Toxic spots: a flea control hazard for cats

Jenny rushes her cat “Sasha” to the emergency clinic. Sasha, who seemed fine a short time ago, just had a full-blown seizure. The veterinarian asks Jenny if she applied any “dog” flea control products to her cat in the past 24 hours. In fact, she has. At home later, Jenny looks closely at the flea control product she put on the back of Sasha’s neck. This time, she notices the warning: “Do not use on cats.” The active ingredient is 45 percent permethrin.

Spot-on flea and tick control products are deservedly popular among pet owners. They’re fast and easy to use, and they are considered safe — as long as they are used according to label instructions. But when flea products designed for use only on dogs are applied to cats, the cats can become very ill and even die.

Over 13 months, the Veterinary Practitioners’ Reporting Program of the United States Pharmacopeia (USP VPR) received reports involving 11 cats who required hospitalization following the application of a concentrated permethrin “spot-on” flea product. Four of them did not survive. Also, between 1994 and 1998, the Environmental Protection Agency (EPA) received reports of 125 cats who became sick or died after having concentrated permethrin applied.

In one instance reported to the VPR Program, the owner did not apply the product to the cat. Instead, the cat became ill when it interacted with two large household dogs who had been treated. Twenty-four similar incidents involving cats who became sick from exposure to permethrintreated dogs were reported to the EPA. (“Exposure” included licking the dog, cuddling or playing with him or her.) Six of the exposed cats did not recover.

Low concentrations (2 percent) of permethrin, as in flea sprays labeled “for cats,” are not considered toxic to cats. It is only the spot-on flea products that contain high concentrations (45 to 65 percent) of permethrin and are approved for use on dogs only that are considered dangerous. They are liquids, usually come in small, single-use ampules and are to be spotted onto an area of the skin once a month. Most mammals, including dogs, tolerate permethrin well because it is quickly detoxified by the liver. However, cats lack glucuronidase, an enzyme that the body uses to detoxify certain compounds. This deficiency is believed to be responsible for cats’ sensitivity to concentrated permethrin, as well as to acetaminophen and other substances.

Signs of Trouble

Cats exposed to concentrated permethrin usually act nervous, twitch, shake and may even develop seizures. If you think your cat has been exposed to concentrated permethrin, immediately call the ASPCA National Animal Poison Control Center at (900) 680-0000 and your local veterinarian or emergency veterinary clinic. Treatment consists of thoroughly removing the permethrin product, giving medication to control tremors or seizures, and providing fluid and nutritional support. Immediate treatment offers the best chance of survival.

Most permethrin spot-on products are readily available and are administered without veterinary advice. The labels of these products do include an explicit warning against use on cats, but the warnings often go unnoticed or unheeded, because owners are not aware of the potential for severe consequences if the product is used on cats. Also, few labels warn consumers that cats can become ill or die by interacting with treated dogs.

Pet owners should be aware that products with similar brand names may contain different active ingredients. Confusion can also result from similar packaging for different types of spot-on flea control products, only some of which are safe for use on both dogs and cats.

The new, more convenient flea-control products are a great boon to cats, dogs and owners. We must not let carelessness turn time-savers into tragedy.


This article is based on ‘Toxicosis in cats erroneously treated with 45 to 65% permethrin products” by E. Kathryn Meyer, V.M.D., in the Journal of the American Veterinary Medical Association, Vol. 215, No. 2, pp. 198-203.1 Dr. Meyer is coordinator of the United States Pharmacopeia Veterinary Practitioners’ Reporting Program located in Rockville, MD.

Do’s and Don’ts for Cat Owners

  • Do read the entire label before buying and again before using any flea product
  • Do buy only products that are specifically labeled for use on cats
  • Do retain original packaging for reference
  • Do seek immediate veterinary advice if your cat is having a reaction to a flea product
  • Do be aware that flea products applied to dogs can affect untreated household cats; call the manufacturer for recommendations on protecting your cats
  • Dont assume that flea products that look the same are the same
  • Don’t assume a small amount of a dog product is safe for cats
  • Don’t assume that cat and dog versions of the same brand contain the same active ingredients

Keep your kitties safe!
Buy your flea products from your veterinarian!


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