(Sustained-Release Layer): The second layer is formulated to provide a controlled and extended release of the drug over an extended period. This layer typically includes the sustained-release formulation of the drug, which may be in the form of granules or pellets with controlled-release properties. Excipients like hydrophilic polymers are often used to regulate drug release from this layer.

Interface: The interface between the two layers should be well-defined to prevent drug migration and ensure clear separation between the immediate-release and sustained-release formulations.

Compression of Bi-Layer Tablets

• Layer Segregation: Before compression, the two separate formulations for each layer are prepared and handled separately to avoid cross-contamination and ensure the integrity of the two layers.
• Tablet Press Setup: Bi-layer tablet presses are used to compress bi-layer tablets. The tablet press is set up with the appropriate tooling that accommodates two separate feed hoppers for each layer.
• Layer Filling: The powders or granules for each layer are fed into their respective hoppers of the tablet press.
• First Compression: The first layer (immediate-release layer) is compressed first. The lower punch descends into the die cavity and compresses the first layer formulation to form the bottom layer of the bi-layer tablet.
• Second Compression: After the first layer is compressed, the lower punch is raised, and the second layer formulation (sustained-release layer) is filled into the die cavity on top of the first layer.
• Bi-Layer Compression: The upper punch descends into the die cavity to compress the second layer, forming the top layer of the bi-layer tablet. The compression force is adjusted to ensure proper bonding between the two layers.
• Ejection: After compression, the lower punch is lifted, and the bi-layer tablet is ejected from the die cavity.
• Quality Control: The bi-layer tablets undergo stringent quality control testing to ensure content uniformity, hardness, thickness, and other critical parameters.
• Coating (Optional): Bi-layer tablets can be coated for various purposes, such as taste masking, improved appearance, or modified drug release.

Conclusion

Bi-layer tablets are formulated to deliver both immediate and sustained drug release from a single tablet. The formulation involves designing separate layers with distinct drug release properties, while the compression process utilizes specialized bi-layer tablet presses to ensure proper layer separation and integrity. Bi-layer tablets offer unique advantages in drug delivery, allowing for more flexible and controlled dosing regimens while maintaining patient convenience.