Permethrin

Permethrin, a synthetic type I pyrethroid, is found in many flea and tick shampoos, dips, foggers, spot-ons, and sprays as well as many household and yard insecticide formulations. While permethrins have a relatively wide margin of safety in dogs, cats appear to be more sensitive to the toxicity of some concentrated pyrethroids, particularly permethrin. The low-concentration products (sprays, foggers) approved for use on cats or in household premise sprays generally contain 0.05–0.1% permethrin and do not cause clinical syndrome that has been associated with the inappropriate use of concentrated products on cats (i.e. undiluted 15% dips, 45–65% permethrin spot-ons). Permethrin toxicosis usually occurs when a concentrated dog product is applied to cats, but cats that actively groom on or engage in close physical contact with recently treated dogs may also be at risk of toxic exposure. Clinical signs of permethrin toxicosis in cats include hypersalivation, depression, ear twitching, facial twitching, generalized muscle tremors or fasciculations, hyperesthesia, hyperthermia, vomiting, anorexia, convulsions, and possibly death. Onset of clinical signs is usually within a few hours of exposure but may be delayed up to 24 hours. The severity of clinical signs often varies significantly among individual cats exposed to similar amounts of permethrin, with some cats developing only mild fasciculations while others develop life-threatening signs.

Treatment of permethrin toxicosis should include control of tremors, supportive care, and decontamination. Methocarbamol (50–150 mg/kg slow IV; do not exceed 330 mg/kg/day) is preferred to control the tremors. If no injectable methocarbamol is available, the oral form may be dissolved in water and administered rectally. If the cat is actively convulsing and methocarbamol is ineffective, propofol, inhalant anesthetics, or barbiturates may be needed. Given alone, diazepam may actually exacerbate the tremors, but once methocarbamol has been used to reduce the tremor activity, diazepam (0.1-0.5 mg/kg) may be helpful at reducing hyperesthesia. The use of atropine is not indicated in pyrethroid exposures and should be avoided. Once tremors are under control, cats should be bathed to remove the product from the haircoat and skin. Liquid dishwashing soap (e.g. Dawn) should be used to bathe the entire cat. Thermoregulation is very important in these cases, as tremoring cats often present hyperthermic only to develop hypothermia following tremor control and bathing. Hypothermic cats may experience recrudescence of tremors as well as decreased metabolism of the permethrin due to decreased metabolic rate. Permethrins appear to have no direct action on the liver or kidneys, but fluids may be helpful in protecting the kidneys from myoglobin breakdown products in severely tremoring or convulsing cats. Potential complications to permethrin toxicosis in cats include disseminated intravascular coagulopathy and rhabdomyolysis due to prolonged seizuring and/or hyperthermia. The prognosis for mildly tremoring cats is usually good, but treatment may be required for up to 24–48 hours. The prognosis for severely affected cats is guarded, although many of these will make full recoveries if given aggressive veterinary care.

Etofenprox is a synthetic non-ester pyrethroid. Although some manufacturers will claim it is not a pyrethroid because it lacks an ester moiety found in most other pyrethroids, etofenprox shares much structural and, more importantly, functional characteristerics of the pyrethroids. Spot-on formulations containing 40-55% etofenprox have been approved for use on cats. Most cats tolerate etofenprox well, but a small percentage of cats will develop signs similar to permethrin toxicosis after administration of the product per label directions. Usually the signs from etofenprox toxicosis in cats are much milder and do not last as long as permethrin toxicosis; in rare instances severe signs may be seen. The clinical signs and management of etofenprox toxicosis in cats is the same as for permethrin toxicosis, with methocarbamol generally working quite well to resolve the mild to moderate tremors. The prognosis for etofenprox toxicosis is generally quite good, and many cats experience no more than mild fasciculations which resolve following bathing. Adverse reactions to products that have been used appropriately (per label) should be reported back to the manufacturer and/or appropriate government regulatory agency. Adverse reactions to appropriately used pesticides may be reported to the EPA via the National Pesticide Information Center (NPIC) at 1-800-858-7378.