Friability is the tendency for a tablet to chip, crumble or break following compression. This tendency is normally confined to uncoated tablets and surfaces during handling or subsequent storage.
It can be caused by a number of factors including poor tablet design (too sharp edges), low moisture content, insufficient binder, etc.
For obvious reasons, tablets need to be hard enough such that they do not break up in the bottle but friable enough that they disintegrate in the gastrointestinal tract.
Based on an original design by Roche, the friability tester has now become an accepted standard throughout the pharmaceutical industry for determining the resistance of uncoated tablets to the abrasion and shock experienced in manufacturing, packing and shipping operations.
Whilst the basic design remains unchanged, considerable advances have been made in terms of reliability and ease of usage which have now been incorporated into current units.
1) Friability Tester (Uncoated Tablets)
The basic Friability Tester comprises of a drum and a motor capable of rotating the drum at 25 rpm. The standard friability drum has an inside diameter of 287 mm and a depth of 38 mm and is fitted with a curved baffle which subjects the tablets to be tested to a drop of 156 mm.
The sample (normally 10 tablets) to be tested is first weighed and then placed into the drum. The drum is then rotated 100 times, any loose dust from the sample removed and the sample re-weighed.
The Friability of the sample is given in terms of % weight loss (loss in weight expressed as a percentage of the original sample weight). A maximum weight loss of not more than 1% is considered acceptable for most tablets.
Abrasion drums for carrying out tests into the attrition of tablets caused by the product rubbing together during transit are also available on request.
In many cases, such as with hard coated and uncoated tablets, granules and spheroids, it is impossible to determine the friability of the dosage form using a conventional tablet friability tester even if the test time is extended simply because the resistance is such that no measurable attrition is obtained – the energy imparted by the friability tester is just not sufficient to generate quantifiable changes in surface mass.
The Friabimat SA-400 is a new instrument specifically designed to address this particular problem by offering an alternative method of friability measurement.
For the purpose of the test, the sample is confined within a standard 105 mL glass bottle horizontally mounted on the end of an oscillating arm. The abrasive action is generated by the horizontal shaking movement of the oscillating arm which causes the samples to rub against and collide with each other and/or the internal surfaces of the sample container.
The intensity of the abrasive action and the duration of the test can be adjusted via the controls mounted on the front panel between 0 and 400 oscillations per minute and 0 and 9999 seconds respectively.