Imatinib

What is imatinib?

Imatinib (brand name: Gleevac®) is a kinase inhibitor chemotherapy used to treat certain types of cancer in humans. In dogs and cats, it may be used to treat mast cell tumors, hypereosinophilic syndrome, fibrosarcoma, and squamous cell carcinoma.

Its use in cats and dogs to treat various types of 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 imatinib given?

• Imatinib is given by mouth in the form of a tablet.
• Give with a full meal and water.
• On the day your pet receives this medication, and for a few days afterwards, use gloves when handling all bodily waste such as urine, feces, cat litter, blood, or vomit. Throw this waste in a sealable plastic bag, then seal the bag and the gloves in another sealable bag. Dispose in the regular trash.

Imatinib is considered a hazardous drug, so it is essential to avoid accidental exposure. Wear gloves when handling the medication and do not handle it if you are pregnant or nursing. If your pet vomits after giving this drug, wear gloves while cleaning up.

Imatinib should take effect within 1 to 2 hours, however, effects may not be noted outwardly, so laboratory tests may be needed to evaluate this medication’s effectiveness.

What if I miss giving my pet the medication?

If you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.

Are there any potential side effects?

Studies in animals are limited for imatinib, so information about side effects is also limited. In humans, side effects include:

• Fluid retention/swelling
• Low blood cell counts
• Nausea
• Vomiting
• Muscle cramps
• Muscle pain
• Diarrhea
• Skin rash
• Lack of energy
• Stomach pain

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

• Heart failure (characterized by cough, difficulty breathing or increased breathing rate)
• Liver failure (characterized by lack of appetite, vomiting, or yellowing of the skin)
• Excessive bleeding
• Fever
• Gastrointestinal ulcers

Because this medication is a long-lasting drug, the effects may occur after the pet has stopped taking the drug.

This short-acting medication should stop working within 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 imatinib in pets that:

• Are pregnant or nursing

USE WITH CAUTION in pets that:

• Have liver or kidney disease (a reduced dose may be necessary in these cases)

Are there any drug interactions I should be aware of?

Several medications should be used with caution when given with imatinib, including:

• Antifungals
• Antivirals
• Benzodiazepines
• Calcium channel blockers
• Cyclosporine
• Iron supplements

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 will likely monitor blood cell counts, blood chemistry profiles, urinalysis, and fecal test.
• 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 imatinib?

• Store this medication at 77°F (25°C) with excursions permitted between 59°F and 86°F (15°C and 30°C).
• Protect from moisture.
• Keep the container out of reach of children and pets.

What should I do in case of 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.