Friday, June 7, 2013

Side Effects of Chemotherapy

by Michelle Spencer
Veterinary Technician, Oncology Specialist
In this article, we discuss common side effects of chemotherapeutic agents and how your veterinary team can work to combat them.

When deciding whether or not to treat your pet’s cancer with chemotherapy, it is very important to keep two things in mind:

·       Quality of life is the driving force behind veterinary oncology
·       Cancer treatment is fluid and there is room for assessment at each step in the road

The occurrence and severity of side effects from chemotherapy in veterinary medicine are significantly less than those found in human medicine. To understand this discrepancy, it helps to look at the goals in veterinary oncology vs. those in human oncology. Veterinary oncology focuses on quality of life, while human oncology tends to focus on quantity of life. For that reason, chemotherapy dosing, schedules and protocols are less intensive in veterinary medicine, often resulting in less severe side effects. Research shows that less than 5% of veterinary oncology patients experience severe side effects requiring hospitalization.1 Most side effects can be managed at home with oral medications and generally last only a few days.

Common Side Effects

Most chemotherapeutic agents work by killing or inhibiting the growth of rapidly dividing cells. However, most agents do not have the ability to discriminate between cancer cells and other healthy, rapidly dividing cells within a pet’s body. It is the destruction of these healthy cells that tends to cause the most common side effects.
Chemo and your pet


Healthy cells in a pet’s GI tract turnover frequently, about every 3-5 days. Because chemotherapy can kill these rapidly dividing cells, your pet my experience GI side effects 3-5 days after treatment  including vomiting, diarrhea and inappetence. Most of these side effects are self limiting and resolve within a couple of days. However, should your pet experience vomiting multiple times per day, vomiting multiple days in a row, prolonged inappetence, prolonged diarrhea or bloody or tarry diarrhea, notify your veterinarian immediately.

If your pet experiences an episode of vomiting,  you will likely be asked to pull food and water away from your pet for 12 hours and then slowly reintroduce it. Your pet may be given antiemetics such as Cerenia, Zofran or Reglan. These will help to combat nausea and vomiting and can usually be taken at home.

If your pet experiences a minor bout of diarrhea, an antidiarrheal such as Flagyl may be given at home. For more severe cases, your pet may need rehydration and injectable medications at your clinic.

Discuss episodes of inappetence with your oncologist. Occasional bouts may be cured by enhancing your pet’s meals with chicken broth, tuna juice, etc. Chronic inappetence should be examined and may be cured with oral medications such as mirtazapine.

Some agents such as piroxicam may cause gastric ulcers. Your veterinarian can give you medications such as carafate to help prevent ulcers by coating the GI tract with a protective barrier.

Bone Marrow Suppression

Your pet’s bone marrow is responsible for the production of blood cells. Because it is a site of rapidly dividing cells, it is a prime target for the effects of chemotherapy treatment. Most side effects arise when your pet’s bone marrow is unable to produce enough platelets (thrombocytopenia) or neutrophils (neutropenia). A lack of platelets can reduce the ability of your pet’s blood to clot properly. This can result in uncontrolled bleeding. A lack of neutrophils reduces your pet’s ability to fight infection. Common indications of infection are lethargy and a fever above 103°. If your pet is neutropenic, but otherwise feeling well, a prophylactic course of antibiotics may be prescribed. Should your pet develop an infection in their blood stream (sepsis), they will be hospitalized for intensive supportive care such as IV antibiotics and fluids. Sepsis is a dangerous situation and should not be taken lightly.

Because of the lifespan of these cells and the rate at which the bone marrow produces replacements, your pet is most likely to experience a drop in platelets or neutrophils about 5-10 days post treatment. During this time, you will be asked to bring your pet to the clinic for a Complete Blood Count to thoroughly evaluate these and other blood cells. This test is extremely important, and should not be missed.

Chemotherapy and your pet

Less Common Side Effects


Though hair loss is much less common in cats and dogs than humans, some breeds may lose hair, especially eyebrows and whiskers, during treatment. Non-shedding breeds are at greater risk for hair loss. Hair growth generally returns, but hair texture and color may differ.


Some agents, such as doxorubicin, may cause irreversible changes to a pet’s heart. A risk vs. benefit discussion should take place with your oncologist prior to treatment. If your pet is treated with an agent known to cause cardiotoxicity, expect them to have frequent ultrasounds of their heart (echocardiograms).

Allergic Reactions

Some pets may experience an allergic reaction to a chemotherapeutic agent. Though the most common culprit tends to be l-asparaginase, it is possible to have a reaction to any drug. These reactions can range from minor to severe, though the latter is quite rare. Normally, they can be treated with a few minor injections and some monitoring at your clinic. If you expect that your pet is experiencing an allergic reaction, call your clinic or visit an emergency hospital immediately.

Prior to treatment, discuss possible side effects of chemotherapy with your veterinary oncologist. Together, you can proactively formulate an action plan to provide your pet with relief.

Thank you for joining us for our third installment on companion animal cancer. In our next article, we will discuss veterinary radiation oncology and how it can benefit your pet.

1Clinical Oncology Service,  Veterinary Hospital of the University of Pennsylvania (VHUP)
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