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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. |
