Wow! That Frontline must be some powerful stuff. :shock: We used it on our Labrador, Molly, when she was about 5 months old. It caused a large sore on her back that had to be drained and then treated for a while with some antibiotic/cortisone spray. After that, we switched to Advantage for Molly and that is what we use on Tucker, also. I'm sorry you and Gadget are having to go through this, but as you said, it won't happen again!!!