Hardness increase induced by partial moisture loss in compressed tablets and its effect on in vitro dissolution

The hardness increase induced by partial moisture loss in compressed tablets was studied. Several factors such as the type and percentage of the excipient, the water solubility and hygroscopicity of the excipient or drug, and the influence of frequently used binders were investigated. The results indicate that the tablets increased in hardness by the recrystallization of the soluble excipient or the soluble drug in the void spaces This recrystallization occurred because of the moisture loss after expulsion of the solution of the excipient or drug in the void spaces on compression. The large increase in hardness induced by the partial moisture loss did not decrease in vitro dissolution appreciably. This result was clearly different from the hardness increase caused by higher compression loads in the absence of a moisture-induced effect, which showed a decrease in the in vitro dissolution as the hardness was increased.