Film Coating Process in Pharmaceutical Manufacturing

For pharmaceutical companies seeking reliable third-party manufacturing, the film coating process is a critical step that enhances the quality and efficacy of their tablets. Today, we’ll outline the essential steps, techniques, and factors involved in achieving a high-quality film coating, ensuring a reliable final product for patients.

Tablets are among the most convenient and preferred oral dosage forms due to their numerous advantages, including ease of administration, high patient compliance, and cost-effectiveness. Among the multiple steps in pharmaceutical tablet manufacturing, coating is a critical process that is often used for both functional and aesthetic reasons. Among three types of tablet-coating processes (sugar coating, film coating, and press coating), film coating is the most widely used approach to solve various issues encountered during manufacturing, transport, storage, and clinical use of drug products. For ex., tablets containing active pharmaceutical ingredients (APIs) sensitive to light, oxidation, or moisture can be protected by film coating, leading to increased stability of drug products during manufacturing and storage. In addition, film coating can control the drug release patterns of tablets in terms of size, rate, and time. Film coating is also applicable to mask taste and improve patient compliance. Accordingly, tablet film coating is widely used to achieve various pharmaceutical and therapeutic goals.

The film coating process for tablets involves applying a thin layer of a polymer-based material to the tablet’s outer surface. This coating enhances various tablet characteristics, such as controlling the release of the active ingredient, improving the appearance, and protecting the tablet from environmental factors like moisture, light, and air. The process is key in pharmaceutical manufacturing to ensure that the tablet is both effective and stable while also enhancing patient experience through better aesthetics and ease of swallowing.

Basic Requirements for Effective Film Coating

The film coating process is essential in pharmaceuticals to improve the appearance, stability, and performance of tablets. When done right, it ensures effective and consistent drug delivery, protecting the active ingredients and enhancing patient compliance. Below, we’ll outline the steps, equipment, and process variables to show why this precision matters in high-quality manufacturing. 

To achieve an ideal film coating, four primary requirements must be met:

1. Distribution: Ensures the coating evenly covers each tablet.

2. Mixing: Provides consistency within the coating solution.

3. Drying: Prevents moisture accumulation and allows for uniform application.

4. Solvent Removal: Ensures no residual solvents remain, aligning with safety standards.

Key Components of Film Coating Process

1. Coating Solution Distribution: In pharmaceutical manufacturing, the even distribution of the coating solution is crucial. The spray guns are instrumental here, with types like airless and air-atomized spray guns providing the necessary flexibility. Air atomized spray guns are preferred in aqueous film coating for precise control, which can be essential in complex products, such as enteric-coated or sustained-release tablets. 

2. Spray Rate Monitoring: The spray rate, controlled by peristaltic pumps, is monitored closely to avoid defects. For optimal quality, a consistent spray rate is maintained by adjusting the tubing size and pump speed, which helps achieve a uniform film without oversaturating tablets. Adjustments to the spray rate are especially important in larger batches or when scaling up, where each variable’s precision becomes even more critical. 

3. Pan Load and Mixing Efficiency: Achieving an optimal pan load helps improve energy efficiency and coating uniformity. With partial pan loads, much of the inlet air escapes into the exhaust, reducing drying efficiency and requiring additional energy. For this reason, modern machines often include adjustable pans to accommodate various batch sizes, making it easier to maintain full load efficiency. 

4. Spray Gun Positioning: Positioning multiple spray guns within the coating pan requires careful alignment to maintain consistent coverage. Proper gun-to-gun and gun-to-bed distances are maintained to prevent over-wetting or under-coating issues. Pre-coating validation ensures that each gun’s spray rate remains within acceptable limits, reducing variations across batches. 

5. Controlling Pressure and Airflow: During coating, the pan should operate under slight negative pressure to prevent solvent loss into the room air, which aligns with GMP standards. Negative pressure also minimizes contaminants entering the coating environment, ensuring the safety and cleanliness of each batch. Ideally, a pan pressure of 10-25 mm is maintained to balance airflow and prevent exhaust loss of the coating solution.

   

Essential Parameters for Monitoring

To achieve a consistent coating quality, several parameters must be controlled and monitored throughout:

• Inlet and exhaust temperatures: Regulate drying rates and prevent moisture retention.

• Bed temperature: Ensures coating adhesion.

• Spray rate and atomization pressure: Critical for film thickness.

• Negative pressure and RPM: Enhances coating consistency and energy efficiency.

