EVALUATION PARAMETERS OF TABLETS

Evaluation of tablets 
Notes on tablets II

Tablets are evaluated for their physical, chemical and bioavailability properties. Stability testing is also an important evaluation parameter.

Theset are divided into official and unofficial tests.

Unofficial tests:

1. Appearance

2. Size and shape

3. Organoleptic properties (color, odor, taste)

4. Hardness

5. Friability

Official tests:

1. Drug content

2. Weight variation

3. Disintegration

4. Dissolution

Let's see important parameters in all the test (from GPAT point of view):

• Measurement of crown thickness: Instruments used are Micrometer and Caliper scale.
• Tablet thickness values variations: ±5% variation of a std value.

• Instruments used for color evaluation:

1. Reflectance spectrophotometry
2. Tristimulus colorimetric measurements
3. Microreflectance photometer (measure the color uniformity and gloss on a tablet surface)

• Hardness and Friability

Hardness: tablet crushing strength

1. Monsanto tester: Two plungers and a barrel containing compressible spring (manual tester)
2. Strong-Cobb tester: Use of hydraulic pressure (manual pump).  An anvil+ stationary platform. Plunger activation by pumping a lever arm.
3. Modified Strong-Cobb tester: force applied by air pressure.
4. Pfizer tester: Holding anvil+piston. Piston is connected to a direct force reading gauge. Rapid measurement and simplicity.
5. Erweka tester: Upper anvil is a test anvil. Motor driven suspended weight moves along a rail, uniformly transmits pressure on tablet placed between upper and lower anvils.  Pointer on scale shows breaking strength in kilograms (Kg).
6. Schleuniger tester: Operates in horizontal position. Anvil is driven by electric motor. Reading is shown in kilograms and Strong-Cobb unit.

Friability: Instrument used is known as Roche friabilator. 

1. Rotations per minute :25
2. Operated for : 100 revolutions
3. Time : approx. 4 min.
4. Acceptable range: less than 0.5 to 1%.

Tablet friability is influenced by-

1. Use of concave and deep concave punches

2. Moisture content of granules and tablets (optimum moisture concentration is 2-4%)

Rough handling tests:

• Drop test
• Inclined plane impact test
• Vibration test
• Actual transportation and then testing

• Weight variation-  

Weight variation tolerance for uncoated tablets (USP)

DISINTEGRATION

Disintegration is the breakdown of tablet into smaller particles or granules.

Disintegration apparatus consists of : Six glass tubes (3 inches long) open at the top. Tubes are held against 10-mesh screen at the bottom end. This is fitted in basket rack assembly. 
Basket rack is positioned in a beaker of fluid (1L).
Media - Water, Simulated gastric fluid or simulated intestinal fluid.
Temperature- 37±2°C.
Distance of 2.5 cm is maintained from surface of liquid and bottom of the beaker during upward and downward movement.
Frequency of movement : 28-32 cycles per minute.
As per USP standards- The tablet must disintegrate and all particles must pass through the 10-mesh screen in the time specified.

DISSOLUTION

In vitro method which correlates the rate of drug absorption and the rate of drug dissolution from tablet.

Importance of this test:

It is essential to perform the dissolution test of tablet to (1) show that the rate of drug release is close as possible to 100% and (2) to show that the rate of drug release is uniform batch to batch.

Apparatus used:(USP)
Type I : Basket (Rotating basket)
Type II : Paddle (Rotating paddle)

There are certain dissolution acceptance criteria according to which tablet or a batch is considered acceptable or else rejected.

Where, Q is the percentage of drug content dissolved in a given time period.