Permethrin (in dog flea treatments) in Pets

Dog flea spot-ons containing permethrin can cause tremors and seizures in cats. Convert a pipette to mg/kg, learn the signs and the 72-hour window, and what to do now.

What It Is

Permethrin is a pyrethroid insecticide used in many spot-on flea and tick treatments for dogs. It keeps nerve sodium channels open. Dogs break it down quickly, but cats metabolise it poorly, so a dog-strength product can cause severe tremors and seizures in a cat.

Where Pets Come Across It

Almost all feline cases come from a dog spot-on (often 45–65% permethrin) applied to a cat by mistake, or from a cat cuddling or grooming a dog treated in the last day or two. Garden and household sprays usually contain much lower concentrations.

Which Animals Are Affected

Cats. Dogs tolerate permethrin well at labelled doses. Fish and many invertebrates are also very sensitive, so keep it away from aquariums.

Published Toxic Dose

No precise feline threshold is published. The Merck Veterinary Manual notes that cats are more sensitive to pyrethroids than other pets, and poison centres report severe signs after a single dog pipette, which can contain hundreds of milligrams of permethrin. Low-concentration products (under about 1%) rarely cause more than drooling. The calculator therefore gives no risk level here, only advice to call.

Signs and How Soon They Appear

Signs usually begin within a few hours of application but can be delayed for up to 24 to 72 hours: twitching of the ears and face, generalised tremors, high temperature, dilated pupils, drooling, wobbliness and seizures.

What to Do Right Now

Call a vet or poison line straight away. They may advise washing the product off with lukewarm water and mild hand dishwashing liquid before you travel; do this only if you are told to and your cat is not already trembling. Keep your cat warm afterwards and apart from recently treated dogs. Do not give any medicine at home.

Frequently Asked Questions

Sources and References

• Merck Veterinary Manual: Plant-Derived Insecticide (Pyrethrins and Pyrethroids) Toxicosis
• ASPCA Animal Poison Control Center

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