In vivo evaluation of a colonic delivery system using isotope techniques.

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