This section is from the book "Botanic Drugs Their Materia Medica, Pharmacology and Therapeutics", by Thomas S. Blair. Also available from Amazon: Botanic Drugs, Their Materia Medica, Pharmacology and Therapeutics.
Tannic Acid, Tannin (U. S. P.). There are many plants from which tannins may be derived. Chemically they differ more or less, but they are similar pharmacologically. The chief quality is astringency dependent upon the power of precipitating albumins. The value of the drug in hemorrhage is due to its precipitation of the blood proteins, which coagulate, checking hemorrhage. From this same power over albumen, tannic acid kills some of the lower organisms, so that the coagulated proteins produced by its local application reduces danger of sepsis. Tannin checks excessive secretion from the sweat glands and limits secretion in the mouth and throat. Large doses cause indigestion in the stomach; in the intestine peristalsis is diminished, and the stools are increased in consistency owing to absorption of fluid, and a mild antiseptic action is exerted. As tannin is changed to gallic acid in the upper bowel, no appreciable astringent action results from its administration by the time it reaches the lower bowel. Tannin possesses no remote astringency through circulating in the blood-stream, and it is not an urinary antiseptic.
Pure tannic acid is applied to wounds, ulcers, and bleeding surfaces in the form of dusting powders in which tannin may be the chief ingredient. Ointments are commonly made 10% (U. S. P. ointment 20%); lotions, 2 to 5%. Weeping ulcers and subacute inflammatory conditions, the hardening of the skin to prevent bedsores, and many other indications are met with local applications of tannin. Various bougies are used for applications to the urethra and vagina, and suppositories in the palliative treatment of hemorrhoids. The U. S. P. glycerite of tannic acid (20%) is a most eligible preparation to harden sore and inflamed nipples in nursing women. In the mouth, in tender gums, tonsillitis, laryngitis, etc., tannin is a valuable local application in 2% gargles or 5 to 10% sprays.
Various gastro-enteric troubles are suitably treated with tannin or tannin derivatives. Here it is proper to say that the vegetable astringents often act more kindly than does a chemical salt. Gambir, krameria, geranium, kino, and others are applicable.
The colloids in these plant structures restrain the irritant properties of the tannic acid. Chronic catarrhal gastritis is much benefited by a vegetable astringent; and some cases of gastric ulcer are relieved by a vegetable astringent with bismuth in combination. The British Pharmacopeia compound powder of catechu (catechu, kino, krameria, cinnamon, nutmeg) is an admirable preparation.
As an antidote in poisoning from alkaloids and the heavy mineral salts, large doses of tannin should be given in dilute solution, followed by an emetic or the washing out of the stomach.
In intestinal disturbances uncombined tannin is decomposed into gallic acid too rapidly to be very effective. The fluidextract of geranium serves well in the case of children and in mild affections in adults. Newer drug preparations available will be named presently. Subacute and chronic diarrhea characterized by an excess of mucus responds well to tannin preparations. Chalk, bismuth, and opium are often combined with the vegetable astringents; but do not forget that an initial dose of castor oil and intestinal antiseptics are often needed before the astringents can serve any useful purpose; and that the vegetable forms of tannin will not restrain hemorrhage in the lower bowel, since they are decomposed before they reach it.
The important vegetable astringents will be separately discussed, each in its proper place. Above everything else, physicians must remember, in the intestinal disturbances of infancy and childhood, that dietetic measures are vastly more important than are drugs.
The newer products of tannic acid are designed to pass the stomach unchanged, or largely so, and thus reach the bowel in an active state. Protan (5 to 30 grains, according to age and condition) is a 50% tannin compound with casein and is a valuable intestinal astringent. Tannalbin (5 to 60 grains in range of dose) is a compound of tannic acid and albumin and is insoluble in the stomach. Tannigen (3 to 10 grains) is an acetic acid ester of tannin, slowly decomposed in the intestines. Tannismuth (5 to 10 granis) is bitannate of bismuth, is said to be astringent in both the stomach and bowel, one molecule of the tannin being liberated by the stomach acids, and the other molecule slowly liberated in the bowel. Tannoform (4 to 8 grains) is astringent and antiseptic, being a product of formaldehyde and gallotannic acid.
The average dose of tannic acid is 5 to 8 grains; but it is seldom used internally in its uncombined state.