one thing to be aware of with permethrin, It is not known to rapidly harm most mammals or birds, but is dangerously toxic to fish and to cats: in cats it may induce hyperexcitability, tremors, seizures, and even death.
This is why I don't use it, I can risk accidentally bringing it into the house and harming my daughters cat. Especially since permethrin claims to last through several washings.
Vet Info