Compressible blends

Generally, when developing a direct compression formulation, efforts to match particle size distribution and density of drug substance to the major excipients help minimize segregation. Meanwhile, the particle size distribution should be relatively narrow (100 im range) to ensure a satisfactory flow for the blend. The commonly used excipients for preparing direct compression blends can be categorized by the... 

Dust Extraction. Adequate dust extraction is necessary to maintain high-speed operation for extended periods of time. The entire compression area should be shrouded to minimize dust infiltration into other press areas. Effective dust extraction minimizes dust and oil contamination on the surface of the tablets, which could produce black specs. Insufficient dust extraction results in excessive material build-up on the lower and upper punches leading to tight punches. However, the proper balance of dust extraction without high levels of material loss must be determined. If the dust extraction level is too high material could be extracted from the die cavities and the recirculation channel. Furthermore, the dust extraction systems preferentially removes the fine particles. Therefore, if the granulation is a direct-compression blend where the active constituent is of fine particle size, minimum dust extraction levels combined with minimal recirculation may be necessary to prevent a loss of active constituents (resulting in possible low assay). 

Lactitol is used as a noncariogenic replacement for sucrose. It is also used as a diluent in solid dosage forms.A direct-compression form is available,as is a direct-compression blend of lactose and lactitol. Lactitol is also used therapeutically in the treatment of hepatic encephalopathy and as a laxative see Section 14. 

Confectioner s sugar is not widely used in pharmaceutical formulations because the poor-flow characteristics prevent its use in direct-compression blends. However, confectioner s sugar is used when a smooth mouth feel or a rapidly dissolving sweetener is required, and when a milled/micronized active ingredient must be blended with a diluent of similar particle size for powders or wet granulations. 

Okoye, P Stephen, H. Lubrication of direct-compressible blends with magnesium stearate monohydrate and dihydrate The influence of magnesium stearate (MgSt) on powder lubrication and finished solid-dose properties presents big challenges to drug manufacturers. Pharm Technol, 2007, 1, 1-12. 

This is the general expression for Gaussian composition fluctuations in incompressible polymer blends derived from EP theory. The original derivation of Shi, Noolandi and coworkers [66,67] uses as a starting point the density functional (Eq. 53) and gives the identical result. A generalization for compressible blends can be found in [13]. 

While the spinodal ciuves [82] depicted in Fig. 8 refer to ECT calculations for compressible blends of semiflexible polymers at a pressme of 1 atm, similar behavior emerges [83] from the SECT where the pressure is infinite. Thus, we analyze the molecular features contributing to this remarkable difference in miscibihties within the framework of the SECT because of its analytical tractability. In order to elucidate the contributing featiues to the observed miscibihty difference, it is convenient to assume first that both blend components are completely flexible. Then, the partial entropic structural parameters rpp and rhhpp are identical (Sect. 3.1), so that all of the calculated miscibility differences between PP/PEP and hhPP/PEP blends emerge from the differ-... 

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