Overview of Polymers and Their Functions in Film Coating

INTRODUCTION

Film coating is the process of covering the surface of a tablet core with a very thin layer of excipient. The composition of this film layer typically includes film-forming agents (polymers), solvents, plasticizers, opacifiers, colorants, and other excipients depending on the intended use. Film coatings are applied to solid dosage forms for various purposes, such as:

• Enhancing the chemical stability of the drug by slowing down oxidation processes, particularly for active ingredients that are prone to oxidation. The film coating can reduce the impact of oxidative agents such as light, oxygen, and humidity on the chemical stability of the active ingredient. Additionally, thanks to the film coating, the tablet is less susceptible to moisture from the environment during storage, making it suitable for moisture-sensitive active ingredients. Furthermore, in the case of enteric-coated tablets, the film layer protects the active ingredient from degradation by the acidic pH of the stomach. Lastly, the film coating also helps prevent interactions or incompatibilities between active ingredients or between the active ingredients and excipients within the same tablet.

• Improving the mechanical strength of the drug, helping the tablet resist chipping or breaking during storage and transportation, thereby ensuring the tablet's quality when it reaches patients.
• Controlling drug release: The film coating can prevent the drug from dissolving in saliva, which is useful for taste-masking. Active ingredients that are irritating to the stomach can be formulated with enteric coatings that dissolve only in the intestines. Drugs intended for treatment in the colon can be formulated as film-coated tablets that release the active ingredient specifically in the colon. Water-insoluble polymers can be used to formulate sustained-release film-coated tablets.
• Enhancing the aesthetic appeal and convenience for patients: The film coating can mask unpleasant tastes, make the tablet shiny and easier to swallow, and improve the overall appearance, making it more attractive and easier to identify. This can enhance patient satisfaction and adherence to the medication regimen.

Water or organic solvents can be used as dispersion or dissolution mediums for the components in film coating solutions. Compared to organic solvents, water is preferred due to several advantages, such as cost savings, reduced risk of fire and explosion, and minimized residual solvents that could impact the health of both manufacturers and patients. Therefore, water-based film coating systems are increasingly being utilized in the formulation of film-coated tablets.

COMMON COMPONENTS USED IN WATER-BASED FILM COATING SOLUTIONS

Among the components mentioned, polymers are crucial and play the primary role in forming the structure and function of the film coating.

The polymers used in film coatings are typically synthetic and are classified into three main groups: water-soluble polymers, water-insoluble polymers, and pH-dependent polymers (enteric).

• Water-soluble polymers are often used for improving aesthetics, protecting the tablet core, providing moisture resistance, and masking unpleasant tastes.
• Water-insoluble polymers are commonly used to modify and extend the drug release process to achieve sustained or controlled release of the active ingredient.
• pH-dependent polymers are typically used for tablets containing active ingredients that irritate the stomach or for those intended to treat conditions in the intestines.

COMMON TYPES OF POLYMERS USING IN FILM COATING SOLUTIONS

The aforementioned polymers can be used alone or in combination, depending on the goals and desired functions of the film coating, the coating process used, the expected weight gain, as well as the properties of the polymer such as solubility, viscosity, etc. Typically, aesthetic film coatings require a weight gain of 3%, moisture-resistant coatings range from 3-5%, and enteric coatings range from 5-7%. These weight gain levels can vary depending on the characteristics of the active ingredient, the tablet core properties, and other specific requirements of the tablet.