Use of swirling airflow to enhance coating performance of bottom spray fluid bed coaters

As there is strong interest in coating increasingly smaller particles or pellets for use in compacted dosage forms, there is a need for better small particle coating systems. This study explored the use of swirling airflow to enhance the performance of the bottom spray coating system. Firstly, pellet coating in the non-swirling airflow of conventional Wurster coating was compared with that of swirling airflow in precision coating under standardized conditions. Secondly, precision coating was studied in greater details at different airflow rates (60–100 m3/h) and partition gaps (6–22 mm). Precision coating was found to have higher Reynolds numbers (Re) than Wurster coating, indicating higher turbulence. It produced coated pellets of better properties than Wurster coating, having less agglomeration and gross surface defects, more uniform coats, increased flow and tapped density, and slower drug release. Higher surface roughness did not affect the yield. In precision coating, increasing airflow rates decreased the degree of agglomeration but had minimal effect on pellet quality attributes (colour intensity, colour uniformity and surface roughness) and yields. Increasing partition gaps increased the degree of agglomeration proportionally, but this effect was small. However, greater changes in yield, surface roughness, colour intensity and colour uniformity were detected. This study showed that precision coating, while having a higher drying ability, was able to maintain the same yield and produce coated pellets with superior quality compared to Wurster coating. In precision coating, airflow rate had greater influence on the drying of pellets while partition gap had greater influence on pellet quality attributes.