Article from the ASPCA (The American Society for the Prevention of Cruelty to Animals)

READ THE LABEL FIRST! also see ‘any flea control’ below
Attention, cat caretakers! If you are using flea-control products on your pet, the ASPCA Animal Poison Control Center (APCC) urges you to always follow the instructions on the label–and never use any product that is formulated “for dogs only.”
There are more than 18 brands of flea-control products for canines that contain permethrin–just a few drops of which can be lethal to felines. Signs of toxicity, which can develop anywhere from a few hours to two days after application, include tremors and seizures. Most cats will recover with prompt, aggressive treatment, but prevention is the best medicine. Simply use species-appropriate products, follow the instructions on the label, and don’t hesitate to consult your veterinarian if you are unsure of the proper use of any flea-control product.
If you suspect that your cat has been exposed to permethrin, call your veterinarian or the APCC’s emergency hotline– 1 888 4 ANI -HELP –for round-the-clock telephone assistance. For more information on what’s toxic and what’s not–and what you can do to prevent your pet from being poisoned–visit APCC online.
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