I hope that the cisapride and chloramphenicol can help him. Fingers very firmly crossed!
PS: If your boy has had such a bad reaction to baytril/enrofloxacin (or whether something else is going on), then giving probiotics would not have changed anything. I know that from my own experiences with adverse reactions to antibiotics. Probiotics are a not an all-heal magic wand measure as you seem to think. If they really were, every vet would prescribe them as a matter of fact.
PS: If your boy has had such a bad reaction to baytril/enrofloxacin (or whether something else is going on), then giving probiotics would not have changed anything. I know that from my own experiences with adverse reactions to antibiotics. Probiotics are a not an all-heal magic wand measure as you seem to think. If they really were, every vet would prescribe them as a matter of fact.