08 April 2015 | 09:00
By Dr Jeremy Wingate | Rotronic Instruments (UK) Ltd.

Tablet coating in general

Pharmaceutical tablet coating involves the application of a coating composition to a moving bed of tablets with the use of heated air to facilitate the evaporation of the solvent. Several different types of coating are typically used.

Tablet coating machine

Tablet Coating Machine. Source: Rotronics UK

  • Sugar-coated tablets are coated with a coloured or an uncoloured sugar layer. The coating is water soluble and quickly dissolves after swallowing. The sugar-coating protects the encapsulated drug from the environment and provides a barrier to objectionable tablet taste or odour.
  • Film-coated tablets are compressed tablets coated with a thin layer of a polymer that forms a skin-like film. This is usually coloured and has the advantage over sugar coatings  that it is more durable, less bulky, and works faster at the desired location in the gastrointestinal tract.
  • Enteric-coated tablets have delayed release properties. They are designed to pass unchanged through the stomach to the intestines, where the tablets disintegrate and allow the drug to dissolve and start its effect. Enteric coatings are used when the drug substance itself would be destroyed by gastric acid or is irritating to the gastric mucosa.

How can accurate measurements help?

Environmental control is the practice of managing the temperature, humidity, air circulation, ventilation and air pressure of a given space. Within certain types of pharmaceutical manufacturing processes, precise environmental control can help limit inefficiencies and potential problems.

Pharmaceutical tablet coating is one such application. Inefficiencies during the coating process may result in contamination and tablet impurity in the form of tablet-to-tablet colour variation, surface pitting from over-wetting, twinning due to spray drying, cracking or peeling. Most of these problems can be overcome by better control of the environment within the process. Over-wetting, for example, occurs when the coating hits the still wet tablet surface and the surrounding air does not dry it quickly enough. Another example involves spray drying, when the coating hits the tablet surface after the moisture has been removed resulting in poor adhesion of the coating.

Gamlen Tablet with GenRH-A

Gamlen Tablet with GenRH-A.

In the case of incorrect cooling and drying of the sugar solution, a rough, translucent and uneven coating may be produced.
Since the required environment for a perfect coating strongly depends on the composition of the tablets, many pharmaceutical manufacturers have scientists who perform experiments to determine the ideal coating procedure including temperature and humidity levels. Once these specific requirements are determined, the set-points can be configured at the controller to enable the precision tablet-coating machines to work at optimal performance.

GenRH series has been successfully added in this area to a research grade tableting compaction solution by Gamlen Tablet press, showing its versatility in multiple pharma applications.


Spoonful of perfectly coated tablet. Source: Rotronics UK

Tablet Coating Benefits-Summary

  • Covers the unpleasant taste, odour and colour
  • Provides physical and chemical protection for the medicine (light, moisture and air)
  • Controls the release of a drug (enteric coating)
  • Improves the appearance of tablets
  • Easier to swallow the tablets
  • Assists and facilitate the identification of a drug

About the author:

Dr. Jeremy Wingate, Area Sales Manager (UK South), Rotronic, UK. Email: [email protected].

We would like to thank Dr Wingate, for an insightful blog. Rotronics supply the high quality precision capacitive humidity probes at the heart of the GenRH series.

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