What Side Effects One May See after Chemotherapy Is Administered?

The goal of chemotherapy in veterinary medicine is to prolong good quality of life. Majority of pets undergoing chemotherapy do not develop side effects.

Side effects are seen when the normal, fast-growing cells are damaged significantly by chemotherapy. Here are some normal cells that grow quickly:

  • cells in the bone marrow (white blood cells, red blood cells and platelets) - this can make you pet feel tired, bruise and bleed easily, or put him/her at a higher risk of infection
  • cells in the stomach and intestines--this can cause your pet to have low appetite, vomiting or diarrhea
  • cells that grow hair--this can cause your pet to lose hair
The effect on these “innocent” cells is short lived and they recover usually within 1 week. Death occurs in less than 2% of patients receiving chemotherapy, when treatment for side effects is pursued by their owner.

Other rare side effects are related to administration of chemotherapy (tissue damage, allergic reactions or heart damage from long term use of certain chemotherapy drugs.

The bone marrow is found in the inner part of some bones. It is where all of the blood cells are made (red blood cells, white blood cells, and platelets). It is often affected by chemotherapy and can cause the bloodwork to be abnormal.

Red blood cells carry oxygen from the lungs to all parts of the body. During chemotherapy, the bone marrow may not be able to make enough red blood cells. Not having enough red blood cells is called anemia. It can make you pet feel weak, have low appetite, and low stamina. Anemia can also make the skin and gums look pale. The red blood cells are monitored closely during chemotherapy and their count is used to make treatment adjustments. If the anemia is severe, a blood transfusion may be indicated.

White blood cells fight infection. Chemotherapy lowers the white blood cell count (called neutropenia), which makes you pet less able to fight infections. This can develop within 5-10 days after chemotherapy. If a patient shows signs of an active infection (fever, acting sick, lethargy, collapse), hospitalization and treatment with intravenous medications is indicated. White blood cells are monitored closely during chemotherapy and their count is used to make adjustments in the drug doses or prescribe antibiotics.

Platelets are tiny pieces that form blood clots to stop bleeding and prevent the blood from “leaking” out of the vessels. If the bone marrow cannot make enough platelets, your pet may be at risk for spontaneous bleeding. This can cause bruises, nose bleeds, blood in urine, bleeding in the abdomen of chest or excessive bleeding from small cuts and be life threatening for your pet.. Fortunately, severe thrombocytopenia and active bleeding are rarely seen with the drugs and doses used in veterinary medicine.

Stomach and Intestinal cells can be damaged by chemotherapy, causing nausea, decreased appetite, vomiting, diarrhea. When seen, these problems develop within 2-7 days after chemotherapy. We are very proactive in prescribing medications to try to prevent or treat the nausea and intestinal discomfort. 

Hair Loss (Alopecia) - Most pets do not have continuous hair growth, like people and their coat is affected at a much lesser extent. Complete hair loss in pets is rare. Exceptions are certain breeds of dogs, such as Poodles, Old English Sheepdogs and other breeds whose hair grows continually. In general, if a pet needs to visit a groomer periodically to be clipped, then the pet may experience some degree of hair loss as a result of chemotherapy. The areas that are shaved for the administration of treatments or evaluations (ex. abdominal ultrasound) will regrow hair slower. Many pets (especially cats) lose all or most of their whiskers (this will not affected their quality of life). Hair and whiskers grow back after treatment, although they might be a different color or texture of hair.

Tissue Damage – Some chemotherapy drugs can cause severe tissues damage if accidentally given outside the vein. In our hospital chemotherapy agents are handled very careful and are only administered by highly trained technicians or doctors. We take a lot of safety precautions to decrease the risk of such accidents, including sedation, if necessary.

Allergic Reactions – This is a rare side effect seen during or shortly after giving certain chemotherapy drugs. Pets are generally pretreated with Benadryl prior to giving these chemotherapy drug, which greatly decreases the risk of seeing allergic reactions.  Also, they are kept for observation for 30-60 minutes after administration, which is the most common time when allergic reactions are seen.

Heart Damage - Some chemotherapy drugs (ie. doxorubicin= adriamycin) can irreversibly damage the heart muscle, especially when given at high doses. The dose used in veterinary protocols is below the dose that usually causes heart disease. Less than 5% of patients develop heart disease as a result of chemotherapy. A cardiac evaluation is recommended prior of using these drugs.