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Pharmaceutical Technology APIs, EXCIPIENTS, AND MANUFACTURING eBOOK 2021 25 there is some understanding of the inf luence of particle properties, such as size, shape, surface roughness, and density, on bulk powder properties, such as f lowability, the relationships are complex, with system variables, such as degree of aeration and moisture content, also having a significant in- f luence. Predicting bulk powder properties is not feasible; measurement is essential. The question of which properties to measure is crucial. An approach gaining traction (2,3) is to measure a broad range of properties, thereby devel- oping a material property database for the powder, and to then identify relevant properties through correlation with process performance. This ap- proach pinpoints the properties that capture the majority of variability in a given unit operation and that can be used to develop a robust specification. Dynamic powder properties, measured using a powder rheometer, are routinely identified as a critical element of specifications developed in this way. Such properties are highly reproducible and sensitive and have a proven track record of process relevance (4). Given that a powder rheometer speci- fied for dynamic powder testing also offers shear and bulk property measurements, such instrumen- tation can be a good place to start when building a bulk powder property database to support supply chain optimization (5). Case study 1: Evaluating pharmaceutical excipients. Flowability testing was performed on six com- mercial samples of lactose intended for oral solid dosage formulation. Three were milled products from DFE Pharma (Goch, Germany): Pharmatose 200M EU, Pharmatose 200M NZ, and Lactochem Figure 1. The intra-batch variability of the lactose products is low (relative standard deviation [RSD]<5%). LCFP is Lactochem Fine Powder. FIGURES COURTESY OF THE AUTHOR