A comparative study of spouted and spout-fluid beds for tablet coating

The performance of spouted, spouted with auxiliary air supply, and spout-fluid beds for the coating of tablets was investigated. The gas-solid regimes of the three systems were confirmed by their hydrodynamic characteristic curves, e.g., pressure drop versus air flow rate. The coating study was developed following a central composite design and using flow regime, suspension feed rate and tablet load in the bed as factors. The dependent variables for the composite design of experiments were weight gain and efficiency. Other coat quality indexes, like tablet surface appearance, hardness, moisture content and gastric resistance are also discussed. The analysis of variance of the experimental data revealed that only the suspension feed rate affected the coating efficiencies and weight gain significantly. The coat quality, e.g., tablet moisture content, hardness, friability, and gastric resistance, were found to be unaffected by the factors studied, according to pharmaceutical standards. The results show that the gas-solid regimes do not affect coating performance.