Competing for water: A new approach to understand disintegrant performance

The understanding of tablet disintegration is still incomplete as not all involved factors and processes are known or accounted for. E.g., the negative influence of soluble fillers, on disintegration is usually attributed to increased viscosity due to dissolved filler. When the most common filler, lactose, dissolves, the viscosity increases only slightly. The impact of binders has hardly been studied systematically. In this study, water uptake and force development as well as water sorption experiments were performed of tablets containing either a soluble or an insoluble filler, one of four different binders, and one of four different disintegrants. For both fillers, one disintegrant performed distinctly worse than the others. For the insoluble filler, dibasic calcium phosphate (DCP), sodium starch glycolate resulted in the longest disintegration, for the soluble filler, lactose, croscarmellose sodium performed worst. Based on the experimental results, the authors introduce the competition-for-water hypothesis, which takes into consideration the amount of freely available water molecules and hydration kinetics of excipients. Soluble fillers bind a large number of water molecules in hydrate shells and prevent, therefore, proper disintegrant action. Previously inconsistent observations can be approached with this hypothesis and a better understanding of the underlying processes and explanations is possible.