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  1. CVM Updates

CVM Drug Safety Communication: Fluorouracil Products Used on People's Skin Can Cause Serious Reactions in Pets


September 7, 2022

The U.S. Food and Drug Administration (FDA) is reminding pet owners, veterinarians, health care providers, and pharmacists that pets may become seriously ill or die when exposed to the FDA-approved prescription topical medication, 5-fluorouracil (also called 5-FU or fluorouracil). Topical fluorouracil is used on the skin to treat various conditions in people, including certain types of skin cancer. It is marketed under the brand names Carac, Efudex, Fluoroplex and Tolak, and the generic name, Fluorouracil Cream USP, 5%. Physicians prescribe topical fluorouracil for people to treat superficial basal and squamous cell carcinomas (two types of skin cancer), actinic or solar keratoses (scaly skin lesions that can develop into skin cancer), vitiligo (loss of skin pigment due to an immune disorder), and warts.

FDA has received reports of dogs having serious reactions after being accidentally exposed to topical fluorouracil. All the dogs died or were euthanized (put to sleep) due to the severity of their condition. FDA has not received any reports about fluorouracil poisoning in cats. However, cats are also likely to be very sensitive to the drug. 

Many people treated with topical fluorouracil have pets, but health care providers and pharmacists may not be aware of the drug’s toxicity to pets. Nearly all cases of pets being exposed to fluorouracil are accidental, mainly from pets chewing on tubes of the medication. 

Pets can potentially be exposed when they lick their owner’s skin where the medication was applied. Pet owners should prevent their pets from having access to the medication and having contact with the treated area.

Signs of fluorouracil poisoning in pets include vomiting (with or without blood), seizures, tremors, difficulty breathing, decreased activity level, and diarrhea (with or without blood). Death may occur without prompt treatment. 

To help increase awareness about the toxicity of fluorouracil to pets, 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.”

FDA will continue to monitor reports of reactions in pets after being exposed to topical fluorouracil products. The agency encourages pet owners, veterinarians, and other health care providers to report reactions in pets associated with these products or with any drug for people or animals. See How to Report Animal Drug Side Effects and Product Problems.

Additional Information

Issued by FDA Center for Veterinary Medicine.
For questions, Contact CVM.

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