1. Size & Shape:It can be dimensionally described & controlled. The thickness of a tablet  is only variables. Tablet thickness can be measured by micrometre or by other device. Tablet thickness should be controlled within a ± 5% variation of standard value.
  2. Unique identification marking:These marking utilise some  form  of embossing, engraving or printing. These markings include company name  or symbol, product code, product name  etc.
  3. Organoleptic properties: Colour distribution  must be uniform with no mottling. For visual colour comparison compare the colour of sample against standard colour.
    The presence of odour in a batch of tablet  indicates a stability problem  such as the characteristics odour of  acetic acid in aspirin tablet. Presence of odour could  be characteristic of the drug (Vitamin), added  ingredients (flavouring agent) or the dosage form  (film  coated tablet have a characteristic odour) For  chewable tablet presence or absence of specified taste can be checked. A  tablet level of flaws such as chip, cracks, contamination from  foreign solid  substances  (hair,  drops  of oil,  dirt), surface texture (smooth vs rough) and appearance (shining vs dull) may have zero defect.
  4. Hardness and Friability:Tablet requires a certain amount of strength or hardness and resistance to friability to withstand mechanical shakes of handling in manufacture, packaging and shipping. Hardness generally measures the tablet crushing strength. The strength of a tablet was determined by following  ways;

(a) By cracking  the tablet between 2nd  and 3rd  fingers  with  the  thumb acting  as a fulcrum. If there is a sharp snap,  the tablet is an acceptable strength.

(b) Tablet hardness can be defined as the force required breaking a tablet in a diametric compression. In this test the tablet is placed between two anvils, force is applied to the anvils, and the crushing strength  that just  causes the tablet to break is recorded.

Generally used Hardness testers are:
(1)Monsanto Tester
(2)Strong-Cobb Tester
(3)Pfizer Tester
(4)Erwika Tester
(5) Schleuniger  Tester

Hardness for compressed tablet is 5 to 8 kg.

Friability of  a tablet  can  determine in laboratory  by Roche friabilator. This consist of a plastic chamber that revolves at 25 rpm,  dropping the tablets through a Distance of six inches in the friabilator, which is then operate for 100 revolutions. The tablets are reweighed. Compress tablet that lose less  than 0.5 to 1.0 % of the Tablet weigh are consider acceptable.

  1. Weight Variation test (U.S.P.):Take 20 tablet and  weighed individually. Calculate average weight and compare the individual tablet weight  to  the average. The tablet  pass the U.S.P. test if  no more that 2 tablets are outside the percentage limit and if no tablet differs by more than 2 times the percentage limit.8
  2. Content Uniformity Test:Randomly select 30 tablets. 10 of these assayed individually. The Tablet pass the test if  9 of the 10 tablets must contain not less than 85% and not more than 115% of the labelled drug content and the 10th  tablet may not contain less than 75% and more than 125% of the labelled content. If  these  conditions  are not met, remaining 20 tablet assayed individually and none may fall out side of the 85 to 115% range.
  3. Disintegration Test (U.S.P.):The U.S.P. device to test disintegration uses 6 glass tubes that are 3” long;  open at the top and 10 mesh screen at the bottom  end. To test for disintegration time, one tablet is placed  in each tube and the basket rack is positioned in a 1-L beaker of  water, simulated  gastric fluid or simulated intestinal fluid  at 37 ± 20  C such that the tablet remain 2.5 cm  below the surface of liquid on their upward movement  and not closer than  2.5 cm  from  the bottom  of the beaker in their downward movement. Move the basket  containing the tablets up and down through a distance of 5-6 cm  at a frequency  of 28 to 32 cycles per minute. Floating of the tablets can be prevented by placing perforated plastic discs on each tablet. According to the test the tablet must disintegrate and all particles must pass through the 10 mesh screen in the time specified. If  any residue remains, it must have a soft mass.
  4. Disintegration time:

    Uncoated tablet: 5-30 minutes
    Coated tablet: 1-2 hour9

    1. Dissolution Test (U.S.P.):

    Apparatus-1:  A single tablet is placed in a small wire mesh basket attached to the bottom of the shaft connected to a variable  speed motor. The basket is immersed in a dissolution medium  (as  specified in monograph) contained in a 100 ml  flask. The flask is  cylindrical  with  a hemispherical bottom. The flask  is maintained  at 37±0.5^C by a constant temperature bath. The motor is  adjusted  to  turn at the specified speed and sample of the fluid are withdrawn at intervals to determine the amount of drug in solutions.

    FIND MORE AT…

    Reference links

    http://www.pharmainfo.net/satheeshbabu/blog/evaluation-tablet

    http://www.srmuniv.ac.in/sites/default/files/files/TABLETS.pdf