Bi-Layer Tablets is suitable for sequential release of two incompatible drugs in combination. It is mainly for sustained release tablet in which one Layer is immediate release as initial dose and second layer is maintenance dose. The production of two layer tablets has been an increasingly popular method for increasing sales appeal. This is a good method to make a product instantly identifiable in the consumers mind. The popularity of these kinds of tablets has been on the rise
It is possible to produce Bi-Layer Tablets on any double sided press with two separate compression stations and two separate feeders for each station. The change over process from single layer to bi layer process is fairly simple procedure with minor modifications. The main challenge lies in keeping the two colours totally separate during production and maintaining the correct weight of the two layers. The requirement of a two layer tablet needs two different colour materials that should be free of mixing and have a clearly defined demarcation line showing separate layers.
In a single layer tablet being produced on a double side tablet press, the two feeders compliment each other. Excess granules or overflow from one feeder normally flows into the feeder on the other side as mixing of the granules is not a problem.
In a Bi-Layer Tablet, since the 2 powders are of different material and colours, mixing cannot be allowed. The two layers have to be completely separate. This effects the look of the final tablet as it requires a definite separation line showing two different colours.
Below is a sketch showing the sequence of Bi-Layer Tablets production.
Procedure: In the sketch below the first layer has blue granules and the second layer has red granules.
- Two special feeders are required that prevent mixing of the two colours. The granules from the first layer are allowed to go around the turret and renter in to the same feeder. The excess granules from the second layer are not allowed to move on to the turret and are collected through a separate outlet.
- To avoid the ejection of the first layer, the ejection cam after the first layer feeder has to be removed. This is to enable the second colour to fill on top of the first colour.
- Press must have a dust extraction system. The feeders have a dust suction facility that can be connected to the dust extraction system. This is extremely useful in preventing the two colours from mixing.
- It is advisable to put the layer with the higher weight as the first layer and the layer with the lesser weight as the second layer. As the filling in the second layer is limited and it depends on the upper punch entry into the die. The maximum amount of fill of the second layer can be controlled by adjusting the upper penetration system.
- It is always advisable to put in only the first layer and set its weight. Once the weight of the first layer is set then the second powder is to be introduced and we can set the weight of the final tablet.
If during production the weights of the separate layers need to be checked, then the pressure at the first layer needs to be slightly increased so that the first layer does not bond with the second layer and the two layers come out separate during final ejection.