By Jonathan Galk , Natoli Scientific
The ideal active pharmaceutical ingredient (API) is one that flows well, is stable, self-lubricates, compacts well and is not strain rate sensitive. While all the listed properties are important, the one that continues to be critical is powder flow. Most challenges in the tabletting process initiate with or can be traced back to flow.
A poorly flowing powder can affect tablet quality at every step in the process. Key factors to consider when encountering a powder that doesn’t flow well are formulation design, storage conditions, tablet design and mechanical design of processing equipment. Powder rheology studies, such as shear strength and wall friction, which can be conducted on a Freeman FT4, and flowability on a Flodex, can be performed throughout the R&D process to help demonstrate a powder’s flow characteristics. A thorough process development, including conducting BU and CU studies and determining turret and feeder speed, helps optimize production and reduce time involved in troubleshooting.
Minor powder flow issues during R&D can turn into major headaches once scale-up to production begins. Conducting studies throughout R&D and scale-up can help identify and isolate where in the process a formulation issue began. Powder flow can also vary from lot-to-lot, which needs to be understood during R&D. Most problems that manifest on the tablet press start with the powder and its flow properties, so it’s important to understand how a powder will perform under every circumstance.