Tablets should be sufficiently hard to resist breaking during normal, handling, packaging, and shipping and must be soft enough to disintegrate properly after swallowing. So the resistance of tablets to capping, abrasion or breaking under conditions of storage, transportation, and handling before being taken by the consumers depends on its hardness. Hardness of the tablet is controlled by the degree of the pressure applied during the compression stage.
Hardness and Friability tests of uncoated tablets also affects disintegration and subsequent dissolution. If the tablet is too hard, it may not disintegrate in the required period of time to meet the dissolution specifications; if it is too soft it may not be able to withstand the handling during subsequent processing such as coating, packaging and shipping operations. The principle of measurement involves subjecting the tablet to an increasing load until the tablet breaks or fractures. The load is applied along the radial axis of the tablet.
Oral tablets normally have a hardness of 4 to 10 kg; however, hypodermic and chewable tablets are much softer (3 kg) and some sustained release tablets are much harder (10-20 kg).
Friability is the tendency of tablet to crumble. The friability test is designed to evaluate the ability of the tablet to withstand abrasion in packaging, handling and shipping. Another application of friability test is to detect incipient capping or laminate when stressed by abrasion inside the rotating cylinder present on the friability tester.
The accepted limit of weight loss after this experiment should not be more than 2%.
Instrumentation: Balance, Hardness tester, friability tester.
Hardness of uncoated tablets Procedure:
- To start, simply press <Zero> to zero the load cell.
- Place a tablet along its radial axis onto the platform between the test jaw and the load cell plunger.
- Using the multi-turn, low-friction hand-wheel, apply load gently to the tablet until it fractures.
- The resulting breaking force is displayed on the LCD display in either newtons (N), grams (g), pounds (lbs) or ounces (oz).
- To test another tablet, simply press <Zero> to zero the load cell and proceed as above.
- Repeat the test for another five tablets.
- Calculate the average hardness of paracetamol tablets in kg and neutons.
Friability tests of uncoated tablets Friability:
- Weight out a total of 10 tablets (if the individual weight of tablet is ≤600 mg) using a balance. This is the initial weight.
- Place these ten tablets into the plastic chamber of Friabilator.
- Set the friabilator at 25 rpm and allow the chamber to rotate for 4 minutes.
- Weight out the above 10 tablets again using the same balance. This is the final weight.
- Calculate the percentage weight loss using following formula.
Percent loss or Friability of tablets =
- Comment on your result.
Hardness and Friability Tests of Uncoated Tablets Reflective questions:
- Average hardness of six uncoated tablets was recorded as 6.54 kg. Calculate the hardness in neutons and pounds.
- 10 tablets weighing initially 3.567 gm were placed into a friabilitor which was allowed to rotate at 20rpm for 5 minutes. If the final weight of these 10 tablets was found to be 3.559, calculate the percentage loss.