Magnesium Stearate and Tableting Lubrication

Nutraceutical manufacturers have had many issues to consider since FDA released the GMP (good manufacturing practice) guidelines for the dietary supplement industry last summer. Among these concerns is the definition or application of a “scientifically valid argument,” a concept presented in the GMPs.

The intent of the phrase is to establish, as a minimum requirement, a documented explanation of well-grounded logic which justifies how and why one conducts a key manufacturing process, material qualification or analytical test using science. The scientific portion of the explanation should be a combination of theory, experimentation and test results. An example of applying this concept is given below for the addition of magnesium stearate (as a lubricant) to a homogenous nutraceutical powder blend.

Magnesium stearate is the most common ingredient used in tablet formulations. For nutraceutical tablet manufacturing, it is the lubricant of choice. It is common manufacturing behavior to add a minimum amount after first achieving a homogenous powder blend of all other ingredients and additionally mixing-in the lubricant for a brief period of time. This enables the powder blend particle surface to be sufficiently coated while limiting penetration of the lubricant within the particle matrix. Within the FDA concept, this is part of the theoretical explanation.

There are several problems associated with incorrect lubrication in tablet compression. Under-lubricating a powder blend leads to adherence of material on the metal surfaces of the punches and die walls of the tablet press. Over-lubrication leads to soft tablets and poor disintegration and/or dissolution. These are some of the experimental outcomes to be used in determining an optimal level of magnesium stearate in a formulation.

Other variables to address when determining magnesium stearate concentration and blend time experiments include:

• Powder blend particle size distribution,
• Powder blend bulk and tapped density,
• Powder blend moisture content,
• Powder blend chemical nature,
• Powder blend filler/component solubility,
• Powder blend filler/component cohesive nature,
• Blender type, and
• Powder blend fill percentage vs. blender capacity.