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The Tablet Coating Process

Many solid pharmaceutical dosage mediums are produced with coatings, either on the external surface of tablets, or on materials dispensed within gelatine capsules. Coating serves a number of purposes:

• Protects the tablet (or the capsule contents) from stomach acids
  
• Protects the stomach lining from aggressive drugs such as enteric coated aspirin
  
• Provides a delayed release of the medication
  
• Helps maintain the shape of the tablet
  
  

Ideally, the tablet should release the material gradually and the drug should be available for digestion beyond the stomach. The coating can be specially formulated to regulate how fast the tablet dissolves and where the active drugs are to be absorbed into the body after ingestion.

Many factors can affect the end-use properties of pharmaceutical tablets:

• Chemical composition
• Coating process
• Drying time
• Storage and environmental monitoring

Coating Process Design & Control

Tablet coating takes place in a controlled atmosphere inside a perforated rotating drum. Angled baffles fitted into the drum and air flow inside the drum provide means of mixing the tablet bed. As a result, the tablets are lifted and turned from the sides into the centre of the drum, exposing each tablet surface to an even amount of deposited/sprayed coating.

 

The liquid spray coating is then dried onto the tablets by heated air drawn through the tablet bed from an inlet fan. The air flow is regulated for temperature and volume to provide controlled drying and extracting rates, and at the same time, maintaining the drum pressure slightly negative relative to the room in order to provide a completely isolated process atmosphere for the operator.

Tablet coating equipment may include spray guns, coating pan, polishing pans, solution tanks, blenders and mixers, homogenizers, mills, peristaltic pumps, fans, steam jackets, exhaust and heating pipes, scales and filters. Tablet coating processes may include sugar coating (any mixtures of purified water, cellulose derivatives, polyvinyl, gums and sugar) or film coating (purified water, cellulose derivatives).

The coating process is usually a batch driven task consisting of the following phases:

• Batch identification and Recipe selection (film or sugar coating)
• Loading/Dispensing (accurate dosing of all required raw materials)
• Warming
• Spraying (application and rolling are carried out simultaneously)
• Drying
• Cooling
• Unloading

A control system must therefore provide flexibility in the way in which accurate and repeatable control of the coating environment is achieved and will include the following features:

• Precise loop control with setpoint profile programming
• Recipe Management System for easy parameterization
• Sequential control for complex control strategies
• Secure collection of on-line data from the coating system for
• analysis and evidence
• Local operator display with clear graphics and controlled access to parameters

The Eycon^TM Visual Supervisor is an ideal solution for the tablet coating process.