Ethyl Cellulose-Coated Cylindrical Granules for Multi-Unit Sustained-Release Tablets: Trade-Off Between Coating Integrity, Compressibility, Tabletability, and Drug Release

Background: Cylindrical granules, rather than spherical pellets, are used in certain multi-unit sustained-release tablets (MUSTs), such as mesalazine (MSZ) sustained-release tablets (Pentasa®). Our previous studies established that porosity and aspect ratio govern the tableting behavior of uncoated cylindrical MSZ granules. However, it is unknown how the compressibility, tabletability and release behavior of the coated cylindrical granules will change. Methods: In this study, ethyl cellulose (EC) was used as a model sustained-release coating polymer to systematically investigate the effects of EC coating film on the compressibility, tabletability, and drug-release performance of MSZ cylindrical granules. Results: It was found that increasing EC molecular weight and coating weight gain compromised the compressibility of the coated cylindrical granules, as reflected by increased yield stress values. Structural analysis demonstrated that thicker coatings and higher-molecular-weight EC films were less susceptible to compression-induced damage, preserving coating integrity after tableting. However, this enhanced coating robustness was accompanied by reduced tabletability, as reflected by lower tablet tensile strength at a given compaction pressure. In addition, increasing EC molecular weight and coating weight gain progressively reduced MSZ release from both coated granules and corresponding tablets. Conclusions: These findings demonstrate a trade-off among coating integrity, compressibility, tabletability, and drug-release control in MUST development. The results provide a mechanistic basis and practical guidance for optimizing coated cylindrical granules and balancing coating protection with tablet manufacturability and sustained-release performance.