Impact of magnesium aluminometasilicates on rheological and compaction properties of moisture-sensitive excipients.

Moisture is a critical external factor affecting the powder behaviour. This work focused on the effect of moisture on the rheological and compaction properties of two moisture-sensitive excipients, microcrystalline cellulose (MCC) and partially pregelatinized starch (PPS). Moreover, the impact of highly porous magnesium aluminometasilicates (MAS) admixed to the excipients was evaluated towards their moisture-controlling or property-improving qualities. The generally negative effects of moisture on rheological properties of pure excipients were positively influenced by MAS addition to achieve acceptable properties also under highest studied humidity (78 % RH). An almost twofold increase in the flow function coefficient value was observed with the addition of 25 w/w % of MAS to MCC and PPS. Increasing moisture leads to weaker tablets of pure MCC (40 % decrease of value) and, on the contrary, improves the tabletability of pure PPS with 54 % increase of tablet tensile strength under 78 % RH at compaction pressure of 250 MPa, respectively. Moisture also causes a decrease in tablet porosity, elastic recovery as well as plasticity factor (ratio between plastic and total deformation energy) for both excipients. The property improvement was proportional to the MAS content in the mixture of MCC-MAS. In PPS-MAS, the properties of PPS dominate the system more and higher MAS additions exhibited limited effect. However, all things considered, the addition of MAS could improve the processability and product quality by mostly predictable means of mixing rules and serve as a moisture-controlling additive. Moreover, these findings demonstrate a cost-effective strategy for mitigating humidity effects at the formulation level.