I am looking for help with cat colds and saw your post...you can help your cat by giving him acidophilus the 'friendly' bacteria we need in our system...same as in yogurt. You can use people version or find some for pets at a good pet store. Unfortunately, when we or animals take antibiotics this only helps destroy the good bacteria that's left and we can take even longer to get better. It's safe, you can't really overdose, and it aids in all kinds of health not just bowel trouble! BUT it's absolutely necessary for that! Get capsules you can pull apart and mix with a small bit of food (to make sure he gets the whole dose). A couple of times a day for a couple of days should do it!
Good Luck!