Disclaimer - I am not making this claim... I saw this on Facebook as a share and I am simply sharing as well. I would get Vet feedback before I use but I think that should be done before we use any over the counter products.
"Just saw this on tumblr. This is a warning against Hartz Flea treatment products. It has caused numerous deaths in cats and dogs, not to mention severe burns (like this one) and seizures. Veterinarians say it is pure poison. If you love your pet DO NOT use Hartz flea treatment products."