Cyclophosphamide

What is cyclophosphamide?

Cyclophosphamide (brand names: Cytoxan®, Neosar®, Procytox®) is an antineoplastic, anticancer medication used in combination with other medications to treat lymphomas, leukemias, carcinomas, and sarcomas. It was previously also used to treat immune-mediated diseases, but newer medications with fewer side effects are now available and are preferred in these cases.

Its use in cats, dogs, horses, and rabbits to treat certain cancers is off label (extra label). Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.

How is cyclophosphamide given?

• Cyclophosphamide is given by mouth in the form of a capsule or a specially compounded liquid. It can also be given as an injection in the hospital.
• Measure liquid forms extremely carefully.
• Give cyclophosphamide with food to minimize stomach upset.
• After dosing, encourage your pet to drink water and to urinate frequently to decrease the risk of bladder toxicity. Cyclophosphamide is frequently given with diuretics or steroids to help increase water consumption and elimination.
• Follow your veterinarian’s directions carefully regarding any medications that should be administered with cyclophosphamide doses.

Cyclophosphamide is considered a hazardous drug.

• Always wear gloves when giving this medication, and do not reuse gloves.
• Do not allow the medication to contact your skin, eyes, or mouth.
• On the day you give this medication and for a few days afterward, wear gloves when handling your pet’s waste; seal the gloves and any waste in a plastic bag before disposing in the garbage.
• Do not allow your pet to lick your skin for an hour or two after oral administration; if this occurs, wash the area thoroughly with soap and water.
• If you are pregnant, do not handle this medication or the pet’s waste or bodily fluids.

This medication can take a few weeks before full effects are noted, but side effects can occur immediately. Gradual improvements are usually noticeable after a few days.

What if I miss giving my pet the medication?

If you miss a dose, contact your veterinarian for instructions, as this medication must be dosed very carefully.

Are there any potential side effects?

Cyclophosphamide may cause the following side effects:

• Hair loss or changes in hair coat

Serious adverse reactions may occur. If any of the following signs develop, stop giving cyclophosphamide and contact your veterinarian immediately:

• Infections
• Bleeding or bruising
• Lack of appetite, vomiting, and diarrhea
• Blood in the urine
• Depression
• Lung damage, difficulty breathing
• Dizziness, seizures, or tremors

Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately. This moderate-acting medication should stop working in a few days, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

DO NOT USE cyclophosphamide in pets that:

• Are allergic to it
• Have urinary obstruction
• Have infection
• Have bone marrow dysfunction
• Cannot be monitored regularly during treatment
• Pregnant animals, except as a last resort
• Lactating animals, unless necessary (use a milk replacer)

USE WITH CAUTION in pets that:

• Have liver or kidney disease
• Are receiving radiation
• Are susceptible to infections (such as diabetic or geriatric pets)

Are there any drug interactions I should be aware of?

Several medications should be used with caution when given with cyclophosphamide:

• Allopurinol
• Cardiotoxic drugs
• Immunosuppressants
• Myelosuppressive agents
• Ondansetron
• Phenobarbital
• Phenytoin
• Thiazide diuretics
• Vaccines (live)
• Warfarin

This medication may also affect certain laboratory tests such as uric acid and antigenic skin tests.

Certain medications may interact with cyclophosphamide, so be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment.

Is any monitoring needed with this medication?

• Your veterinarian must regularly monitor blood cell counts, kidney function tests, and urine tests for toxicity.
• Your veterinarian will let you know when and how they want to reassess your pet to ensure the medication is working and not causing side effects.
• At home, monitor for any side effects such as those noted above. If any occur, stop using the medication and contact your veterinarian.

How do I store cyclophosphamide?

• Store cyclophosphamide capsules between 68°F and 77°F (20°C and 25°C) with brief excursions between 59°F and 86°F (15°C and 30°C) allowed.
• Store liquid forms in the refrigerator, in a glass container, for up to 14 days or as directed by the compounding pharmacy.
• Protect from light.

What should I do in case of emergency?

Any overdose, no matter how small, should be considered an emergency. If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility. Be prepared to provide information about the product and your pet’s weight and symptoms.