrees Fahrenheit) in a tightly closed container away from sunlight. Solutions prepared with water can be stored up to six days if kept in a refrigerator.

Cyclophosphamide should not be stored in a bathroom, near the kitchen sink, or other damp places because it breaks down quickly if exposed to heat or moisture.


Since this medication can cause immunosuppression in humans, gloves should be worn while administering cyclophosphamide and hands should be washed after.

The dosage for immunosuppression in canines is 2.5mg/kg every 48 hours. The dose should be given in the morning hours so the medication does not sit in the bladder overnight.

Consistency is the most important variable in the success of this medication. If a dose is missed, the dose should be given as soon as it is remembered unless it is within a few hours of the next regularly scheduled dose. In that case, the missed dose may be skipped and the dosing schedule should resume as before.

It is very important this medication is never split, crushed, or altered in any way, as this may result in an unpredictable amount of cyclophosphamide getting into the animal's blood stream.

This information is for general reference only and should not be used for the diagnosis or treatment of any condition of your pet. It's intended as a general reference, this information may not include all possible uses, precautions, directions, reactions (including allergic), drug interactions, or withdrawal times. Always consult your local veterinarian and have your pet examined for any advice concerning the diagnosis and treatment of your pet, including which products and doses are most appropriate. Any trademarks are the property of their respective owners. VetDepot is not a pharmacy. All prescription products are dispensed by our Pharmacy Partner. Article last updated 2/2014.