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In a sad reminder about how life-saving drugs can also be extremely dangerous, five dogs have died after eating skin cream their owners were using to treat cancer, the Food and Drug Administration announced in a statement yesterday.

The FDA is warning pet owners who have this medication—known as 5% Fluorouracil cream USP (or 5-FU) and sold under the brand names Carac, Effudex, and Fluoroplex—to use care when storing and applying the chemotherapy drug, which can be fatal when ingested even in tiny amounts.

In one report received by the FDA, a dog was playing with a tube of Fluorouracil cream and punctured it before the owner could get it away. Within two hours, the pet began vomiting and having seizures, and it died 12 hours later. In another case, a veterinarian attempted to treat a dog after it had eaten the contents of a tube—but he still got sick, and had to be euthanized three days later. 13 Fun Ways to Work Out With Your Dog

While the agency hasn’t received any reports involving cats, health officials expect that they would be extremely sensitive to the drug, as well. Even touching a pet after applying Fluorouracil cream to your own skin could be dangerous, they say, if the pet then ingests traces of the medicine.

Fluorouracil is a type of drug known as an antimetabolite, which works by killing fast-growing cancer cells. It’s prescribed to treat a type of skin cancer called superficial basal cell carcinoma, and precancerous skin lesions caused by sun exposure, called actinic keratosis.

If you have Fluorouracil cream in your home, the FDA recommends storing it safely out of reach of all pets. Be sure to discard or clean any cloth or applicator you use to apply the cream, and don’t leave any residue on your hands, clothing, carpet, or furniture.

Check with your doctor, as well, about whether it makes sense to cover the area of skin that’s being treated.

In 2001, the American Society for the Prevention of Cruelty to Animals reported in a toxicology brief that dogs weighing less than 160 pounds could get sick by eating half the contents of a 25-gram tube of Fluorouracil cream, and that dogs less than 70 pounds could die. These tubes are quite small, the brief states—about 11 centimeters long—so even small dogs could easily ingest their entire contents.

If your pet does become exposed to this drug or other human medicines—or shows symptoms of poisoning, such as vomiting or seizing—get him or her to the vet immediately, and provide them with as much information as you can. Pet owners and vets are encouraged to report adverse events to the FDA, as well.

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