by Michael Gamlen
Gamlen Tableting Ltd
Biocity Nottingham, Pennyfoot Street, Nottingham NG1 1GF, UK
What is a good tablet?
To check if a powder will make a good tablet is a complex process because good tablets require qualities that can sometimes conflict with each other. For example, the powder needs to be well-lubricated but the tablet also needs to be easily penetrated by fluid in the gut. The tablet needs to be physically robust but also break down rapidly in the body. As is stated by Amidon et al (1):
“A critical process in manufacturing the tablet dosage form is that of powder compression. Although this process has been used routinely for over a century, problems persist related to powder compression in pharmaceutical formulation development and manufacturing. Common problems include tablet failures such as capping and lamination; powder sticking to punch surfaces or die wall; and insufficient mechanical strength to withstand stress in downstream processing. The properties of compressed tablets are sensitive to both material characteristics and process parameters.”
The most important powder requirements are, therefore, for it to be readily compressible, well-lubricated, and to exhibit acceptable elastic recovery during and after ejection, while retaining the essential property of dissolving at the speed required by its quality characteristics.
What is the link between powder and tablet properties?
Currently there are very few measurements, if any, in regular use to assess the likely compaction properties of a powder. Typical powder measurements prior to compaction include particle size, bulk density and moisture content. Materials that differ in these parameters may compact in a different way, but there is no established link between any of these parameters and material compaction.
Tablet properties and compaction have been studied for over 100 years. In that time, three attributes have been identified as being of particular importance. These are: relative density, compaction pressure, and tablet tensile fracture stress. These attributes are all interrelated and the relationship between them is unique for each material; they are also each important in their own right.
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