If you or someone in your home is being treated with topical medications for skin cancer, you’ll want to pay very close attention: The FDA has issued a statement warning pet owners about the use of the prescription medication 5-fluorouracil (5-FU).

5-fluorouracil is a topical medication prescribed for the treatment of human skin cancers, like superficial basal cell carcinoma or squamous cell carcinoma. It is sold under the following brand names:

  • Carac
  • Efudex
  • Fluoroplex

The medication is also used intravenously as a chemotherapeutic agent in dogs with some types of cancer, but if pets are exposed to the drug orally it is deadly - even in tiny amounts.

Signs and symptoms of 5-fluorouracil toxicity in pets

Dogs and cats are extremely sensitive to the effects of 5-FU if exposed orally. Clinical signs usually show up about 30 minutes to six hours after exposure, and death can ensue in as fast as seven hours.

Signs of 5-FU ingestion include:

  • severe vomiting
  • diarrhea
  • staggering
  • tremors
  • seizures

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How to keep your pets safe

The prognosis for pets who have been exposed to 5-FU is grim. Only a quarter of dogs will survive and the stats are even worse for cats. If you use 5-FU, please keep your medications well out of reach of your pets.

Additionally, talk to your doctor about whether or not it is appropriate for you to cover the skin that you’ve treated to prevent accidental ingestion if your pet licks you. Keep in mind that if you’ve applied the medicine and then pet your dog or cat, they can then be exposed through routine grooming of their own fur.

The FDA reports that five dogs have died after being exposed to their owner’s topical medication. These five dogs are the ones that have been reported to the FDA—but we know many more pets may have died in veterinary clinics across the country without their pet parent filing an adverse reaction claim to the FDA about 5-FU.

Wash your hands thoroughly after application of 5-FU and dispose of any dressings appropriately. Your pets may not have the good sense to stay out of the trash can, so either get a covered can or place it out of pets’ reach. Their lives depend on you!

Updated October 17, 2019

Apr 3, 2017
Pet Health

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