Maseeh uz Zaman, Nosheen Fatima


Iodinated contrast agents are among the most commonly administered drugs worldwide. In United State more than 80 million CT examinations are performed annually and almost half are performed with iodinated contrast agents[i].  Iodinated contrast media are used in imaging techniques to enhance the differences between body tissues on images. These have been in use since 1950 and in current era almost all medical imaging modalities use contrast agents to improve image interpretation.

Iodinated contrast agents are classified on the basis of their osmolar characteristics. Hyperosmolar contrast agents (HOCA) are 5-6 times more hyperosmolar than plasma. These are ionic, monomeric derivatives of tri-iodinated benzoic acid and its molecule dissociates in solution into anion and cation. The anion is iothalamate, diatrizoate or metrizoate while cation is sodium, meglumine or mixture of two.    In middle of 1980s, low osmolality contrast agents (LOCA) were introduced which are 2-2.5 time more hyperosmolar than plasma. LOCAs are either ionic dimers (like ioxaglate) or non-ionic monomers which don’t dissociate in solution (like iohexol, ioversol, iopamidol). Iso-osmolar contrast agent (IOCA) has osmolality equal to plasma and iodixanole is the only agent which non-ionic dimer.


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