Dog flea/tick spot-on products applied to cats

Hazard

High-concentration (45-65%) permethrin spot-on products made for dogs are highly toxic to cats, which lack the enzyme needed to detoxify permethrin. Cats can also be poisoned secondhand by grooming a treated dog. Causes tremors, seizures, and hyperthermia; there is no antidote, only supportive care.

Notes

Low-concentration (~2%) permethrin sprays labeled for cats are not considered toxic to cats at that concentration.

Source: ASPCA Professional; veterinary literature · view original