5-fluorouracil (5-FU) is an anti-cancer medication commonly prescribed by dermatologists to treat basal cell carcinoma and actinic keratosis on the skin of humans. Unfortunately, this medicine is highly toxic to animals. Pets develop gastrointestinal and neurologic symptoms. Gastrointestinal signs include vomiting, bloody diarrhea, intense abdominal pain and sometimes, sloughing of the intestinal lining. The neurologic …