What is Film Coated Tablet?

Coated tablets

Tablets are among the most convenient and preferred oral solid dosage forms because of their many advantages. Among the multiple steps in pharmaceutical manufacturing of tablets, coating is a critical process . Qualities such as color, texture, taste and flavor masking depend on the coating technique. The coating can provide physical and chemical protection for the drug, and it can also alter the release of the drug.

Type of tablet coating

Tablet coating is mainly divided into the following categories:

Sugar coated tablets: The traditional coating method, with sucrose as the main coating material, has good taste and the role of covering the bad smell of drugs, but there are shortcomings such as easy moisture absorption and poor stability.

Film coated tablets: The polymer is used as the coating material, the formed thin and uniform film layer, with moisture, light, air isolation and other functions, is an important development direction of modern pharmaceutical preparations.

Enteric coated tablets: A layer of insoluble gastric fluid but easily soluble intestinal fluid coating is wrapped around ordinary tablets to realize the positioning and release of drugs in the intestine and reduce the irritation to the stomach.

Slow-release and controlled-release coated tablets: Through special coating materials or technologies, the drug is controlled to release slowly or at a specific rate in the body, extending the efficacy time and reducing the number of doses.

Film coated tablets definition

Film coating (FC) is to spray the coating solution to the surface of the rolling core, and hot air is poured into the rolling core to vaporize the solvent, so as to form a connected film on the surface of the core. Film coating has a variety of uses, making the tablet easy to identify and swallow, controlling the drug release curve of the tablet, etc. The film coating process is an advanced and complex technique that may require computational modeling and a variety of coating techniques to achieve the desired effect. Microencapsulation can be regarded as an improved version of FC, the main differences are reflected in the size of the particles to be coated and the coating method. This rapidly growing field relies on mechanical or physicochemical means. In particular, the mechanical technology covers air suspension, porous centrifugation and improved spray drying methods; The physicochemical pathway involves a condensed phase separation process that requires the drug to be dispersed in a suitable polymer solution for coating.

Different FC techniques and processes (A) Conventional FC pan, (B) Fluid bed FC, (C) Phases of FC, (D) Phases of microencapsulation. (Zaid, A. N., 2020)

Advantages of film coated tablets

Tablets containing active pharmaceutical ingredients (APIs) can be protected by film coating, leading to increased stability of drug products during manufacturing and storage. Regarding the photostabilization of photosensitive APIs, the use of shading agents, such as titanium dioxide, in the coating formulation can improve the ability of the coating to protect the drug from photodegradation. For moisture-sensitive APIs, moisture-proof coating can be utilized. For oxygen sensitive APIs, an oxygen insulating coating can be used.

With the improvement of film coating technology in the application of excipients, talcum powder is no longer the main ingredient of excipients, which only increases the core by 2%-4%.

Film coated tablets can control the site, rate and time of drug release.

Film coated tablets can mask the bad smell and taste of drugs, reduce the bitter taste of drugs, and make it more convenient to take.

Classification and formulation of film coating tablets

Film coating can be broadly divided into two categories: Non-functional film coating, whose role is to improve the appearance, sensory properties, swallowing ability of the tablet, and protect the tablet from the adverse effects of humidity, oxidation, and light. Functional film coatings are designed to improve stability of drugs, modified release coating, sustained drug release and control drug release, while providing the benefits of non-functional coatings.

Examples of the most used components in functional and non-functional film coating. (Zaid, A. N., 2020)

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Film coated tablets disintegration time

Disintegration time of film coated tablets is a key parameter, which is usually tailored to meet specific treatment requirements. Polymer composition, plasticizer and coating thickness all play a role in regulating the disintegration speed of tablets in gastrointestinal tract. For example, a tablet designed for rapid release may only have a disintegration time of several minutes, while a controlled release tablet may take several hours.

Difference between sugar coating and film coating

Sugar coated tablets are coated with a layer of sugar coating on the surface of tablets, which can mask the bad smell and taste of drugs, but the manufacturing process of sugar coating is relatively complicated and the cost is high. The skin of sugar-coated tablets contains a small amount of sugar, which may cause harm to diabetic patients and people who avoid sugar for a long time. Defects such as split and mildew are easy to appear during storage. With the development of preparation technology, film coated tablets tend to gradually replace sugar coated tablets. Sugar coated tablets examples include betahistine hydrochloride tablets, paracetamol.

The production process of film-coated tablets is more advanced, which has less influence on disintegration and dissolution, and the weight gain of auxiliary materials is only 2%-4% of the drug core, so the drug effect is relatively high; Its skin contains no sugar, is easy to absorb, and has no obvious side effects after long-term use. At the same time, polymer materials with different characteristics provide more possibilities for preparations, which can be made into various film-coated materials such as stomach-soluble, intestinal-soluble, sustained-release, controlled-release and targeted preparations to meet the needs of different patients.

Film coated tablets vs enteric coated

Although both film coated tablets and enteric coated tablets involve the application of polymer layers, their uses and characteristics are obviously different.

Film coated tablets mainly focus on the protection of drugs, covering up bad smell and taste, and moisture-proof and light-proof, which is suitable for many types of drugs. The enteric coated tablets use enteric coated materials, which can control the release position of drugs and prevent drugs from decomposing in gastric juice and only being absorbed in the intestine, and are suitable for acid-sensitive drugs.

Enteric coated tablets examples include omeprazole, aspirin. Aspirin is a non-steroidal anti-inflammatory drug, which easily destroys the gastric mucosal barrier when taken orally, so ordinary tablets should be taken half an hour after meals, which can alleviate gastrointestinal discomfort; Aspirin enteric-coated tablets can avoid the stimulation of drugs to the stomach, and will not disintegrate within 2 hours in the stomach. After reaching the intestine, the enteric-coated materials on the outer surface dissolve, and the drugs are released, thus achieving the purpose of localized release in the intestine.

Recent advances in pharmaceutical coating

Zhu et al. have developed a novel method of applying powder coatings using electrostatic charges.70 This process involves sequential spraying of a liquid plasticizer to the tablets being coated. After that, the powder of the remaining coating materials is applied and then completing the formation of the coating using a heat-curing phase.

Qiao et al. also worked on an electrostatic dry powder film coating technique, successfully applying immediate-release coatings. Their process involved spraying a liquid plasticizer onto tablet cores to increase conductivity, followed by the electrostatic spraying of charged coating particles. The optimized process resulted in tablets with good coating uniformity, smooth surfaces, and release profiles similar to those of the uncoated cores. This technique has shown promise as an alternative to traditional aqueous or solvent-based FC processes and can be applied to various pharmaceutical materials for both immediate- and modified-release formulations.

3D printing technology is emerging as a novel approach in pharmaceutical manufacturing, addressing challenges such as personalized drug delivery and on-demand production. Elini et al. used a semi-solid 3D printer to partially coat tablets with Precirol ATO 5, achieving controlled release of Melevodopa and Acyclovir. By adjusting parameters like the percentage of the tablet surface coated and the number of coating layers, they were able to tailor the release profiles of the APIs.