[edit ] Tablet Compaction Simulator
Tablet formulations are designed and tested using a laboratory machine called a Tablet Compaction Simulator
or Powder Compaction Simulator
. This is a computer controlled device that can measure the punch positions, punch pressures, friction forces, die wall pressures, and sometimes the tablet internal temperature during the compaction event. Numerous experiments with small quantities of different mixtures can be performed to optimise a formulation. Mathematically corrected punch motions can be programmed to simulate any type and model of production tablet press. Small differences in production machine stiffness can change the strain rate during compaction by large amounts, affecting temperature and compaction behaviour. To simulate true production conditions in today's high speed tablet presses, modern Compaction Simulators are very powerful and strong.
Initial quantities of active pharmaceutical ingredients are very expensive to produce, and using a Compaction Simulator reduces the amount of powder required for development.
Load controlled tests are particularly useful for designing multi-layer tablets where layer interface conditions must be studied.
Test data recorded by the Simulators must meet the regulations for security, completeness and quality to support new or modified drug filings, and show that the designed manufacturing process is robust and reliable [edit ] Tablet presses
The tablet pressing operation
An old Cadmach rotary tablet pressTablet presses
, also called tableting machines, range from small, inexpensive bench-top models that make one tablet at a time (single-station presses), no more than a few thousand an hour, and with only around a half-ton pressure, to large, computerized, industrial models (multi-station rotary or eccentric presses) that can make hundreds of thousands to millions of tablets an hour with much greater pressure. Some tablet presses can make extremely large tablets, such as some of the toilet
cleaning and deodorizing products or dishwasher
soap. Others can make smaller tablets, from regular aspirin
to some the size of a bb gun
pellet. Tablet presses may also be used to form tablets out of a wide variety of materials, from powdered metals to cookie crumbs. The tablet press is an essential piece of machinery for any pharmaceutical and nutraceutical manufacturer. Pill-splitters
It is sometimes necessary to split tablets into halves or quarters. Tablets are easier to break accurately if scored, but there are devices called pill-splitters
which cut unscored and scored tablets. Tablets with special coatings (for example enteric coatings or controlled-release coatings) should not be broken before use, as this will expose the tablet core to the digestive juices, short-circuiting the intended delayed-release effect. Tablet coating
Many tablets today are coated after being pressed. Although sugar-coating was popular in the past, the process has many drawbacks. Modern tablet coatings are polymer
based, with plasticizers
included. Tablet coatings must be stable and strong enough to survive the handling of the tablet, must not make tablets stick together during the coating process, and must follow the fine contours of embossed characters or logos on tablets. Coatings can also facilitate printing on tablets, if required. Coatings are necessary for tablets that have an unpleasant taste, and a smoother finish makes large tablets easier to swallow. Tablet coatings are also useful to extend the shelf-life of components that are sensitive to moisture or oxidation. Opaque materials like titanium dioxide
can protect light-sensitive actives from photodegradation
. Special coatings (for example with pearlescent effects) can enhance brand recognition.
If the active ingredient of a tablet is sensitive to acid, or is irritant to the stomach lining, an enteric coating
can be used, which is resistant to stomach
acid and dissolves in the high pH of the intestines. Enteric coatings are also used for medicines that can be negatively affected by taking a long time to reach the small intestine
where they are absorbed. Coatings are often chosen to control the rate of dissolution of the drug in the gastro-intestinal tract. Some drugs will be absorbed better at different points in the digestive system. If the highest percentage of absorption of a drug takes place in the stomach, a coating that dissolves quickly and easily in acid will be selected. If the rate of absorption is best in the large intestine or colon, then a coating that is acid resistant and dissolves slowly would be used to ensure it reached that point before dispersing. The area of the gastro-intestinal tract with the best absorption for any particular drug is usually determined by clinical trials.
This is the last stage in tablet formulation and it is done to protect the tablet from temperature
constraints. It is also done to mask the taste
, give it special characteristics, distinction to the product, and prevent inadvertent contact with the drug substance. The most common forms of tablet coating are sugar coating and film coating.
Coating is also performed for the following reasons:
- Controlling site of drug release
- Providing controlled, continuous release or reduce the frequency of drug dosing
- Maintaining physical or chemical drug integrity
- Enhancing product acceptance and appearance
coating is done by rolling the tablets in heavy syrup
, in a similar process to candy making
. It is done to give tablets an attractive appearance and to make pill-taking less unpleasant. However, the process is tedious and time-consuming and it requires the expertise of highly skilled technician
. It also adds a substantial amount of weight to the tablet which can create some problems in packaging and distribution
In comparison to sugar coating, film coating is more durable, less bulky, and less time consuming. But it creates more difficulty in hiding tablet appearance. One application of film-coating is for enteric protection, termed enteric coating. The purpose of enteric coating is to prevent dissolution of the tablet in the stomach, where the stomach acid may degrade the active ingredient, or where the time of passage may compromise its effectiveness, in favor of dissolution in the small intestine
, where the active principle is better absorbed