Different Methods of Tablet Coating

Tablet coating is a process used to apply a thin layer of coating material onto the surface of tablets. The coating can serve various purposes, including improving tablet appearance, taste masking, providing gastro-resistance, or modifying drug release characteristics. There are different methods of tablet coating, each with its own advantages and suitability for specific formulations. The main methods of tablet coating are as follows:

1. Film Coating

Film coating is the most common method of tablet coating used in the pharmaceutical industry. It involves applying a thin polymer film onto the tablet surface to form a protective and uniform coating. The film is typically prepared using a coating solution or suspension that contains the polymer, plasticizer, and other additives. The coated tablets are then dried in a controlled environment to remove the solvent and form a solid film. Film coating is performed using specialized equipment like pan coaters or fluid bed coaters. This method offers several advantages, including precise control over coating thickness, reduced manufacturing time, and improved tablet appearance.

2. Sugar Coating

Sugar coating is one of the oldest methods of tablet coating. It involves the application of multiple layers of sugar-based solutions onto the tablet surface, followed by drying and polishing. Sugar coating is a labor-intensive process and requires several coating steps to achieve the desired coating thickness and appearance. While it has become less common due to its time-consuming nature, sugar coating is still used for certain traditional or specialty products, as it provides excellent taste masking and an attractive appearance.

3. Enteric Coating

Enteric coating is a specialized form of coating used to protect tablets from the acidic environment of the stomach and release the drug in the alkaline environment of the small intestine. Enteric coatings are typically made of polymers that are resistant to stomach acid but dissolve or become permeable in the higher pH of the intestine. Enteric-coated tablets are often used to prevent gastric irritation, improve drug stability, and achieve delayed or targeted drug release. The coating process is similar to film coating, but with the use of specific enteric polymers.

4. Functional Coating

Functional coating is a type of coating applied to modify the drug release characteristics of the tablet. It can include coatings designed for sustained release, extended release, or controlled release of the drug. These coatings control the release rate and duration of the drug, allowing for less frequent dosing and improved patient compliance. Functional coatings can be achieved using various polymers and coating techniques, depending on the desired drug release profile.

5. Compression Coating

Compression coating is a unique method where a coating material is compressed between two layers of the tablet blend to form the coating. It eliminates the need for a separate coating process and reduces processing time and cost. Compression coating is often used for certain bi-layer or multi-layer tablets, where one layer contains the drug and the other layer functions as the coating material.

Conclusion

Tablet coating is an essential process in pharmaceutical manufacturing, providing various benefits such as improved tablet appearance, taste masking, drug protection, and modified drug release. The selection of the coating method depends on the specific requirements of the tablet formulation and the desired properties of the finished product. Manufacturers use film coating, sugar coating, enteric coating, functional coating, and compression coating, among others, to achieve different coating objectives and meet patient needs effectively.