Ask your vet about Vit B12 (cobalamin) injections, which can sometimes be helpful in cases of extreme GI distress. Here's a link from Texas A&M University: http://vetmed.tamu.edu/gilab/researc...in-information
Also, maybe the pup needs a dextrose solution in the subQ fluids? How are the rest of his electrolyte levels?
"To close your eyes will not ease another's pain." ~ Chinese Proverb
“We must not refuse to see with our eyes what they must endure with their bodies.” ~ Gretchen Wyler