Simultaneous wetting and drying; fluid bed granulation and tablet film coating

Simultaneous wetting and drying occur in processes such as fluid bed (top spray) granulation, Wurster coating and tablet film coating. This gives control challenges, as the spraying and evaporation processes must be carefully balanced and the operating window is significantly narrower than for standalone drying processes. Significant recent advances in modelling have led to effective scale-up and operational strategies. Factors such as flow cessation during filter bag shaking can have a major effect. A design space can be predicted which is often non-orthogonal, and pharmaceutical regulatory authorities have accepted filing submissions using a design space justified by mechanistic modelling.