This is the pink stuff, right? I think over here it goes by "trisul".
If it's the same stuff, then it's okay for chins, but the only time I've had it for one of my girls was when my old chin Poppy got pyometra. Hopefully someone with better knowledge will chime in soon, and let you know how it works for cases of diarrhea.
Did your vet did any light microscopy on a poop sample to check for flagellates? Send a sample away for culturing and resistance analysis? The vet really needs to know what bacteria is causing the diarrhea, to be certain that the antibiotic will work.
In the meantime, do you have critical care on hand in case your chin loses it's appetite? That can often happen when they're on antibiotics. Also you might want to get some probiotics to offset the effect on the chins gut flora. You can get the capsules from any pharmacy, then just open the capsule and add to the critical care, or just sprinkle over their pellets.
Also, keep an eye on the water bottle... make sure your chin isn't getting dehydrated.