Some of his ribs are showing and at times he eats pebbles and passes them out in his stool.He was dewormed last Sunday and the dog chow he was eating has been discontinued and another brand chosen.Cannivites are also being given along with some tonic.

How old is he and when was his last vet check?

Usually when they eat rocks, it's a sure sign of worms. What type of de wormer are you using? And where did you get it from? What types of worms does it treat for? And how many doses have you given your dog? What is the type of dog food that you are feeding? Have you treated for fleas along with the worms?