The aim of this study was to evaluate the influence of tableting process parameters, i.e. turret rotation speed, pre-compaction and main compaction pressures, and their interactions on layer adhesion of bilayer tablets. The elastic recovery after compaction was used as estimation for the elasticity of the material. Three potential pharmaceutical formulations were evaluated as combinations of immediate (microcrystalline cellulose, lactose, calcium phosphate, pregelatinized starch) and controlled drug release excipients (ethyl cellulose, hydroxypropyl methylcellulose, polyvinyl acetate/polyvinylpyrrolidone). A 3-levels 3-factors central composite Design of Experiment was performed on each formulation, with layer adhesion selected as response. A custom-made shear test was used to determine the tablet tendency to delaminate. Main compaction and turret rotation speed were the most important parameters to be optimized during tablet manufacturing. Main compaction was the principal parameter leading to delamination in case of formulations with plastic materials, particularly at high pressures where the difference in elasticity of excipients had a major impact and was followed by turret rotation speed. The rotation speed did not have an effect on layer adhesion in the case of formulations with brittle excipients.
Keywords: Bilayer tablets; Delamination; Elastic recovery; Layer adhesion.
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