Budesonide-beta-D-glucuronide: a potential prodrug for treatment of ulcerative colitis

Budesonide-beta-D-glucuronide is a potentially useful orally administered prodrug for the treatment of colonic inflammatory bowel disease. Budesonide is a topically active glucocorticosteroid that exhibits low oral bioavailability (15%) in humans and laboratory animals. Oral delivery of budesonide to the inflamed tissues of the large intestine as its glucuronide prodrug should lead to locally high concentrations of active drug. Following liberation and absorption of the active drug, a large portion should be inactivated due to hepatic metabolism. Budesonide-beta-D-glucuronide was chemically stable in solutions at pHs of 1.5, 4.5, 6.5, and 7.4 at 37 degrees C. The enzymatic lability of the prodrug was assessed in luminal contents and mucosa obtained from conventional, germ-free, and colitic rats under in vitro conditions. There was a substantial change in glycosidase activity between the small intestine (proximal and distal portions) and the cecum in both conventional and colitic rat luminal contents. Luminal hydrolytic activity was low along the entire rat gastrointestinal tract of germ-free rats. Mucosal glycosidase activity was relatively low along the entire gastrointestinal tract of all three types of rats. The hydrolysis of prodrugs budesonide-beta-D-glucuronide and dexamethasone-beta-D-glucuronide in human fecal samples from patients with ulcerative colitis and normal volunteers was also measured. There were no statistically significant differences between the normal and colitic fecal samples for hydrolysis of the either prodrug or between the relative rates of hydrolysis of the two prodrugs. Hydrolysis rates of the prodrugs were about two orders of magnitude less in human fecal samples compared with those in cecal and colonic contents from the rat.