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5-fluorouracil (5-FU)


Poisonous to: Cats, Dogs

Level of toxicity: Generally severe and life-threatening

Common signs to watch for:

  • Drooling
  • Abdominal pain
  • Vomiting
  • Diarrhea
  • Walking drunk
  • Tremors
  • Seizures
  • Acute death

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One of the most dangerous topical toxins to be aware of is 5-fluorouracil (5-FU), which is a prescription anti-cancer medication used topically for humans with superficial basal cell carcinoma or actinic keratosis. While the intravenous form of this chemotherapy drug is often safely used in dogs, the topical version is very poisonous when ingested by dogs or cats. Even tiny amounts can be very toxic, resulting in acute gastrointestinal signs (e.g., vomiting, diarrhea), central nervous system signs (e.g., severe 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 up to 6 hours; death has been reported as early as 7 hours. The prognosis with 5-FU ingestion is grave in cats and guarded in dogs (with a reported survival in dogs of approximately 25%).

Poison type: Medications

Alternate names: 5-FU, Efudex, Carac, Adrucil, Fluoroplex, topical chemotherapy