66 TABLETING
Lighthouse probe FLUID BEDDRYING Dr Harald Stahl reveals a 21st century solution to final moisture content control P
rocess Analytical Technology (PAT), the final frontier.1 Tese are the voyages of FDA’s
initiative to provide a framework for innovative pharmaceutical development, manufacturing and quality assurance … and boldly go where no regulatory agency has gone before. Before this programme was launched,
more than 10 years ago, pharmaceutical production relied on process validation and end product testing, complemented by in-process controls (IPCs). Te idea was that if every process parameter was maintained within a given, validated range, the intermediates and final products would always comply with the required quality specifications. However, this approach relied on a validated array for each and every parameter that could potentially influence the operation.
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If we look at a real-life example, such as dispensing, predetermined quantities of the ingredients in a specific formulation are weighed into an intermediate bulk container (IBC). Assuming a total amount of 300kg, a further 45kg of binder solution is added when the mixture is processed in a high shear granulator and subsequently transferred to a fluid bed dryer. Here, the material needs to be dried to obtain a moisture content of, for instance, <2.5%. As the drying process is itself validated, the material will be exposed to 4,500m³/h of drying gas at an inlet temperature of 60°C for 50 minutes. Surprisingly, the material is not simply discharged after that time but, in nine out of ten examples, the process is merely paused while an operator removes a sample for offline moisture testing. If the material happens to be sufficiently dry, an extra 10 minutes
of time may elapse; but if the material is still too wet, drying continues for a few minutes more before another sample is taken … and another 10 minutes pass. If the specification simply demands
a moisture content of less than a certain percentage (2.5% in our example), this procedure works – but productivity suffers. Te fluid bed dryer is just acting as a simple holding container during what is essentially downtime. If, however, the target moisture content requirement is more complex and must fall within a specific range – 1.5-2.5%, for example – the situation becomes much more challenging.
Chemical stability And, last but not least, a moisture content of less than 2.5% ensures chemical stability, which results in an acceptable
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