I feel for both of you. You’re stuck in a tough place. There are different types of antibiotics if memory serves me well so it may be best to see if there is something else they can prescribe that might be less devastating or at the very least some probiotics that you can put him in that will help offset the gut issue. I am only speaking from what I’ve heard my wife talk about for herself. I was on antibiotics so much as a kid that my gut bacteria has never properly recovered. I have yet to find a probiotic that works for me. They all make me sick. Almost everything makes me gassy and in pain so I really feel for your pup. Not sure if they make a gasX product for pets but that may help too.