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26 Pharmaceutical Technology APIs, EXCIPIENTS, AND MANUFACTURING eBOOK 2021 P h a r mTe c h . c o m Excipients Fine Powder (LCFP); the others were competitor products. Dynamic f low properties were mea- sured in triplicate (FT4 Powder Rheometer, Free- man Technology) for each of three batches of each product. The relative standard deviation (RSD) of basic flowability energy (BFE), a baseline dynamic property that quantifies f lowability under forced- f low conditions, was used to assess consistency. Figure 1 shows data comparing intra-batch vari- ability (the %RSD associated with the triplicate measurements of each batch). These results show no evidence of variability within an individual batch, for any of the products. They also highlight the repeatability of the measurement technique. Many powder testing techniques exhibit poor re- peatability, compromising their ability to detect variability between samples, so this is an impor- tant observation. Figure 2 shows data comparing inter-batch vari- ability (the %RSD associated with measurements on three different batches of each product). These results highlight significant differences, which, be- cause of the repeatability of the instrument already demonstrated by the low intra-batch variability, can securely be associated with batch-to-batch variabil- ity. While three of the products exhibit relatively low RSDs of ~6% or less, that of Competitor 3 is around 15%. BFE has been securely correlated with perfor- mance in processes such as die-filling and blend- ing (4), so variability in this parameter could be sig- nificant from the perspective of process efficiency. More generally, the study demonstrates the ability of dynamic testing to reliably differentiate the con- sistency of supplies and support supplier selection. Case study 2: Focusing on flow additives. In a second study, dynamic, shear, and bulk powder proper- Figure 2. Inter-batch variability is significant for certain lactose products indicating that they could exhibit variable process performance. RSD is relative standard deviation, and LCFP is Lactochem Fine Powder.