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Good Manufacturing Practice

Manufacturing and testing a product using an agreed set of procedures to help ensure the product is of a consistent high quality

Excipients

Other substances that are added to the drug when making a tablet, capsule, cream, ointment etc.

Inhalation

Breathing in

Secondary manufacturing

In secondary manufacture, companies must follow a strict code of good manufacturing practice. The active ingredient is turned into a medicine that can easily be taken by the patient, by mixing it with other substances. These are called excipients and they make up most of the volume of a medicine. Although they have no active role in curing a patient, they allow the active ingredient to be made into a medicine, such as a tablet.

There are a number of different ways of formulating a medicine to create a tablet, capsule, syrup, injection, cream, ointment or aerosol for inhalation. However, in this section you will see how tablets are made.

Flow diagram

The six basic stages in manufacture are:

Inputs
  1 delivery of ingredients to the factory
  2 checking that the ingredients meet the required specification

Processes
  3 mixing and granules
  4 drying
  5 pressing
  6 coating.

The powdered ingredients are placed inside a mixer like a large food mixer. They are mixed to ensure that the active ingredients are combined uniformly with the excipients. Unless this process happens thoroughly, one tablet may have too much activity and another none at all. Water is then added to granulate the mixture. The water binds the powders together to form granules (like instant coffee). This stops the powders from separating (or demixing) whenever the mixture is moved.

Photograph of a granulator

The granules are dried in a fluid bed drier. This has a large fan facing upwards. It creates giant currents of heated air. The air picks up the granules and carries them up in a warm flow. The granules fall down and are picked up by more hot air.

The granules pass from the fluid bed drier through a sieve. This breaks up the oversized granules and ensures the size is uniform. The powder of fine granules is then ready to be pressed into tablets.

The tablet press is a high-speed mechanical device. It 'squeezes' the ingredients into the required tablet shape with extreme precision. It can make the tablet in many shapes, although they are usually round or oval. Also, it can press the name of the manufacturer or the product into the top of the tablet.

Each tablet is made by pressing the granules inside a die made of hardened steel. The die is a disc shape with a hole cut through its centre. The powder is compressed in the centre of the die by two hardened steel punches that fit into the top and bottom of the die.

The punches and dies are fixed to a turret that spins round. As it spins, the punches are driven together by two fixed cams - an upper and lower cam. The shapes of the two cams determine the sequence of movements of the two punches. This sequence is repeated over and over because the turret is spinning round.

The force exerted on the ingredients in the dies is very carefully controlled. This ensures that each tablet is perfectly formed. The turret holds up to 75 dies and pairs of punches. It spins extremely fast and can produce up to 600, 000 tablets per hour.

2nd stage of tablet punch sequence
Stage 4 of tablet punch sequence
5th stage of tablet punch sequence

Samples of tablets from the press are checked regularly, whilst the machine is running to ensure that:

  • they are within the specified weight limits
  • their strength in compression is within specified limits
  • their thickness is within specified limits
  • there are no metal particles accidentally trapped within the tablet
  • they disintegrate in a liquid at 37.7° C (body temperature)
  • they are chemically pure.

Some tablets are then coated. The coating performs a number of jobs. For example it can be to

  • prevent the tablets cracking or breaking in transit
  • allow the controlled release of the active ingredient over a longer time than simply allowing the tablet to dissolve
  • mask the taste
  • prevent the tablet from breaking up
  • make the tablet easier to swallow.