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Efudex® (Fluorouracil) Toxicity in Dogs

By: Dr. Debra Primovic

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Can skin cream really be toxic? Efudex® (5-flouorouuracil or 5-FU), is a common prescription medication for humans used to treat actinic keratoses (also known as solar keratoses) and superficial basal cell carcinoma. It is classified as an anti-cancer or anti-neoplastic drug. The box suggests that the toxicity is low which is true for humans, but this is NOT true of dogs. The medication comes in a solution or cream and the most common method of toxicity is a dog that chews on and ingests the contents of the container.

The toxicity is severe and life threatening in dogs. If your dog has ingested any amount of Efudex®, see your veterinarian or call your local veterinary emergency clinic immediately. The agent is extremely toxic to rapid dividing cells, which can cause severe gastrointestinal symptoms. Initial signs may include vomiting, diarrhea and lethargy and quickly progresses to dementia, seizures and possibly death.

What to Watch For

  • Poor appetite
  • Vomiting
  • Diarrhea (may be bloody)
  • Abdominal pain
  • Dehydration
  • Weakness
  • Lethargy
  • Progressive dementia and inappropriate behavior
  • Seizures


    The diagnosis of toxicity is generally based on physical exam findings and a history of access or exposure to the drug.

    Blood tests are done to determine the overall health of the dog. If Efudex® was ingested, blood tests may reveal abnormal electrolyte concentrations, low white blood cell counts, kidney value elevations from dehydration. Repeat blood work is recommended to determine ongoing organ damage and effectiveness of treatment.


    Treatment is often symptomatic depending on the symptoms and condition of the pet. Gastrointestinal protectants will be given to combat related symptoms and anti-seizure medications will be given to combat seizures.

  • Expect your veterinarian to recommend hospitalization with continuous intravenous fluids.

  • Activated charcoal may be given if ingestion was recent (less than 2 hours).

  • Medications such as sucralfate (Carafate®), cimetidine (Tagamet®) or famotidine (Pepcid®) will be given to treat stomach ulcers.

  • If the dog has a severely low white blood cell count, drugs to promote white blood cell stimulation such as "Neupogen" may be recommended. This may develop quickly or up to 3 weeks after ingestion.

  • Seizures can persists for more than 24 hours and are often very difficult to control. They may be treated with different drugs including diazepam, phenobarbital, propofol, and sometimes gas anesthesia.


    The product is highly toxic. According to ASPCA Animal Poison Control Center, a dose as low as 8.6 mg/kg can cause signs (which would be about 4 g of a 5% cream in a 50-lb dog). In cases seen at the Animal Poison Control Center, the death rate from this toxicity was almost 65%.

    Home Care and Prevention

    There is no home care for Efudex® toxicity. Veterinary care is strongly recommended to treat severe gastrointestinal symptoms and life-threatening seizures.

    While recovering from Efudex® toxicity, feed your dog a bland diet for one to two days. Gradually return to a normal diet. Watch for failure to eat, vomiting and continued black tarry stools.

    The best preventive care is to give your dog medications only if directed by your veterinarian. Medications that may be safe for people can be fatal to pets. Also, make sure that all medications are kept out of the reach of inquisitive pets. Keeping medicine safely stored away can prevent many tragedies.

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