An Investigation into the In Vivo Performance Variability of pH Responsive Polymers for Ileo-Colonic Drug Delivery Using Gamma Scintigraphy in Humans

Gastrointestinal performance of tablets coated with pH responsive acrylic polymers (Eudragit) was investigated in human volunteers. Tablet cores were coated with Eudragit S dissolved in ethanol (organic), Eudragit S aqueous dispersion (aqueous), or Eudragit FS aqueous dispersion. Eight fasted volunteers received the tablets in a two-way crossover design-treatment 1: Eudragit S (organic) and Eudragit FS coated tablets; treatment 2: Eudragit S (aqueous) and Eudragit FS coated tablets. Eudragit FS coated tablets were included in both treatments to assess its intra-subject performance. Tablets were radiolabelled and followed by gamma scintigraphy; the disintegration times and positions were recorded. Tablets coated with Eudragit S (aqueous) disintegrated in all volunteers mainly in the proximal to mid small intestine. Eudragit S (organic) tablets failed to disintegrate in three out of eight volunteers, while disintegration was in the ileo-caecal junction and ascending colon in all others. Eudragit FS coated tablets disintegrated in 14 out of the 16 administrations. The Eudragit FS coated tablets that did disintegrate exhibited consistent intra- and inter-subject performance, with the site of disintegration focused on the ileo-caecal junction and ascending colon. These in vivo results correlate better with our published in vitro dissolution data in physiological bicarbonate buffers compared to phosphate buffers.