Flea Products Dangerous to Cats

by catfood

E. Kathryn Meyer, V.M.D.


Jenny rushes “Sasha,” her cat, to the hospital. Sasha had a full-fledged seizure after appearing to be fine just moments before. Jenny is asked if she has used any “dog” flea-control products on her cat within the last 24 hours. In fact, she had. The Environmental Protection Agency (EPA) received 24 reports of similar incidents involving cats who became ill after being exposed to permethrin-treated dogs. This time she notices the warning: “Do not use on cats.” Permethrin accounts for 45% of the active ingredient.

Toxic Spots

Pet owners prefer spot-on flea and tick control products. They are quick and easy to use, and if used according to the label instructions, they are considered safe. When flea products intended for dogs are used on cats, the cats can become very ill, if not die.

During a 13-month period, the United States Pharmacopeia’s Veterinary Practitioners’ Reporting Program (USP VPR) received 11 reports involving cats who required hospitalization after using a concentrated permethrin “spot-on” flea product. Four of them were assassinated. Furthermore, between 1994 and 1998, the Environmental Protection Agency (EPA) received reports of 125 cats becoming ill or dying after being exposed to concentrated permethrin.

In one case reported to the VPR Program, the owner did not apply the product to the cat. Instead, the cat became ill after interacting with two previously treated large household dogs. Jenny inspects the flea control product she later applied to the back of Sasha’s neck at home. (“Exposure” was defined as licking, cuddling, or playing with the dog.) Six of the exposed cats did not survive.

Permethrin at low concentrations (2%) in flea sprays labeled “for cats” is not toxic to cats. Although the labels of these products include a clear warning against using them on cats, the warnings frequently go unnoticed or unheeded because owners are unaware of the serious consequences of using the product on cats. They are liquids that are typically packaged in small, single-use ampules and are applied to the skin once a month.

Because permethrin is quickly detoxified by the liver, it is well tolerated by most mammals, including dogs. Cats, on the other hand, are deficient in glucuronidase, an enzyme that the body uses to detoxify certain compounds. This deficiency is thought to contribute to cats’ sensitivity to concentrated permethrin, as well as acetaminophen and other medications.


Signs of Trouble

Cats exposed to concentrated permethrin usually act nervous, twitch, shake and may even develop seizures. If you believe your cat has been exposed to concentrated permethrin, immediately call the ASPCA 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. 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. 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.


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 put on dogs can affect untreated household cats; call the manufacturer for recommendations on protecting your cats
  • Don’t 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 exactly the same active ingredients

[Editor’s note: 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.]

Dr. Meyer is coordinator of the United States Pharmacopeia Veterinary Practitioners’ Reporting Program located in Rockville, MD.

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