In recent years, multi-layer tablets have risen in popularity as an efficient and cost-saving oral drug delivery method. These tablets consist of two or more separate layers/levels of drugs pressed together into a single-dosage form. Each drug layer/level may have a different release rate. This quality is beneficial if the person needs to take two different drugs at the same time or the same drug at different times since each drug can be engineered to be introduced at the appropriate time.

Medicinal Advantages of Multi-Layer Tablets

Multi-layer tablets can be medicinally beneficial in many ways. For example:

• They can enhance drug effectiveness. Multi-layer tableting can allow immediate release and sustained-release active ingredients to be combined into a single pill. By separating actives into two distinct layers within the tablet, manufacturers allow a user to experience pharmacological effects shortly after ingestion from the immediate release active and over a longer period of time from the sustained-release active.
• They can combine incompatible ingredients. Certain active ingredients and / or excipients may be incompatible with each other, which makes it harder for them to be blended into the same final formulation. For these ingredients, a multi-layer tablet form is ideal since the effects of these incompatibilities can be mitigated.
• They can extend the life of a product line. Existing single-layer tablets can sometimes be reformulated into a new multi-layer variation in the hopes that a new patent will be accepted for the revised form. If successful, this effort could breathe new life into a product line, and ideally prove suitable for other patient uses
• They can prevent product misuse. Some drugs have powerful ingredients that can be used for purposes unintended by the manufacturer. One way manufacturers are combatting this issue is by adding an antagonistic layer to the tablet that stops people from extracting the desired ingredient (i.e. that which may be abused).

Overview of the Multi-Layer Tableting Process

Multi-layer tableting has become increasingly complex, in terms of the overall functionality offered by leading press suppliers, but the basic steps in the process always include the following: 

1. The tablet press is charged with the different ingredients needed for the final product, via two separate hoppers.
2. The ingredients for the first layer—i.e., the bottom layer—feed into the dies as the cavities pass under the first feed frame.
3. The cavities proceed to the initial compression station, which tamps the ingredients to form the first layer. The resulting layer is soft enough to ensure good cohesion with the second layer.
4. The dies pass under the second feed frame and fill with the ingredients for the second layer. The amount added increases the total weight of the tablet to the desired level.
5. The dies pass through the final compression station, which uses compression rolls to apply the appropriate amount of force to achieve the desired tablet hardness.
6. The dies pass into the ejection station of the press, which raises the upper and lower punches using raising and ejection cams, allowing the lower punch tips to move to the top of the dies, thus ejecting the finished tablets from the die cavities.

Key Considerations for Multi-Layer Tableting

The inherent complexities of producing good multi-layer tablets, at appreciable speeds, take many forms. The following represent some of the most common that manufacturers encounter:

• Cross-contamination, or color “bleeding”, between layers
• Delamination (when the layers of the final tablet physically separate)
• Poor load cell resolution, especially for very thin first layers requiring almost no force
• Inefficient first-layer sampling processes, either in terms of speed, or transitional rejects
• Off-target weights for individual layers
• Lower output than single-layer tablet operations

Those with significant tableting experience often consider the manufacturing of multi-layer tablets a true art form. While it can provide a myriad of advantages similar to those referenced earlier in this blog, the pharmaceutical industry’s requirements for pinpoint accuracy with active ingredients guarantee a robust challenge. Fortunately there are equipment suppliers, such as Fette Compacting, with a wealth of multi-layer experience developed over many decades.

Learn More About Multi-Layer Tablets From the Experts at Fette

Want to find out more about why multi-layer tablets are beneficial and how to make them? Ask the tablet press experts at Fette! As the world’s leading provider of integrated industrial tablet production solutions, we are well-equipped to answer or address any of your tablet press questions and concerns. For information on how to enhance the performance of your tablet press, download our eBook, A Guide to Optimizing and Enhancing Your Tablet Press Performance.