This toxin is considered to be a very high risk and your pet should be evaluated as an emergency at your nearest veterinary hospital. You may want to contact whiskerDocs or the hospital if your pet has recently ingested this toxin to see if there are additional steps you need to take before leaving home.
5-FU, also known as 5-Fluorouracil or just as Fluorouracil, is commonly used in humans to treat superficial basal cell carcinoma or actinic keratosis, and has even been used in dogs for treatment for certain cancers. However, while the IV form at the proper dosage can be safe, eating or licking the cream that has been prescribed for you can cause some very serious side effects, ranging from stomach upset with vomiting and diarrhea to seizures and death. Signs of toxicity have been known to appear anywhere from 30 minutes to a few hours after exposure. Any suspected ingestion of a topical chemotherapy agent warrants an immediate trip to the emergency room!