Continuous mixing systems for the production of pharmaceutical tablets and granulates

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Courtesy of Gericke

The Process Analytical Technology initiative demands the implementation of in-process monitoring systems and controls along with the mixing process. Gericke has developed continuous mixing and metering systems that meet the stipulated accuracy and the highest hygienic requirements. Own testing and model calculations demonstrate that their efficiency is determined not only by process parameters such as average residence time and metering constancy but also by the particle size distribution and the concentration range of the active substance.

Mixing processes in the pharmaceutical industry have grown out of traditional practices. With a multitude of regulations governing the industry, it is difficult to introduce technical improvements. Once a batch size has been defined and validated; it can no longer be changed. This rigid system has a number of disadvantages. The minimum production volume is determined by the batch size (such as 10001). In some cases the mixing process is validated up to three times prior to the approval of a new medication: at laboratory scale during preparation of the initial product for clinical testing, for the pilot plant and for the final production system. Planning and implementation of a mixing process that has to be designed and validated threefold takes time and money. The continuous mixing process is much more compact. Instead of, for example, a 10001 batch mixer, continuous machines with a mixing chamber of only a few litres are used. Gravimetric metering systems for the base components (lactose etc.), exci-pients and the active substance components feed these components into the small mixer continuously. The capacity of the mixing process can be anything from 10 to 15kg/h up to a maximum of lOOkg/h for blockbuster products. These compact units can be installed immediately above a tablet press or another granulation process. There is no interim storage and the mixing process can be matched perfectly to the continuous compaction process. Tt is conceivable that the same mixing process could be used to manufacture the product for the initial clinical trials and the subsequent actual production volume. The only variable is the production time, from a few minutes to several days. The batches are no longer determined by the size of the mixer but by the volume manufactured over a defined time. The tablet press (compaction) and the mixing system can be combined to form a single compact module. Similar processes have already been implemented for blockbuster products in Asia for some years. Although the patent protection had expired, efficient production was still essential. Other industries have been using continuous mixing processes for a long time now. The food and animal feed industries already have highly complex mixing tasks. Complex in this case means mixing tasks in which the components have very different flow properties or are only used in a very low concentration (vitamins).

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