Dry Granulation in Tablet Manufacturing

Dry granulation, also known as pre-compression or slugging, is a tablet manufacturing process that involves
compacting the powder blend without using any liquid binder. This method is suitable for drugs that are sensitive
to moisture or heat and cannot undergo wet granulation. Dry granulation is particularly advantageous when dealing
with potent drugs or those with poor flow properties. Below, I’ll explain the step-by-step process of dry
granulation in tablet manufacturing:

Step 1: Weighing and Blending

The first step in dry granulation is to accurately weigh the active pharmaceutical ingredient (API) and other
excipients. These components are then blended together to ensure a homogeneous mixture. The blend’s uniformity is
crucial to achieving consistent drug content in the final tablets.

Step 2: Slugging

In the slugging process, the dry powder blend is compressed into large tablets or slugs using a tablet press or
a heavy-duty roller compactor. The slugs typically have a larger diameter and thickness than the final tablets.
The compaction process may involve the application of high pressure to ensure proper consolidation of the powder.

Step 3: Milling

After slugging, the large slugs are reduced to granules through a milling process. The slugs are passed through
a suitable mill, such as a hammer mill or a conical mill, to break them down into granules of the desired size.
The milling step is essential for achieving uniform particle size and facilitating subsequent tablet compression.

Step 4: Blending and Lubrication

Once the granules are obtained, they are blended again with any additional excipients, such as disintegrants or
lubricants. The lubricants help reduce friction during tablet compression. Magnesium stearate is commonly used as
a lubricant in dry granulation processes.

Step 5: Tablet Compression

The final step in dry granulation is tablet compression. The lubricated granules are fed into a tablet press,
where they are subjected to high pressure to form the final tablets. The tablets are then evaluated through
quality control tests to ensure they meet the required specifications for weight, hardness, disintegration, and
dissolution.

Advantages of Dry Granulation:

• Preserves drug stability: Dry granulation is suitable for moisture-sensitive drugs, as it avoids exposure
  to water or solvents.
• Better flow properties: The process can improve the flowability of the powder blend, making it easier to
  handle during manufacturing.
• Cost-effective: Dry granulation requires fewer equipment and processing steps compared to wet granulation,
  making it more economical.
• Less processing time: The absence of drying steps reduces the overall processing time for tablet
  manufacturing.

Disadvantages of Dry Granulation:

• Compaction issues: Some materials may not compress well or may exhibit poor compressibility, leading to
  difficulties in obtaining suitable slugs.
• Tablet hardness: Dry granulated tablets may have lower hardness compared to tablets made through wet
  granulation.
• Less control over particle size distribution: Achieving a narrow particle size distribution can be
  challenging in dry granulation.
• Potential for segregation: During the blending process, there is a risk of ingredient segregation, leading
  to content non-uniformity.

Conclusion:

Dry granulation is a valuable alternative to wet granulation in tablet manufacturing, especially for drugs that
are sensitive to moisture or heat. The process involves slugging and milling to obtain granules, which are then
compressed into tablets. While dry granulation offers various advantages such as preserving drug stability and
cost-effectiveness, it also has some limitations that need to be carefully addressed during formulation and
process development.