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36 September 2020 Tablets & Capsules to 0.30 A w , the final water status at which the sample equilibrates will be 0.297 A w . Again, free moisture con- tent is generally not linearly correlated with water activ- ity, and you can obtain more accurate results by increas- ing the number of measurement points of the isotherms. As these examples show, the water activity of ingre- dients alone is not enough to predict the resulting water activity and, therefore, stability of a blend. For pre- dicting stability, full knowledge of moisture behavior combined with control of environmental conditions and packaging is key. Conclusion Moisture is a critical factor for the physical, chemical, and biological stability of many materials, and different moisture parameters exist. For pharmaceutical excipients, total moisture content by KF (for lactose) and free mois- ture content by LOD are leading moisture parameters from a regulatory perspective. Water activity describes the energy status of water in a sample and can be used to provide information about the sample's recent history and predict relative reaction rates. It can also be used to predict the direction of moisture migration in a blend, although the amount of moisture migration also depends on the hygroscopicity. Knowing the actual moisture status and sorption isotherms allows you to describe a blend component's full water status and make more reliable predictions. T&C References 1. T. P. Labuza and B. Altunakar, "Water activity pre- diction and moisture sorption isotherms," Water activity in foods: fundamentals and applications, 2020, pages 161-205. 2. Decagon Devices, "Fundamentals of Water Activity," 2006, Accessed via: www.graintec.com.au/ media/12856/Fundamentals.pdf. 3. Safefood 360, "Water activity (a w ) in Foods," 2014, Retrieved April 2020 from: safefood360.com/resources/ Water-Activity.pdf. 4 . o n l i n e . u s p p f . c o m / u s p p f / d o c u m e n t / G U I D - B5DDDC52-0DC8-4603-B81B-03EA4FB025B8_10101_ en-US. 5. D. S. Reid, "Water activity: fundamentals and rela- tionships," Water activity in foods: Fundamentals and applications, Wiley-Blackwell, 2020, pages 13-26. 6. DRSJSCHMIDT, "Moisture Content and Water Activity" [video], Available at: www.youtube.com/ watch?v=-LiSankbfSk. 7. L. Skowronsky, "Inhibition of microbial growth in solid dosages at ICH stability storage conditions," Euro- pean Pharmaceutical Review, 2011. 8. M. Lally, "Introduction to USP <922>: General Chapter for Water Activity Measurement," Available at: vertassets.blob.core.windows.net/download/e97f8ab4/ e 9 7 f 8 a b 4 - 5 b a d - 4 6 a 7 - b f 1 8 - f 4 0 b f 3 0 1 f 2 9 2 / a r t i c l e _ introduction_to_usp_922_general_chapter_for_water_ activity_measurement.pdf. 9. K. C. Waterman, and R. C. Adami, "Accelerated aging: prediction of chemical stability of pharmaceuti- cals," International Journal of Pharmaceutics, 2005, Vol. 293, No. 1-2, pages 101-125. 10. G. V. Barbosa-Cánovas, A. J. Fontana Jr., S. J. Schmidt, and T. P. Labuza (Eds.), Water activity in foods: fundamentals and applications, Wiley-Blackwell, 2020. 11. M. Lutovska, V. Mitrevski, T. Geramitcioski, V. Mijakovski, and I. Andreevski, "Water Activity vs. Equi- librium Moisture Content," Journal on Processing and Energy in Agriculture, 2016, Vol. 20, No. 2, pages 69-72. 12. T. P. Labuza, S. R. Tannenbaum, and M. Karel, "Water content and stability of low moisture and inter- mediate moisture foods," Food Technology, 1970, Vol. 24, pages 543-550. 13. R. Ergun, R. Lietha, and R. W. Hartel, "Moisture and shelf life in sugar confections," Critical reviews in food science and nutrition, 2010, Vol. 50, No. 2, pages 162-192. 14. M. Lally, "A Guide to USP <922> For Water Activity Determination" [Webinar], Pharmaceutical online. June 18, 2020. 15. USP-NF 2020. Lactose monohydrate monograph. European Pharmacopeia 10.0 – lactose monohydrate monograph. 16. K. Fischer, "Neues Verfahren zur maßanalytischen Bestimmung des Wassergehaltes von Flüssigkeiten und festen Körpern," Angewandte Chemie, 1935, Vol. 48, No. 26, pages 394-396. 17. B. Ahrenholz, J. Tölke, P. Lehmann, A. Peters, A. Kaestner, M. Krafczyk, and W. Durner, "Predic- tion of capillary hysteresis in a porous material using lattice-Boltzmann methods and comparison to exper- imental data and a morphological pore network model," Advances in Water Resources, 2008, Vol. 31, No. 9, pages 1,151-1,173. 18. M. Chen, B. Coasne, R. Guyer, D. Derome, and J. Carmeliet, "Role of hydrogen bonding in hysteresis observed in sorption-induced swelling of soft nanoporous polymers," Nature communications, 2018, Vol. 9, No. 1, pages 1-7. 19. J. L. Ford and R. Willson, "Thermal analysis and calorimetry of pharmaceuticals," In Handbook of thermal analysis and calorimetry, Vol. 4, Elsevier Science BV, 1999, pages 923-1,016. P. H. M. Janssen is product application specialist, oral solid dose; R. J. Blezard is product application specialist, inhalation; and B. H. J. Dickhoff is development manager, oral solid dose, at DFE Pharma (+492823 9288 770, www.dfepharma.com).