"It is critical for owners to be aware of the severe consequences of using flea products incorrectly -- particularly when cats are involved -- because cats can be very sensitive to certain chemicals," said Meyer, who coordinates the U.S. Pharmacopeia Veterinary Practitioners' Reporting Program.
The organization, which identifies quality problems with products, medication and chemicals used in veterinary medicine, published a report on the topic in Thursday's issue of the Journal of the American Veterinary Medical Association.
While flea products often are packaged similarly, the active ingredients can vary greatly, especially among popular "spot-on" products in which a small amount of liquid is applied directly to the animal's skin.
A common chemical in such products is permethrin, which can be toxic to cats. In products made for dogs, permethrin is usually concentrated at levels of 45 percent to 65 percent. Flea sprays intended for cats contain much lower -- and safer -- concentrations, often about 2 percent.
Meyer advised cat owners to closely follow directions on flea products because even small amounts of permethrin can be bad for cats.
"Furthermore, people who own both dogs and cats should be aware that 'dog-only' flea products applied to their dogs can cause illness in cats that are in close contact with the treated dogs," she said.
Meyer's organization received 11 reports between August 1997 and September 1998 involving 12 cats that were hospitalized after exposure to a concentrated permethrin flea product. Four of the cats died.
The article also cites similar cases reported to the Environmental Protection Agency, which received accounts of about 125 cats that got sick or died following incorrect applications of permethrin. About two dozen of the felines became ill or died because of contact with treated dogs.
Symptoms of permethrin toxicity in cats include excitability, twitching and seizures. Cat owners noticing signs should quickly bathe their pet in mild dishwashing detergent and seek veterinary care.