Chemotherapy in Veterinary Medicine

By November 14, 2018Articles

by Edwin Brodsky, DVM, Diplomate ACVIM (Oncology)

Chemotherapy in Veterinary Medicine

When people think of chemotherapy they generally assume horrible side effects such as severe vomiting, diarrhea, weight loss, lethargy and an overall poor quality of life.  However, in veterinary medicine, the majority of patients (80-85%) have minimal to no side effects when receiving chemotherapy. There are a couple of reasons for this result. First, in veterinary medicine, we do not use the large doses and aggressive chemotherapy protocols used in human medicine.  Our primary goal in veterinary oncology is to maintain and extend your pet’s quality of life. Therefore, we design our chemotherapy protocols with this goal in mind. Second, pets generally do not experience severe adverse effects from chemotherapy because they tolerate the drugs better than people.

In veterinary oncology, we are very proactive to prevent adverse side effects from chemotherapy.  If a dog or cat does experience side effects while going through chemotherapy, they can usually be mitigated with protocol adjustments and supportive medications at home.  There have been great advances in antiemetic therapy, as well as antibiotic therapy, which have been able to greatly reduce the number and severity of adverse events secondary to chemotherapy.

Why does chemotherapy cause side effects?  Chemotherapy works by killing rapidly dividing cells.  In a dog or cat with cancer, the most rapidly dividing cells in the body are the cancer cells. However, there are two locations in the body where normally rapidly dividing cells are located: the bone marrow (where our infection fighting white blood cells are produced); and the gastrointestinal tract. Sometimes chemotherapy can damage the bone marrow cells to the point where the white blood cell count decreases to a critical level allowing infection to take hold and resulting in fever, lethargy, anorexia, etc, requiring medical intervention.  This side effect of chemotherapy is rare (less than 5%). The gastrointestinal tract is lined with little finger like projections called villi which allow absorption of the nutrients we eat. The villi are constantly replaced by precursor cells in the villi crypts. The villi crypt cells are rapidly dividing and can be affected by the chemotherapy resulting in anorexia, nausea and diarrhea. These effects are generally mild, occurring in 15-20% of patients receiving chemotherapy and are usually responsive to supportive medications and diet change. Rarely do the gastrointestinal side effects require more advanced medical intervention.

Indications for chemotherapy: Chemotherapy is used to treat systemic cancers, cancers that have already spread or metastasized or cancers that are likely to spread or metastasize. Sometimes chemotherapy can used to treat cancers that cannot be treated with other methods such as surgery or radiation therapy.

How chemotherapy is administered: Chemotherapy can be given intravenously (the most common method), orally, subcutaneously, intramuscularly or potentially into the tumor.

Caution: When administering oral chemotherapy medications at home it is very important to follow the oncologist’s instructions regarding frequency of administration, whether to administer the medication with food and whether other medications are contraindicated with the chemotherapy agent. In addition, chemotherapy pills or tablets should never be opened or crushed. Latex gloves should always be worn when handling chemotherapy pills at home. Hands should be washed thoroughly after handling any chemotherapy agent.

Edwin Brodsky, DVM, Diplomate ACVIM (Oncology)
Veterinary Medical Center of Long Island
75 Sunrise Highway
West Islip, New York 11795
(631) 587-0800; fax (631) 587-2006