Tablet flowability

It is generally agreed that one of the more important parameters of interest to formulators is the flowability of their powdered solids [57,58], The process-ability of these materials is greatly affected by flowability concerns, since the materials invariably need to be moved from place to place. For example when tablets are to be compressed at high speeds, the efficiency of the machine will only be suitable if the powder feed can be delivered at a sufficiently high rate. 

Flowability is important to the successful scale-up of a tableting process. The rate at which the precompacted blend flows into the hoppers of the tablet press and subsequently into the die cavity could be crucial to dose uniformity. Three measurements are most commonly used to measure flow ... 

Due to the poor flowability of the powder the tabletting machine should be equipped with a special technical device providing a continuous and homogenous filling of the dies. 

To enhance the flowability of the tabletting mixture the amount of Aerosil 200 could be increased. 

The flowability of the tabletting mixture should be increased by higher amounts of Ludipress or/and Aerosil 200. 

If the flowability of the powder mixture for tabletting is not high enough some Aerosil 200 [4] should be added. 

When manufacturing a tablet formulation by direct compression, the particle size and size distribution of excipients have a significant impact on blending homogeneity, powder segregation, and flowability. This can result in unacceptable content uniformity and high tablet weight variation. In such situations, control of excipients can be critical to product quality. 

Microcrystalline Cellulose. Microcrystalline cellulose is a purified, partially depolymerized cellulose that occurs as a white, odorless, tasteless, crystalline powder composed of porous particles. It is widely used in pharmaceutical dosage forms, primarily as a filler-binder in oral tablets and capsules with both wet granulation and direct compression processes. Microcrystalline cellulose was marketed first in 1964 by the FMC Corporation under name Avicel PH in four different particle size grades, each with different properties.37 Addition of Avicel into a spray-dried lactose-based formulation overcame compressibility problems. At the same time, the lactose enhanced the flowability of the Avicel products available at that time. The direct compression tableting process became a reality, rather than a concept, partially because of the availability of Avicel. As of 2007, Avicel PH is commercially available in 10 types with different particle size, density, and moisture grades that have different properties and applications (Table 7.6).38 Other brands of microcrystalline cellulose are also available on the pharmaceutical market, including Pharmacel 101 and 102 from DMV International and Emcocel 50 M and 90 M from JRS Pharma. 

Microcrystalline cellulose is the most compressible of any direct compression excipient. Producing a tablet of a given hardness requires less compression force for other materials. Therefore, it is usually mixed with another filler to achieve ideal compactibility and flowability of a direct compression formulation. Large particle size grades of microcrystalline cellulose are made by spray-dried processes to form dry and porous particle surfaces. The porous surfaces provide adsorption sites needed for fine dmg particles in low-dose formulations. However, microcrystalline cellulose contains trace amounts of peroxides that may lead to chemical incompatibility with oxidatively sensitive dmg substances.34... 

Most drug and inactive excipients used in tablet formulation are in the solid state as amorphous powder or crystals of various morphological structures. There may be substantial differences in particle size, surface area, crystal morphology, wetting, and flowability as well as many physical properties of drug, excipients, and their blends [16]. Table 12 describes common micromeritic topics important to pharmaceutical preformulation. 

In order to formulate the optimal tablet, various properties should be considered, including drug-excipient compatibility, flowability, lubricity, appearance, dissolution, and disintegration [2], The prepared tablet must also meet physical specification and... 

In the manufacture of tablets it is important to define and appreciate the physical properties of the active substance, in particular particle size and flowability. The technology involved in direct compression assumes great importance in tablet formulations because it is often the least expensive, particularly in the production of generics that the active substance permits. The limiting factors are the physical properties of the active substance and its concentration in the tablets. Even substances such as ascorbic acid, which are not generally suitable for direct compression owing to the friability of the crystals, can normally be directly pressed into tablets at concentrations of 30-40%. Ffowever, this technique is not as suitable if the content of ascorbic acid is higher. This limit may be shifted upward by special direct-compression auxiliaries, for example, Ludipress (BASF). 

Due to the relatively small particle size, irregular shape, and unique surface characteristics, many pharmaceutical powders have a high tendency to be extremely cohesive. This high level of cohesion results in sticky powders that have poor flowability, commonly resulting in large mass variability within the final product owing to unpredictable and variable filling of tablet dies. 

Needle-shaped crystals exhibit poor flowability and cause bridging in hopper Platy crystals exhibit greater dissolution, but are not preferred for tablet dosage form... 

A wet granulation end-point should be defined empirically in terms of wet mass density and viscosity, PSD, flowability or tableting parameters (e.g., capping compression). 

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