[Selection of contrast media: current status of understanding]

The structure of currently used contrast media is based on the fully substituted benzoic acid with 3 iodine atoms at positions 2, 4 and 6 of the benzene ring. Contrast media can be differentiated according to their physicochemical characteristics as follows: a) iodine content, b) osmolality (hyper-, low- and iso-osmolar), c) level of ionization (ionic, non-ionic), and d) degree of polymerization (monomeric, dimeric). The non-ionic, low- or iso-osmolal contrast media are the most used in clinical practice due to their excellent tolerability and safety profile. Concerns exist on the higher tolerability of iodixanol, a non-ionic, dimer, iso-osmolal contrast medium, as compared to the low-osmolal contrast media. While early studies suggested a role for osmolality in the pathogenesis of contrast-induced nephropathy at high osmolalities (> 1000 mOsm/kg of H2O), it may be that either osmolality in the range of 290 to approximately 800 is not toxic to the kidney, or that for contrast media within this range of osmolality other characteristics of contrast media, such as direct molecular toxicity or viscosity, play a greater role. Iodixanol, indeed, is more viscous than low-osmolal contrast media. Finally, because of the higher cost of iodixanol, a cost-effectiveness analysis is mandatory.