Our five year old American Staffordshire Terrier had a dose of Iverhart Max (first time he took this) last Friday and Monday he started limping on his back legs. It has gotten worse every day. We took him to the vet yesterday (had to carry him into the truck) and when we got there I was getting ready to pick him up, but he mustered up enough strength to walk into the vets office by himself, so the vet said it was probably arthritis. This morning he could barely walk to go to the bathroom. After he was done he just laid down on his side, and I had to carry him inside. He never had leg problems before taking Iverhart Max. Was wondering if it's caused by the pill and if it's temporary or permanent? He still eats his food (not quite as much as before) and barks at people that pass by but he does everything while lying down.