As a veterinarian, I always worry about my patients coming into contact with medicated creams from their owners. One of the worst is 5-Fluorouracil (5-FU) which is used in humans to treat basal cell carcinoma and actinic keratosis of the skin. The patient applies a cream containing 5-FU to the affected area. Unfortunately, 5-FU is highly toxic to animals. Common brand names include Efudex®, Carac®, Adrucil® and Fluoroplex®.
Dogs and cats are exposed when they lick the cream off the human or get the cream on their fur and then lick it. I have also heard of people who forget to wash their hands after applying 5-FU and accidentally transfer it to their pets. Once 5-FU gets into an animal’s gastrointestinal system, it is rapidly absorbed. Common early symptoms include vomiting, bloody diarrhea, severe abdominal pain, problems with balance and seizures. With time, this toxin will destroy the animal’s bone marrow resulting in anemia, leukopenia (lack of white blood cells used to fight infection) and thrombocytopenia (lack of platelets used to clot blot.) Death often results from infection, failure of several organs or bleeding into the brain.
Please be extremely careful with 5-FU around animals. Most cats will die from exposure to a small amount. Dogs have a slightly better prognosis with 25% survival. To prevent accidental exposure:
1) Keep all medications in a safe, animal-proof cabinet.
2) Wash your hands thoroughly after handling.
3) Keep the area covered with a waterproof bandage to prevent accidental exposure.
4) Dispose of all bandages, packaging supplies, etc., immediately in an animal-proof container.
5) Do not let your pet lick your skin after application.
-Lee, Justine A. Top Ten Small Animal Toxins: Recognition, Diagnosis, Treatment. ACVIM 2010 Proceedings
-Peterson, ME, Talcott PA. Small Animal Toxicology. Elsevier, St. Louis, Missouri, 2006.