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With every measurement you
include in your inspection SOP, the FDA may want to see
evidence of: training, validation, calibration, etc. The
TM-II system recommends that you only inspect critical
dimensions.
The following are Natoli
Engineering Company's recommendations for the proper
approach to dimensional inspections of upper and lower
punches in order to assure tablet quality. The
recommendations are based on dimensions that provide
consistency with regard to tablet hardness, weight and
thickness.
Punch Inspection Critical
Dimensions - We believe there are three (3) critical
dimensions that should be included in a dimensional
inspection of an upper or lower punch. Measuring any other
dimension is either A) unnecessary because it rarely, if
ever changes and therefore is not worthy of the time and
expense of measuring or B) cannot be properly measured with
current equipment and is better served by a visual
inspection.
The three (3) critical
dimensions include the following:
Working Length
- The
working length is the most critical punch dimension because
it determines tablet thickness and hardness. Tolerances
should be based on the measurement of a punch in relation to
other punches as opposed to being based on a specific
length. Uniformity of punch working lengths is the key. In
other words, as long as the punches are the same length (or
within the specified tolerance) it doesn't matter how they
compare in relation to a specific pre-defined length.
Cup Depth
- To find the
cup depth, subtract the measured working length from the
measured overall length. Cup depth is not a critical
dimension with regard to controlling tablet weight.
Overall Length - The
overall length is not critical except that it is necessary
to accurately calculate Working Length and Cup Depth. You
should assume a 5.250" overall length measurement.
For additional references,
please see pages 168 - 169 "Encyclopedia of Pharmaceutical
Technology - Volume 15" and the sixth edition of
the "Tableting Specification Manual" pages 13 - 15. |
