Cancer cream poses little-known risk to pets

An undated handout photo shows Ruby the Yorkshire Terrier. REUTERS/Archives of Dermatology/Handout

NEW YORK (Reuters Health) - Scientific journals usually aren’t the province of puppy pictures, but the October 2010 issue of Archives of Dermatology contains an image of pitiable Ruby, a young Yorkshire Terrier with a tragic medical history: Ruby died of accidental poisoning after gnawing on a tube of her owner’s cancer therapy, a potent cream called 5-fluorouracil.

Doctors who reported the case caution that pet owners using the drug-commonly prescribed to patients with a form of skin cancer called actinic keratosis-should be aware of the risk it poses to their animals and take steps to keep the medication away from curious snouts.

“5-fluorouracil cream is extremely toxic to dogs, for unknown reasons,” said Dr. Nicholas Snavely, a dermatologist at the University of Virginia, Charlottesville, and a co-author of the report on the case. “Very small doses will send them into seizures and they die-and people don’t know about this.”

Poisoning officials receive 30 to 40 reports a year of pets, almost all dogs, ingesting 5-fluorouracil, said Dr. Safdar Khan, director of toxicology at the Animal Poison Control Center, in Urbana, Illinois. That’s more than for other cancer drugs, but fewer than reports involving antidepressants and stimulants, which cause most cases of animal poisonings by human medications, he said.

5-fluorouracil is so toxic to pets that even the residue that remains on a person’s skin can be deadly to a small animal if licked. But most cases of poisoning linked to the drug involve tubes left in places where they can fall prey to chewing.

That’s precisely what happened to Ruby, a 4.5-pound Yorkie whose owner came to see Dr. Snavely and a colleague about the actinic keratoses on his face. When they suggested that the man use 5-fluorouracil he declined, telling the physicians that he’d previously received a prescription for the drug, which his dog had managed to bite open. Ruby soon began vomiting, suffered seizures and died several hours later at a local animal hospital.

Scarred by the episode, the patient did not want to risk accidentally poisoning another of his dogs, Dr. Snavely and his colleagues wrote in a letter to the journal.

Dr. Khan told Reuters Health that pet owners with a prescription for 5-fluorouracil cream should avoid handling their animals after applying the drug. And leaving it within reach of any pet, he said, “is absolutely not a good idea.”

SOURCE: Archives of Dermatology, October 2010.