A preliminary report on teridax, a new cholecystographic medium.

Abstract

Numerous investigators agree that the ideal cholecystographic medium should fulfill the following requirements: (1) low systemic toxicity and minimal unpleasant side reactions; (2) ease of administration; (3) ready elimination; (4) selective localization within the gallbladder; (5) preferential renal excretion, to eliminate confusing opaque bowel shadows; (6) the optimal degree of density to provide adequate visualization and yet not obscure stones. Tetrabromphenolphthalein, the original compound, was soon replaced by its iodine homologue which was in turn supplanted by iodoalphionic acid (Priodax) in 1940. Priodax has proved to be a very satisfactory contrast substance but unfortunately has a significantly high degree of unpleasant side effects, particularly diarrhea. In various reports from the literature, the diarrhea ranged from 2 per cent to 43 per cent (3, 4, 5). In one of the author's unpublished studies with Priodax, the incidence of diarrhea was 30 per cent, with severe diarrhea in 8 per cent of the cases. In 1951, a new cholecystographic medium, iodopanoic acid (Telepaque) was introduced (1, 2). This is superior to Priodax in several respects: (1) The increased density of the gallbladder shadow results in better visualization, and fewer repeat examinations are required. (2) Fewer unpleasant side reactions occur. (3) There is frequent visualization of the extrahepatic biliary ducts. Telepaque, however, has the disadvantage of being excreted through the bowel. In addition, the opacification of the gallbladder is frequently so great that it is possible for stones occasionally to be obscured by the medium. In an effort to obviate the shortcomings of Telepaque, a new compound, ethyl triiodoalphionic acid (Teridax) has been synthesized. Teridax is excreted principally by the kidneys and produces a gallbladder shadow which is intermediate in density between that produced by Priodax and Telepaque. In addition, it has the same low level of side reactions as Telepaque. The close chemical relationship of these three substances can readily be ascertained by inspection of their structural formulae. Teridax is a white, odorless, crystalline powder which contains 66.5 per cent iodine, has a molecular weight of 572, and melts sharply at 143–144·C. It is almost insoluble in water but is soluble in methyl and ethyl alcohol and other organic solvents (6). Pharmacology Mode of Elimination: In experimental animals and in man, oral Teridax is eliminated principally by the kidneys and to a very minor extent by the gastrointestinal tract. The similarity of Teridax to iodoalphionic acid in this respect is advantageous since masking of the gallbladder by radiopaque material in the colon does not occur. Time of Visualization: In man, Teridax begins to concentrate in the gallbladder within four hours following oral administration (Fig. 1). Maximal concentration is reached between eight and twelve hours. Teridax is more slowly excreted than iodopanoic acid.