A review of particulate design for pharmaceutical powders and their production by spouted bed coating

This paper focuses on how fine particles are processed in a fluidized/spouted bed coater without agglomeration and what kinds of functions are desired for particulate dosage forms, in order to preview the future contributions of fluidization technology in pharmaceutical dosage form development. Coating operation of particles smaller than 100 mum is very often troubled with particle agglomeration and adhesion due to the excessively high binding strength of coating materials and to electrostatic charging. In order to avoid these troubles, the binding strength has to be adjusted corresponding to the size of particles to be processed. The most efficient way to produce single-core microcapsules is to separate the drying and film formation of spray droplets. This can be achieved by using latices whose softening temperature (T-s) is higher than the inlet air temperature. Particulate designs of the latex polymers based on this idea are also effective for solving some other troubles such as electrostatic charging and poor film formability in fine particle coating. Meanwhile, multiple functions and high performance are required for particulate systems to exhibit desired characteristics in practical uses. The fluidized/spouted bed process, which can easily produce multi-layered and composite structures, is an excellent method for multi-functional adaptation of particulate systems. This is demonstrated in this paper in the preparation of microcapsules for cancer therapies, such as neutron capture therapy (NCT) and chemoembolization therapy, and for stimuli-sensitive controlled-release therapy. In pharmaceutical technology, requirements for producing functional particles of around 30 mum, which can be used, for example, as injectable suspensions for cancer therapy, will increase in the future. This will require the processing of around 10-mum particles, though the smallest particle size that a fluidized/spouted bed can steadily process seems to be 20 mum so far. Membrane and core formulations to process such fine particles seem available already, but we have no technique to steadily fluidize or circulate 10-mum particles at high velocity in a dispersed condition. Furthermore, nanoparticulate systems will be required for more efficient cancer treatments. Although the fluidized/spouted bed is unable to process nanoparticles directly, development of some smart devices as their generators will be made possible by its high potential to make multi-layered and composite structures. (C) 2000 Elsevier Science S.A. All rights reserved.