Physicochemical Properties of Iodixanol

Iodixanol, the radiopaque in Visipaque, is a new nonionic, dimeric roentgen contrast medium for intravascular use. Compared to aqueous solutions of nonionic monomers, which have a higher osmolality than blood, aqueous solutions of iodixanol have a lower osmolality due to the dimeric structure of the molecule. As a consequence of this advantageous property, solutions of all clinical concentrations of iodixanol can be made isotonic by the addition of salts of the key electrolytes sodium and calcium to the formulation. The viscosity of all iodixanol (Visipaque) solutions is less than or equal to that of iohexol (Omnipaque) 350 mg I/ml. Iodixanol itself is an amorphous and hygroscopic solid which is freely soluble in water. Partition coefficients show that iodixanol is even more hydrophilic than the nonionic monomers such as iohexol. The high hydrophilicity and the good aqueous solubility of iodixanol are due to the hydroxyl group in the dimer linkage and the hydrophilic amide side chains of the molecule.