Purpose: Develop a procedure to optimize the required lubricant level for tabletting operations.
Method: Magnesium stearate, a commonly used lubricant to enhance flow and reduce tablet ejection force is also a bad actor. Multistage blending is an accepted practice, adding the lubricant last for a short blend time. Additional blending in paddle feeder systems can continue to over lubricate the product, causing loss of tablet strength and an increase in dissolution times. Too little lubricant will cause wear on ejection cam tracks and tooling heads, tips and dies. An alternate approach is to use less and blend longer, in affect deliberately overcoating the particles but with less available lubricant. If this can be successful, additional blending in the paddle feed system is no longer of concern and the initial blend process is greatly simplified. Using an instrumented tablet press, ejection forces were measured at different lubricant levels and blending times to see if the theory, "use less, blend more" could be applied in practice. Ejection forces were evaluated for varying compaction pressures and turret speeds.
Results: The amount of lubricant varies with the excipient and of course the API; there is no magic single level that can be established. For a given excipient the "use less, blend more" concept has merit. With one excipient as little as 0.02% magnesium stearate provided as much benefit as 0.25%, yet offered many advantageous as to strength of the resulting compact. Results will be shown with different MCC excipients as well as lactose and Emcompress.
Conclusions: Most formulations contain excessive lubricant. This results in complex blend operations, process considerations and scaling nightmares. The "use less, blend more" concept can be used successfully provided that the amount of lubricant required is carefully evaluated using an instrumented rotary tablet press, taking into account compaction pressures and loading rates.
The attached document provides more details and more in-depth explanation of the testing, results, and conclusion summarized here.