Manufacturing of compressed tablets, Granulation: Wet Granulation, Dry Granulation, Advantages of granulation

Manufacturing of compressed tablets:

There are mainly two steps to manufacture compressed tablets. These are

• A. Granulation: Most medicaments and excipients are available as fine powder. These powders are properly mixed to form a powder of uniform composition. Then this powder mixture is converted into granules by granulation methods. There are three methods to prepare granules from powder.

  • a. Wet granulation (Moist granulation): It is the most widely used method to prepare granules for compressed tablets. Weigh and mix finely divided powdered medicaments, diluents, binding agents, and part of disintegrating agents uniformly. Pass it with the sieve the number 30 to 60. Mix a sufficient quantity of granulating agent to form a coherent mass. Pass coherent mass through sieve number 8 or 10 to get wet granules. Dry-weight granules in the air oven at temperatures of 60 degrees C. Pass dried granules through sieve number 20. Add lubricant and the remaining part of the disintegrating agent into dried granules. Now granules are ready to be compressed as a tablet.

• Explanation (Reason):

  • i. Powder ingredients are passed through sieve numbers 30 to 60 to get powder particles of uniform size. This step will ensure a uniform mixing of ingredients.

  • ii. A proper amount of granulating agents is used to form a coherent mass. This will form granules of uniform size with a small amount of powder. Coherent mass will not stick with the sieve. Low coherent mass will not form proper granules. There will be large amounts of fine powders in granules. This will lead to the formation of a soft tablet and capping of tablets. More amount of granulating agents shall form a wet mass that will stick with the sieve and not form granules. Thus amount of granulating agent should be used properly.

  • iii. Granules are dried at 60 degrees C in a hot air oven for uniform drying and to avoid over-drying of granules. Over-dried granules will form soft tablets.

  • iv. Granules are passed through sieve 20 to get granules of uniform size with a small amount of fines. This will ensure the proper flow of granules inside the tablet machine.

  • v. Flavouring agents are added after drying of granules to avoid volatilization of flavoring agent during drying.

  • vi. Lubricants are added after granulation. Because lubricants act on the surface of granules, not inside granules.

  • vii. Half a portion of disintegrating agents are added before granulation and the next other part after granulation. The disintegrating agent will break the tablet into granules and then granules into particles.

• Precaution (Disadvantages):

  • 1. It is not suitable for heat-sensitive and moisture-sensitive medicaments.

  • 2. It is a time-consuming method.

  • 3. It requires more manpower.

• b. Dry granulation (Precompression method double compression method or slugging method): It is suitable for heat-sensitive and moisture-sensitive medicaments. Medicaments in crystalline form or granular form are used in dry granulation. Compress uniformly mixed ingredients into a slug. Slugs are flat large-size tablets prepared by heavy compression inside A tablet machine. Pass slug through sieve number 20 to break into granules. Mix granules with lubricants and other required additives. Compress granules into tablets in a tablet machine.

• c. Direct compression: Medicaments available in crystal form can be compressed directly into tablets. Examples are sodium chloride, potassium bromide, acetylsalicylic acid crystal, etc.

Advantages of granulation over fine powder in tablet manufacturing:

• 1. Granules flow uniformly inside the tablet machine. This ensures tablets of uniform weight. Fine powders do not flow uniformly inside the tablet machine. Thus there will be weight variation in tablets.

• 2. Granules will have uniform composition irrespective of their size variation. Powders contain ingredients of different densities. Thus there will be segregation inside the tablet machine due to tablet machine vibration.

• 3. Fine powders blow out from the die during compression. Granules do not blow out during compression.

• 4. Granules have more kneading capacity. Thus it forms an intact tablet. The fine powder does not have much knighting capacity. Thus it forms soft tablets. Tablets may disintegrate during handling and transportation.

Alok Bains