FDA warns that topical drug for humans can be deadly to pets

The Food and Drug Administration is reminding pet owners, veterinarians, pharmacists, and other health care providers that pets can become seriously ill or die when exposed to the FDA-approved prescription topical medication 5-fluorouracil, also called 5-FU or fluorouracil, used to treat various conditions in people. The agency asked manufacturers of topical fluorouracil products to add a warning to medicine containers.

“As of September 2022, the FDA had received 14 reports involving 20 dogs that had been accidentally exposed to fluorouracil,” said Juli Putnam, a spokesperson for the FDA Center for Veterinary Medicine. “It’s important to note that every event reported to FDA ended in death of the dog, even when only a small amount of drug was ingested. Also, because consumers and veterinarians may not always report these incidents to the drug manufacturer or FDA, we are concerned that the actual number of exposures and deaths could be higher. That’s why we also worked with the drug sponsors to include information about the hazard of pet exposure in the new labeling.”

The agency has not received any reports about fluorouracil poisoning in cats. However, cats are also likely to be very sensitive to the drug.

Topical fluorouracil is used on the skin to treat various conditions in humans, including certain types of skin cancer. It is marketed under the brand names Carac, Efudex, Fluoroplex, and Tolak, as well as the generic name fluorouracil cream, 5%. Physicians prescribe topical fluorouracil for people to treat superficial basal and squamous cell carcinomas, actinic or solar keratoses, vitiligo, and warts.

Nearly all cases of pets being exposed to fluorouracil are accidental, mainly occurring when pets chew on tubes of the medication. Pets potentially can be exposed if they lick a person’s skin where the medication was applied.

Signs of fluorouracil poisoning in pets include vomiting, seizures, tremors, difficulty breathing, decreased activity, and diarrhea. Death can occur without prompt treatment.

To help increase awareness about the toxicity of fluorouracil to pets, the FDA asked the manufacturers of topical fluorouracil products to add the following warning to the medicine containers: “May be fatal if your pet licks or ingests. Avoid allowing pets to contact this tube or your skin where [name of specific fluorouracil product] has been applied. Store and dispose out of the reach of pets.”

The FDA will continue to monitor reports of reactions in pets exposed to topical fluorouracil products. The agency encourages pet owners, veterinarians, and other health care providers to report adverse events in pets associated with these products or with any drug for people or animals.