By Rania Gollakner, BS, DVM, MPH

What is imatinib?

Imatinib (brand names: Gleevac) is a kinase inhibitor chemotherapy used to treat myeloid leukemia in humans, mast cell tumors, hypereosinophilic syndrome, fibrosarcoma, and squamous cell carcinoma in dogs and cats. Its use in cats and dogs to treat various types of cancers is ‘off label’ or ‘extra-label’. Many drugs are commonly prescribed for off label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully as their direction 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 and wear gloves when administering this medication. 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. Pregnant women should not handle this medication. Imatinib should take effect within 1 to 2 hours, however, effects may not be noted outwardly and laboratory tests may need to be done to evaluate this medication’s efficacy.

What if I miss giving my pet the medication?

If you miss a dose, give it when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Studies in animals are limited for this medication and therefore information regarding 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, or stomach pain. Serious side effects include 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, or gastrointestinal ulcers. Because this medication is a long-lasting drug, the effects may occur after the pet has stopped taking the drug.

Are there any risk factors for this medication?

Do not use in pets that are pregnant or nursing. Use cautiously in pets with liver or kidney disease. Dose reductions may be necessary in these cases.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with imatinib: antifungals, antivirals, benzodiazepines, calcium channel blockers, clarithromycin, cyclosporine, erythromycin, fentanyl, iron supplements, phenytoin, quinidine, rifampin, tacrolimus, and warfarin. Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

Blood cell counts, blood chemistry profiles, urinalysis, and fecal tests will likely be monitored. Your veterinarian may monitor your pet to be sure that the medication is working. Monitor for side effects.

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.

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.

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