Characterization of die wall pressure to predict capping of flat- or convex-faced drug tablets of various sizes

Abstract

Die wall pressure during compaction of drug powders was measured to elucidate the mechanisms involved in capping. More than 200 kg/cm 2 of die wall pressure remained after decompression, whereas in the case of capping, the die wall pressure rapidly dropped at the final stage of the decompression process. These results suggested that capping was the fracture of compacted powders caused by high residual die wall pressure. The extrapolated residual die wall pressure of convex-faced tablets was higher than that of flat-faced ones. For the convex-faced tablets, the thinner ones indicated a higher residual die wall pressure. These results coincided with the capping tendency seen in drug tablets and should pave the way for a better design of tablet formulation.