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,
According to BP
Weight variation ranges according to BP are as follow,
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.
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 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.
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.
Moisture should be properly removed during the drying process.
- 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.
Granules size should be suitable according to tablet size for proper die filling.
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 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.
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.
Flow through feeder housing should be critically monitored and in case of any blockage compression machine should immediately be stopped.
- 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.
Powders or granules feeding system should be synchronized with compression machine speed to balance the die filling and compression machine speed.
- Stages and Mechanism of Tablet Compression.
- Advancements in tablet compression machines.
- Calculation of compression machine capacity.