Ionic
Ionic contrast media chemically are salts of weak organic acids containing iodine. Like most salts they will split into two particles, called an anion and a cation, when dissolved in water. The anions are iodinated benzene rings, where one of the side chains is a weak organic acid (benzoic acid). They are either single benzoic rings (monomeric contrast media) like diatrizoate, metrizoate or iothalamate, or as two linked rings (dimeric contrast media) like iocarmate or ioxaglate. The cations are either metals like Na+ (sodium), Ca++ (calcium) or Mg++ (magnesium) or organic cations like meglumine (methylglucosamine). Ionic monomeric contrast media will have an osmolality of more them 7 times the osmolality of blood at the highest clinically used concentrations. Ionic dimeric contrast media have a lower osmolality but unfortunately at the cost of increased chemotoxicity. Ionic monomeric contrast media are also called high osmolar contrast media, (HOCM). See also term non-ionic.
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