You could give him Tagamet, (an anti-acid) safe for dogs. For diarrhea, soft-boiled eggs
always work great for my dogs, (eggs
are binding, but other soft/easily digestable foods for a few days might also do the trick- such as cottage cheese, macaroni & cheese). Or, canned pumpkin works for diarrhea- (not the pumpkin pie stuff w/spices...plain canned pumpkin) - feed a couple of tablespoons several times a day, or mix in with food- it adds fiber and will stop diarhea within 24-48 hours.