Abstract
Lubrication plays a key role in successful manufacturing of pharmaceutical solid dosage forms; lubricants are essential ingredients in robust formulations to achieve this. Although many failures in pharmaceutical manufacturing operations are caused by issues related to lubrication, in general, lubricants do not gain adequate attention in the development of pharmaceutical formulations. In this paper, the fundamental background on lubrication is introduced, in which the relationships between lubrication and friction/adhesion forces are discussed. Then, the application of lubrication in the development of pharmaceutical products and manufacturing processes is discussed with an emphasis on magnesium stearate. In particular, the effect of its hydration state (anhydrate, monohydrate, dihydrate, and trihydrate) and its powder characteristics on lubrication efficiency, as well as product and process performance is summarized. In addition, the impact of lubrication on the dynamics of compaction/compression processes and on the mechanical properties of compacts/tablets is presented. Furthermore, the online monitoring of magnesium stearate in a blending process is briefly mentioned. Finally, the chemical compatibility of active pharmaceutical ingredient (API) with magnesium stearate and its reactive impurities is reviewed with examples from the literature illustrating the various reaction mechanisms involved.
Highlights
A lubricant, an additive to reduce friction, is an essential component of a drug formula since lubrication is often required to ensure the success of pharmaceutical manufacturing
It was concluded that the ribbon tensile strength and tablet hardness significantly increased as the specific surface area of magnesium stearate decreased, which is consistent with the results reported previously
The flowability of ibuprofen particles of various sizes was shown to be significantly improved by lubrication using magnesium stearate based on internal angle measurement [30]. This can be explained by the fact that small particles of active pharmaceutical ingredient (API) typically cause a flow issue, and the incorporation of the lubricant as a flow agent can coat the surface of particles to reduce inter-particle friction, which improves the powder flow
Summary
A lubricant, an additive to reduce friction, is an essential component of a drug formula since lubrication is often required to ensure the success of pharmaceutical manufacturing. For the blending of active pharmaceutical ingredients (APIs) of small particles with other excipients, the adhesion force between particles can significantly reduce the powder flowability by increasing inter-particle friction; poor flow can cause insufficient mixing of the blends (content uniformity) and rat-holing in the hopper of a tablet press (segregation issue), impacting both product quality and operation. To overcome these issues, lubricants are added (glidants) to enhance powder flow by reducing the inter-particle friction. We conclude by presenting a general principle for selecting a lubricant for a pharmaceutical formulation
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