i had 2 small dogs, my older one was a male jack russell/chihuahua mix. he was 12 years old. we had used the flea and tick killer from the vet, but had run out. i purchased the hartz brand at walmart and applied it to both dogs. both dogs weighed about 10 pounds, so i purchased the one for small dogs. we applied it as instructed, immediately the female ran frantically through the house, we finally shampooed her and she calmed down. the male dog “rambo” went under the bed and would not come out, this was not really alarming because he slept there quite frequently. overnight he developed diaherra, i cleaned 8 places up by morning. he always used the yard and lets us know he wants to go. the next day it continued and he would not eat very much. he then would not eat at all by the 3rd day and was thowing up yellow liquid in small spots. we took him to the vet and he was dehydrated and in renal failure. the vet said those products can be hard on the kidneys. we tried to nurse him back but he could not walk anymore, would not drink or eat. after three days on iv he was still throwing up and had diaherra. he developed a high fever, had trouble breathing. several times he stopped breathing and was on oxygen. we could see he was suffering so we had him put to sleep. i truly believe that the hartz flea and tick killer did this. the hartz companyshould put a warning on this product not to use on older animals.