Pharmaceutical Film Coating Process: How It Works

The pharmaceutical film coating process is a critical technique in drug manufacturing used to apply a thin, uniform layer of coating onto tablets or other dosage forms. This coating enhances the stability, appearance, taste, and functionality of the drug.

Here's a step-by-step breakdown of the film coating process.

Step 1: Formulation Preparation

The first step involves preparation of the film coating solution or suspension, which typically includes the following components:

• Polymer(s): These provide the structural integrity to the coating. Common polymers include hydroxypropyl methylcellulose (HPMC), ethyl cellulose, and acrylates.
• Plasticizers: These make the coating more flexible and prevent it from becoming brittle. Examples include polyethylene glycol (PEG) or triacetin.
• Colorants: Used to give the tablet its desired colour, making it more recognizable.
• Other additives: These can include stabilizers, opacifiers, and sweeteners, depending on the desired properties of the coating.

Now a days formulation companies are avoiding the first step as pre-formulated premixes are available in the market. Such companies may follow on from the next step.

Step 2: Coating solution preparation

The pre-formulated powder is simply added into water or solvent and carefully mixed to ensure the ingredients are uniformly distributed.

Step 3: Spraying the Coating and Drying

The tablets are then placed in a coating pan, which is a large, rotating drum. The coating solution is sprayed onto the rotating dosage forms while the pan is turning. This spraying creates a fine mist that is evenly applied to the surface of the dosage forms. The rotation of the pan ensures that the coating is applied uniformly to all surfaces of the tablets or capsules.

• Spray Rate and Rotation Speed: These are optimized for achieving uniformity in the coating layer and to avoid defects such as uneven coating or excessive buildup.
• Airflow: Heated, controlled airflow is typically used during the process to help evaporate the solvents in the coating solution, ensuring that the coating sets and dries quickly. The temperature and humidity levels are carefully controlled during the drying phase to prevent the coating from cracking or peeling.

Step 4: Quality Control

Once the film coating has been applied and dried, the coated tablets are tested for various qualities: Ensuring the coating is smooth, glossy, and free from defects. Ensuring that the coating is applied evenly without streaks or patches. Parameters such as coating thickness, uniformity, color, and texture are rigorously monitored to guarantee the consistency and efficacy of the final product.