If the dog gets to that point of foaming at the mouth it unfortunately is almost certainly too late to do anything about it. This sounds gruesome, but a friend of mine who has and loves dogs found his dog in the same situation on his land and he shot it in the head with a shotgun to end his suffering faster. It was a very difficult trigger to pull for him because he loved that dog.

The fact of the matter is that with poison, if it has been in the dog's system for too long there probably isn't anything a veterinarian can do for them because the poison has already liquified their internal organs.