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. Modeling shows that the spraying and evaporation processes must be carefully balanced and the operating window may be significantly narrower than for standalone drying processes, giving control challenges. Effective scale-up and operational strategies are developed. Intermittent spray and air flow during filter bag shaking can have a major effect. The design space for fluid bed granulation is heat balance controlled while that for coating is rate controlled. Both can be non-orthogonal and this has been accepted by pharmaceutical regulatory authorities.

Automated summary

Simultaneous wetting and drying processes, such as fluid bed granulation and coating, require careful balance of spraying and evaporation, which can lead to narrower operating windows than standalone drying processes. Effective scale-up and operational strategies have been developed, with intermittent spray and air flow during filter bag shaking having a major impact on the process. Design spaces for fluid bed granulation and coating differ in control mechanisms but both may be non-orthogonal, as accepted by pharmaceutical regulatory authorities.