The development of cracks on delayed release film of hygroscopic cores: A review of the tablet and coating formulations, coating processes and storage conditions

Methacrylic Acid Copolymer Dispersion NF (aqueous dispersin of Methacrylic Acid Copolymer Type C in water) has been used extensively for delayed release coating in the pharmaceutical industry. However, a concern is that the Methacrylic Acid Copolymer Dispersion NF may cause cracks to develop in the coating film in hygroscopic tablets. These develop because the polymer is inherently brittle and therefore cracks during storage, especially when exposed to elevated heat and/or humidity. A crack in the coating film develops as the polymer is unable to accommodate the stresses that are generated during the coating process or because of changes in, e.g., tablet dimensions during storage. The important factors to maintain the integrity of the coating film are (i) formulation of the tablet core and its hardness, (ii) formulation of the coating dispersion, and (iii) coating process parameters. Tablet core hardness, its relaxation properties, water content, content of the insoluble component in the coating formulation, and temperature and relative humidity (RH) of the inlet air influences the film quality and integrity. In this paper, the probable causes for the development of cracks in the film coating on a hygroscopic core are discussed with reference to the properties of the tablet core, coating formulations (e.g., polymers, plasticizers, insoluble excipients) and the coating process parameters.