If you were diagnosed correctly with UC, then it is something you will always have, though you may have times of remission and times of flare-ups. I take Flagyl sometimes cause it seems to help when I am in a flare-up. You could have C diff along with your UC, but have you been tested for it? My guess is the doctor is giving you the Flagyl to try to prevent a flare-up from tapering the Prednisone. Why is he doing such a rapid taper of the Prednisone? I also don't understand why you are not still taking the Asacol.
Diagnosed with Left-sided UC in 1995 at age 15,
Prednisone, Rowasa & Hydrocort. Enemas, Proctofoam, Sulfasalazine, Asacol, Probiotics, Fish Oil, Aloe Juice, Canasa, Enotcort, Colazol, Anamantle, Remicade, etc... had 1 inch deep rectal ulcer 2004, put on Remicade, August 2007:Increased Remicade dosage-700mg every 6 weeks,diagnosed w/ Psoriatic Arthritis & Fibromyalgia Current meds: Clorazepate, Lomotil, Tylenol pm, Lyrica started 1/17/08, Flagyl 750 mgs started 4/2/08, Humira started 4/4/08