Ispaghula and Colonic Water Content

The Rome III diagnostic criteria for constipation must include two or more of the following symptoms > 25 % of the time: straining, hard or lumpy stools, sense of incomplete evacuation, sensation of anorectal obstruction/blockage, the use of manual manoeuvres to facilitate defecation and fewer than 3 defecations per week. Treatments include osmotic laxatives such as polyethylene glycol and lactulose, stimulant laxatives such as bisacodyl, secretagogues like sodium docusate, and bulking agents such as psyllium.

A better understanding of the modes of action of these drugs is required, in order to provide better treatment for chronic constipation. This is somewhat challenging; partly because techniques available to study intestinal contents are limited, and some are unpleasant for the patients. The GI MRI group at the University of Nottingham has recently developed a non-invasive, patient friendly MRI technique for studying the colon. The technique allows assessment of colonic volumes, the response to meals, motility of the colon and transit time of ingested meals. This technique has been used to demonstrate the laxative effect of mannitol and its subsequent reversal with loperamide.

Using MRI, water provides a bright image on T2-weighted images in the small bowel, but the signal is rapidly lost once it reaches the colon. Pilot studies suggest that ispaghula; which is highly hygroscopic and can form a 1.5% gel with water, is able to maintain water in a form which produces bright images on T2-weighted scanning of the colon. The GI MRI group now want to confirm this pilot data by performing a placebo controlled trial of ispaghula husk in healthy volunteers, with the aim of further understanding the mode of action of bulking agents and further improve understanding of MRI parameters when applied to the colon. The aims will be achieved by performing a dose-finding mechanistic study in healthy volunteers, assessing their response to a test meal while taking either placebo, or 2 different doses of ispaghula. Stools will be collected, assessed for water content and compared to water content assessed from T2 weighted MRI. The studies will validate the current technique, optimise current MRI parameters and provide insights into the modes of action of ispaghula.