Factors Affecting Film Coating Quality in Tablet Coating

In solvent-based pan coating, tablets are coated in a rotating pan, with droplets of coating solution forming a film as they pass through the spray zone. A smooth, uniform coating is achieved by optimizing process parameters. Key factors affecting coating quality include: 

• Spray Airflow Rate: Both atomization and pattern air are essential for uniform droplet spray. A 1:1 ratio of atomization to pattern air improves coating efficiency and droplet size.

• Spray Rate: Higher spray rates increase droplet size and decrease velocity, affecting coating quality. The atomization air/spray rate ratio is crucial for controlling droplet size and drying efficiency.

• Inlet/Outlet Air: Inlet air temperature and humidity influence drying. Excessive drying leads to rough coatings, while insufficient drying causes agglomeration and poor adhesion.

• Droplet Size: Smaller droplets lead to a smoother coating. Droplet size depends on spray air flow, spray rate, and solution characteristics.

• Solid Content and Viscosity: High solid content increases viscosity, affecting spray efficiency. Lower viscosity improves sprayability but may impact drying efficiency.

• Gun-to-Bed Distance: An optimal distance ensures effective coating. Too much distance leads to droplet drying before reaching the tablet, while too little causes wet surfaces and agglomeration.

• Curing Time: Post-coating curing allows residual solvent to evaporate, hardening the coating and affecting tablet dissolution.

Optimizing these parameters is crucial for achieving uniform, high-quality film coatings.

Advantages of Proper Film Coating

Beyond aesthetics, the pharmaceutical application of film coating plays a critical role in modifying the release of drugs, improving drug stability, masking taste, and enabling active drug release. Below are the key areas where film coating is applied:

4.1 Modified Drug Release

4.1.1 Delayed Drug Release: Film coating can be used for delayed drug release to protect drugs from gastric degradation and to control where the drug is released in the gastrointestinal (GI) tract. Enteric coatings, which dissolve at specific pH levels, are used to ensure drug release primarily in the small intestine, rather than the stomach. This approach is beneficial for drugs like proton pump inhibitors (e.g., esomeprazole and pantoprazole) that are acid-labile. Other examples include enteric-coated insulin tablets and colon-targeted drug delivery systems for treating conditions like Crohn’s disease and irritable bowel syndrome (IBS). Dual coating technologies, incorporating both pH-sensitive and bacterially-triggered release mechanisms, are being explored for more precise delivery in the colon. Chronotherapeutic release aims to release drugs in sync with circadian rhythms, addressing diseases with symptoms that worsen at specific times of the day (e.g., cardiovascular disease or asthma). This approach has been used to optimize the timing of drug release, such as in the development of a combination tablet for hypertension and cholesterol.

4.1.2 Sustained Drug Release: To control the rate of drug release over time, film coatings made from water-insoluble, pH-independent polymers (e.g., ethyl cellulose and polyvinyl acetate) are applied. These coatings control drug release by altering the thickness and permeability of the coating. Systems like osmotic pump delivery can also be used for sustained release by allowing GI fluids to dissolve osmotic agents, causing drug release at a controlled rate.

4.2 Improved Drug Stability

Film coating also enhances drug stability by protecting the active pharmaceutical ingredient (API) from environmental factors like moisture, light, and air. Hydrophobic coating materials (e.g., waxes or lipids) are often used for moisture protection, and light-sensitive drugs are coated to prevent degradation from light exposure. For example, tablets with APIs like nifedipine or sorivudine can be coated to improve photostability.

4.3 Taste Masking

Taste masking is essential for improving patient compliance, especially for pediatric or geriatric patients. Film coating helps mask the unpleasant taste of bitter drugs by preventing them from contacting taste receptors in the mouth. This can be achieved using water-soluble (e.g., hypromellose) or water-insoluble (e.g., ethylcellulose) polymers.

4.4 Active Film Coating

In active film coating, APIs are incorporated directly into the coating, allowing for more precise control of the drug release rate and improving drug stability. This technique is often used for fixed-dose combination (FDC) products to avoid interactions between APIs and to control the release profiles. For example, metformin and glimepiride have been combined into a fixed-dose tablet using active film coating to optimize dosing schedules.

In conclusion, film coating technologies are integral for enhancing the performance, stability, and patient acceptance of pharmaceutical products. At Walter®, we prioritize a controlled film coating process for every batch. Our precise approach to equipment setup, process variables, and quality assurance helps us deliver consistent results across our clients’ pharmaceutical products. By partnering with a contract manufacturer that emphasizes quality at every step, you can be confident that your products meet the highest industry standards.