Fluidized bed film coating of an ordered powder mixture to produce microencapsulated order units.

Very finely divided particulate salicylic acid (2-5 micrometers) was microencapsulated using conventional fluidized bed coating techniques. The process involved spray coating a preformed ordered mixture, in which the micronized particles are adsorbed on the surface of a coarser carrier material. The mixtures contained 0.1, 1.0 and 5.0% weight of microfine model drug (salicylic acid). Between 75 and 95% of the micronized particles were retained on the carrier surface beneath the film. This process offers a novel method of microencapsulating very fine particulate materials, which may find an application in the production of enteric coated and sustained release microdose products. A recent publication on electrostatic charge interactions in ordered mixtures reported that the addition of a third component can affect the stability of a binary ordered mixture. Addition of 2% talc increased the stability of some mixtures during coating and resulted in the microencapsulation of a significantly greater amount of micronized model drug. A 0.1% salicylic acid binary ordered mixture retained 74% of model drug beneath the film, the 0.1% ternary mixture (2% talc) gave a mean retention of 99%.