Chemotherapy in Small Animals
Veterinary Hospital of the University of Pennsylvania.
© Copyright, 1994 OncoLink See HomeVet
Introduction
Chemotherapeutic
drugs (anticancer drugs) are used in the treatment of
several types of cancer in pets. The type of cancer
and extent of disease help us decide what protocol(type
of drugs, dose, and schedule) to use for treatment.
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When
do we use chemotherapy to treat animals with cancer?
We use
it in the event of:
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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. In animals,
we use lower doses, and do not combine drugs as often.
Most of the chemotherapeutic
drugs are not specifically toxic to cancer cells, but
to all cells that are dividing rapidly. This is why
we see toxic effects in normally rapidly growing cells
of the body, and many of the side effects are due to
this.
The cells in
the bone marrow, the intestinal lining, and hair follicles
in some breeds of dogs (e.g. poodles, terriers) are
rapidly dividing cells, and consequently more sensitive
to chemotherapy.
The most common
side effects are bone marrow suppression and vomiting/diarrhea.
Whiskers of cats usually fall out, but regrow when chemotherapy
is stopped.
Bone marrow suppression
may cause a drop in the white blood cell count and increased
susceptibility to infections. Severe infections may
require intensive supportive care, including intravenous
fluids and antibiotics.
The gastrointestinal
signs may be mild, moderate, or severe. Although infrequent,
some dogs may develop severe diarrhea requiring fluid
therapy in the hospital.
We see side effects
as described above very seldom (i.e., less than 5% of
all pets receiving chemotherapy). With proper therapy,
most animals recover uneventfully within several days.
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 with drugs known to cause side effects, we will
give you instructions on what to do if there is a problem.
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How
are the drugs given? How often and how long does treatment
last?
This
varies, depending upon what type of cancer we are treating
and which drugs we are using. Some of the drugs are
oral medication (pills) that you give at home, while
others are injections or slow intravenous infusions
that may require 1-2 days in the hospital. The treatments
are usually repeated weekly, every other week or every
third week.
It is most important
that you, as an owner, are committed to treatment and
bring your pet in when scheduled for therapy.
The duration
of the chemotherapy depends on the type of cancer and
stage. Some animals need to receive chemotherapy for
the rest of their lives, but in others, treatment may
be discontinued for a period (weeks to months) if the
tumor is in remission (i.e., not evidence of disease
or NED). Chemotherapy is resumed when there is a tumor
relapse.
We usually recommend
that every patient receive at least two cycles of chemotherapy
and then be evaluated for response before we decide
to continue the treatment, change the drugs, or discontinue
chemotherapy.
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What
can you expect from chemotherapy?
In many
cases, we are not able to cure our patients with cancer.
We are often talking about palliation, i.e., prolonging
your pet's life and slowing down the progression of
the disease. From what we know about the type of cancer
your pet has, we may be able to give you a prognosis
about life expectancy with chemotherapy. We want to
give your pet a long life while striving for a good
quality of life.
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Please note:
The information provided here is meant to supplement
that provided by your veterinarian. Nothing can replace
a complete history and physical examination performed
by your veterinarian. - Dr. Jeff
I greatly value your feedback. Please let me know what
you think of this site and what you would like to see
on it. drjeff@homevet.com
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