What is chemotherapy?
Strictly speaking, chemotherapy means the use of a drug to treat any illness; however in recent years the term has been used to describe anti-cancer drug treatment. Chemotherapy can also be used in conjunction with surgery and/or radiotherapy in “combination therapy”. Chemotherapy has proved useful in the treatment of several types of cancer in dogs and cats
The aim of chemotherapy
In veterinary practice, we use chemotherapy in order to prolong your pets life, but more importantly, to maintain a good quality of life. Although we use the same drugs as used in human chemotherapy, we tend to use lower doses so as to reduce or (hopefully) avoid the side effects seen. We feel this is important because the animals do not understand that we are trying to help them.
How does it work?
Most cancers are caused by rapid, uncontrolled growth of cells. Anti-cancer drugs interfere with the normal process of cell growth, and so “kill” rapidly growing cells. We rely on the rapid growth of tumour cells to target cancers. In many cases, using a combination of drugs that interfere with cell growth in different ways will increase the effectiveness of treatment while reducing the risk of side effects.
How is chemotherapy given?
Most drugs are given either by mouth (orally) or by injection. Some drugs can be injected under the skin but others need to be given into the vein, as they can be very irritant to skin and muscle. Occasionally, we may need to sedate pets to give the drugs by “slow intravenous infusion”.
How long will treatment last?
The length of time and frequency of treatment will depend on the cancer, and the treatment used. Treatment may be given daily, weekly, or monthly, and may be tailored to individual cases depending on response and any side effects. Tablets can usually be given at home, but injections will need to be given at the practice for safety reasons.
Are you at risk of exposure to these drugs?
As with all medication, precautions should be taken to keep orally administered drugs out of the reach of children and pets, in child-proof containers. Most oral chemotherapy drugs have a protective coating, but we recommend that you wear gloves when administering the medications. Tablets and capsules should not be split or crumbled.
It is also important to avoid unnecessary contact with urine and faeces of animals receiving treatment, especially in the first week after a drug is given. Normal hygienic precautions should be adequate. If your pet uses a litter tray or has an accident in the house, wear gloves to clean it up.
Will your pet experience side effects?
Steroids are often used at quite high doses in the initial stage of chemotherapy protocols and side effects may include increased thirst and appetite, and panting.
We try to use drug combinations and doses to minimise the risk of side effects, however the following side effects may also be seen:
Fever - Most dogs with a high temperature are miserable and refuse to eat. If your pet has a fever, it may be necessary to prescribe antibiotics, and occasionally to give intravenous fluids (a “drip”).
Vomiting and diarrhoea - Vomiting once or twice without signs of fever should be monitored, but does not usually require treatment. Withholding food for 24 hours may be helpful. If it continues for more than 24 hours please contact us. Diarrhoea without vomiting or fever is usually self limiting and can be managed by feeding a bland diet.
Cystitis - Signs of bladder discomfort or bloody urine are occasionally seen with cyclophosphamide treatment. To reduce the risk of this, make sure water is freely available at all times.
Heart disease - Doxorubicin has been associated with heart problems in dogs. With the doses currently used in dogs, this is not usually a problem.
Hair loss - Pets do not usually lose hair through chemotherapy; however hair that has been clipped (for surgery or injections) may be slow to grow back. The coat of long haired dogs may change in texture.
The above list of potential side effects sounds very alarming – but most animals show no or only minimal effects of treatment. There are recommended doses for all treatments, but these serve as a “starting point”, and we may adjust treatment according to how your pet is responding. If you have any concerns about the way in which your pet responds, either before or during treatment, please ask us.
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