Physicochemical parameters of x-ray contrast media

Osmolality, including "dynamic osmolality," which is observed during dilution in the plasma, viscosity, density, and partition coefficient of 11 commercially available contrast media and two new nonionic monomers were determined.

Osmolality was measured by vapor pressure osmometry, viscosity by determining flow in microcapillaries, and partition coefficient in n-octanol or n-butanol/water mixtures by inductively coupled plasma mass spectroscopy or x-ray fluorescence analysis of iodine concentrations.

For the commercially available contrast media, the following statistically significant ranking of osmolality was obtained at 300 mg iodine/mL: iotrolan << ioxaglate < iopromide < iopamidol < ioversol = iohexol < iopentol << meglumine diatrizoate. The novel nonionic monomers, ZK 119095 and ZK 139129, had very low osmolalities, and ZK 139129 was isotonic to blood. The partition coefficient for the system n-octanol/water was lowest for the ionic compounds ioxaglate and diatrizoate followed by the nonionic dimer iotrolan. In n-butanol, iotrolan showed the lowest partition coefficient.

"Dynamic osmolalities" of contrast media may differ from static values possibly because of the formation of "quasi-oligomers." Especially for ZK 139129, disaggregation occurred during dilution and the osmolality increased slightly. However, osmolality was lower than for any other monomer during the whole dilution process.