Twin product/process approach for pellet preparation by extrusion/spheronisation. Part I: hydro-textural aspects

The extrusion/spheronisation technique has made a notable contribution to the existing range of pharmaceutical forms especially in the area of modified-release products. The twin product/process approach adopted in this work is based on the on-line monitoring of the hydro-textural characteristics of the product up to its final form. The objective is to balance the influence of the operating parameters for each successive stage against the influence of product characteristics. A coherent "representational framework" is proposed for insoluble substances through a diagram locating intergranular porosity value depending on water content. The wetting/kneading operation brings the material to a state in which porosity is linked to water content. The extrusion operation densifies the material to saturation point, while spheronisation is only a shaping process which maintains hydro-textural state. The drying operation finalises the textural characteristics of the product by densifying the medium through induced shrinkage.