My Clinic:

What is chemotherapy?

Chemotherapy is the name given to a group of drugs that have the ability to kill cancer. Once treatment with chemotherapy has begun, the protocols are often further modified to provide the most efficacious treatment possible with the fewest side effects. Therefore, each chemotherapy protocol is tailored to meet the specific needs of each patient.

Will chemotherapy make my pet sick?

Many people are initially hesitant to use chemotherapy to treat their pet’s cancer because they do not want to compromise their pet’s quality of life by making them sick.  While side effects are possible with chemotherapy, the main goal of chemotherapy use in veterinary patients is different than it is in human patients. Our primary goal in using these drugs is to provide the pet with a good quality of life for as long as possible, rather than attempt to cure the pet at the cost of extreme side effect. Hence if the pet starts to experience significant side effects, we alter or even stop our treatment plan. Fortunately, most dogs and cats tolerate chemotherapy much better than human patients.

Generally, dogs and cats that receive chemotherapy feel normal the day they are given the drug. Perhaps 3 to 5 days later, an owner might report that their pet does not feel 100%. But within 24 to 48 hours, the pet is back to his or her normal self until the cycle continues with the next dose of drug. After each dose of chemotherapy, we discuss with an owner whether or not the side effects seen in his or her pet would warrant a change in the pet’s therapy. If everyone agrees that the pet’s quality of life is good, and as long as there is evidence that the chemotherapy drug is working against the pet’s cancer, we continue with the treatment.

However, every pet is different. A small percentage of pets are more sensitive to chemotherapy, and it is impossible to predict which pets will experience more severe chemotherapy toxicity. If severe toxicity occurs, hospitalisation for a few days in a vet clinic may be necessary to help the pet recover. Fortunately, the need to hospitalise pets due to chemotherapy-related side effects is uncommon, and some studies show that hospitalisation is necessary in less than 10% of patients receiving chemotherapy. If you are unhappy with the side effects associated with chemotherapy, you may choose to stop treatment at any time. Many dogs and cats are able to complete chemotherapy protocols without experiencing any toxicity at all or only experience mild toxicity.

What are side effects associated with chemotherapy?

The side effects most commonly experienced in dogs and cats receiving chemotherapy involve the gastrointestinal tract and the bone marrow. Chemotherapy-related side effects generally occur at a predictable time, allowing treatment to be instituted early to prevent or lessen your pet’s clinical signs. Also, the side effects are generally temporary, commonly resolving within several days.

Gastrointestinal Side Effects:

When the cells lining the stomach and intestine are affected by chemotherapy, the result may be vomiting, diarrhea, and loss of appetite. If this occurs, it tends to happen 3-5 days after receiving chemotherapy and resolves within 1-2 days. To prevent a pet from experiencing significant nausea, we provide the owner with anti-nausea and anti-diarrhea medications to use if needed

Bone Marrow Side Effects:

The bone marrow is responsible for producing white blood cells, and when it is affected by chemotherapy, these white blood cell levels may decrease temporarily. Typically, this occurs 7 days after a dose of chemotherapy is given, but the timing may vary with the drug used. Decreases in the white blood cell count may be mild, moderate, or severe. Because the body regenerates these cells very quickly, even if a pet experiences a very severe drop in their levels, the count will usually return to normal within 24-48 hours.

White blood cells are very important in fighting infections. If the body has a very low white blood cell count, it is susceptible to developing an infection. Most pets with low counts may feel well and have no clinical signs at all. However, if an infection develops, he or she may spike a fever, decline food, and act lethargic, which would require treatment. White blood cell counts of all canine and feline chemotherapy patients are monitored carefully throughout treatment.

Miscellaneous Side Effects:

Unlike people receiving chemotherapy, hair loss in canine and feline patients is usually very minor. Cats may lose their whiskers, and long-haired cats may lose their outer coat. Dogs may develop mild hair thinning. Spots where hair is clipped for surgery or chemotherapy administration may grow back very slowly. However, there are some dog breeds that are more likely to experience hair loss due to chemotherapy. If you own a Poodle, Old English Sheepdog, Schnauzer, Puli, Lhasa Apso, Shih Tzu, Bichon Frise, Yorkshire Terrier, Maltese, or curly coated terrier such as an Airedale or Welsh terrier, you should expect that your pet will lose a more significant amount of hair during the initial stages of chemotherapy. For all pets, the hair that is lost due to chemotherapy will grow back after the course of chemotherapy has been completed or once treatments are given less frequently. Sometimes hair may grow back a slightly different color.

