Tannin

TANNIN, Tanninum, an old name for tannic acid, Acidum tannicum (Ph. VII). Chemically, it is probably an ether-like compound of glucose with gallic or digallic acids. According to the research of E. Fischer and K. Freydenberg, the structure of T. is close to that of penta-meta-di-galloyl-β-glucose, C₆H₇O₆. C₆H₂(OH)₂CO. O. C₆H₂(OH)₂CO]₅. Tannin is a representative of depside glycosides; this latter name was given by E. Fischer to complex esters of phenol acids, e.g., didepside digallic acid, C₆H₂(OH)₃COOC₆H₂(OH)₂COOH, which is obtained from 2 molecules of gallic acid, C₆H₂(OH)₃COOH. Similarly, polydepsides are analogous to polypeptides. T. is an amorphous powder of a yellowish color. It is soluble (colloidally) in water, alcohol, glycerin, and insoluble in ether, chloroform, gasoline, etc. The addition of 1-2 drops of a solution of ferric chloride to a solution of T. produces a blue-black precipitate that decomposes upon the addition of sulfuric acid. T. is precipitated (salted out) from concentrated aqueous solutions by the addition of salts or acids. T. is obtained from gallnuts (Gallae turcicae), which are pathological formations developing on the branches of the Anatolian oak from the puncture of an insect called the gall wasp (Cynips). In industry, Chinese gallnuts—growths on Rhus semialata formed by the bites of Aphis chinensis and containing up to 77% tannin—are more commonly used. Pharmacologically, T. belongs to the large group of organic astringent substances, being the main representative of this group. The action of T., like that of other astringent substances, depends on its ability to coagulate proteins. This process occurs if the pH of the medium lies between 1 and 8.3. The optimal reaction of the medium is a pH in the range of 3-5. More pronounced shifts of pH to the alkaline or acidic side hinder the protein precipitation process. Upon contact with the protoplasm of living cells, tissue fluid, and secretions, e.g., when lubricating the mucous membrane, partial coagulation of proteins occurs, resulting in the so-called astringent action, which is expressed in the condensation of tissue and a reduction in its volume. In addition, there is constriction of blood vessels, a reduction in gland secretion, and a certain degree of anesthesia. The action of T. is completely reversible; therefore, a complete coagulation of the proteins of the cellular protoplasm cannot be spoken of, provided the solution of T. taken is not excessively strong and the duration of exposure is not too great. The action of T. is especially distinct when its solutions are applied to inflamed tissues, where the intensity of inflammatory symptoms decreases, which is why T. is considered an anti-inflammatory agent. In strong solutions, T. exerts an irritating action and can even cause tissue necrosis. When solutions of T. are introduced into the oral cavity, a sensation of constriction, dryness, and difficulty in moving the tongue appears. After the solutions of T. enter the gastrointestinal tract, T. manifests its action by causing a reduction in gland secretion, a slowing of resorption, and a weakening of peristalsis. The feces become firmer. T. possesses exclusively a local action. It is absorbed in a modified form and has no resorptive action. In former times, some authors admitted the possibility of the action of T. after absorption into the blood; however, more recent researchers have shown the complete untenability of such views. As for the fate of T. in the organism, the majority of authors who have studied this question consider that it is oxidized in the organism and is excreted in the form of gallic acid and pyrogallol. Thus, T. can be applied for therapeutic purposes exclusively for local action on pathological processes, and its application for resorptive purposes is irrational. In connection with the aforementioned method of excretion, after the administration of its preparations, the urine gives a coloration (black, blue, or violet) with solutions of salts of iron oxide, which must be taken into account to avoid errors in urine analysis. Tannin is most often applied externally, in aqueous and glycerin solutions (0.5-10%), in certain skin diseases accompanied by strong exudation, in catarrhal inflammations of mucous membranes, and in hemorrhages. In addition, T. is applied as an antidote in poisoning by alkaloids and salts of heavy metals, for the purpose of precipitating and binding the mentioned compounds, but it is important to remember that the precipitate formed dissolves in the gastrointestinal tract over time and the poison may be absorbed. For these reasons, T. is suitable only for temporary binding of the poison, and further measures are required for the removal of the poison. In conclusion, it should be noted that T. has a certain antiseptic power and deodorizing properties, which are also sometimes used in medical practice. Preparations: 1. Tanni-gen (Tanni-gen, Acetiltannin), a compound of T. with acetic acid. Contains 85% T. A yellowish-gray powder, almost odorless and tasteless (sometimes faintly smelling of acetic acid). Slightly hygroscopic. Insoluble in water, slightly soluble in alcohol, and well soluble in alkalis. As the research of Meyer showed, T. reaches the large intestine in an unchanged form after oral administration, manifesting its astringent action there. It is applied in the same cases as tannalbin, in doses of 0.5-2.0 (see Tannalbin). Recognition reaction. When acetic lead salt is added to an alcoholic solution of tanni-gen, a pink coloration appears first, then an intense red coloration. When the solution of tanni-gen is heated with alcohol and sulfuric acid, the smell of acetic ether appears. 2. Tannobrominum, a formaldehyde compound of dibromtannin. A brownish powder; applied in the form of ointments (1-3 : 30) or in alcoholic solutions (2.5-5%) against hair loss. 3. Tannoform (Tannoform), methylene ditanin, a condensation product of T. with formaldehyde. Applied like tanni-gen. 4. A series of T. preparations with aluminum (neo-tannil-Aluminium aceto-tannicum; tannal-Aluminium tannicum), with bismuth (tannibismuth, Bismutum tannicum; ibit-Bismutum oxyjodo-gallicum and others); with protein compounds of T. (tannipokol, kontin, tannalbin-see Tannalbin).