Evaluation of lubricants for optimal use in tablets
As an essential formulation component for large-scale tablet manufacturing, the lubricant preserves tooling by reducing die-wall friction. Unfortunately, lubrication also often results in adverse effects on tablet characteristics, such as prolonged disintegration, slowed dissolution, and reduced mechanical strength. Therefore, the choice of lubricant and its optimal concentration in a tablet formulation is a critical decision in tablet formulation development to attain low die-wall friction while minimizing negative impact on other tablet properties. Three commercially available tablet lubricants, i.e., magnesium stearate, sodium stearyl fumerate, and stearic acid, were systematically investigated in both plastic and brittle matrices to elucidate their effects on reducing die-wall friction, tablet strength, tablet hardness, tablet friability, and tablet disintegration kinetics. Clear understanding of the lubrication efficiency of commonly used lubricants as well as their impact on tablet characteristics would help future tablet formulation efforts.
We have systematically quantified effects of three common commercial lubricants and their concentrations on lubrication efficiency and several key tablet characteristics of both plastic and brittle powders. Lubrication also led to greater plasticity and lower hardness for either plastic or brittle formulations. MgSt was more plastic than SSF and SA and, hence, more effective in facilitating powder packing and consolidation. The lubrication efficiency of MgSt was the highest. However this advantage is shadowed by the much reduced bonding strength of MgSt, resulting in a more significant decrease in particle-particle bonding interactions and, therefore, more reduction in tablet strength than SSF and SA. Therefore, a slightly higher concentration of SSF is equally effective to MgSt but without overtly reducing other important tablet properties, including tablet strength, friability, and disintegration. In the era of quality-by- design, the choice of a lubricant and its optimum amount in a tablet formulation should be made based on systematic evaluation, as demonstrated in this work, instead of personal preference or empiricism.