Dry binders

Several adjustments were made to the formula and process to improve the com-pactibility of this product. The moisture specification was adjusted, additional dry binder was added to the formula, and the tooling design was re-engineered. 

In this process, the component powders are first prepared by conventional powder processing, such as co-precipitation, sol-gel, spray-drying and freeze-drying. Binders,... 

Microcrystalline cellulose is one of the most commonly used filler-binders in direct compression formulations because it provides good binding properties as a dry binder, excellent compactibility, and a high dilution potential. It also contributes good disintegration and lubrication characteristics to direct compression formulas. When compressed, microcrystalline cellulose undergoes plastic deformation. The acid hydrolysis portion of the production process introduces slip planes and dislocations into the material. Slip planes, dislocations, and the small size of the individual crystals aid in the plastic flow that takes place. The spray-dried particle itself, which has a higher porosity compared with the absolute porosity of cellulose, also deforms... 

Microcrystalline cellulose (Avicel) is purified partially depolymerized cellulose, prepared by treating a-cellulose with mineral acids. In addition to being used as a filler, it is also used as dry binder and disintegrant in tablet formulations. Depending on the preparation conditions, it can be produced with a variety of technical specifications depending on particle size and crystallinity. It is often used as an excipient in direct compression formulations but can also be incorporated as a diluent for tablets prepared by wet granulation, as a filler for capsules and for the production of spheres. 

An alternative to the Ludipress grades is the outstanding dry binder Kollidon VA 64 together with excipients (e.g., calcium phosphate, microcrystalline cellulose, lactose, or starch) and a disintegrant (e.g., Kollidon CL). This combination even allows 500 mg of paracetamol to be pressed into good tablets with a weight of 700 mg. 

No other dry binder has binding power and plasticity comparable to Kollidon VA 64. Plasticity, in particular, is an important parameter in direct compression. As can be seen in Figure 6 (99.5% binder + 0.5% magnesium stearate), this property of Kollidon VA 64 is not adversely affected by increasing the pressure. The beneficial... 

Nystrom, C. Glazer, M. Studies on direct compression of tablets. XIII. The effect of some dry binders on the tablet strength of compounds with different fragmentation propensity. Int. J. Pharm. 1985, 23, 255-263. 

There are conflicting reports on the preferred method of adding the binder. For example, Holm does not generally recommend adding dry binder to the mix (as commonly done in order to avoid preparation of a binder solution) because homogeneity of binder distribution cannot be assured. Others recommend just the opposite. " " ... 

Muzikova J, Horacek J. The dry binders, Vivapur 102, Vivapur 12 and the effect of magnesium stearate on the strength of tablets containing these substances. Ceske Slov Farm 2003 52(4) 176-180. 

Sheskey PJ, Dasbach TP. Evaluation of various polymers as dry binders in the preparation of an immediate-release tablet formulation by roller compaction. Pharm Tcchnol 1995 19 98-112. 

Nystrbm C, Mazur J. Sjogren J. Studies on direct compression of tablets II. The influence of the particle size of a dry binder on the mechanical strength of tablets, Int J Pharm 1982 10 209-18. 

Although most drug substances do not fulfil these criteria, they can be directly compressed with copovidone [68c, 213,458,459,464,615]. It could be considered as the best dry binder of all substances usually applied in drugs for this purpose. The main reasons of the excellent dry binder properties are the plasticity shown in Fig. 110, the lower glass transition temperature (see Section 4.4.3.1) and the irregular structure of its particles (see Figs. 94 and 95 in Section 4.2.4.2). 

Fig. 110. Plasticity of different dry binders mixed with 0.5% of magnesium stearate in tablets (Plasticity = plastic energy/total energy)...

It is normally difficult to produce tablets with ascorbic acid by direct compression, but as is shown in Table 174, they can be produced much more readily using copovidone. When this dry binder is added, the hardness of the tablets increases and the friability decreases much more than after the addition of povidone K 30 or hydroxypropylmethylcellulose (HPMC) which had no effect on the hardness in this formulation. Similar results were shown in Fig. 111 for acetaminophen tablets. 

Table 174. Dry binding effect of different dry binders in ascorbic acid tablets...

Fig. 111. Influence of the type of dry binder on the hardness of acetaminophen tablets 500 mg obtained by direct compression (3.5% dry binder, tablet weight 700 mg, compression force 25 kN)...

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