Impact of solid-state properties on lubrication efficacy of magnesium stearate

The advent of high-speed tableting and slug capsule-filling machines has ushered in an increasingly important role for the lubricants to enact during manufacturing of dosage forms. Although lubricants help in processing, they can also adversely affect the flow properties and dissolution profile of the drug. It is thus critical to maintain a balance between these two behaviors, by understanding the underlying mechanisms and using their optimum concentration in the formulation. The source and manufacturing process inculcate different solid-state properties to magnesium stearate, the most commonly used lubricant, leading to variations in its lubrication efficacy. However, there has been no complete study relating the lubrication efficacy of magnesium stearate to various levels of solid state. Hence, this study was aimed at comprehensively scrutinizing the role of molecular, particle, and bulk level properties of solid state on the lubrication efficacy of magnesium stearate. A method based on net work done during compression using texture analyzer, was developed and validated to analyze its performance. Particle and bulk-level properties were studied using microscopy, particle size analysis, and particle surface area determination, and molecular level was characterized using thermal, spectroscopic, and crystallographic methods. Interplay of solid-state characteristics such as particle size, degree of agglomeration, and crystal habit were found to markedly influence the lubrication potential of magnesium stearate.