Prediction of the compressibility of complex mixtures of pharmaceutical powders

The development of predictive models for the pharmaceutical compaction process is of great interest for not only the formulation step but also in the context of the quality by design development. This paper deals with the prediction of the compressibility, i.e. the prediction of the evolution of the density and the porosity of the compact along with the compaction pressure, both "in-die" (during the compaction) and "out-of-die (after the ejection of the compact). For this purpose, four different mixtures composed of five different pharmaceutical products were studied using a rotative press simulator. The excipients and formulations were chosen to be as near as possible to real industrial formulations. Using the volume as an additive property and a reformulation of the Kawakita equation as a function of the density, it was possible to predict the density of the compact both "in-die" and "out-of-die" with a good accuracy (residuals <3.5%). In most of the cases, for the pressure levels used in the pharmaceutical industry, the absolute error on the prediction of the porosity was below 2%. This study demonstrates that this approach could be well suited to predict the compressibility of real pharmaceutical formulations in the industrial context.