At the end of summer I gave these drops to one of my cats within 48 to 72 hours he was throwing up and foaming at the mouth. He was lethargic and acted like he was going to die. After hours of trying to get a vet to answer on a Sunday, I took him into the vet. They started him on an IV and said he had kidney problems. They gave him an oral medicine, pills and the IV. Well he got better and I did not relate the drops to the episode until I gave the drops to another one of my cats this past week and he had the same signs. Unfortunately, he was not as lucky, he died with in hours of the symptoms. I called Hartz and they said that the cats probably licked the treatment. Well it was on the back of their necks and in my opinion, could not possibly lick that part of their bodies. I told them that I have other cats and they would more than likely be the ones licking the treatment. Hartz offered no suggestions and did not want to test the third treatment but wanted my dead cat. Hartz needs to be off of the market.