Shape and Size of Tablets:
Thickness of the tablets should be controlled within ± 5% variation with a standard value. It may change with die-wall, particle size, distribution, packing of particles and compressive load. The crown thickness of tablets may be measured by micrometer (sliding caliper scale). This test is necessary for packaging of tablets as well as drug content uniformly.
1. Organoleptic properties:
Some tablets may contain organoleptic substances such as flavoring agent, coloring agent and sweetener. Color uniformity of the tablet can be evaluated by reflectance spectrophotometry, tristimulus colorimetry or microref- lectance photometery.
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2. Hardness:
Suitable hardness is necessary for handling during manufacturing, packaging and shipping. Hardness of the tablets can be measured by Monsanto tester, Strong-cobb-tester, Pfizer tester and Erweka tester.
3. Friability:
Friability is another measurement of tablet strength as tablet hardness is not an absolute indicator of strength. Roche friabilator is used as laboratory equipment for the determination of friability. It has a plastic chamber that revolves at 25 rpm, tablet drops a distance of six inches with each revolution and operated for 100 revolutions. Compressed should not lose more than 1.0% of their weight.
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4. Weight variations:
It is measured to ensure that tablet contains the proper amount of drug and is a satisfactory test for determination of content uniformity of tablets. Usually ten tablets are taken for this test.
5. Disintegration:
Breaking of tablets into smaller particles or granules is known as disintegration and time taken for breaking of tablets in a suitable medium is called disintegration time (DT). IP apparatus consists of 6 glass tubes each 3 inches long, open at top and has 10 mesh screens at the bottom end of basket rack.
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One tablet is placed in each tube and placed in a one litre beaker of water, simulated gastric fluid or simulated intestinal fluid at 37 ± 2°C. It moves up and down through a distance of 5 to 6 cm at 28 to 32 cpm. Uncoated tablets have disintegration times as low as 5 minutes. Majority of tablets have DT of 30 minutes. Disintegration time of enteric coated tablet is one hour in simulated gastric fluid and two hours in simulated intestinal fluid.
6. Dissolution:
The rate of absorption depends on the dissolution of the product. It is directly proportional to the bioavailability of the products. For dissolution study two types of apparatus are used, basket assembly and paddle assembly. It consists of a hemispherical flask of 1000 ml capacity, temperature is maintained at 37 ± 0.5°C, t90% obtained within 30 min. is satisfactory.
7. Drug content:
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Drug uniformity in tablet is determined by assay. It is calculated on batch to batch or lot to lot basis. It is estimated by the titration, spectrophotometer and HPLC.