Studying pharmaceutical tablet coating process with real-time terahertz in-line sensing

Terahertz in-line sensing was successfully demonstrated previously for measuring the coating thickness of individual pharmaceutical tablets during a production scale film coating process. This paper investigates how this technology can be used to evaluate the impact of changes in the process conditions on the inter-tablet coating thickness distribution. The process changes that were investigated in this study were the removal of the mixing baffles from the coating pan, blockage of one of the spray guns and the addition of uncoated tablet cores to a bed of partially coated tablets. Using the terahertz sensor the coating thickness of more than 20 individual tablets was sampled per minute in situ throughout the coating process. By analysing the resulting variation in coating thickness distribution it was possible to resolve the effect of all these process changes on the coating thickness homogeneity within the batch.