The use of mixer torque rheometry to study the effect of formulation variables on the properties of wet granulations

Mixer torque rheometry was used to investigate the rheological behavior of wet granulations with different concentrations of drug, binder, and water. An experimental design was employed to systematically study the effects of the three formulation variables on the torque profiles of the wet masses over time. Under comparable conditions, increasing binder and water concentrations tended to produce higher wet mass consistencies. Friability of the dried granules was measured as an indication of the strength of the granules. A reduced quadratic model in terms of each of the three variables was found to satisfactorily predict granule friability. Granule friability decreased with increases in the binder level and increased slightly with increasing drug concentration. An inverse relationship was seen between granule friability and the amount of water added to the formulation, especially at lower drug concentrations. Mixer torque rheometry is a useful method for studying the properties of wet granulations when minimal amounts of drug are available for the development of a wet granulated formulation.