Tablet coating

Tablet Coating: Its importance in the pharmaceutical industry and challenges

1. Introduction
Tablets are one of the most used methods of dosage to administer a drug in current use. For that reason is important to address the things that affect the manufacturing of these tablets and one of the important things in the tablet’s manufacturing is the coating of the tablet. The process itself isthe application of a thin layer or film on the surface of the tablet cores with the intention of conferring benefits and properties to dosage form over the uncoated variety.
These benefits and change in properties can address many issues in the production of such dosage form. Within these issues are some like masking an odor or taste (i.e. when the core contains a material which has a bittertaste in the mouth or has an unpleasant odor), improve stability (i.e. the core contains a substance which is incompatible in the presence of light and subject to atmospheric oxidation), brand recognition (i.e. brand logos or color coding), modification of the drug-release profile (i.e. enteric delivery, osmotic delivery, pulsed delivery), improve ingestion (i.e. slippery surface when in contact ofwater), improved bulk handling (i.e. by reducing friction and increases packaging rate) and as a binder for adding an active ingredient (i.e. the matrix with a second API).
But although coating processes is useful and have been used for many decades, there are still serious challenges, as there is a lack of understanding of how material and operating parameters impact product quality and causeproblems, such as chipping (i.e., films become chipped due to attrition, usually this is the result of high pan speed, a friable tablet core, or a coating solution that lacks a good plasticizer [4]), blistering (i.e., local formation of blisters due to entrapment of gas, high pressure application of the coating can lead to this), cratering (i.e., penetration of the coating solution into the bulk ofthe tablet causing crater-like structures), pitting (i.e., pits occur on the surface due to overheating of the tablet and partial melting), picking (i.e., parts of the film are removed due to sticking to other wet tablets), blushing (i.e., formation of spots due to phase-transitions of the polymer film), blooming (i.e., plasticizer concentrates at the surface, leading to a change of appearance),film cracking (i.e., cracking of the film upon cooling due to high stresses), Twinning (i.e. when two tablets stick together, and it’s a common problem with capsule shaped tablets and can be caused by over wetting and poor drying[4]) and many others [1]. While poor scale-up and poor process design can be the cause of these problems, the real problem strives in the poor understanding of some keyfactors that affect the process.
Coating technology has changed since its first application began in the ninth century B.C., with the Egyptians. At that time the primary solid dosage form was the pill, a hand-shaped spherical mass containing drug, sugar, and other diluents [2]. At first many the coatings proved to be impervious to chemical attack in the digestive tract; as a result, the pillnever released its active ingredient and was thus ineffective. Improvement and refinement was needed, some of these development came from the candy-making industry and greatly improved the art of coating [2]. The pharmaceutical industry took the concepts behind candy coating and produced sugar coated pills; the first sugar-coated pills produced in the United States came out of Philadelphia in 1856[2]. Meanwhile the evolution of the coating technology led to the introduction of new coating material with different properties; coatings resistant to enteric or gastric fluids were developed in the 1880s [2]. With the introduction of the first compression-coated tablet in 1953, a new field was created. Since then numerous types and ways of coating a tablet have been developed, but process control...