Tablet Evaluation Tests/Introduction
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Contents |
Introduction
The quantitative evaluation and assessment of a tablet‘s chemical, physical and bioavailability properties are important in the design of tablets and to monitor product quality. These properties are important since chemical breakdown or interactions between tablet components may alter the physical tablet properties, and greatly affect the bioavailability of the tablet system. There are various standards that have been set in the various pharmacopoeias regarding the quality of pharmaceutical tablets. These include the diameter, size, shape, thickness, weight, hardness, disintegration and dissolution characters. The diameters and shape depends on the die and punches selected for the compression of tablets. The remaining specifications assure that tablets do not vary from one production lot to another. The following standards or quality control tests should be carried out on compressed tablets1.
General appearance
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Introduction |
The general appearance of tablets, its visual identity and overall ‘elegance’ is essential for consumer acceptance, control of lot-to-lot uniformity and general tablet-to-tablet uniformity and for monitoring the production process. The control of general appearance involves measurement of attributes such as a tablet’s size, shape, color, presence or absence of odour, taste, surface textures, physical flaws and consistency 2.
Size and shape
The shape and dimensions of compressed tablets are determined by the type of tooling during the compression process. At a constant compressive load, tablets thickness varies with changes in die fill, particle size distribution and packing of the powder mix being compressed and with tablet weight, while with a constant die fill, thickness varies with variation in compressive load. Tablet thickness is consistent from batch to batch or within a batch only if the tablet granulation or powder blend is adequately consistent in particle size and particle size distribution, if the punch tooling is of consistent length, and if the tablet press is clean and in good working condition.
The thickness of individual tablets may be measured with a micrometer, which permits accurate measurements and provides information of the variation between tablets. Tablet thickness should be controlled within a +_5% variation of a standard value. Any variation in thickness within a particular lot of tablets or between manufacturer’s lots should not be apparent to the unaided eye for consumer acceptance of the product. In addition, thickness must be controlled to facilitate packaging.
The physical dimensions of the tablet along with the density of the material in the tablet formulation and their proportions, determine the weight of the tablet. The size and shape of the tablet can also influence the choice of tablet machine to use, the best particle size for granulation, production lot size that can be made, the best type of tableting processing that can be used, packaging operations, and the cost of production.
The USP has provided limits for the average weight of uncoated compressed tablets. These are applicable when the tablet contains 50mg or more of the drug substance or when the latter comprises 50% or more, by weight of the dosage form. Twenty tablets are weighed individually and the average weight is calculated. The individual tablet weights are then compared to the average weight. Not more than two of the tablets must differ from the average weight by not more than the percentages stated in Table 1. No tablet must differ by more than double the relevant percentage. Tablets that are coated are exempted from these requirements but must conform to the test for content uniformity if applicable 3.
| Average weight | Percent difference |
| 130mg or less | 10 |
| More than 130mg through 324mg | 7.5 |
| More than 324mg | 5 |
Organoleptic properties
Color is a vital means of identification for many pharmaceutical tablets and is also usually important for consumer acceptance. The color of the product must be uniform within a single tablet, from tablet to tablet and from lot to lot. Non uniformity of coloring not only lack esthetic appeal but could be associated by the consumer with non uniformity of content and general poor product quality. Non uniformity of coloring is usually referred to as mottling. The eye cannot differentiate small differences in color nor can it precisely define color and efforts have been made to quantitate color evaluations. Reflectance spectrophotometry, tristimulus colorimetric measurements and micro reflectance photometer have been used to measure color uniformity and gloss on a tablet surface 2.
Odor may also be important for consumer acceptance of tablets and can provide an indication of the quality of tablets as the presence of an odor in a batch of tablets could indicate a stability problem, such as the characteristic odor of acetic acid in degrading aspirin tablets. However, the presence of an odor may be characteristic of the drug (e.g. vitamins), added ingredients (e.g. flavoring agent) or the dosage form (e.g. film-coated tablets).
Taste is also important for consumer acceptance of certain tablets (e.g. chewable tablets) and many companies utilize taste panels to judge the preference of different flavors and flavor levels in the development of a product. Taste preference is however subjective and the control of taste in the production of chewable tablets is usually based on the presence or absence of a specified taste.
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