I hope some others will chime in bc there are a few on here that have a LOT of experience w/ colitis/IBD - and they're really helpful.
I think Marcel has IBD and I've just started Tylan powder (about 1 week ago) - I think we may be getting somewhere. Also, whenever I hear his stomach start to make the liquidy/gurgly sounds, I give some Pepto - and that has REALLY been helping too.
This thread is excellent:
http://www.yorkietalk.com/forums/showthread.php?t=86817