-----Chemotherapy in Small Animals

River Road Veterinary Clinic
Box 309
Norwich, Vermont 05055
Phone: 802-649-3877 Fax: 802-649-1345
email: RRVC@Valley.net.com
www.rrvetclinic.com

Dr. Christine Pinello - Dr. JoAnne Giel - Dr. Kathy Ling Newcomb

CHEMOTHERAPY IN SMALL ANIMALS

Chemotherapeutic drugs (anticancer drugs) are used in the treatment of a variety of types of cancer in pets. The type of cancer and extent of disease help us decide what treatment protocol (type of drugs, dose and schedule) to use.

When do we use chemotherapy to treat animals with cancer?

There are some diseases for which chemotherapy is the primary treatment method (i.e. lymphosarcoma) while there are others for which chemotherapy is used along with radiation or surgery. Chemotherapy can also be used in those situations for which other treatment options do not exist. The following is a list of situations where chemotherapy may be recommended for your animal.

Will there be side effects from the drugs?

Compared to people treated with chemotherapy, we see fewer side effects in pet
animals receiving these drugs because we use lower dose and do not
combine drugs as often.

Most of the chemotherapeutic drugs are not specifically toxic to cancer cells, but
to all rapidly dividing cells. This is why we see toxicity in normal, rapidly
growing tissues of the body, and most side effects are due to this.

The cells of the bone marrow, the intestinal lining , and hair follicles in some
breeds of dogs (e.g. any wire-haired or non shedding breeds such as terriers and poodles) are rapidly dividing cells, and are consequently more sensitive to chemotherapy.

The most common side effects are bone marrow suppression and
vomiting/diarrhea. Certain breeds may lose their hair while other animals may be slow to grow hair where it has been clipped. Whiskers may fall out in both cats and dogs. Hair growth will resume when chemotherapy is stopped. Certain drugs may have other side effects that may be specific for that drug. Your doctor will discuss these types of side effects with you if your animal will receive one of these drugs.

Bone marrow suppression may cause a drop in the white blood cell count and
increase susceptibility to infections. Complete blood counts are done on a regular basis to monitor the white blood cell count. Animals with low white blood cell counts that are asymptotic are often placed on prophylactic oral antibiotics. Animals with evidence of a systemic infection (sepsis) may require intensive supportive care, including intravenous fluids and antibiotics.

The gastrointestinal signs may be mild, moderate or severe. Anti-nausea drugs
may be prescribed. For mild and moderate signs , withholding of food for 12-24 hours and a diet change may be all that is required. Although infrequent, some dogs may develop severe bloody diarrhea requiring hospitalization and fluid therapy.

We seldom see severe side effects as described above (i.e. less than 5% of all
pets receiving chemotherapy). With proper management most animals recover uneventfully within several days. If an animal experiences severe side effects, we will either lower the next dose of that drug, skip that drug entirely or change to a different drug. Most of our patients experience only mild side effects, such as transient nausea, lethargy, reduced appetite, and mild diarrhea for a few days after treatment.

If your pet is treated for drugs known to cause side effects, we will give you
instructions on what to do if and when there is a problem.

How are the drugs given? How often are treatments? How long do
treatments last?

This varies, depending upon what type of cancer we are treating and which drugs
we are using. Some of the drugs are oral medications (pills) that you give at home, while others
are brief injections or intravenous infusions. In most cases, chemotherapy is done on an outpatient basis. There are a few drugs that need to be given over 1-2 days. Your doctor will discuss scheduling appointments for your pet's treatment.

The treatments are usually repeated from weekly to every third week.

It is most important that you, as an owner, are committed to treatment
and bring your pet in when it is scheduled for therapy

The duration of chemotherapy depends on the type of cancer and the and the
stage of the disease. Some animals need to receive chemotherapy for the rest of their lives, but in
others, treatment may be discontinued for a period of weeks to months if the tumor is in remission (i.e. there is no detectable evidence of disease). Chemotherapy is resumed when there is tumor relapse.

We usually recommend that every patient receive at least 2 cycles of
chemotherapy and then be evaluated for response before we decide to continue the treatment, change drugs, or discontinue chemotherapy.

What can you expect from chemotherapy?

From what we know about a variety of cancers in pets, we may be able to give you a prognosis about life expectancy with and without treatments. In many cases, we are not able to cure our patients with cancer. We are often talking about palliation, which means prolonging your pet's life and slowing down the progression of disease while maintaining a good quality of life. Regardless of the type of treatment we choose, we always consider your pet's quality of life to be one of the most important factors in evaluating a treatment.