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A gravity feed extruder was adapted to monitor the extrusion forces, the temperature during processing and the rotational speed of the extruding cylinders. The extruder was used to evaluate the influence of particle size of insoluble material and of product solubility on the extrusion forces. Microcrystalline cellulose, dicalcium phosphate dihydrate and different lactoses were used as model compounds. Difference in lactose and microcrystalline cellulose particle size did not influence extrusion forces. The amount of water in the mixtures to be processed and the initial difference in solubility for some of the lactose types investigated influenced the extrusion forces dramatically. Extrusion forces recorded during processing of a mixture previously granulated in a high shear granulator were higher than when processed in a planetary mixture. Loss of water during high shear granulation is probably the main cause of this phenomenon.

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This communication reports on the correlation between extrusion forces and sphere characteristics. Dicalcium phosphate dihydrate, alpha-lactose monohydrate and anhydrous beta-lactose were models for respectively an insoluble, a medium soluble and a highly soluble drug and were used to produce spheres. Phase diagrams for ternary mixtures consisting of microcrystalline cellulose, water and a third excipient were constructed. The region where good spheres were obtained correlated well with the area of extrusion forces between 630 and 1260 N. This correlation was seen for the insoluble, the medium and the highly soluble products.