Oh Boy!!! Amoxicillin is not safe as an oral drug...it has to be injected. It is a "kill all" in the gut. I would immediately start giving him a probiotic such as Bene-Bac. While this does not replace the natural bacteria in the gut, it willstart to stabilize the pH in the gut and hopefully will allow the beneficial bacteria a proper environment to repopulate. I would offer him as much hay as possible and keep him hydrated.Except for the Bene-Bac, I would try to keep things as basic as possible going in that gut. No nutrical, no Pepto, no treats. These type of things only "confuse" the gut even more....you want to "steady the ship" as quickly as possible.Pepto also contains a form of aspirin...salicylate...which is not a good thing in a rabbit's compromiseddigestive system (due primarily to the formation of gastric ulcers).The Bismuth Salicylate in Pepto also acts as an antacid...and you need a stable acidic climate to grow the beneficial bacteria. The way to do that is lots of hay and hydration. If you can do sub-q fluids (or IV) that would be great....if not, unflavored Pedialyte is the way to go.
As far as the Baytril not working against pasteurella, not at all surprised. We stopped using that drug quite some time ago as a front line treatment for most anything. Zithromax....it has to be used in proper dosing for a longer time to be effective. Couple of things, the only way to know it's pasteurella is to culture the current infection. Next, pasteurella can never be cured, only contained. Anything that can cause the slightest compromise in the immune system can allow this bacteria to make an undesired appearance. And to be honest, we are starting to see some resistant bacteria to zithromax. I have been using more Doxycycline of late. But the only true way to know what to treat is get a current culture.
Many drugs such as amoxicillin, spiramycin, amikacin and ampicillin (to name a few) can be used in certain situations. These "situations" should always involve a highly skilled rabbit vet and should never be attempted by anyone other than that.
I think I would have a very serious sit-down with the vet that prescribed oral amoxicillin and get a detailed explanation of why this drug was prescribed as an oral drug. I think most everyone knows that I do "explore outside the box" due to having so many very sick rabbits....but amoxicillin, whileI won't say I would never use it, it would never be one of my first half dozen choices even when used as an injectable. And with the ongoing mutations of bacteria, it might have to be the drug on choice sometime in the near future. And it can be used safely....but only when injected.
We are hoping for a positive outcome here....healing vibes to Buster.
Randy