Palladia, the new drug from Pfizer.

07/22/2009
There has been much buzz and excitement surrounding FDA approval of Palladia (Pfizer), which is new drug licensed for treatment of mast cell tumors in dogs. Palladia is in the family of drugs called tyrosine kinase inhibitors which have been used in the treatment of cancer in humans for many years. Not only does Palladia provide veterinarians with a novel way to treat some of the more difficult mast cell tumors, it represents a commitment from drug companies like Pfizer to developing therapies specific for our veterinary cancer patients. Palladia is currently available only through veterinary oncologists and other selected specialists.

What dogs would benefit from Palladia?
Patients that would benefit from Palladia are generally the same group that would benefit from chemotherapy. This would include dogs with metastatic or non-resectable mast cell tumors, dogs with multiple mast cell tumors, dogs with recurrent mast cell tumors and dogs with "high risk" mast cell tumors. "High risk" mast cell tumors are those that have a significant chance of spreading to other areas of the body. Palladia is NOT indicated for use in dogs that can be treated successfully with surgery with or without radiation therapy.
Although Palladia has been shown to be effective for a significant percentage of dogs with mast cell tumors, it is not effective for all dogs and does not supersede the use of chemotherapy. Until more is known about the drug, standard chemotherapy (prednisone, vinblastine, CCNU) is still recommended as the first option. Currently Palladia is recommended for those dogs who have failed chemotherapy. It is not recommended that Palladia be given simultaneously with chemotherapy although it may be an option to decrease the size of the tumor first with chemotherapy and then use Palladia as maintenance. As with chemotherapy, there is the potential that a tumor could become resistant to the drug and other treatments may be required.

What is the likelihood of benefit from this drug?
In dogs that have measurable mast cell tumors, about 40% of them will have a response to this drug. This can be either a complete response or a partial response (more likely). In addition, 20% of dogs may have stabilization of their disease which can be of benefit for some patients. These responses lasted about 12-18 weeks. Palladia has not been studied in dogs that have only microscopic amounts of disease although it is likely that patients will benefit from treatment in this situation.

What are the side effects from the drug?
Although Palladia is a novel method of treating mast cell tumors and is not a chemotherapy drug, there are still potential side effects from this drug that may require treatment or dose adjustments. Dogs that are already ill from mast cell cancer may be at higher risk of side effects. It is important that you let your veterinarian know what medications your pet is on as some medications can increase the risk of side effects. If your pet receives Palladia, is it also very important that you work closely with your veterinary oncologist to identify side effects early. The most significant side effect with this drug has been gastrointestinal problems including diarrhea, loss of appetite and weight loss. In most cases, these side effects can be effectively treated with medications but need to be addressed promptly to prevent more serious consequences. Some dogs will need to have a treatment break and/or modifications in the dose or dosing schedule. Palladia has also been shown to cause a decrease in the normal white blood cell count and it has been recommended that CBC's (complete blood count) be monitored initially on a weekly basis. Less common side effects have included lameness, muscle cramps, changes in kidney function, changes in protein levels or pigmentation changes.

How is the drug given?
Palladia is an oral drug that is given every other day at home. Due to the type of drug that Palladia is, it is likely that chronic treatment (6-12+ months) is needed for those dogs that respond to Palladia. Standard pre-cautions should be taken when handling Palladia. Tablets should not be broken or crushed and wash your hands well after handling the drug or wear gloves when administering the drug. Women that are pregnant, nursing or planning to become pregnant should not handle the drug and the drug should be safely stored out of the reach of children.

What type of follow-up will be needed?
We recommend weekly rechecks with a CBC (complete blood count) for the first 6 weeks. We also recommend a chemistry profile 4-6 weeks after starting treatment. During that period we will be able to determine if a dog is going to have significant side effects to the drug and if there will be a response to the drug. After the first 6 weeks, rechecks will most likely be once every 6-8 weeks.


To locate a veterinary oncologist in your area, go the ACVIM website: www.ACVIM.org.