The relationship between the bulk density and the compactibility of lactose granulations was studied. The granulations were prepared from different α-lactose monohydrate and roller dried β-lactose powders by wet granulation, using different techniques with only water as a binder, or by slugging. The results demonstrate that by the process of granulation of one lactose powder, granules with different bulk densities and different compactibilities can be prepared. In addition to the type of lactose used, the compactibility of the granule fractions is dependent on the bulk density of the granule fraction. Generally, with an increase of the bulk density, the compactibility of a granule fraction decreases. Little variation is observed between the intergranular porosities of the granule fractions. More differences are found between the intragranular porosities of the granule fractions. However, the compactibility of granule fractions of one lactose type is mainly determined by the total porosity of the granule powder bed. Mercury porosimetry determinations on tablets compacted from the granule fractions show a relationship between the tablet pore system and the compact strength: compression of granulations with a low bulk density results into tablets with a small average pore diameter and a high crushing strength. Obviously, the possibility to deform a granule fraction during compression, the deformation potential, is determined by the total porosity of the powder bed. A high deformation potential, i.e., a high compactibility, can be obtained by using a granulation procedure in which granulations with a low bulk density are produced.
