Hi Cathy
For any dog requiring sustained use of metronidazole (a bitter, cold, drying influence) and corticosteroids, I always wonder whether Si Miao San could do the job instead. Additionally, it supports the Spleen to lessen the regurgitation tendencies and promote assimilation
For now, you could try it in small doses with the BZYQT, and see what happens. If there are any residual symptoms the drugs aren't getting, and they improve on the SMS, then you have exceeded what the drugs can do with the herbs, and the way is clear to try to reduce the dependencies on the drug
Another thought is a probiotic. Apart from the steroids, BZYQT and metronidazole form a good pair to manage IBS. If they are doing the heavy lifting relative to the budesonide (i.e. he has been okay when they ran out of budesonide), then you may be dealing with IBS. Studies in humans show it as indistinguishable from IBD in some cases, and as likely being due to dysbiosis. Probiotics form a third prong in the treatment of IBS, the other two being immune support (via BZYQT) and antimicrobial control (via metronidazole).
Hope that helps you out
Steve