In vivo evaluation of a colonic delivery system using isotope techniques

Aim: To evaluate, using isotope techniques, the in vivo effectiveness of a pH-dependent colonic delivery system. Methods: In order to dispose of differently labelled substrates for measurement of orocaecal transit time, inulin-C-14-carboxylic acid was evaluated as an alternative substrate to inulin and lactose-C-13-ureide. Secondly, the time of release of C-13- and N-15-urea from the colonic delivery system was compared with the orocaecal transit time, measured using inulin and inulin-C-14-carboxylic acid. This study was repeated after a 2-week lactulose intake period. Results: The orocaecal transit time determined using inulin-C-14-carboxylic acid (398 min) was not significantly different from the orocaecal transit time determined using inulin (420 min) or lactose-C-13-ureide (396 min). Before lactulose intake, the (CO2)-C-13 excretion time was 358 min and the orocaecal transit times determined with the inulin-C-14-carboxylic acid and inulin breath test were 376 and 375 min respectively. After lactulose, the (CO2)-C-13 excretion time was 383 min and orocaecal transit times were 354 min for inulin-C-14-carboxylic acid and 392 min for inulin. A highly significant correlation was found. Good agreement was found between the urinary N-15 excretion and the appearance of (CO2)-C-13 in breath. Conclusion: Isotope techniques provide an excellent non-invasive tool for the in vivo evaluation of a colonic delivery system.