The various process steps involved in wet method are as follows:
- Sifting/milling: Weighed ingredients are passed through the desired sieve number such that the drug and the additives are of uniform size and shape.
- Dry mixing: In this process, the drug along with additives such as diluents, disintegrating agents (half the weighed quantity as intragranular disintegrating agent), and color lakes if present in the formulae are mixed in a suitable mixer for a predetermined time.
- Granulation: In this stage, the powder mixture is converted into granules by adding binder in form of solution and mixed for suitable time period to get a coherent mass or dough mass. The concentration of binder and amount of solution added should be optimized; otherwise, the granules obtained may contain large amounts of fines and may be fragile with less concentration of binder or with excess binder the granules obtained may be very hard and sometimes sticky in nature, which may impose problems during compression and disintegration.
- Wet sifting: The dough mass or coherent mass obtained is then passed through a specified sieve to get the desired size wet granules. The sieve number is usually selected based on the weight of the tablet to be compressed. For example, for weights above 500 mg of the tablet weight, the sieve no. selected can be 12, for weights between 200–400 mg, the sieve no. selected can be 16.
- Drying: Wet granules obtained were dried in a suitable dryer for a predetermined period of time and temperature to get the dried granules with the required moisture content.
- Regranulation: Dried granules are then passed through desired sieve number to get the granules as per requirement.
- Blending: In this stage, granules are transferred into a suitable blender such as double cone blender, V-cone blender, and other additives such as lubricants, glidants, anti-adherents and remaining quantity of disintegrating agents (intergranular disintegrating agent) were added and mixed for a suitable time period.
- Compression: The blended granules should be carefully handled and the granules are compressed into tablets with predetermined weight, hardness and thickness using suitable punches and dies in a multi-station tablet compression machine.
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