Cyclophosphamide (Cytoxan®, Neosar®) for Dogs and Cats

Overview of Cyclophosphamide for Dogs

Cyclophosphamide, also known as Cytoxan® or Neosar®, is one of a number of drugs that is effective in treating some cancers and tumors in dogs and cats. Cyclophosphamide is also used to suppressive the immune system for a variety of conditions.
Cyclophosphamide also suppresses the immune system and is commonly used in the treatment of autoimmune diseases.
Cyclophosphamide belongs to a class of drugs known as nitrogen mustard-based agents.
Cyclophosphamide interferes with DNA and other genetic factors within rapidly growing cells, leading to cell death.
Cyclophosphamide is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.
This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug.

Due to its effect on rapidly growing cells, cyclophosphamide is used in the treatment of various types of cancers. One common example is its use in a multiple-drug treatment plan for lymphoma in dogs.
Cyclophosphamide is also used in the treatment of specific immune system disorders. It is frequently prescribed when other treatments, such as prednisone, fail to work satisfactorily.

While generally safe and effective when prescribed by a veterinarian, cyclophosphamide can cause side effects in some dogs and cats.
Cyclophosphamide should not be used in animals with known hypersensitivity or allergy to the drug.
Because of its effects on rapidly growing cells, cyclophosphamide should be used with caution in animals with bone-marrow problems. Formation of white cells and other blood cells can be depressed with high doses.
Due to effects on the immune system and bone marrow, the drug should not be used when there is a serious infection.
Use caution when giving this drug to animals with kidney or liver problems.
Cyclophosphamide may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with cyclophosphamide. Such drugs include phenobarbital, allopurinol and digoxin.
Some of the adverse effects of cyclophosphamide treatment include vomiting, diarrhea, loss of appetite, bladder irritation (sterile cystitis) and bone-marrow suppression.
With bone-marrow suppression, dangerously low red blood cell counts can lead to the need for blood transfusions.

Medication should never be administered without first consulting your veterinarian.
For cancer treatment, cyclophosphamide is dosed at 0.5 to 1 mg per pound (1 to 2 mg/kg) once daily.
For treatment of immune disorders, cyclophosphamide is dosed at 1 mg per pound (2.2 mg/kg) per day.
The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.