The current state-of-the art in pharmaceutical continuous film coating - A review

In this decade, one of the major trends in the pharmaceutical industry is the adoption of continuous manufacturing. This requires the development of continuous equivalents of essential pharmaceutical processes such as film coating. The process of film coating is the last step of the processing of solid dosage forms and is critical because it determines the visual appearance of the end product, along with ensuring its stability and possibly even defining the rate of drug release. Several manufacturers advertise continuous solutions for film coating, these include semi-continuous and fully continuous appliances. State-of-the-art continuous coaters can match the throughput of continuous manufacturing lines, because largest appliances have a capacity of 1200-1500 kg/h. The paper also describes the main challenges related to continuous film coating including waste production at the beginning and end of the process and the problem caused by elastic recovery of the tablets when film coating is performed immediately after tablet compression. Lastly, we give an overview of the in-line sensors that can be used to monitor the quality of the film coated tablets, enabling real-time quality control of the process. Near-infrared and Raman spectroscopy can measure the mass gain of the tablets, while terahertz pulsed imaging and optical coherence tomography enable coating thickness measurement of individual tablets and even the characterization of intra-tablet coating thickness variability. UV imaging and machine vision can also measure coating thickness, and they are also excellent for detecting tablets with defective coating.