Chemotherapy Drug Poisoning in Dogs and Cats

By Renee Schmid, DVM, DABT, DABVT & Ahna Brutlag, DVM, MS, DABT, DABVT; Heather Handley, Staff Veterinarian, Pet Poison Helpline

What are chemotherapy drugs?

Chemotherapy drugs are used to treat cancer or control an overactive immune system in people and animals. There are many types of these drugs that act in different ways. Chemotherapy medications are available in injectable, oral, or topical forms. Some medications are more likely to cause poisoning in pets than others. Always contact a veterinarian or Pet Poison Helpline (1-800-213-6680) immediately if your pet is exposed to chemotherapy drugs that are not intended for its use or if your pet is exposed to its own chemotherapy drug in an amount exceeding the prescribed dosage.

Animals may be exposed to these medications in the home if they are dropped or spilled, by licking a topical form off after application, or by chewing into the medication container.

The actions of chemotherapy drugs have changed over the years and while many traditional chemotherapy drugs are still used, newer forms that have a much wider margin of safety are available. Traditional chemotherapy drugs act by targeting and killing rapidly dividing cells. Since cancer cells tend to divide more rapidly than normal cells, they are the main target for chemotherapy drugs. However, these drugs cannot tell the difference between cancer cells and healthy cells that divide rapidly, such as intestinal cells, hair, skin, or bone marrow. This means normal cells may be damaged as well, resulting in toxicity. Many newer forms of chemotherapy can target certain types of cancer cells, minimizing or eliminating the potential damage to healthy cells.

What are the clinical signs of chemotherapy drug poisoning in a dog or cat?

Pets may initially show no signs of toxicity. Signs can vary depending upon the type of drug and species exposed. Gastrointestinal upset is common. Pets may have decreased appetite, depression, drooling, vomiting, diarrhea, and abdominal pain. Some drugs may cause a rapid onset of neurologic signs such as drunken gait, difficulty walking, weakness, tremors, and seizures. Damage to the rapidly dividing cells in the bone marrow may result in low white blood cells, red blood cells, or platelet numbers. Pets with bone marrow effects may develop lethargy, decreased appetite, fever, pale gums, weakness, high heart rate, rapid breathing, bleeding, bruising, and an increased risk of infections. Bloody or discolored urine may also occur. These effects may be delayed several days to weeks. Other organs which can be damaged include the liver, kidneys, heart, pancreas, and lungs.

How is chemotherapy drug poisoning in dogs and cats diagnosed?

Most cases are diagnosed in pets that have the expected signs and a known or suspected exposure to chemotherapy drugs. Blood work is often necessary to evaluate the kidneys, liver, electrolytes, and blood cell counts.

Is there an antidote for chemotherapy drug poisoning in dogs and cats?

While there is no direct antidote for chemotherapy drug poisoning, there are some medications that can help stimulate the bone marrow and increase the white or red blood cell counts toward normal ranges.

Are there treatments for chemotherapy drug poisoning in dogs and cats?

Early decontamination and treatment decrease the risk for serious toxicity. If ingestion occurred within a few hours of treatment, the veterinarian may induce vomiting. Once vomiting is controlled, activated charcoal may be administered. This can decrease the absorption of drugs by the gastrointestinal tract. Activated charcoal should only be administered by a veterinarian. Otherwise, aspiration into the lungs and life-threatening changes in sodium levels may occur. Antacids, anti-nausea medications and gastrointestinal protectants are commonly administered. Depending upon the dose ingested, hospitalization may be needed. Fluid therapy administered under the skin or intravenously may also be necessary. Pets developing serious signs may require intensive therapy to minimize their risk for long-term effects or death. Blood work to monitor liver and kidney function as well as the blood cell counts may be performed. Pets that develop a low red blood cell count (anemia) or difficulty breathing may require oxygen supplementation or a blood transfusion. Liver protectants, muscle relaxants, medications to control seizures, antibiotics, or drugs to stimulate white and red blood cell production may be necessary.

What is the prognosis for recovery in dogs and cats exposed to chemotherapy drugs?

"With early treatment, pets are less likely to develop long-term effects."

The outcome depends on many factors including the initial health of the pet, amount ingested, other drugs ingested, and time to treatment. With early treatment, pets are less likely to develop long-term effects. Some pets may have permanent organ damage. Death may occur with high doses or when treatment is delayed.

How can I prevent chemotherapy drug poisoning in my pet?

Never give any medication to a pet without first consulting a veterinarian. Do not leave any medications, including vitamins and supplements, where unattended pets may reach them. Pets should be prevented from licking any chemotherapy ointments applied to the skin. Intravenous administration supplies should be secured and disposed of properly. It is not uncommon for pets to chew through closed bottles and other containers. Curious pets may want to go through purses, backpacks, lunch boxes, or suitcases. These items should not be left in areas where pets can get into them. Some pets will even open lower cabinets or get into open drawers. Keep in mind that pets can get on counters or knock items off counters and tables. Do not assume a pet will avoid eating a medication just because it has a bad taste. If medications are dropped, confine all pets in another area of the home until all the medication can be picked up.

"Whenever a toxic exposure is suspected, immediate action is recommended. Early consultation and treatment are often less expensive and can help prevent serious health effects."

Pet Poison Helpline, an animal poison control center based out of Minneapolis, MN is available 24/7 for pet owners and veterinary professionals that require assistance treating a potentially poisoned pet. The staff provides treatment advice for poisoning cases of all species, including dogs, cats, birds, small mammals, large animals and exotic species. As the most cost-effective option for animal poison control care, Pet Poison Helpline’s per incident fee includes follow-up consultations for the duration of the poison case. Pet Poison Helpline is available in North America by calling 800-213-6680. Additional information can be found online at

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