Now most cat pet owners know NEVER to use Flea meds for dogs on cats, but what some owners do not realize is that your cat sniffing your pup after a dose flea meds or sleeping in his or bed can result in the same toxic side effect.
Pyrethroid toxicosis, typically involving Permethrin, is one of the most commonly reported toxicities in cats to the ASPCA Animal Poison Control Center. Inappropriate exposure of cats to Permethrin products results in as many as 97% showing clinical signs with 10.5% ending in death if not treated early and aggressively.
Cats liver’s do not have the ability to process Pyrethrin so even small dose of this substance can cause a reaction. Pyrethrin is also commonly used in bug sprays etc. So always read your labels and be sure that you do not accidentally apply dog flea meds to your cat. If you have a multi- pet household be sure to flea your dogs in an area away from your cats and keep them separated until the medicine is absorbed.
Flea meds for cats are available but just be cautious as it is a poison so apply sparingly and carefully.
For more info see the excerpt and link below
Pyrethroid insecticidal products are neurotoxicants targeted toward the nervous system of fleas and other insects, and are used in topical spot–on and household products available over-the-counter and at veterinary hospitals. Topical flea control products are used commonly on pets due to ease of administration and overall good efficacy. Pyrethroids have replaced natural pryrethrins in may products to increase efficacy and stability. Products labeled for use on dogs-only and not intended or safe for cats are often mistakenly or purposely applied to cats. Cats are often intolerant of some insecticides and medications probably because of their livers reduced ability to metabolize some compounds. Adverse reactions can result from an unusual sensitivity at low doses, immune-based allergic sensitively or true toxic reactions at labeled or high doses.
Clinical signs of permethrin poisoning in cats range from facial tremors and ear twitching to generalized muscle tremors and seizures. Some cats salivate profusely and vomit, but this is more likely from ingesting insecticide during grooming or inhalation of mist if sprayed.
http://www.petside.com/condition/cat/pyrethroid-poisoning-feline