Some chemotherapy drugs, if they leak outside of the vein during injection, can be extremely irritating to the skin and tissues under the skin. Examples include the chemotherapy drugs vincristine, vinblastine, Doxorubicin. Severe swelling, ulceration, and inflammation can be seen. However, this complication is very rare.

Some chemotherapy drugs have unique toxicities. These will be explained to you if your pet receives one of these medications, and appropriate steps will be taken to avoid them.

How is chemotherapy given?

Most chemotherapeutic drugs are given by injection, typically into the vein. These drugs cannot be given at home and must be administered at the vets. Some chemotherapy drugs can be given orally either at home or at the vets.

Is it safe for me to be around my pet during the time he or she is receiving chemotherapy?

Generally speaking, the risk to a person handling their pet that is receiving chemotherapy is very low. We do not recommend changing your or your pet’s lifestyle as a result of chemotherapy treatments. This means that they may continue to sleep in your bed, do not need to be separated from other household pets, can continue to share a litter box with other household cats, and may even eat their normal breakfast the morning of their chemotherapy treatments.

However, because repeated, long-term exposure to chemotherapy drugs can result in severe health problems, some precautions are necessary. A small amount of chemotherapy may be excreted in your pet’s urine and feces for up to 72 hours after a dose of chemotherapy is given. It is important to avoid contact with your pet’s urine or feces during this time.

  • If your pet has an accident in the house, wear disposable gloves when cleaning it up. Wipe up the waste first and then clean the area with a mild soap and water solution three times using disposable paper towels. Place these materials in a plastic bag and dispose of them in an outside bin.
  • In general, for cats, change the entire litter box once daily for the first 2 days after chemotherapy administration, and wear gloves when doing so. Be diligent about scooping waste throughout the entire time your cat receives chemotherapy. Dispose of the waste in an outdoor bin.
  • Dogs should urinate or defecate in low-traffic areas (i.e., not in the sandpit where children play, not near the family outdoor table, etc.).

Although exposure of a pet owner to significant amounts of chemotherapy from routine handling of their pet is unlikely, certain people are more at risk if they are exposed to chemotherapy. Women who are breast feeding or pregnant, children, people trying to conceive (both men and women), and immunosuppressed individuals should never handle chemotherapy drugs or contaminated urine or feces.

Are there any special precautions I should take if I have to give oral chemotherapy drugs to my pet?

Always wear gloves when handling chemotherapy pills, and wash hands thoroughly when administration is complete. For dogs, you can put the pills into a “meatball” of tasty food and give the pill before the pet’s meal when he or she is most hungry. Unfortunately, this does not work for cats, and you often have to "pill them." Please ask your vet or nurse for a demonstration on how to administer a pill to your pet if you are not sure.

Never split or crush the pills, and do not open the capsules. This can aerosolise the chemotherapy drug and cause you to become exposed. If your pet spits out the pills and they begin to “melt” or break apart, wear gloves and use paper towels when picking up the medication. Wipe the floor with a diluted soap and water solution three times. Put the paper towels and medication into a plastic bag and dispose of it in an outside bin. Do NOT re-dose your pet, as they may have absorbed some amount of the chemotherapy, and administration of another pill may cause them to be overdosed. Call your vets for advice about what to do next.

Again, women who are breast feeding or pregnant, children, people trying to conceive (both men and women), and immunosuppressed individuals should never handle chemotherapy drugs.

Final Thoughts

It is important for the owners of dogs and cats receiving chemotherapy to realise that some cancers we treat are not cured. Many of our patients ultimately have recurrence of their cancers. However, most cats and dogs receiving chemotherapy have an excellent quality of life both during and after treatment. It is often possible to provide many additional months, or sometimes even years, of happy life with chemotherapy. The vast majority of owners tell us that they have no regrets about their decision to pursue chemotherapy for their pet.

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