Iohexol and iopamidol: second-generation nonionic radiographic contrast media

Iohexol and iopamidol are new second-generation nonionic contrast media. We review their physical/chemical properties and describe the improvements made over the first-generation nonionic prototype, metrizamide, and conventional ionic contrast media. The significance of low osmolar solutions is discussed and the relationship between osmolality and adverse reactions is emphasized. The convenience of a ready-to-use stable solution that offers an advantage over the lyophilized metrizamide in practical application is suggested. Clinical studies using randomized, double-blind comparison techniques are cited. An attempt is made to define the exact role for iohexol and iopamidol.