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Permethrin is a pyrethroid insecticide used in topical (spot-on) flea treatments for dogs. These products are contraindicated in cats because of a high risk of toxicosis but there have been many reports of owners ignoring or not noticing warnings on the product packaging.
The authors describe the findings in 286 cases of inappropriate use in cats reported by veterinary practitioners to the Veterinary Poisons Information Service in London. In 96.9% of these cases, the cats showed clinical signs, with increased muscle activity (twitching, tremor, fasciculations or convulsions) occurring in 88% of cases.
The duration of this muscle activity was long, with convulsions lasting for an average of 39 hours and tremors for 32 hours. Recovery typically occurred within two to three days but in some cases it took up to seven days. In 10.5% of cases the affected cat died.
Journal of Feline Medicine and Surgery 9 (4): 335-339.
Abstract reproduced by kind permission of Veterinary Practice magazine.