CHAPTER 16. Dry Powder Coating of Pharmaceutical Solid Dosages

Derived from powder coating of metals, pharmaceutical dry powder coatings have received great attention in the past ten years, owing to their striking potential to replace the organic solvent coating and aqueous coating used in the current pharmaceutical industry. After several initial trials of dry coating, electrostatic dry powder coating was developed and has attracted more attention due to its high coating efficiency and low overall cost. In this technology, coating powders containing coating polymers, pigments, and other excipients are directly sprayed onto the surface of the solid dosage forms without using any organic solvent or water. The deposited coating powders are cured to form a coating film. This dry powder coating technology has many advantages compared to organic solvent coating and aqueous coating. It eliminates the limitations caused by the organic solvent in solvent coating such as environmental issues and health problems. It also surpasses aqueous coating due to its shorter processing time and much greatly reduced energy consumption, leading to a lower overall cost. Specifically, electrostatic powder coating utilizes electrical attraction to promote the movement of coating powders towards the dosage forms, resulting in an enhanced coating powder adhesion, uniformity and coating efficiency, making it more promising compared to other dry coating technologies. This technology has already been developed and applied to various solid dosage forms successfully.