The Manufacturing Process — Part 4

Tablet Compression — While an experienced operator can take a marginal granulation and make a good quality tablet, an inexperienced operator (not fully understanding tablet press operation) will be unable to produce a quality tablet.

Understanding the machine operation and being able to identify the difference between a machine issue and a granulation issue is important. Operators should be qualified, tested and certified in the operation of a tablet press.

While tablet presses are used for many applications, the basis of formula development is the same for each application. The final granulation to be compressed must have three basic characteristics, all of which are critical: Flow, Compress and Eject.

A tablet press can be fully automated to the point that it can be operated in a lights out operation. This puts all the emphasis on the cleaning and proper set up of the machine. This is also true of a non automated machine. The emphasis is on cleaning and proper setup.

With few exceptions, rotary tablet presses operate the same basic way. Many machines have very advanced features that may provide better compression and weight control at high speed.

However, understanding the basics of compression is the key to understanding all tablet presses. The tablet press is the report card on all previous unit operations; the tablet press is only half responsible for the final tablet quality, the formula and powder preparation operation is the other half. A good press cannot improve a bad formula.

Tablet Weight Control

Having consistent flow of a granulation provides the needed avenues to control tablet weights. Consistent tablet weight will result in repeatable tablet hardness. Tablet hardness is a function of tablet thickness and tablet weight.

A given volume of granulation compressed to a specific thickness will result in a given hardness. Though excipients play a large roll in the dissolution rate of a tablet, so does tablet hardness.

A tablet press and tools will not improve a granulation. If used correctly though, the press and tools can be used to maximize the granulation and maintain a consistently hard tablet with acceptable disintegration & dissolution rates.

The three most important variables of making a good tablet are; weight control, weight control and weight control.

Tablet Coating

Once a good tablet is made, we often need to add a coating. The coating can serve many purposes; it makes the tablet stronger and tougher, improves taste, adds color, and makes the tablet easy to handle and package. The coating can be a thick sugar based coating or a very thin film. Most pharmaceutical tablets are coated with a thin film coating. This coating is sprayed as a solution (a mixture of solids in a liquid).

For many years the liquid was a solvent such as alcohol or some other quick drying solvent. The use of solvents can present problems in handling, operator safety, solvent recovery and the odor of the tablet can smell like the solvent, which is not a desirable attribute.

In general, many manufacturers have moved to a water based solution instead of using a solvent. This presents a challenge in applying and quickly removing this water based solution so it does not disrupt the integrity of the tablet.

Tablet film coating equipment has evolved to enhance this drying capability. Essentially a tablet coating system is much like a fancy clothes dryer. The water based solution is sprayed in a very fine mist so as to dry almost immediately as it reaches the tablets. As the water dries it leaves the solids as a thin film on each tablet.

The coating system continuously supplies hot air, at the same time pulling air through small holes in the coating drum. The drum is commonly referred to as the coating pan, with small holes called perforations. This process can take as little a 30 minutes or it can take several hours.

Tablets must be tough enough to tumble while the solution is added. The solution is distributed from tablet to tablet during the tumbling and drying process. The spraying, distribution and drying all takes place at the same time.

Coating Equipment

Tablet coating equipment combines several technologies and is commonly referred to as a coating system. This system consists of the coating pan, spraying system, air handling unit, dust collector and controls. The coating pan is really a drum within a cabinet, allowing for control of air flow, air temperature and controlled solution application.

The spraying system consists of spraying guns, a solution pump, tank & mixer and air lines. The solution is pumped into the guns and the air combines with the solution for atomization into a very fine mist.

The air handling unit (AHU) is basically a way of heating and filtering the air. Dehumidification and/or humidification maybe be needed depending on your location and application requirements.

The Dust Collector collects the dust during the preheat and tumbling cycles and the Controls connect all of the components creating a complete coating system.

The Coating Process

Tablets are loaded into the coating pan, creating a bed of tablets. There must be enough tablets to attain good mixing, but not too many or the tablets will spill when the door is opened. Consistent batch sizes are important to attain consistent results. The tablet bed is tumbled slowly, as the warm air is introduced; the dust collector pulls the dust off the tablets and into a collection bin.

When the tablet bed temperature reaches the proper temperature the spraying can begin. Once tablets have an initial base coating the spray rate can be increased. The controls are monitored by the operator or computer, recording data frequently. Tablet defects can occur if the temperature, spray rate and air volume are allowed to fluctuate.

-Michael Tousey, Techceuticals

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