Coating Techniques in the Pharmaceutical Industry

Pharmaceutical Coating and Coating History

Pharmaceutical coating has been an important technique for the manufacture of pills and other medicines, and pharmaceutical coating techniques continue to change and develop as the pharmaceutical industry develops. Originally, the use of sugar was common with pharmaceuticals - the addition of a sugar-coating would give a more pleasant taste and more attractive appearance to tablets, as well as mitigating the bitterness of unpleasant drugs. Today, many forms of coating have developed, such as enteric coating, which delays the release of the drug until the pill reaches the intestines. Even though pharmaceutical coating is a messy, complicated, and risky process (as errors in coating can lead to rejection of an entire batch of pharmaceuticals), pharmaceutical coating continues to this day. Pills are coated for a variety of reasons, but mostly to prevent bitter taste, to improve stability (prevent oxidation of active drug ingredients), or to modify the release of a drug.

Transition from Sugar-Coating to Compression-Coating

Sugar coating could take up to five days, and the pressure to develop alternative methods of pharmaceutical coating (besides sugar-coating) was high; sugar pills suffered from the lengthy process, a high degree of required operator skill, and difficulties in labeling individual tablets with the house logo and the product name. In the last twenty-five years, pharmaceutical coating processes for sugar-coating have undergone major changes - such as the use of air suspension techniques, atomizing systems for spray-on sugar-coating, the use of aluminum dyes to improve evenness of color, and more efficient drying systems. As a result, in the 1950s and 1960s, pharmaceutical firms began to experiment with compression coating - a process in which the core-coating material is compressed around the pill core. However, the coating process was still relatively slow and difficult.

Modern Coating

Modern pharmaceutical coatings are often film-coated tablets, which are made from cellulose derivatives such as hydroxyproply methylcellulose or other cellulose polymers, such as cellulose ethers, acrylic polymers, and occasionally materials such as polyethylene glycols or polyvinyl alcohol and other waxy materials. A film-coating is a thin, polymer-based coat applied to a pill, and upon close examination the film structure often is non-homogenous - resulting from the deliberate addition of insoluble pigments for coloring, and from the repetitive coating process. A single tablet (pill) is passed through a spray zone, where the adherent material is sprayed and allowed to dry before the next portion of coating; this process is repeated multiple times. A derivative of this film-coating process is used for enteric polymer coatings, which are used for extended-release drugs and other delayed-release pills. Enteric polymer coatings are designed to resist the acids of the stomach, but dissolve rapidly in the intestines.