Wet granulation is the process of size enlargement in which a liquid is added to a powder with agitation to produce agglomeration or granules. It is the oldest and most conventional method of tablet production. It is also the method of choice when large-dose drugs are to be compressed.
Wet granules are prepared using oscillating granulators, high-speed mixers/granulators, fluid-bed granulators or even extruders and spheronizers. The wet granules are properly dried and mixed with other essential excipients and finally compressed into tablets using a tablet press.
This article focuses on the advantages and disadvantages of wet granulation.
1. Wet granulation modifies the properties of formulation ingredients to overcome their tableting deficiencies. Granules formed are relatively more spherical than the powders and have better flow properties.
2. Improved compressibility of powders resulting from wet granulation process allows the use of low pressure during compression. This reduces machine wear and thus improves the life of the machine.
3. The process makes use of conventional excipients and therefore is not dependent on the inclusion of special grades of excipients.
4. It ensures better content uniformity, especially for soluble low-dose drugs.
5. The process may improve the dissolution rate of poorly soluble drugs by imparting hydrophilic properties to the surface of the granules.
6. Wet granulation prevents segregation of components of a homogenous powder mix during processing, transferring, handling and/or storage, leading to reduced intra- and inter-batch variability.
7. Tablets manufactured by wet granulation are amenable to post-processing unit operations such as tablet coating.
8. Wet granulation reduces the level of dust present during manufacturing process thereby reducing the incidence of cross-contamination and risk to workers.
9. Wet granulation reduces the amount of air entrapment thereby increasing powder compressibility.
1. Wet granulation often requires several processing steps.
2. The cost of wet granulation is higher because of the time, labour, energy, equipment and space required for the process.
3. The process is not suitable for thermolabile and moisture-sensitive materials.
4. Migration of soluble dyes may occur during the drying process.
5. Incompatibilities between formulation ingredients will be aggravated by the granulating solvent which tends to bring them into close contact.
6. There is a possibility of material loss during processing due to the transfer of material from one unit operation to the other.
7. The dissolution rate of tablets manufactured by wet granulation may decrease with aging.
In spite of all these limitations, the manufacture of tablet using wet granulation still persist due to the following reasons:
a. Availability of extensive data on manufacture of existing products by wet granulation. This has made pharmaceutical companies reluctant to adopt new techniques except there exist a compelling reason to do that.
b. Experience over the years in formulation has also shown that wet granulated granules and tablets assure good content uniformity.
c. The drying process can be manipulated to produce granules with the desired moisture content.
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