Direct compression method process

Direct Compression. This process is relatively simple and time saving. AH the ingredients are blended and then compressed into the final tablet. This is an excellent method, but encumbered by a number of problems. Not all substances can be compressed directly, necessitating a granulation step. Likewise, the flow properties of many blends of fine, particle-sized powders are not such as to ensure even filling of the die cavities of tablet presses. In addition, air entrapment can occur. 

Both wet and dry granulation methods of tablet manufacture are complex multistage processes, but are necessary to convert the components of the formulation into a state that can be readily compressed into acceptable tablets. If, however, a major component of the formulation already possesses the necessary degree of fluidity and compressibility, granulation would be unnecessary. This is the basis of the direct compression method of tablet manufacture. ... 

Roll action is the process of reducing rock by means of a hard-faced solid wheel traveling over the rock and breaking it by crushing between the wheel and a rigid surface. While it is a form of compression, it is not the same as the direct-compression method and its results are different. Roll action may be accomplished by means of a wheel traveling over a stationary surface or by means of passing the rock between two wheels wherein the reduction is accomplished. This is a feature of many well-known machines. 

Measurements of particle porosity are a valuable supplement to studies of specific surface area, and such data are particularly useful in the evaluation of materials used in direct compression processes. For example, both micromeritic properties were measured for several different types of cellulosic-type excipients [53]. Surface areas by the B.E.T. method were used to evaluate all types of pore structures, while the method of mercury intrusion porosimetry used could not detect pores smaller than 10 nm. The data permitted a ready differentiation between the intraparticle pore structure of microcrystalline and agglomerated cellulose powders. 

The manufacturing process used to make the test product should be described briefly to provide information on the method of manufacture (e.g., wet granulation vs. direct compression). A list of excipients used, the amount used, and their intended functions should be provided. Excipients used in the test product should have been used previously in FDA-approved IR solid oral dosage forms. 

The first direct compression excipient, spray-dried lactose, was introduced in the early 1960s as a filler specifically designed for direct compression processes. Over many years, more direct compression API and excipients, especially diluents and binders, were developed. Since these are now commercially available, design of direct compression formulations is readily possible. However, despite the simplicity of the direct compression process, the pharmaceutical industry still produces most tablets by wet granulation methods.1... 

Theophylline tablets made by both direct compression and wet granulation have been assessed. There is almost no difference between direct compression and wet granulation methods (see Figures 12-14) under the following conditions appropriate formulation (sufficient level of HPMC in the tablet) and precise control of the wet granulation process. Direct compression using Metolose SR is recognized as a suitable process for matrix tablets. 

Regardless of the granulation method, the comparative simplicity of the direct compression process offers obvious advantages, such as... 

There are three methods of tablet manufacture designed to confer these essential attributes to a tablet formulation. Wet granulation and direct compression are the most important, with dry granulation (also known as precompression or slugging) used in some circumstances. Fig. 1 shows the processes of wet granulation and direct compression broken down into their constituent stages. 

A faulty batch of tablets can sometimes be recovered by grinding up the tablets and recompressing them, a process which is known as reworking and is analogous to the dry granulation method of tablet manufacture. This can sometimes cause problems with a direct compression formulation. Many direct compression diluent particles are in the form of aggregates, e.g., spray-dried lactose is composed of small crystals of lactose embedded in amorphous lactose. If these aggregates are compressed, their structure may be broken down to such an extent that subsequent recompression will result in impaired tablet quality. 

In general, the manufacturing process used for the majority of these tablets are the same as those used for humans and are discussed elsewhere (chap. 13, vol. 1). Direct compression and granulation (wet, dry) are both used. Chewable tablets can also be made by these methods or sometimes are molded via excursion and cut into appropriate sizes. The terms chewable tablets and treats are sometimes confusing. One way to classify is to state that chewable tablets that are made by direct or granulation processes are then called tablets. This would be similar to the mannitol-based chewable tablets prevalent for humans. The term treat is used for the more soft tablets that are produced via extrusion or cast molding. 

Today, wet granulation is the most commonly used granulation method. Formulation teams will usually target a direct compression or dry granulation formulation where possible but in approximately 80% of the cases they end up with a wet granulation formulation due to processing issues (Figure 21.15). 

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