Tablets manufactured by the wet granulation method involve the kneading of powder particles with a binder solution or solvent to form a wet mass & this wet mass is dried using a fluid bed dryer or tray dryer to remove the excessive moisture.
Role Of Moisture In Granules
When we dry the granules in a dryer we don’t remove all the moisture content, rather a suitable percentage of moisture is retained in the granules ranging from 1 to 3% or depending on the type of excipients or API used in the formulation.
This retained moisture level is essential for granules to give them strength during compression because this little amount of moisture helps to create strong bondings between granules when pressure is applied.
Impact Of Over Drying
The granules must be dried under controlled conditions in a dryer and these conditions include,
- Drying Temperature
- Drying Time
If the drying temperature is set higher than the standard value for a defined time or drying time is increased for a specific value of temperature, the moisture level of granules will be disturbed.
Suppose a product is validated to dry in FBD at 70 °C for 40 minutes & its LOD is 2 % after the above specifications.
If someone does not follow the instructions & dry the product at 80°C for 40 minutes or dry at 70 °C for 60 minutes the 2 % recommended moisture level will not be achieved & granules will lose more moisture suppose the resultant value is 0.5%, this condition is known as over-drying of granules & it has following impacts on our process.
- Tablet Capping
- Tablet Lamination
We are familiar that capping and lamination are caused by the low level of moisture content in tablet formulation so due to over-drying of granules the above-mentioned defects are observed during tablet compression.
How To Deal With Over Dried Granules?
When you are in a situation where your granules are over-dried and you are facing tablet capping or lamination problems, use the following technique to overcome this issue.
Moisten The Granules.
Moistening the granules is a very basic & traditional technique in which we simply apply moisture to the over-dried granules.
How To Apply Moisture To The Granules?
To apply moisture, sprinkle trial-based quantity of the solvent over some granules, mix them thoroughly,sive them & check the moisture content, if it is in the required range apply moisture to all granules with the same ratio as determined in trial quantity.
Sometimes when we dry our product, the moisture level is within specified limits but at the time of compression we face tablet capping or lamination problems.
The reason is that the moisture content is lost during the storage period so following moisture application procedure is used.
Weigh some quantity of final mixed material, suppose 10 kg and apply it some moisture, 200 ml (Calculated on basis of trial i.e 5 ml for 1 kg) & we have 40 kg product so 200 ml for 40 kg.
Sieve this 10 kg moisten product from a specified mesh & mix this 10 kg moisten product with the remaining 30 kg product.
By mixing process, the moisture is uniformly distributed to the 40 kg and the issue of capping & lamination is resolved.
- For moisture application Always use the same Solvent which was used during the Granulation or kneading process.
- Do not apply excessive moisture otherwise it will result in sticking or picking.
- Reasons and solutions of tablet capping.
- Reasons and remedies of tablet sticking and picking.
- Wet granulation & Dry Granulation in pharmaceutical industries.