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The equipment modifications and process changes necessary to perform hot-melt particle coating in a fluid bed granulator are reviewed. A specific case is presented in which partially hydrogenated cottonseed oil is coated onto fine granules (mean particle size, 77 microns; range, 10-150 microns; one standard deviation is 10 microns) composed of a hydrophobic drug and sucrose. The major variables were product bed temperature, temperature of the wax, spray rate, and atomization air pressure. The product bed temperature was selected to give the optimum congealing rate, and the latter three variables were varied in a statistically designed experiment. The physical properties of wax-coated granules fabricated using combinations of process variables were examined. Response surface analysis was used to determine the optimum process settings in terms of dissolution, particle size, and density of the coated product. This system proved quite adequate for the production of uniformly coated granules, with the best product being obtained at the optimized conditions using 120 degrees C atomization air and molten coating temperature, 30 g/min as the spray rate, and an atomization air pressure of 5 bar.

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Substrate cracking occurred during film coating of a bilayered tablet. The cause was traced to differences in the expansion characteristics of the two layers upon exposure to heat. Thermal mechanical analysis was used to determine the coefficients of thermal expansion of the respective layers.