Weight Variation During Tablet Compression.

Weight variation is a frequently used term during tablet compression operation in pharmaceutical industries.As the name indicates Weight Variation is a defect in which weight differs from the defined ranges given by the  official pharmacopoeias.

According to USP

Weight variation ranges according to USP are as follows,

Tablet Weight(mg)

%age Difference

130 or less than 130

10%

130 to 324

7.5%

Above 324

5%

According to BP

Weight variation ranges according to BP are as follow,

Tablet Weight(mg)

%age Difference

80 or less than 80

10%

More than 80 & less than 250

7.5%

250 or above 250

5%

If the weight of  tablets is higher than the recommended range then the assay or content uniformity may also be high.

&

If the weight of  tablets is lower than the recommended range then the assay or content uniformity may also be low.

So weight of tablets should carefully be monitored during compression operation.

In this article we will discuss some main  reasons which may result in weight  variation of tablets during compression operation.

Weight Variation During Tablet Compression.

 

1. Formulation Related

  • More Fine
  • High Moisture Content
  • Granules Size

2. Machine Related

  • Hoper Adjustment
  • Blockage Of Feeding Housing
  • Feeding Rate

1. Formulation Related

Formulation related means the factors which occur during the manufacturing stage.

Manufacturing of granules by wet granulation is a multistep process and variation in any step may directly affect the compression stage.

So each and every stage of granulation should be carried out with great care to make the compression process trouble free and smooth.

Following are some formulation related important factors which may result in weight variation.

More Fine

  • More fine means our final product has less granules and more fine powders.
  • If we have more fine in our formulation it may result in poor flow of product from compression machine hoper to the feeder.
  • More fine may also result in a rat hole.
  • Rat hole is a defect in which powder adheres to the walls of the hoper and in the middle a hole is formed like the hole of a rat.
  • So due to poor flow or rat hole, dies are not properly filled during compression and results in weight variation.

Solution

There should be a proper ratio of fine powder and granules to improve flow and to prevent weight variation.

High Moisture Content

  • High moisture content is another factor which may result in weight variation during compression operation.
  • If moisture content is not properly removed from the final product it may result in a rat hole.
  • As mentioned above, rat hole is a flow defect and results in weight variation.

Solution

Moisture should be properly removed during the drying process.

Granules Size 

  • Granules size is another factor which may result in weight variation during tablet compression.
  • For small size tablets if we use large size granules it will result in improper die filling and improper die filling results in weight variation.
  • For large size tablets if we use small size granules it may also result in weight variation of tablet during tablet compression.

Solution

Granules size should be suitable according to tablet size for proper die filling.

Also Read: 

2. Machine Related

Machine related reasons for weight variation means that the final product which we have manufactured is fault free but the machine parts or tooling is creating weight variation of the tablets.

Following are some machine related important factors which may result in weight variation.

Hoper Adjustment

  • Hoper position may result in weight variation in case of conventional compression machines where powder or granules flow through the hoper to the machine feeder under the influence of gravity.
  • If the hoper base is low it may result in poor feeding of powders or granules and results in weight.

Solution

Hopers of compression machines should be adjusted in such a way  that powders or granules should flow smoothly under influence of gravity.

Blockage of Feeder housing

  • In conventional compression machines during normal compression operation, sudden blockage of any housing in the feed frame results in weight variation due to less supply of powders or granules to the dies.

Solution

Flow through feeder housing should be critically monitored and in case of any blockage compression machine should immediately be stopped.

Feeding Rate

  • In advance compression machines powder from feed frame to dies is supplied through force feeding system.
  •  If the rpm of the force feeding system is very low and machine speed is high, proper feeding to dies will be distrubed and results in weight variation.

Solution

Powders or granules feeding system should be synchronized with compression machine speed to balance the die filling and compression machine speed.

Also Read: 

  1. Stages and Mechanism of Tablet Compression.
  2. Advancements in tablet compression machines.
  3. Calculation of compression machine capacity.
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