C14H10O9 = 322.08.
Tannic acid, C13H9O7COOH, is a monobasic organic acid, obtained from galls. The B.P. formula for tannic acid is C14H10O9, 2H2O, but according to the most recent work on the subject, tannic acid from galls is anhydrous, and is represented as such in the U.S.P. It occurs as a light, yellowish or brownish powder, with a faint characteristic odour and a strongly astringent taste. Many commercial samples contain gallic acid, the presence of which reduces the solubility of the tannic acid, and may be detected by the production of a pink colour on the addition of a 5 per cent. solution of potassium cyanide. These commercial varieties of tannic acid are used in dyeing, in the manufacture of ink, etc., and are not suitable for medicinal use; they are in coarse powder or lumps, darker in colour than the official substance.
Soluble in water (2 in 1), alcohol (10 in 6), and, slowly, in glycerin (1 in 3, or 1 in 1 on heating); almost insoluble in pure ether, chloroform, or benzene.
Action and Uses.—The properties of tannic acid depend upon its chemical interaction with proteins and gelatin. A solution of the acid added to albumin or gelatin produces a dense precipitate, soluble in excess of albumin or gelatin, and in acids or alkalies. With connective tissue tannin forms an exceedingly insoluble compound (leather). The free acid only is astringent, and when it is neutralised by albumin or alkalies its astringent properties are lost. When taken by the mouth it gives the characteristic feeling of astringency, coagulates the protein material surrounding the epithelium, and even penetrates some of the superficial cells. In the stomach it combines with alkalies and albumin to form tannates; albumin tannate is digested like other coagulated protein, the tannin being liberated and rendered free to recombine. Its presence in the small intestine, by coagulating proteins and diminishing secretions, tends towards constipation; it is therefore occasionally used in diarrhoea. In the alimentary canal it is converted into gallic acid, and absorbed as sodium gallate; the greater proportion is apparently not absorbed, as only about 1 per cent. appears in the urine. The acid is sometimes placed on bleeding points with the object of coagulating the albumin and arresting haemorrhage; it is used also as an application to inflamed mucous membranes, to diminish discharge, and to stimulate healing. It is of no value as a remote astringent, and cannot control any form of remote haemorrhage. Tannic acid is seldom given internally; it exerts a powerfully astringent effect in the stomach, but as intestinal astringents the combined tannic acids existing in catechu, kino, and rhatany are more active, as they are less readily absorbed. The acid may, however, be administered in the form of mixture, or as a pill massed with one-eighth part of its weight of glycerin, or with glycerin of tragacanth, and in cachets. It is much more generally used for external application. A solution of tannic acid, 8, in water, 6, has been used for ingrowing toe-nail. As a styptic the powder may be applied, or a solution (5 per cent.) on lint, or Collodium Stypticum may be employed. As an astringent in relaxed sore throat the glycerin may be painted on, or the lozenges sucked, or a gargle or spray may be employed. The powder is used for insufflation and for rubbing on the gums as an astringent. Solutions (1 or 2 per cent.) are used as lotions and injections for douching the nostrils in epistaxis and for use in gonorrhoea, leucorrhoea, and haemorrhoids. Tannic acid is a valuable ingredient of liquid and solid dentifrices for use when the gums are spongy and receding. A 20 percent. solution in alcohol has been found useful for application to such gums. Suppositories, pessaries, and bougies are prepared with oil of theobroma. Several synthetic compounds of tannin are preferred to tannin as intestinal astringents. Such are acetannin (Tannigen), tannin-albumin (Tannalbin), methyl-ditannin, tanno-gelatin (Tanocol), and albumin tannate (Honthin). They are decomposed slowly in the intestine, and their action is more prolonged. It is incompatible with alkalies and their carbonates, salts of iron, lead, antimony, and silver, mineral acids, alkaloids, albumin, gelatin, and lime water. Tannic acid is sometimes given as an antidote in cases of poisoning by alkaloids, with the object of rendering insoluble such alkaloids as may still be in the stomach; it is also used as an antidote in cases of antimonial poisoning.
Dose.—1 to 3 decigrams (2 to 5 grains).
- Cereoli Acidi Tannici et Opii, B.P.C.—TANNIC ACID AND OPIUM BOUGIES.
- Each bougie contains tannic acid, 1 grain; opium, 1 grain.
- Collodium Stypticum, B.P.C.—STYPTIC COLLODION. Syn.—Styptic Colloid.
- Tannic acid, 15; tincture of benzoin, 15; collodion, to 100. Used to arrest bleeding from leech-bites, small wounds, and abrasions.
- Collodium Stypticum, U.S.P.—STYPTIC COLLODION, U.S.P.
- Tannic acid, 20; alcohol, 5; ether, 25; collodion, to 100.
- Gargarisma Acidi Tannici, B.P.C.—TANNIC ACID GARGLE.
- Glycerin of tannic acid, 1; distilled water, 9. Used for relaxed and inflamed throats; it diminishes the secretion of mucus.
- Glycerinum Acidi Tannici, B.P.—GLYCERIN OF TANNIC ACID.
- Tannic acid, 1; glycerin, sufficient to produce 5. Used as a paint in relaxed throat, and as a spray solution (1 part with 6 or 8 parts of water) in stomatitis, ozoena, inflamed tonsils, and pharyngeal irritation.
- Glyceritum Acidi Tannici, U.S.P.—GLYCERITE OF TANNIC ACID.
- Tannic acid, 1; glycerin, by weight, 4.
- Pessus Acidi Tannici, B.P.C.—TANNIC ACID PESSARY.
- Each pessary contains tannic acid, 10 grains. Used in vaginal leucorrhoea.
- Solutio Acidi Tannici, B.P.—TEST SOLUTION OF TANNIC ACID. 1 in 10.
- This solution should be freshly prepared as required.
- Suppositoria Acidi Tannici, B.P.—TANNIC ACID SUPPOSITORIES.
- Each suppository contains tannic acid, 3 grains. Used as an astringent application in haemorrhoids, extract of belladonna being sometimes added to allay pain.
- Trochisci Acidi Tannici, U.S.P.—TROCHES OF TANNIC ACID.
- Each lozenge contains nearly 1 grain of tannic acid.
- Trochiscus Acidi Tannici, B.P.—TANNIC ACID LOZENGE.
- Each lozenge contains tannic acid, ½ grain. Used as an astringent in "sore throat."
- Unguentum Acidi Tannici, U.S.P.—OINTMENT OF TANNIC ACID.
- Tannic acid, 1 glycerin, by weight, 1; ointment, 3.