GASTROINTESTINAL TRANSIT OF PELLETS OF DIFFERING SIZE AND DENSITY

The gastrointestinal transit of four multiple unit pellet dosage forms of two sizes 0.5 and 4.75 mm and two densities 1.5 and 2.6 g cm-3 was examined by gamma scintigraphy in eight healthy fasted subjects. The pellets were prepared by the processes of extrusion and spheronisation and radiolabelled with Tc-99m or In-111. Small pellets of normal and high density were examined on one occasion and large pellets of normal and high density on another. The small and large pellet data from each administration were analysed separately, and then pooled to determine the overall effects of size and density on gastrointestinal transit. A distinct lag phase before gastric emptying commenced was observed for all pellets. The onset of emptying was not affected by size or density. Thereafter gastrointestinal transit did appear to be prolonged with an increase in density. This effect was more clearly demonstrated by the smaller pellets. Small pellet data and the pooled data indicated that an increase in density delayed gastric emptying and prolonged small intestinal residence time (p < 0.05). The large pellet data alone, also indicated that the increase in density caused a delay in gastric emptying (p < 0.05) but the prolongation of small intestinal residence time was not significant. Gastric emptying of the pellets was not affected by their size, although small intestinal residence time was prolonged by the large pellets (p < 0.05). These results and those previously reported by the authors (Clarke et al., Int. J. Pharm., (1993 in press) suggest that there may be a threshold density, of the order of 2.4-2.6 g cm-3, above which gastric emptying is prolonged. The delayed gastric emptying and prolonged small intestinal residence time have important implications for the rational design of sustained release oral dosage forms.