Application of a novel electrostatic dry powder coating technology on capsules for enteric release

Dry coating of pharmaceutical dosages represents the future of functional coating given its environmental friendliness and cost effectiveness. Based on the electrostatic dry powder coating technology developed by our group, hard gelatin capsules and HPMC capsules were successfully coated for the first time to achieve enteric release. In the coating process, plasticizer was sprayed prior to coating powder to lower the glass transition temperature and to increase the powder adhesion. Sufficient weight gain is required to ensure enough coating film thickness to achieve enteric release. And higher weight gain comes with increased powder adhesion rate by using more plasticizer. Accelerated stability tests demonstrated good stability for coated gelatin and HPMC capsules. The powder coating also avoided the commonly encountered stickiness issue associated with the organic or aqueous coating process. Comparatively, gelatin capsules appear to be advantageous over HPMC capsules as they have higher powder adhesion rate, more rapid drug release when exposed to buffer solution and better performance in accelerated stability test.