Tablet excipients, functional

Shangraw RF, Wallace JW, Bowers FM. Morphology and functionality in tablet excipients for direct compression Part I. Pharm Technol 1981 5 69-78. 

Coprocessed tablet excipient composed of chitin and silicon dioxide [52] Chitin is a water-insoluble hydrophilic polymer that can absorb water and function as a disintegrant. Due to the unacceptable flow and compression properties of chitin, coprecipitation with silicon dioxide was used to provide a new excipient with excellent flow, compaction and disintegration properties when compared to the individual components or commercially available direct compression fillers and disintegrants. The optimal composition of the coprocessed excipient contains a silicon concentration of about 50% (w/w). 

Table 1 Summary of types and functions of tableting excipients...

Shangraw, R.F. Wallace, J.W. Bowers, F.M. Morphology and functionality of tablet excipients for direct compression. Pharm. Tech. 1981, 5, 69-78. 

Experimentally, measurements should be carried out in accordance with the manufacturers instructions. However, it is worth noting that artefacts may occur. For example, Figure 6.8 shows the measured true density of a number of tableting excipients as a function of sample weight. As can be seen, at low sample weights, the measured true density increased, making the measurements less accurate. 

Nowadays some tablet excipients present multi functionalities. New excipients are designed to allow a fast and effective mixing with the active substance prior to compression. Although more expensive, they save production time and diminish difficulties on designing a new formulation. 

There are two major functional classifications of tablet excipients. The first class includes those additives which affect the compressional characteristics of the tablet, including diluents, binders and adhesives, lubricants, antiadherents, and glidants. The second class of excipients includes those which affect the biopharmaceutics, chemical and physical stability, and marketing considerations of the tablet. This category includes disintegrants, colors, flavors and sweeteners, and miscellaneous components such as buffers and adsorbents. All of these must meet certain criteria as follows ... 

The Cadila system [13] has been designed to formulate tablets for drugs based on their physical (solubility, hydroscopicity, etc), chemical (functional groups), and biologically interrelated (dissolution rate) properties. The system first identifies the desirable properties for optimum compatibility with the drug, selects those excipients that have the required properties, and then recommends proportions based on the assumption that all tablet formulations comprise at least one binder, one disintegrant, and one lubricant. Other... 

The USP/NF provides a listing of excipients by categories in a table according to the function of the excipient in a dosage form, such as tablet binder, disintegrant, and such. An excellent reference for excipient information is the APA s Handbook of Pharmaceutical Excipients (1994). 

Excipients are sub-divided into various functional classifications, depending on the role that they are intended to play in the resultant formulation, for example, fillers, disintegrants, binders, lubricants and glidants. An added complexity is the fact that certain excipients can have different functional roles in different formulation types. Thus, lactose is widely used as a filler or diluent in solid oral dosage forms, for example, tablets and capsules [2] and as a carrier for inhalation products [3]. 

The use of excipients goes back to centuries. Even before the advent of the capsule and later the tablet, the available botanical drugs were made into powders or mixtures to make them more convenient for the patient, although sometimes not that palatable. Ointments and salves, with similarities to topical formulations that have been used in more recent times, were known in Ancient Greece. However, the scientific basis for the use of certain excipients has emerged only in the last few decades for example, tablet lubricants—until a few years ago we knew they were needed and when to use them, but not why they functioned as they do. 

One very common beneficial interaction involving an excipient is the interaction between magnesium stearate and the metal of tablet punches and dies, or the equivalent parts on a powder encapsulation machine. Magnesium stearate is an example of a boundary lubricant. As such it has a polar head and a fatty acid tail. It is believed that the polar head of the magnesium stearate is oriented toward the die wall or tablet punch face. In these ways it is able to reduce the ejection force (the force required to eject the tablet from the die after compaction) and prevent sticking to the punch faces. The other boundary lubricants, e.g., calcium stearate and sodium stearyl fumarate, will also function in a similar manner. However, the so-called liquid film lubricants function in a very different manner (19). 

We include certain excipients in a formulation specifically because they interact with the physiological fluids and the bodily functions in a certain way. For example, as discussed above, we include disintegrants in immediate release tablet and capsule formulations, because we know that when they encounter the aqueous environment of the stomach, they will cause the tablet or capsule to disintegrate and thereby aid dissolution of the API. Another example is the general case of hydrophilic colloid matrices used as prolonged release drug delivery systems. We know that when these materials contact the aqueous environment of the GIT they swell and create a diffusion barrier that slows the rate of dissolution of the dissolved drug. 

Tableting process, since being introduced in the early 1840s, has witnessed numerous changes in the form of stringent regulatory requirements for the excipients and product stability. Increasing regulatory pressure on purity, safety, and standardization of the excipients has catalyzed the formation of an international body, the International Pharmaceutical Excipients Council (IPEC) (13). IPEC is a tripartite council with representation from the United States, Europe, and Japan, and has made serious efforts to harmonize requirements for purity and functionality testing of excipients (14).

Can the equipment perform a specialized function in addition to basic encapsulation (e.g., tablet in capsules with excipient backfill) ... 

---