What friability tells you
Friability is the tendency of a tablet to crumble, chip or break when it is handled. Tablets are shaken and dropped in the coating pan, on the packing line, in the bottle and in transport, and a tablet that loses material or breaks along the way reaches the patient with a different weight, a poor appearance and sometimes a different dose. The friability test reproduces that wear in a controlled way and expresses it as a percentage of the weight lost.
The test uses a friabilator, a drum that rotates at about 25 rpm for 4 minutes, which makes 100 rotations. A tablet is lifted and dropped from a fixed height on every turn. The tablets are weighed before and after, and any loose dust is removed before each weighing so that only material actually lost from the tablet is counted.
The formula
The initial and final weights are for the whole sample, not for single tablets, and both must be in the same unit. A lower percentage means a stronger tablet.
Sample size
For tablets with a unit weight of 650 mg or less, the sample is a number of whole tablets that weighs as near as possible to 6.5 g. For tablets heavier than 650 mg, 10 whole tablets are used. The helper above turns the average tablet weight into a tablet count. Because the count is rounded, the sample weight will rarely be exactly 6.5 g, and that is acceptable.
Worked example 1: a single run
A sample of whole tablets weighs 6.500 g in total. After 100 rotations and dedusting, the same tablets weigh 6.460 g.
Weight lost = 6.500 − 6.460 = 0.040 g.
Friability = 0.040 ÷ 6.500 × 100 = 0.62%.
The result is below 1.0% and no tablet is cracked or broken, so the sample complies.
Worked example 2: repeating the test
If a result is doubtful, or the loss is above the limit, the pharmacopoeial approach is to repeat the test twice and take the mean of the three determinations. Suppose three runs on 6.500 g samples finish at 6.430 g, 6.450 g and 6.440 g.
Run 1 = 0.070 ÷ 6.500 × 100 = 1.08%.
Run 2 = 0.050 ÷ 6.500 × 100 = 0.77%.
Run 3 = 0.060 ÷ 6.500 × 100 = 0.92%.
Mean = (1.08 + 0.77 + 0.92) ÷ 3 = 0.92%.
The first run was above 1.0%, but the mean of the three runs is within the limit. The record must show all three results and the reason for repeating, not only the mean.
Acceptance criteria
For most tablets a mean weight loss of not more than 1.0% is acceptable. Cracked, cleaved or broken tablets in the sample after the test are a failure, even when the weight loss is small. Some products have a different limit in their own monograph or specification, so use the limit in your approved documents and enter it in the calculator.
Friability and hardness are different tests
Hardness, or breaking force, tells you how much load a tablet withstands when it is crushed. Friability tells you how well it resists abrasion and shock. A tablet can have good hardness and high friability, for example when it laminates or caps, or when the surface is weak because of excess fines. That is why both tests are done together during compression, and why they are read alongside the weight variation results.
Common causes of high friability
- Low compression force, or tablets compressed too thin or too fast for the blend.
- Too little binder, or a binder that is poorly distributed in the granules.
- Granules that are too dry, or a blend with too many fines.
- Capping and lamination from air trapped during compression, or from over-compression.
- Worn or damaged punches and dies that leave rough or weak tablet edges.
- Poor powder flow, which makes the die fill uneven. See the Carr’s Index guide.
Check the compression force against the punch area with the force to pressure guide before changing any other setting. Edge chipping in the coating pan is a related problem, covered in Tablet Coating Defects: Causes and Fixes.
Mistakes in the friability test
- Not removing the dust from the tablets before the initial or the final weighing.
- Using a sample far from 6.5 g, or the wrong number of tablets for the unit weight.
- Weighing on a balance that is not accurate enough for a loss of a few milligrams.
- Running the drum at the wrong speed or for the wrong time.
- Using tablets from only one moment of the compression run, so the sample does not represent the batch.
- Ignoring cracked or broken tablets because the percentage looks acceptable.
- Reporting only the mean when the test was repeated.
Standards and references
The checks on this page relate to the documents below. Standards are revised from time to time, so confirm the current edition and follow your own approved procedures.
- USP <1216> Tablet Friability
- Ph. Eur. 2.9.7, Friability of uncoated tablets
- USP <1217> Tablet Breaking Force
- 21 CFR 211.110, Sampling and testing of in-process materials and drug products
Questions on tablet friability
What is an acceptable friability for tablets?
For most products a mean weight loss of not more than 1.0% is acceptable, and the tablets must not be cracked or broken after the test. Always follow the limit in your own monograph or specification.
How many tablets are used in the friability test?
For tablets of 650 mg or less, a sample of whole tablets weighing as near as possible to 6.5 g is used. For tablets heavier than 650 mg, 10 whole tablets are used.
What should I do if friability is above 1.0%?
If the loss is above the limit or the result is doubtful, the pharmacopoeial procedure is to repeat the test twice and take the mean of the three results. If it still fails, investigate hardness, binder level, moisture, fines and tooling.
Is friability the same as hardness?
No. Hardness, or breaking force, measures the load needed to crush a tablet. Friability measures how much material a tablet loses by abrasion and shock. A tablet can be hard and still friable, so both are checked.
Does the friability test apply to coated tablets?
The pharmacopoeial test is written for uncoated tablets. For coated tablets, follow the monograph and your own approved procedure.
Related tools and guides: Weight Variation Calculator · Weight Variation Test Guide · Compression Reconciliation · Bulk and Tapped Density · Batch Reconciliation Explained
By Sajjad Ahmad. For reference and education only; verify limits against your SOPs and the current pharmacopoeia. See the methodology.