Extracts

EXTRACTS, or decoctions, Extracta, galenical preparations obtained by extracting plant or animal raw materials with liquids followed by evaporation of the solvent (extractant). Depending on the extractant used, one distinguishes aqueous, alcoholic (by international agreement, in the absence of indication, this always implies alcoholic extracts), and ethereal extracts; in factory production, chloroform, benzene, petroleum ether, and other extracts are also prepared. Aqueous extracts are prepared by evaporating infusions (see Infusum) or decoctions (see Decoctions) or macerates (cold infusions, see Infusum); alcoholic extracts by evaporating alcoholic extracts (see Tinctures). The methods of producing extracts were developed taking into account the capabilities of the pharmacy and its small laboratory; only with the development of the pharmaceutical industry (from the mid-19th century) did the introduction of more modern methods and technical means begin (extractors, diffusers, vacuum apparatuses, vacuum, belt, and spray dryers, etc.). In pharmacopeias, including the VII Pharmacopeia, production methods for extracts designed for pharmacies are regulated; therefore, pharmacopeial methods are reduced solely to the following: 1) Extraction is carried out by maceration (see Tinctures) or percolation. The latter method strives for the most complete extraction from the raw material of all soluble substances in the given extractant and is carried out in special apparatuses, so-called percolators (Fig. 1). For percolation, the dry and crushed material is moistened with a certain amount of extractant sufficient for impregnation and placed in the percolator, after which enough extractant is added so that there is still a layer of liquid above the material. Having placed a receiver underneath, the tap of the percolator is opened just enough so that the dripping liquid can be counted (pharmacopeias regulate the rate of outflow). Percolation is continued until an uncolored extract begins to flow from the tap; the inflow of liquid is regulated by pouring or automatically so that above the material all

Figure 1. Percolators.

still some amount of extractant. For aqueous extracts, the hot extraction method is also used, i.e., boiling with water or pouring boiling water over the material. 2) Separation of the extract from the material residues is necessary only in the maceration or hot preparation method; for this purpose, pressing (Fig. 2) followed by filtration is used. 3) Evaporation of the extract. Extracts containing substances that easily change upon heating (especially in contact with air) must be evaporated in a vacuum (see); the rest are evaporated on water or steam baths. Evaporation over an open fire always leads to partial destruction (burning) of the extract at the walls of the boiler. Depending on the degree of removal of the extractant, one distinguishes dry extracts (Extr. sicca, moisture content below 10%), thick extracts (Extr. spissa, moisture around 10% and higher), thickish or semi-fluid extracts (Extr. tenua, moisture around 25%), and liquid extracts (Extr. fluida, of which only part of the extractant is evaporated so that from 1 part of material 1 part of liquid extract is obtained). The introduction of liquid extracts or fluidextracts (first adopted by the British Pharmacopoeia in 1864, but previously prepared in the USA) took into account the difficulty for pharmacies to evaporate extracts under conditions ensuring the constancy of constituent substances; therefore, these fluidextracts are prepared in such a way that 100 parts of material are percolated only until 85 parts of extract are obtained; then, changing the receiver, percolation is continued until complete extraction (exhaustion) of the material. Only this second extract is evaporated and mixed with the previously obtained 85 parts; the mixture is then brought with the prescribed extractant to a weight of 100 parts. Thus, 85% of the fluidextract is not subjected to heating. In view of the great advantages of dry extracts (greater stability, convenience in weighing, and the possibility of inclusion in both powders and liquid dosage forms), so-called dried extracts were introduced; they are prepared by mixing into the thick extract some substance that easily absorbs water but is not hygroscopic; by adding such substances, the thick extract is brought to a certain specified weight relative to the thick extract (after drying) or to a certain content of active principles.

Figure 2. Presses: a-hand screw; b-differential (winemaking); c-hand hydraulic.

or to a certain content of active principles. The main purpose of the production of extracts is to extract the necessary substances from the raw material (plant or animal organ) while avoiding as much as possible unnecessary (ballast) substances (such as fiber, resins, etc.), and then to bring the extract to the smallest possible, convenient volume for use. In connection with the use of modern chemical methods in the production of extracts, preparations of a new type have arisen—extracts purified from ballast substances by additional extraction with other extractants (e.g., aqueous extract is additionally extracted with chloroform or benzene), precipitation (e.g., the extract is dissolved in water, filtered from insoluble particles, and the filtrate is precipitated by adding acetone or alcohol, etc.), or adsorption (clarification with carbon, kaolin, etc.); these extracts or their solutions are produced under the name of neo-galenical preparations (neogalenics). Concentrated infusions (see Infusum) should be classed among extracts; recently, a number of such concentrated infusions have also been produced in dry form. The use of extracts is most convenient in pills, since most extracts contain mucous, protein, resinous substances, or dextrins having adhesive properties. Extracts are less frequently used in powders, mixtures, etc. Fluidextracts are used per se, in the form of drops or in liquid dosage forms. In addition to the pharmaceutical preparations mentioned, extracts are also prepared for other purposes. Extracts from organs (internal secretion) belonging to organotherapeutic preparations (see) require special care in manufacture; in the process of their preparation, compliance with both temperature conditions and strict asepsis is required, and only in special cases is the use of antiseptics possible. Often the exclusion of the influence of atmospheric oxygen is also required, especially at high pH. In many cases, it is necessary to carry out all operations at a temperature below 56° (critical temperature of protein denaturation), including evaporation; but often, especially in a slightly acidic environment, brief heating to a higher temperature necessary for the removal of proteins by coagulation is allowed. Similar precautions are necessary in the preparation of extracts from other tissues and organs (e.g., external secretion organs, such as the gastric mucosa, pancreas, etc.), embryonic extracts (see Tissue culture) or bacterial preparations; the latter include some tuberculins (see) and preparations of the antivirus type (see). Extracts are also prepared in various branches of industry both for food purposes (meat extract and malt extract) and for technical needs (tanning extracts in the leather industry, licorice extract for fire extinguishers-foam generators and for tobacco products, dye extracts, and many others).

I. Oberhard