Double Layer Tablets In Pharma

Tablets are the most widely used dosage form in the world. Tablets are manufactured in different shapes and dimensions. Double-layer tablet is a unique concept in the history of tablet manufacturing where two APIs (Active Pharmaceutical Ingredients) are compressed together in two different layers to form a single tablet.

When to Use

Double layer tablet system may be used for the following

Combining Different Release Patterns.
Incompatible APIs
Avoid Multiple Tablets intake

Combining Different Release Patterns

Double layer tablets are used for the situations where we want to obtain two release patterns in a single tablet i.e one is controlled release and other is Immediate release.
In this case, first, we compress one layer that may be controlled release and then the second layer is compressed to form two layers of tablets.

Incompatible APIs

Double layer tablets are produced for those APIs which are not compatible with each other and we can not combine these two APIs through a single granulation process.
We manufacture granules of these 2 APIs in 2 separate steps.
In one step we prepare granules of one API and in the second step we manufacture granules of the second API.Or we can prepare granules of one API by wet granulation and other API blend can be manufactured by simple blending process (direct compression)
Later on the blend of these two APIs is compressed to form a double layer tablet.

Avoid Multiple Tablets intake

By Combining two APIs in a single tablet it reduces the number of tablets intake by the patient at a time.
One tablet having two APIs in different layers can be used instead of two tablets.

Also Read:

Principle of Double-Layer Tablet Compression

To compress a double layer tablet, a double feed system or double hopper compression machine is used.
D type compression machines are used to compress double layer tablets.
Granules or powder of one layer are fed in one hooper and granules or powder of the second layer is fed into the second hopper.
Powder or granules of the first layer to be compressed are filled in dies and pre-pressure is applied over it to form a thin soft tablet.
The tablet formed is not strong enough because less amount of pressure is applied.
The weight of this layer is adjusted according to BMR (Batch Manufacturing Record)
When the turret rotates the dies pass below the second feeder containing powder or granules of the second layer and it is filled over the pre-compressed tablet.
Suitable pressure is applied to form a tablet by combining both layers.
At this stage main compression rollers are used to apply the pressure.
The hardness of the tablet is adjusted according to BMR and weight of both layers is verified according to BMR.

How To Check Layers Weight

First layer weight is checked by ejecting the tablet after pre-compression.
As the second layer is compressed over the first layer so its weight can not be checked separately after compression.
To check the weight of the second layer a Separating Knife or cutter is used.
Carefully apply pressure with a sharp edge of separation knife at the spot where two layers combine.
This will separate both layers and the weight of each layer can be checked.

Note

Experience and skilled person separate the layers more accurately.

Defects of Double Layer Tablets

The following defect may occur during compression of double-layer tablets

Color Bleeding
Delamination

Color Bleeding

Colour bleeding is a defect also known as colour contamination,in which color granules or powder of one layer are leaked from the feeder and are mixed with a second layer.
It may affect the content uniformity of individual layers if color mixing occurs in excess.
In color bleeding physical appearance of tablets looks bad.

Solution

Following solution may be used

Feeder Adjustment
Vacuum Suction
Double or Triple Granulation

Feeder Adjustment

Feeder of compression machine should be in such a way that there should be no chances of leakage of colour powder or granules of one layer to the second.

Vacuum suction

Proper vacuum suction systems should be installed to remove any leakage of powder or granules.

Double or Triple Granulation

Try to keep one layer in more granular form to achieve maximum granules because leakage of product from the feeder is reduced when granules are in more ratio.
For this, wet granulation method for a single layer is repeated for two or three times i.e after drying we sieve the granules through a suitable sieve and fines or less granular material retained on the specific sieve is kneaded (Granulated) again, dried and sieved.
This produces more granules and less fine so color bleeding is prevented by this method.

Delamination

Delamination is also known as layer separation.
In this defect,two layers are not bound well and are separated after compression.

Reason

Granules size may be large.
Pre-pressure of the first layer may be high.

Solution

Reduce the size of granules.
Reduce the pre pressure to make a proper substrate for second layer binding.