Gut PH and transit time in ulcerative colitis appear sufficient for complete dissolution of PH-dependent 5-ASA-containing capsules

Abstract

Background: A pH-dependent formulation of 5-aminosalicylic acid (5ASA) requires exposure to pH> 7.0 for at least 30 minutes for complete dissolution to occur in vitro (Riley SA, Br J Clin Pharmacol 1988;26:1737). It has been suggested that low colonic luminal pH in patients with ulcerative colitis (UC) may impair the release of 5-ASA from these capsules. Aim: To compare gut luminal pH and transit time in normal controls and in patients with UC taking a 5-ASA preparation. Methods: Using a standardised ambulatory and dietary protocol, 4 normal controls and 8 patients with active UC had gut pH and segmental transit recorded by a freefall pH-sensitive radiotelemetry capsule(RTC). Results: See Table (mean and (SD) are shown). In all subjects small bowel pH rose as the RTC passed distally and exceeded pH 7.0 for at least 4 hours. There was no difference in mean colonic pH between healthy controls and UC patients. However, low pH «5.5)in the left colon was found in 2 patients, both with active distal UC. Transit time of the RTC through the small bowel was similar for controls and UC patients. RTC transit in UC through the left colon was slower than through right (p< 0.03). Conclusion: We have confirmed that colonic pH is sometimes low and shown that left colonic transit is prolonged in patients with active Uc. Using the RTC as a marker of transit, small bowel pH appears to be sufficiently high for a long enough time to ensure complete dissolution of a pH-dependent capsule containing 5-ASA.