Chemotherapy Side Effects
All of the chemotherapy treatment protocols in common use for veterinary patients are designed to have a fairly low risk of causing unpleasant side effects. With most treatments, 50% of patients will have very little in terms of side effects, except for perhaps some slight tiredness or decreased appetite for 1-2 days following treatment. However, there are approximately 25% of patients that may experience some type of mild side effect and 5% that can experience a side effect severe enough to require hospitalization. We cannot usually predict which patients are likely to experience a serious side effect.
Most chemotherapy drugs work by targeting rapidly dividing cells. Although cancer cells are typically the most rapidly dividing and this is why they are preferentially killed, other rapidly dividing cells, such as cells lining the intestinal tract, cells in the bone marrow, and hair follicle cells, can be damaged as well, and this damage is responsible for most of the side effects we encounter.
DIGESTIVE TRACT
One of the side effects that can be seen with certain medications is digestive tract upset, in the form of unwillingness to eat/drink, nausea/vomiting, or diarrhea. In most cases, these signs are mild, and can often be self-limiting within a short period of time. These side effects are most commonly seen 2-5 days following chemotherapy treatment.
Decreased appetite can occasionally be seen and is not worrisome if it persists for less than 48 hours. It is important, however, that your pet continues to drink. Unwillingness to drink water for greater than 24 hours or prolonged, complete unwillingness to eat are problems that should be reported to your veterinarian.
Some animals can develop problems related to nausea or vomiting as well. Vomiting can occasionally occur and is not a cause for undue concern if it occurs less than 3 times in pet that is otherwise feeling well. Should your pet vomit, an antiemetic (anti-nausea medication) should be administered and food and water should be withheld for approximately 4-8 hours to give the digestive tract a “rest”, then if not further vomiting, water can be re-introduced first. If no vomiting occurs several hours after water is given, then a small amount of bland food (i.e. boiled chicken or lean ground beef mixed with a starch like rice, pasta, or potatoes) can be offered in small amounts. We often prescribe oral anti-nausea medications that can be given to address mild nausea, inappetance or vomiting. Repeated vomiting, vomiting after every meal, (“can’t keep anything down”), or repeated nonproductive retching (dry heaving) should be reported to your veterinarian or your nearest emergency facility. Animals experiencing these effects will need to be evaluated for dehydration and may need hospitalization for intravenous fluids and anti-nausea medications.
We can also see diarrhea as a side effect of certain chemotherapy drugs. This can range from mild soft stool or increased frequency of defecation to profuse, watery diarrhea that can contain blood. Mild diarrhea in a bright, eating pet can be treated with the bland diet described above. Some oral medications can also help to resolve diarrhea. Severe, watery diarrhea, blood in the stool, or diarrhea associated with lethargy, weakness, depression, or unwillingness to drink should be brought to the attention of your veterinarian.
WHITE BLOOD CELLS
If there is damage to the rapidly dividing cells in the bone marrow, a low white blood cell count can develop. We check the white blood cell count prior to each and every chemotherapy treatment to insure that it is not too low for treatment to be safely given. Occasionally, the white blood cell count may be low enough that we need to delay a treatment for a few days. In other cases, the white blood cell count may be low enough that an increased susceptibility to infection is a concern. Lowering of the white blood cell count happens most commonly 7-10 days after chemotherapy is given but can vary with differences in the type of drug given.
If your pet has a very low white blood cell count but is acting normal, eating and drinking, and does not have a fever, we will often prescribe a broad-spectrum antibiotic for you to give at home. We would then recommend that your pet’s temperature be taken once or twice per day to ensure that they are not developing a fever. Taking a pet’s temperature is easy. A standard digital thermometer that you can buy at the store is used. The thermometer is lubricated with a small amount of Vaseline or K-Y jelly and inserted approximately 1/2 inch into the rectum. Most digital thermometers will beep when the temperature is recorded. A normal dog or cat’s temperature at home (not stressed) should be between 99 and 102 degrees Fahrenheit. If your pet’s temperature is higher than 103 degrees or they show signs of weakness, lethargy, depression or unwillingness to eat, please contact a veterinarian. Hospitalization may be necessary.
If your pet has a low white blood cell count and has a fever, or is depressed, lethargic or not eating, hospitalization for intravenous fluids, antibiotics, and very careful monitoring is recommended. Most animals will improve rapidly with this treatment, and hospitalization is rarely necessary for more than 72 hours. They are ready to go home when their temperature has become normal, and their white blood cell count is no longer in the dangerous range.
If serious side effects are seen after a treatment, we always try to make changes so that they are much less likely to happen again. Some of these changes include decreasing the dose of chemotherapy given for subsequent treatments, adding some medications to help prevent adverse effects, or switching to an entirely different drug. It is always our goal to make it so that serious side effects are not encountered more than once.