The tablet is the most commonly used oral dosage form. It is also quite complex in nature. The biggest problem is overcoming the reduction in effective surface area produced during the compression process. One may start with the drug in a very fine powder, but then proceeds to compress it into a single dosage unit.
Tablet ingredients include materials to break up the tablet formulation.
Drug - may be poorly soluble, hydrophobic
Lubricant - usually quite hydrophobic
Granulating agent - tends to stick the ingredients together
Filler - may interact with the drug, etc., should be water soluble
Wetting agent - helps the penetration of water into the tablet
Disintegration agent - helps to break the tablet apart
Coated tablets are used to mask an unpleasant taste, to protect the tablet ingredients during storage, or to improve the tablets appearance. Another barrier is placed between the solid drug and drug in solution. This barrier must break down quickly or it may hinder a drug's bioavailability.
Also see pharmaceutical validation
Disintegration time is the time to pass through a sieve while agitated in a specified fluid. Indicates the time to break down into small particles. Not necessarily solution. In the process of tablet manufacturer the drug is often formulated into a granular state (that is small but not fine) particles. This is done as the granule often has better flow properties than the a fine powder and there is less de-mixing leading to better uniformity. The granules are then compressed to produce the tablet. The disintegration test may lead to an end point of tablet to granule only.
Also see Validation
The time is takes for the drug to dissolve from the dosage form. Numerous factors affect dissolution. Thus the dissolution medium, agitation, temperature are carefully controlled. The dissolution medium maybe water, simulated gastric juice, or 0.1M HCl. The temperature is usually 37 degree C. The apparatus and specifications may be found in the U.S.P. The U.S.P. methods are official however there is a wide variety of methods based on other apparatus. These are used because they may be faster, cheaper, easier, sensitive to a particular problem for a particular drug, or developed by a particular investigator.
Dissolution tests are used as quality control to measure variability between batches which maybe be reflected by in vivo performance. Thus the in vitro test may be a quick method of ensuring in vivo performance. Thus there has been considerable work aimed at defining the in vitro/in vivo correlation.
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