Tablets diluents

In pharmaceutical applications, sorbitol is used as a tablet diluent in wet granulation or dry compression formulations. It is commonly used in chewable tablets because of its sweet taste, and it is also used as a plasticizer for gelatin in capsule formulations. Sorbitol is utilized in sugar-free liquid preparations and as a stabilizer for drug, vitamin, and antacid suspensions. When it is used in syrups, crystallization around bottle caps is prevented. 

Armstrong NA, Palfrey LP. The effect of machine speed on the consolidation of four directly compressible tablet diluents. J Pharm Pharmacol 1989 41 149-151. 

A Comparison of Physical and Mechanical Properties of Common Tableting Diluents... 

MCC, lactose, calcium phosphate dibasic, and mannitol were selected as common tableting diluents and were evaluated as received from their vendors. These materials are summarized in Table 2. Each material is available from several vendors with multiple grades. Three grades within each excipient were selected for their diverse range of physical and mechanical properties (3). These materials typically comprise 5% to 70% of a formulation. The samples were stored at environmentally controlled laboratory conditions of 20 2°C and 40% 10% relative humidity. 

Terra alba or dead-burned, fine white gypsum is used as a paper filler, in plastics, and as an exlender far titanium dioxide. Pharmaceutically pure gypsum can be added to bread and other bakery products, finds use in beer production, and as a pharmaceutical-tablet diluent. In Japan, calcium sulfate is used in making tofu, a soyabean curd. 

Cellulose (Figure 8.19) may be extracted from wood pulp, and is usually partially hydrolysed with acid to give microcrystalline cellulose. These materials are used as tablet diluents. Semi-synthetic derivatives of cellulose, e.g. methylcellulose, hydroxymethylcellulose, and carboxymethylcellulose, are used as emulsifying and suspending agents. Cellulose acetate phthalate is cellulose with about half the hydroxyl groups acetylated, and the remainder esterified with phthalic acid. It is used as an acid-resistant enteric coating for tablets and capsules. 

Allen LV. 2000. Featured excipients capsule and tablet diluent. Int. J. Pharm. Compound... 

Tablet diluent Inert substance used as filler to create desired bulk, flow properties, and compression characteristics in preparation of tablets Dibasic calcium phosphate, kaolin, lactose, mannitol, microcrystalline cellulose, powdered cellulose, precipitated calcim carbonate, sorbitol, starch...

A great many of the materials that are used as pharmaceutical excipients occur naturally in the amorphous or partially amorphous state (e.g., gelatin and starch). Many others have been found to possess improved handling and mechanical properties when processed in such a manner as to render them at least partially amorphous. Examples of this include the grades of microcrystalline cellulose and lactose monohydrate used as pharmaceutical tableting diluents. ° ... 

Table 1 List of commonly used tablet diluent/fillers ...

At about the same time, two materials were introduced that were specifically designed to act as tablet diluents and would not require preliminary treatment. These were spray-dried lactose and microcrystalline cellulose, introduced in 1962 and 1964, respectively. These two substances can be said to have initiated the direct compression revolution. Since that time, a wide range of direct compression tablet diluents has become available. The properties of some of these materials will be reviewed later in this article. 

The primary limitation on the use of direct compression is that it depends on the fluidity and compressibility of a tablet diluent. Therefore, it cannot be used for low potency, high dose active ingredients where the inclusion of sufficient diluent in the formulation to permit direct compression would lead to unacceptably large tablets. Thus, active ingredients such as paracetamol and aspirin do not lend themselves to the direct compression process. However, as stated earlier, such ingredients are often available in pregranulated form. 

The simplicity of the direct compression process should obviously bring financial benefits. However, it must be borne in mind that direct compression tablet diluents are considerably more expensive than conventional diluents such as a-lactose monohydrate. 

FACTORS INFLUENCING THE CHOICE OF A DIRECT COMPRESSION TABLET DILUENT... 

Sorbitol can exist in four crystalline forms. Guyot-Hermann, Leblanc, and Draguet-Brugmans compared 11 commercially available varieties of sorbitol, and found three of these four forms to be present. y-Sorbitol was found to be the most useful as a tablet diluent. The method of manufacture has also been shown to affect tabletting properties, differences being attributed to variations in particle shape and surface properties. Spray-dried varieties of sorbitol are available as direct compression diluents which are claimed to have overcome problems associated with the different crystalline forms. ... 

Starch is a very widely used tablet excipient, but in its natural state, it does not possess the fluidity and binding characteristics needed as a tablet diluent. The major consolidation mechanism of starch is by deformation with a high elastic component.In addition, starch shows a high degree of lubricant sensitivity. 

Minchom, C.M. Armstrong, N.A. A proposed technique for expressing the capacity of directly compressible tablet diluents. J. Pharm. Pharmacol. 1989, 39, 69. 

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