Auxiliary excipients

The excipients used in solid dispersions can be broadly classified as (a) polymeric and (b) non-polymeric excipients. Polymeric excipients are the primary excipients, whereas the non-polymeric ones are the auxiliary excipients. Polymeric excipients are further classified based on their charge into the following categories (a) nonionic or non-pH-dependent and (b) ionic or pH-dependent polymers. Further, nonionic polymers are classified as polyvinyllactam polymers and cellulose ethers. The ionic polymers are further classified as cationic and anionic polymers (Fig. 4.2). 

Dry blending of the primary powder material, i.e., active substance and auxiliary substances in a mixer. Preference should be given to demineralized water as granulating liquid and the excipients and the drug should show relatively low water solubility with the exception of the binder. The binder should be preferably added in a dry state as part of the powder components. 

We endeavoured to select typical and often used representative substances for particular classes of compounds. These then can be used as representatives for similar compounds. This also is the reason why the number of substances covered here is rather low compared with some lists of excipients such as, e. g., Fiedler Encyclopedia of Excipients or Index der Hilfsstoffe/Index of Auxiliary Substances by H. P. Fiedler. It would not have been meaningful to include numerous, very similar substances - all showing virtually identical IR spectra. 

The technology involved in direct compression assumes great importance in the tablet formulations, because it is often the cheapest means, 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 (cf. Chapter 2.5). Even substances such as ascorbic acid that are hardly suitable for direct tabletting owing to the friability of their crystals can normally be directly pressed into tablets at concentrations of 30-40%, However, this technique is not as suitable if the content of ascorbic acid is higher. This limit may be shifted upwards by special direct compression auxiliaries, e.g, Ludipress. Two important alternatives, viz. Ludipress and Koi lid on VA 64, can be found in the BASF line of pharmaceutical excipients for direct compression. 

Auxiliary material Any excipient and additive used in the production of a pharmaceutical or in dispensing a formulary. 

Cosmetic formulations are composed of active ingredients and excipients. Active ingredients are compounds directly related with the efficacy of the cosmetic product. Excipients can have different functions such as to facilitate the preparation of the formulation, to achieve the required physicochemical properties, to improve the efficacy or to provide stability to the finished product. On the other hand, active ingredients in some cosmetic formulations can act as auxiliary ingredients in other formulations. 

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