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A film coating is a thin polymer-based coat that is typically sprayed onto a solid pharmaceutical dosage form, such as a tablet, capsule, pellet, or granule. Film coating can affect both its appearance and pharmacokinetics making it an essential process in the manufacture of the final drug product.
Film coating is the most common form of drug coating and is commonly applied to orally administered pharmaceuticals. The motivation for applying film coating to dosage forms ranges from cosmetic considerations (color, gloss, and branding), improving shelf life by providing a protective barrier between the drug and the surrounding environment, and making the dosage form easier to swallow. This type of film coating is known as non-functional film coating. They can also be used to delay or enhance the delivery and uptake of a drug, or to delay release and uptake until the drug has passed through the stomach. These types of film coatings are known as functional film coatings.
Conventional methods of film coating application to oral dosage forms include both a spraying stage and a drying stage. In the spraying phase, polymers, plasticizers, colorants, opacifiers, solvents, and a vehicle are applied to the core of the oral dosage form. Once applied, the oral dosage form is dried by blowing hot air over the dosage form, which usually also removes the solvent. The end result is a thin film coating with the desired plasticizer, color, opacifier and vehicle.
Types of Film coating
1. Organic solvent-based coatings The use of organic solvents in film coating is commonly used to incorporate a protective coating into oral dosage forms, which helps increase the shelf life of the final drug product. Such film coatings can be hazardous due to the toxicity and flammability of the final product during the film coating process. As such, proper safety measures and ventilation are integral during film coating.
2. Aqueous coating Aqueous film coating is the most common film coating method used today. This type of film coating uses water to aid in the film coating process instead of organic solvents. The result is a safer way of film coating, as it avoids the toxic and flammable properties of organic solvents. Aqueous film coating requires the use of water insoluble polymer mixtures, with the addition of a plasticizer. Despite its widespread popularity, aqueous film coating is more time-consuming than organic solvent-based coatings, due to the increased time required for complete evaporation of the water.
3. Solvent-free coating Solvent-free film coating is commonly used to coat heat-sensitive drugs because a drying step is not required. The end result of this type of film coating is an inert film coating that does not react with the active pharmaceutical ingredients. Some methods of producing solvent-free film coatings include injection molding coating, hot-melt coating, and spray congealing. Each method has its own advantages and disadvantages, but common to them is the need for very precise conditions that can satisfactorily apply a film coating to an oral dosage form. As such, it is an inefficient type of film coating resulting in its lack of widespread use.
