Accessed from 128.83.63.

20 by nEwp0rt1 on Sat Dec 03 01:53:31 EST 2011

868 〈1216〉 Tablet Friability / General Information USP 35

hands of the end users (patients/consumers). Manufacturing

processes such as coating, packaging, and printing can in-
volve considerable stresses, which the tablets must be able
to withstand. For these reasons, the mechanical strength of
tablets is of considerable importance and is routinely meas-
ured. Tablet strength serves both as a criterion by which to
guide product development and as a quality control
specification.
One commonly employed test of the ability of tablets to
withstand mechanical stresses determines their resistance to
chipping and surface abrasion by tumbling them in a rotat-
ing cylinder. The percentage weight loss after tumbling is
referred to as the friability of the tablets. Standardized meth-
ods and equipment for testing friability have been provided
in general chapter Tablet Friability 〈1216〉.
Another measure of the mechanical integrity of tablets is
their breaking force, which is the force required to cause
them to fail (i.e., break) in a specific plane. The tablets are
generally placed between two platens, one of which moves
to apply sufficient force to the tablet to cause fracture. For
Tablet Friability Apparatus conventional, round (circular cross-section) tablets, loading
occurs across their diameter (sometimes referred to as diam-
For tablets with a unit weight equal to or less than 650 etral loading), and fracture occurs in that plane.
mg, take a sample of whole tablets corresponding as near as The breaking force of tablets is commonly called hardness
possible to 6.5 g. For tablets with a unit weight of more in the pharmaceutical literature; however, the use of this
than 650 mg, take a sample of 10 whole tablets. The tablets term is misleading. In material science, the term hardness
should be carefully dedusted prior to testing. Accurately refers to the resistance of a surface to penetration or inden-
weigh the tablet sample, and place the tablets in the drum. tation by a small probe. The term crushing strength is also
Rotate the drum 100 times, and remove the tablets. Re- frequently used to describe the resistance of tablets to the
move any loose dust from the tablets as before, and accu- application of a compressive load. Although this term de-
rately weigh. scribes the true nature of the test more accurately than does
Generally, the test is run once. If obviously cracked, hardness, it implies that tablets are actually crushed during
cleaved, or broken tablets are present in the tablet sample the test, which often is not the case. Moreover, the term
after tumbling, the sample fails the test. If the results are strength in this application can be questioned, because in
difficult to interpret or if the weight loss is greater than the the physical sciences that term is often used to describe a
targeted value, the test should be repeated twice and the stress (e.g., tensile strength). Thus, the term breaking force is
mean of the three tests determined. A maximum mean preferred and will be used in the present discussion.
weight loss from the three samples of not more than 1.0%
is considered acceptable for most products.
If tablet size or shape causes irregular tumbling, adjust the TABLET BREAKING FORCE
drum base so that the base forms an angle of about 10° DETERMINATIONS
with the horizontal and the tablets no longer bind together
when lying next to each other, which prevents them from Early measuring devices were typically hand operated. For
falling freely. example, the Monsanto (or Stokes) hardness tester was
Effervescent tablets and chewable tablets may have differ- based on compressing tablets between two jaws via a spring
ent specifications as far as friability is concerned. In the case gauge and screw. In the Pfizer hardness tester, the vertically
of hygroscopic tablets, an appropriate humidity-controlled mounted tablet was squeezed in a device that resembled a
environment is required for testing. pair of pliers. In the Strong Cobb hardness tester, the break-
Drums with dual scooping projections, or an apparatus ing load was applied through the action of a small hydraulic
with more than one drum, for the running of multiple sam- pump that was first operated manually but was later motor-
ples at one time, are also permitted. ized. Problems associated with these devices were related to
operator variability in rates of loading and difficulties in
proper setup and calibration. Modern testers employ me-
chanical drives, strain gauge–based load cells for force meas-
urements, and electronic signal processing, and therefore
are preferred. However, several important issues must be
considered when using them for the analytical determina-
〈1217〉 TABLET BREAKING tion of breaking force; these are discussed below.

FORCE Platens
The platens should be parallel. Their faces should be pol-
ished smooth and precision-ground perpendicularly to the
direction of movement. Perpendicularity must be preserved
INTRODUCTION during platen movement, and the mechanism should be
free of any bending or torsion displacements as the load is
There are a variety of presentations for tablets as delivery applied. The contact faces must be larger than the area of
systems for pharmaceutical agents, such as rapidly disinte- contact with the tablet.
grating, slowly disintegrating, eroding, chewable, and loz-
enge. Each of these presentations places a certain demand
on the bonding, structure, and integrity of the compressed Rate and Uniformity of Loading
matrix. Tablets must be able to withstand the rigors of han-
dling and transportation experienced in the manufacturing Either the rate of platen movement or the rate at which
plant, in the drug distribution system, and in the field at the the compressive force is applied (i.e., the loading rate)

Official from May 1, 2012

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