Toxicity to pets

One of the most dangerous topical toxins to be aware of is 5-fluorouracil (5-FU), a prescription anti-cancer medication used topically to treat human skin cancers (e.g., superficial basal cell carcinoma) and actinic keratosis. While the intravenous form of this chemotherapy drug can safely be used in dogs, the topical version is very poisonous when ingested by dogs or cats. Even tiny amounts can be very toxic and can result in acute gastrointestinal signs (e.g., vomiting, diarrhea), central nervous system signs (e.g., tremors, seizures, etc.), and bone marrow suppression. 5-FU is rapidly absorbed from the gastrointestinal tract, and clinical signs can often be seen within 30 minutes to 6 hours with deaths reported as early as 7 hours after ingestion. Immediate treatment is necessary, and the prognosis with 5-FU ingestion is grave in cats and guarded in dogs.