Use of a power-consumption-controlled extruder in the development of pellet formulations.

Shape is an important characteristic of pellets that is highly influenced by the water content of the extrudate during spheronization. The power-consumption-controlled extruder (pcc-extruder) is an appropriate tool to adjust the required water content to yield round pellets. For this purpose, it is necessary to run the extruder at a specific level of power consumption. In the first part of the study, this approach was employed to screen different drugs as well as excipients to prove the concept of the pcc-extruder. Usually round pellets were obtained but a few formulations did not produce round pellets. In the second part of the study, the influence of screw speed and powder feed rate on the required level of power consumption was investigated. A correlation between the water content and the shape of pellets was evident. To account for screw speed, it was necessary to adjust net power consumption instead of total power consumption. The influence of the screw speed on water content of extrudate and consequently on the shape of pellets was not significant in the studied range. Variations of the powder feed rate affected both the water content and the shape of pellets. However, the water content was not only dependent on the level of net power consumption. The specific power is the ratio of net power consumption to extrusion rate, and it correlates well with water content and pellet shape. Using the specific power, it is possible to adjust the net power consumption in response to changes in powder feed rate.