Tannic acid and the barium enema.

Abstract

The routine addition of tannic acid to barium enema preparations to enhance colonic evacuation and mucosal detail was suggested by Hamilton in 1946 (6). According to Weber, however, tannic acid was used as early as 1930 by some radiologists (6). Following Hamilton's report, it gained widespread acceptance and was employed by a large number of radiologists in this country. In recent years Clysodrast, a bowel evacuant in which tannic acid is the active agent, has been introduced. On March 21, 1964, the Food and Drug Administration banned the use of tannic acid in barium enemas as well as in pre-enema preparations, effective in sixty days (4). This ban followed the publication of two papers (10, 11), reporting a total of 8 cases of hepatic necrosis and death presumed secondary to tannic acid in the preparation and∕or the performance of barium enemas. Since this decision so profoundly affects many radiologists, it is believed worthwhile to review and evaluate the importance of tannic acid or similar compounds in the practice of radiology. Pharmacology Tannic acid (5) is a yellowish-white powder with a faint characteristic odor and astringent taste, found in a variety of forms in nature. It is present in high concentrations in tea and Burgundy. Chemically, these acids are polymers of various hydroxybenzoic acids. The one called specifically tannic acid is really gallotannic acid, the internal ester of gallic acid. It is usually obtained from nutgall, an excresence on the young twigs of various species of Quercus (oaks). The chemical relationship between gallic and tannic acid is as follows: The only important pharmacological property of tannic acid is its activity as a precipitant with proteins as well as with many heavy metals and alkaloids. Advantage of this characteristic has been taken in the treatment of bedsores, open wounds, various dermatitides, and especially burns. Its use for this last purpose was largely discontinued about the middle of the 1940's, when it was suggested by Wells et al. (17) that the toxemia of many burn patients was secondary to centrilobular liver necrosis associated with tannic acid therapy. This view was supported experimentally by Wells and his associates and by others reporting subcutaneous, intravenous, and intramuscular injections in animals (1–3, 8, 9, 12). The LD-50 was shown to vary with dose, method of administration, sex (male more sensitive), and species. Internally, tannic acid has been administered in a variety of disease states as a chemical antidote. It has been employed in various forms of alkaloid, glycoside, and heavy metal poisoning. Here it partially precipitates the poison, preventing absorption; gastric lavage must be performed, however, before the precipitant redissolves.