I was on the same dipentum dose as you for several months after trying asacol and colazol which didn't work. It was the last resort before going on prednisone (Lialda wasn't out yet). Luckily, I did well with dipentum until it eventually just stopped working too. For some reason, my doctor put me on dipentum reluctantly, because he didn't feel it worked as well as the others--never explained why--I guess they all have their preferences. 2-250mg twice a day is the usual dose, though I often wonder if a higher dose would have worked better. My doctor put me on Lialda then, and I've been on that ever since. Dipentum is one of the older mesalamine medications and physicians nowadays usually put people on the newer asacol or colazol. They are all basically all the same mesalamine drug, just different coatings, delivery systems and where, when and how they break down--so switching to different one sometimes helps.
Left sided UC almost 4 years
Current Meds: Lialda 3 in the morning, one at night
Winding down from flare that started in January
Alternating Cortenema and cortifoam at night--trying to wean off
Multi Vitamin/Mineral/Fish oil, Biotin, Extra Cal/Mag/D