The influence of pellet shape and surface properties on the drug release from uncoated and coated pellets

Pellets of different shape, varying from spherical to cylindrical, without and with film coating were tested for their drug release properties. For non-disintegrating uncoated pellets, drug release was found to be inversely related to the pellet porosity. A change of 5% in porosity doubled the value of the mean dissolution time (MDT). As coat thickness increased, the MDT value of coated pellets increased. For those pellets, which are nearly spherical, once a thickness of about 20 μm had been achieved, there was little further reduction in retardation. Pellets produced by extrusion/spheronisation appeared to prolong drug release to a larger extent than those where the extrusion step had been omitted. There was a strong inverse relationship between the surface area by volume of the coated pellets and the value of the MDT. The values of the relative dispersion coefficient (RD), which is an indicator of the drug release mechanism, were related to the amount of fluid used to manufacture the pellets and the pellet shape, in a similar fashion for both uncoated and coated pellets. This suggested that the presence of the film coating changed the rate but not the mechanism of drug release.