Tablet Evaluation Tests/Disintegration
From Pharmpedia
For a drug to be absorbed from a solid dosage form after oral administration, it must first be in solution, and the first important step toward this condition is usually the break-up of the tablet; a process known as disintegration26. The disintegration test is a measure of the time required under a given set of conditions for a group of tablets to disintegrate into particles which will pass through a 10 mesh screen. Generally, the test is useful as a quality assurance tool for conventional dosage forms.
The disintegration test is carried out using the disintegration tester which consists of a basket rack holding 6 plastic tubes, open at the top and bottom, the bottom of the tube is covered by a 10-mesh screen. The basket is immersed in a bath of suitable liquid held at 37oC, preferably in a 1L beaker. For compressed uncoated tablets, the testing fluid is usually water at 37oC but some monographs direct that simulated gastric fluid be used. If one or two tablets fail to disintegrate, the test is repeated using 12 tablets. For most uncoated tablets, the BP requires that the tablets disintegrate in 15minutes (although it varies for some uncoated tablets) while for coated tablets, up to 2hours may be required3. The individual drug monographs specify the time disintegration must occur to meet the Pharmacopoeial standards.
In the past, the only release index required for a tablet was its disintegration time which does not necessarily measure the physiological availability of the drug in a patient. Studies have shown that the agitation of the gastric contents during normal contractions is quite mild in contrast to the turbulent agitation produced in the disintegration test apparaus27. The low order magnitude of agitation in the stomach produces substantially higher disintegration in vivo than those obtained using the USP apparatus. Furthermore, the particles of the disintegrated tablets are not dispersed throughout the stomach but remains as an aggregate. Thus, the tablet disintegration test is limited to manufacturing control of lot-to-lot variations in individual products and is not a measure of bioavailability27. Nevertheless, it is used to provide a simple and useful means for monitoring and controlling the quality of tablets.
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Theories of disintegration
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Introduction |
Several mechanisms of tablet disintegration have been proposed. Some of these are given below. Even though these concepts are listed separately, inter-relationships probably occur in almost all tablet formulations.
Evolution of gas
If a gas is evolved by a chemical reaction when the tablet comes into contact with water, then the tablet will disintegrate. This is the basis for the manufacture of effervescent tablets. An example of such a reaction is of sodium bicarbonate with citric and tartaric acids, which yields carbon dioxide. Peroxides incorporated in certain formulations decompose in the presence of oxygen and this also causes disintegration28.
Heat of wetting
The heat produced when a tablet is immersed in water causes the entrapped air in the tablet to expand and exert sufficient pressure to disintegrate the tablet28.
hgfgfg===Effect of water absorption===
The water absorbed by the tablet initiate disintegration, but this depends on the solubility of the drug and other ingredients present29.
Swelling
The grains of the disintegrant, particularly of starches, swell in the presence of water and exert pressure on the granules to force them apart30,31. Shangraw et al32 reported that tablets of water insoluble drugs disintegrated faster with starches than those of water soluble drugs due to the diminished water absorption capacity of the starches in the latter case.
Porosity of tablets
It has been shown that penetration of water into a tablet is proportional to its mean pore diameter or porosity33,34. The porosity and permeability of tablets decrease as the tabletting pressure is increased35, and as the porosity decreases, the disintegration time increases 31,32. Though no quantitative relationships have been reported between disintegration and penetration times, generally short disintegration times are associated with rapid fluid penetration36,37.
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