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Chemical & Pharmaceutical

More solid despite less liquid

13 September 2011 - 1537 views

ENNIGERLOH - Prof. Klaus-Jürgen Steffens of Bonn University has tested the new extruder from L.B. Bohle Maschinen + Verfahren GmbH.

Professor, you have already carried out a number of tests with the BCG (Bohle Conti Granulator). Please explain to us the basic operation method of the system.

The core of the system is a newly designed GMP-compliant twin-screw extruder, which is supplied by a continuous mass-controlled powder dosing unit and a continuous liquid dosing unit. The finished granulate falls directly into the continuous rotating vacuum contact dryer, without requiring transport. The dryer operates with an innovative blending and dispersing unit to reliably prevent the wet granulate caking to any surface. The final granulate size is then adjusted using the well known Bohle BTS Turbo Sieve.

Which tests have you carried out with the system so far?

We have carried out tests with substances that are difficult to granulate, such as Paracetamol and Ibuprofen at a high dosage of 75% active concentration. We have made comparisons with highshear granulation, tested various binding agents as well as the impact of different screw configurations. Our targets were always the properties of the tablets produced from the granulates, such as strength (format-independent as “tensile strength”), disintegration and substance release.

Can you tell us about the initial results?

Out of the many tests, a few results stand out. With regard to the tablet strength of Ibuprofen tablets which were granulated with PVP as the binding agent, two throughput rates in the extruder were compared to high-shear granulation (VMA). The results show the clear superiority of extrusion thanks to a better binding agent distribution. The same applies to paracetamol, where a higher throughput in the extruder resulted in even higher strength values. We carried out a further test (Fig. 3) on the tablet strength of a Paracetamol formulation granulated with HPMC 4000 as the binding agent instead of PVP. Surprisingly, virtually the same strengths were achieved as with PVP, although in extrusion the binding agent is normally a dry powder mixture which must first be dissolved in the extruder. We actually expected significant problems with the tablet strength, as HPMC 4000 has a much lower dissolution rate in water than PVP. Specimens A to F were granulated with different screw configurations and different amounts of liquid. Only specimen E showed a significant capping tendency of the tablets. This specimen was produced with the least amount of liquid. Despite having virtually the same strengths, in the range of 2.5 MPa, the tablets from the other specimens revealed varying disintegration times, ranging from 133 sec (specimen F) to 390 sec (specimen A). Scanning electron microscope images showed the typical structure of the granulates which does not differ from that of other granulating processes.

What are the benefits of the Bohle system in your opinion?

Compared to other extruders the BCG extruder is characterized by the typical Bohle GMP design. The monoblock design features no gaps or connections which make it easy to install and clean. The “real” torque measurement – separately on each screw – is particularly noteworthy, allowing outstanding control of the process. This is another step forward in implementing Process Analytical Technology. Last but not least, the new continuous rotating vacuum dryer of the BCG system features significant advantages vs. other systems.

What do you make of other solutions available on the market? For instance, common features / differences compared to Bohle solutions?

So far, a number of tests for continuous wet granulation have been carried out, such as the continuous fluid bed system or the semi-continuous process utilizing very small pulsed batches. They have not taken hold on the market for wet granulates because of their low shearing force and complicated, failure-prone transport systems. Extrusion, however, is a promising solution. During granulation the shearing forces can be significantly better tuned to the product properties than in any other process.

What are the future trends in pharmaceutical production?

The pharmaceutical market will be dominated by dualism. On the one hand, we will have innovative and expensive pharmaceuticals which will be produced in relatively small batches and for which the production costs will be less important. In contrast, we have been observing global cost pressure and a high concentration of manufacturers on the constantly growing generic drug market. This will result in a greater market share for cost-cutting continuous production systems.  It is therefore vital that the control and machine technology of the systems are state-of-the-art to ensure elegant and enhanced failure-free production.

© L.B. Bohle Maschinen + Verfahren GmbH

This article is published by L.B. Bohle Maschinen + Verfahren GmbH

L.B. Bohle Maschinen + Verfahren GmbH is a global acting manufacturer for the pharmaceutical industry. The range of products includes process and handling equipment for the pharmaceutical solids production. For instance, film coater, blending systems, ...

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