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Pets and chemotherapy: Side effects to prepare for

When a pet is diagnosed with cancer, chemotherapy treatment is often offered as a possible treatment option. The thought of putting a pet through chemotherapy can be frightening for some pet owners, though, particularly those who may have seen family or friends suffer through the side effects of chemo, or even experienced those side effects themselves. Dogs and cats, however, usually fare much better than their human counterparts when undergoing chemotherapy and dealing with the side effects of treatment.

Your veterinarian will advise you of specific side effects associated with the drugs they’re using to treat your pet’s cancer. While it is important to be aware of these possible side effects, it is also wise to watch your pet closely for any other signs that something is awry. Fever is a sign of infection and should be brought to the attention of your veterinarian immediately. Also watch for signs of lethargy or changes in appetite. Remember: No one knows your pet better than you, so if you think something is wrong, tell your veterinarian.

The three most common side effects of chemotherapy are bone marrow suppression, alopecia, and gastrointestinal upset.

Bone marrow suppression
Chemotherapy drugs attack cells in the body that are rapidly dividing and producing, which is precisely what cancer cells typically do. There are “good cells” in the body, however, which also rapidly divide. White blood cells, produced in the bone marrow, are an example of these. Red blood cells can also become suppressed during chemotherapy, causing anemia in the animal.

Your veterinarian will check your pet’s white blood cell count through regular blood tests to determine how the chemotherapy is affecting the bone marrow. If the level of white blood cells is low, your veterinarian may prescribe antibiotics to prevent infection introduced by opportunistic bacteria, which are normally kept in check by the white blood cells.

While alopecia, or hair loss, is a common side effect of chemotherapy in humans, it is not all that common in animals. Certain breeds are more likely to experience hair loss, and they are usually breeds with continuously growing hair, such as poodles, Portuguese water dogs, shih tzu, and Maltese. These breeds may expect to see a general thinning of the hair coat, rather than a total loss of hair.

Hair may also be slow to regrow in areas that have been shaved. If your pet is receiving chemotherapy via injection into a blood vessel, your veterinarian will need to shave a spot to place an IV catheter to give the injection.

The coat usually grows back after the course of chemotherapy is completed, however, like humans who receive chemotherapy, the hair that regrows is sometimes a different color or texture than it was before chemotherapy. This may or may not change back over time.

Cats, and sometimes dogs, can also lose their whiskers during chemotherapy treatments. Like the hair coat, the whiskers may grow back after chemo looking different than they previously did.

Gastrointestinal upset
Like blood cells in the bone marrow, the gastrointestinal tract (throat, stomach, and intestines) is also made of rapidly dividing cells. Chemotherapy drugs are unable to discern these good cells from the bad cancer cells and will attack them. If the “good” gastrointestinal cells are seeing more than their fair share of attack from the chemo drugs, your veterinarian may adjust the dose of the chemo to balance the effect on your pet.

Vomiting and diarrhea may be seen 1-3 days post-chemotherapy treatment. Duration is usually short term, and your veterinarian may prescribe medications to ease these side effects. You might also want to adjust your pet’s diet during this time; a bland diet may be easier on your pet’s tender tummy. Boiled chicken and rice are often go-to options to try when your pet’s regular food doesn’t seem to be sitting well.

If you notice signs of gastrointestinal upset, be sure to notify your veterinarian: she may want to treat the side effects if they warrant it.

Are the side effects worth it?
The main goal of veterinary cancer treatment is to maintain quality of life. Although pets may experience some side effects of treatment, those symptoms are typically milder than symptoms that humans experience, and many pets go into remission after just a few doses of chemotherapy.

If your veterinarian recommends chemotherapy for your pet, be sure to discuss all the ramifications thoroughly. While your pet may experience some unpleasant side effects, the hope is that all those bad cancer cells will be wiped out by the chemotherapy drugs, and your pet will go on to live a happy life. 


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