on administration the tablet disintegrates to release the individual microgrenules that are believed to act as discrete sustained-release units. In vitro tests have shown that 5-ASA release occurs in all pH environments between pH 1 and 7.5 and this suggests that in vivo drug release could occur throughout the gasileostomy patients about 50-60% of 5-ASA from Pentasa may occur in the small intestine; other data from healthy volunteers indicates much of the remainder is released in the large intestines