Pharmaceutical Coating Techniques

Coating in pharmaceutical industry is an essential process in the formulation of pharmaceutical dosage form to achieve superior aesthetic quality, quality in terms of color, texture, mouth feel, and taste. With coating physical and chemical protection for the drugs in the dosage forms is achieved. Pharmaceutical coating machines make use of various coating techniques, some of which are described below:

Sugar Coating
Earlier the use of sugar coating was common with pharmaceuticals because a single layer of sugar-coating would give a pleasant taste and an attractive appearance to tablets. Today, many forms of coating are used, one of them is enteric coating, which actually delays the release of the drug until the pill reaches the intestines. Tablets and pills are sugar coated for a variety of reasons, which include, prevention of bitter taste, to improve stability and to modify the release of the drug. Spray coating machines are used in sugar coating of tablets and pills.

Film Coating
Today film coated tablets are in use and this film coating is made of cellulose derivatives such as hydroxyproply methylcellulose or other cellulose polymers. A film-coating is a thin, polymer-based coat applied to a capsule or tablet, and if you closely examine the tablet or capsule, you will be able to see non-homogeneous film structure. And this non homogeneous structure is the result of deliberate addition of insoluble pigments for coloring and because of the repetitive coating process. Each and every tablet is passed through a spray zone, where the adherent material is sprayed and allowed to dry before the next portion of coating and this process is repeated number of times. Most film coatings are applied as aqueous or organic based polymer solutions. Both organic and aqueous film coating have their own disadvantages.

Solventless Coating Technology
To overcome the disadvantages of film coating, Solventless coating technology has come up with the use of solvents like solvent exposure, solvent disposal, and residual solvent in product in pharmaceutical coating. Solventless processing enables to reduce the cost by eliminating the tedious and expensive processes of solvent disposal/treatment. Moreover, the technology can significantly reduce the processing time because there is no drying and evaporation step. And the entire process goes environment friendly, as it is done without any heat in most cases and thus can provide an alternative technology to coat temperature-sensitive drugs.

Some Other Methods
There are other coating methods also that are used to coat pharmaceutical tablets and capsules. Some of them are:
Compression coating, hot-melt coating, supercritical fluid spray coating, electrostatic coating, dry powder coating, and photocurable coating.