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32 July 2019 Tablets & Capsules In the next issue of Tablets & Capsules, I'll discuss addi- tional ways blending can influence tablet compression and hardness. T&C References 1. A. Pandeya and P. M. Puri, "Rate-dependent mechanical properties of dry blended pharmaceutical powder formulations for tabletting applications," Powder Technology, Vol. 207, Issues 1-3, pages 26-34, 2011. 2. H. Leuenberger, "The application of percolation theory in powder technology", Advanced Powder Technology, Vol. 10, Issue 4, pages 323-352, 1999. 3. J. S. Gill, A. K. Jha, and V. M. Puri, "Distribution of fines during percolation segregation for varying bed depths in binary size mixtures of potash," Particulate Science and Technology: An International Journal, Vol. 27, Issue 1, pages 97-106, 2009. Fred A. Rowley is president and chief guest lecturer at Solid Dosage Training (925 352 5724, www.soliddosagetrainin gandtroubleshooting.com). Rowley is also a member of Tablets & Capsules' editorial advisory board. percolation profiles and mustn't be allowed to sit in a pro- duction or laboratory queue before tableting. While the formulation may meet the blend uniformity acceptance criteria immediately after blending, the API may segre- gate or agglomerate over time due to air percolation. It's important to identify this behavior during a hold-time study as part of an overall process validation to avoid introducing a potentially serious process variable that may go unnoticed and become institutionalized. Once complete compaction occurs, a powder blend may never be fluid again, and it will be difficult or impos- sible to run it through a tablet press. This is often imme- diately evident when an IBC is engaged at the tablet press dumping station, but the powder will not flow unless excessive mechanical force is applied. Even with hand scooping, powder placed into the tablet press hopper will not flow. This causes productivity to suffer as the opera- tor must place a vibrator on the tablet press hopper or reduce the tablet press speed to achieve the target tablet weight. In some cases, the blend will exhibit erratic flow into the feeder, causing excessive hardness or content and weight variations, problems that might have been avoided if the formulation had been compressed sooner after blending.