Gadolinium-DTPA-Diamides

Analogous to the development of the non-ionic X-ray contrast agents many years ago neutral chelates have been sythesized to reduce the osmotic pressure of the aqueous solutions. However, for MRI, injection volumes are used that are much smaller than for X-ray contrast agents. That means that the osmolality of the solutions is of minor importance for MRI contrast agents. The increase in blood osmolality after intraveneous injection of up to 0.3 mmol/kg Gd-DTPA will not cause disturbance of the organism s osmotic balance. 

Two extracellular contrast agents which contain neutral gadolinium chelates have entered the market gadodiamide (Omniscan) (Fig. 4 a) and gadoverse-tamide (Optimark) (Fig. 4b). 

Both ligands are amides of DTPA and are obtained by treating the dianhydride of DTPA with the corresponding amine (methyl amine [15] and methoxyethylamine [16] respectively). These gadolinium complexes are freely soluble in water. As expected, the osmolality of the 0.5 molar solution of gadodiamide is lower (0.79 osmol/kg water) than that of the 0.5 molar solution of Gd-DTPA (gadopentetate) (Table 2) [17,18]. 

Other parameters such as their physico-chemical properties, pharmacodynamics and the clinical application are very similar to the ionic agents gadopentetate and gadoterate [19]. 

Generic name Concentration (mol/1) Osmolality (osmol/kg water) Viscosity (cP) References 

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