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3. Scientists must establish a direct or indirect property to measure that enables establishing a specification and must standardize a test method by which to measure it. |
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Studies investigating the relationship of properties of excipients to their functionality are not new to the pharmaceutical literature. For example the basic properties of six commonly used direct-compression excipients have been studied. The properties include |
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volumetric flow of the excipients, |
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effect of particle size on binding, |
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filler weight required to produce tablet of desired volume, |
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dissolution and disintegration of drug of equal volume, |
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lubricant sensitivity, and |
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filler effect on tablet hardness and friability. |
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Bolhuis and Lerk (1973) studied 11 excipients including microcrystalline cellulose, powdered cellulose, lactose, dextrose, pregelatinized starch, dicalcium phosphate, and others as direct-compressible tablet excipients. The investigation compared the tableting characteristics of each excipient and studied the influence the various excipients had on each other in this regard. Direct-compression tablet formulations containing large amounts of noncompressible active ingredients were also tested. As with many such investigations, individual comparisons were clear; however, general rules were not apparent. |
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Information on the reworking potential of excipients, tablet diluents in particular, is sparse. Precompression, often referred to as slugging, is many times used for reworking tablet and capsule formulations. However, the mechanism by which precompression (slugging) facilitates bonding in the manufacture of these dosage forms is not fully understood. The reworking potential is defined as the ratio of the areas under the tensile strength-compression profiles for recompression and for initial compression (Fig. 1). Often the results show that recompression generally reduces tablet strength and that this reduction is more significant when the initial compaction is carried out at a higher pressure. |
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Armstrong and Lowndes (1984) evaluated the effect of reworking on formulations containing both microcrystalline cellulose and lactose. The compressed mixtures of the former and spray-dried lactose were characterized over a range of compaction pressures. Although the strength of the original compact was directly proportional to the content of microcrystalline cellulose, the quality of the tablets increased after reworking as spray-dried lactose was increased; however, tablet weight uniformity decreased. The higher the initial |
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