Coating

 

History of Pharmaceutical Coating

The history of pharmaceutical coating dates back to the early 1950s, when tablets were first coated with sugar to mask unpleasant taste and improve ease of administration. In the decades that followed, increasingly efficient and functional coating technologies came into focus. These processes were not only more economical but also enabled precise control over drug release.

As a result, classical coating methods based on aqueous systems or organic solvents were developed. These techniques are still widely used today and continue to be refined. At the same time, solvent-free coating technologies are gaining increasing importance. In these processes, coating materials are applied directly in dry form without prior dissolution. Such innovative approaches are considered particularly resource-efficient, energy-saving, and environmentally friendly and may replace conventional processes in the long term.

 

Pharmaceutical Coating – Controlled Drug Release

Pharmaceutical coating is a versatile field of application. Depending on the composition and structure of the coating, it is possible to precisely define when, where, for how long, and in what quantity an active pharmaceutical ingredient (API) is released.

Different components can be coated, including:

  • the active ingredient itself
  • granules or pellets
  • the finished tablet or capsule

By using differentiated coating systems, gastro-resistant, delayed-release, or site-specific release profiles can be achieved.

 

Benefits of Coating Processes

The coating of tablets and solid dosage forms is primarily applied for three key reasons:

1. Improved Compliance and Drug Safety

Coated tablets are easier to identify, more convenient to take, and easier to swallow. The coating masks taste and odor and prevents the tablet from absorbing moisture from the oral mucosa—an important factor in improving patient acceptance.

2. Protective Function

The coating reliably protects the active ingredient from external influences such as moisture, oxygen, light, and gastric acid. In addition, it reduces mechanical abrasion during transport, minimizes dust formation, and enhances product safety. In formulations containing multiple active ingredients, coatings can also prevent unwanted chemical interactions.

3. Optimization of Biopharmaceutics

Through the targeted use of suitable coating materials, drug release can be accurately controlled—for example, via enteric or intestinal-soluble coatings. Furthermore, the coating protects the gastric mucosa from irritating substances.

 

Sugar Coating (Dragée) – A Classical Coating Process

Sugar-coated dosage forms, commonly known as dragées, represent a classic type of coated solid pharmaceutical form. A distinction is made between conventional dragées and rapid sugar-coated tablets.

In conventional dragées, the tablet core is coated with multiple layers of a sugar solution until the coating weight equals the core weight. This method provides high stability but is time-consuming and material-intensive. Rapid sugar-coated tablets require a lower sugar content (approximately 20–50% of the core weight), resulting in shorter production times.

Manufacturing takes place in rotating coating pans or fluid bed systems, ensuring uniform coating quality.

 

Film Coating of Tablets

In film coating, the tablet core is covered with a thin polymer layer accounting for only about 5–15% of the core weight. Unlike sugar-coated tablets, the shape and size of the tablet remain unchanged.

Advantages of Film Coating

  • short production times
  • improved stability and shelf life
  • flexible control of dissolution and release properties

The polymer coating formulation typically contains film formers, plasticizers, anti-tacking agents, opacifiers, and colorants and may be based on aqueous or organic solvent systems.

 

Film Formers – Chemical and Functional Classes

Common film formers used in pharmaceutical coatings include:

  • cellulose derivatives
  • polyacrylates and polymethacrylates
  • vinyl polymers (e.g. PVP)
  • shellac

From a functional perspective, film formers are classified as:

  • fast-dissolving film formers
  • gastric- and intestinal-soluble systems
  • insoluble film formers for sustained-release formulations

 

Coating in Additional Application Areas

Beyond pharmaceutical applications, coating technologies are also used in the food industry and in technical applications. Products that can be coated include:

  • powders and crystalline raw materials
  • fruits and vegetables
  • industrial raw materials

Key objectives include:

  • improved flowability
  • dust reduction
  • protection against oxidation and moisture
  • controlled release of functional ingredients

 

Research and Outlook

Current research focuses on solvent-free coating technologies, such as dry powder coating combined with external energy input or innovative matrix-based systems. The goal is the development of sustainable, efficient, and future-oriented coating solutions for both pharmaceutical and food-related applications.