Cats are especially sensitive to permethrin, a pyrethroid insecticide used in spot-on flea treatments in dogs. Despite cautionary labeling, these products are still sometimes used inappropriately on cats. Cats are also at risk for secondary exposure through other pets treated with a permethrin spot-on (PSO). A veterinary poison telephone service in the United Kingdom reviewed 286 cases of feline exposure to PSO products. Clinical signs of toxicosis usually manifest within 3 hours of exposure, but may be delayed for 72 hours. The study found 96.9% of the cats developed clinical signs, the most common of which were convulsions (43.7%), muscle twitching (35.3%), tremors (33.6%), hypersalivation (22.7%), and ataxia (22.0%). Convulsions lasted an average 38.9 hours (range, 2 hours to 5 days) and tremors 32 hours (range, 2 hours to 3 days). Overall recovery took approximately 61.5 hours (range, 3 hours to 7 days). Death resulted in 10.5% of the cases. None of the surviving cats appeared to have long-term sequelae. Treatment of exposed cats consists of washing in lukewarm (not hot) water with a mild detergent and supportive care. There is no specific antidote-control of seizures is the top priority. Methocarbamol can also be used to control increased muscle activity and can be effective when barbiturates fail. This study suggests feline PSO exposures are common and dangerous and that current labeling of these products is not sufficient. The authors recommend reviewing warning labels for effectiveness and increasing owner awareness about the risks of permethrin exposure in cats.

COMMENTARY: It is not uncommon for owners to look for less expensive alternatives to flea control. Many do not realize (until educated by the veterinary team) that the spot-on treatment they are purchasing at the store is not the same as the spot-on treatment being offered at their vet's. It is not surprising, then, that despite label warnings, permethrin spot-on toxicity remains one of the top 10 toxicoses in cats. Clearly, as shown in this article, exposure is highly dangerous, with most cats showing clinical signs. Client education aimed at prevention is key. However, the veterinary team must be acutely alert for any signs of toxicoses in cats or any history of exposure-apparently, even from other treated animals in the household.

Clinical effects and outcome of feline permethrin spot-on poisonings reported to the Veterinary Poisons Information Service (VPIS), London. Sutton NM, Bates N, Campbell A. J Feline Med Surg 9:335-339, 2007.