A comparison of screen and ram extrusion-spheronisation of simple pharmaceutical pastes based on microcrystalline cellulose.

The performance of two laboratory-scale extrusion apparatuses used to approximate the action of an industrial screen extruder, namely a multi-holed die ram extruder and a roller screen extruder, were compared. Both devices featured short dies (ram 2mm, screen 1mm) with die diameter 1mm and hole area fraction approaching 0.25. A series of water/microcrystalline cellulose (MCC) pastes with water contents varying from 45 to 60 wt% were extruded and pellets obtained from subsequent spheronisation of the extrudates characterised in terms of size and shape. Each device exhibited a different range of processing windows for acceptable spheronised products, with the ram apparatus being able to extrude a wider range of paste water contents than the screen device. The pellets obtained from extrusion-spheronisation (E-S) of the pastes via the screen device were in general smaller, with a wider size distribution, than those from ram E-S. These results are attributed to the different mechanical histories experienced by the pastes in the two types of extruder, which lead to different extrudate densities being achieved. MCC/water/calcium carbonate pastes were also tested, where the latter component represented a 'hard' (non-deformable) active pharmaceutical ingredient. Addition of calcium carbonate increased the stiffness of the paste, which could be countered by adjusting the water content of the deformable MCC/water matrix within the extrudability limits of the latter material.