Rosana,
I haven't had time to read many posts lately and I just read all of yours. I'm so glad to know that after all your sleepless nights, finally, Rex is yours to keep. Those owners # 1 and 2 sound like awful people; I heard of bad things being done to dogs, but I never heard of an owner giving drugs to a poor pup.
From now on Rex will know that he is in his forever home where he will be loved and taken care of. Bless you for having rescued him from a terrible situation and best wishes for a very long and healthy life for Rex. Many hugs to him and you.
Alicia