The use of a drug or chemical to treat any illness is chemotherapy, but this term commonly refers to the use of drugs in the treatment of cancer. The goal of chemotherapy in companion animals is either to increase the life span or to improve the quality of life for the animal with cancer.

Cancer can be defined as a rapid, uncontrolled growth of cells. Anticancer drugs work by blocking cell growth and division. Different drugs interfere with different steps in these processes. In many cases, a combination of drugs is the most effective way to kill the cancer cells.

Most anticancer drugs are given by mouth or by injection. The route chosen depends on the type of drug and the type of cancer.

The length of time and frequency of drug administration depend on the kind of cancer being treated and how well the therapy is tolerated by the patient. Treatment may be given daily, weekly, or monthly.

Yes. Most anticancer drugs are very potent and must be handled with care. Some are "carcinogens" and can cause cancer with prolonged exposure. With orally administered drugs, it is important that the pills or capsules are kept out of reach of children in childproof containers. When handling these drugs, the owner should wear latex or polyvinyl gloves to avoid unnecessary exposure. With oral and injectable drugs, the urine and feces of the animal may be contaminated with active drug compounds for several days after administration.

Always avoid contact with the urine and feces of animals receiving chemotherapy. Wear latex or polyvinyl gloves to clean up accidents or the litter box. Rinse exposed surfaces well.

Maybe. Veterinarians try to choose drug doses and combinations that cause the fewest side effects. Ideally, the animal receiving chemotherapy does not even realize that he or she is ill. The drugs used in chemotherapy, however, are extremely potent and side effects can occur. The potential for side effects must be balanced against the benefits of the chemotherapy and the side effects of the cancer if left untreated. Choosing chemotherapy for your pet is an individual decision.

Side effects arise because the normal cells in the body are also exposed to the anticancer drug. J The most sensitive normal cells are found in the blood, gastrointestinal tract, skin, and reproductive system. Consequently, potential side effects include infection, bleeding, decreased appetite, vomiting, diarrhea, thin haircoat or skin color changes, and sterility. Rare side effects associated with specific drugs include bladder discomfort, kidney damage, and heart failure. The most serious side effect is overwhelming infection leading to death.

The most common side effect reported by owners is that the pet seems to be "off" for a day or two. This might mean that the pet has slightly less energy or seems less excited than normal about eating. Less commonly, the pet may skip a meal or two, have one episode of vomiting or diarrhea, or seem lethargic. Unfortunately, there is no way to predict which pet will develop the most serious reactions. The animal receiving chemotherapy needs to be watched closely and taken to his or her veterinarian at the first signs of illness.