All contrast agents are not equal
The two main types of iodine-based contrast media are ionic and nonionic. The development of ionic contrast media in the 1920s and 1930s allowed radiologists to visualize vessels and organs on various imaging studies. However, these have some degree of toxicity, and the introduction of non-ionic media in the 1970s led to fewer adverse reactions. 1 Newer contrast media include low-osmolar ionic, iso-osmolar and gadolinium-based media. The last type is used in magnetic resonance imaging.
Adverse reactions are more common with ionic contrast media
Nonionic contrast media are well tolerated and have a better safety profile than ionic agents (Table 1). 2,3
A previous adverse reaction to intra-vascular contrast media increases the risk of a subsequent reaction
The risk of a subsequent adverse reaction is 17%–35% with ionic contrast media and 5% with nonionic media. 1
High-osmolar ionic contrast media should not be used intravascularly
High-osmolar ionic contrast media are no longer used intravascularly because of the increased risk of adverse reactions. Safer, low-osmolar ionic formulations are now available. Although higher costs limited the widespread use of nonionic agents in the past, the cost differential is now low. 4 There are only limited data available on the use of iso-osmolar contrast agents.
Avoid oral administration of ionic contrast media
If aspirated, ionic contrast media are much more likely than nonionic media to be associated with adverse reactions. Reactions in the lungs include bronchospasm, pulmonary edema, increased pulmonary vascular resistance and histamine release from lung mast cells and basophils. 5 Avoid using ionic agents in endoscopy of the upper gastrointestinal tract or when checking chest drains or assessing the position of nasogastric feeding tubes.
Footnotes
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Previously published at www.cmaj.ca
This article has been peer reviewed.
Competing interests: None declared.
For more information on the use of contrast media, see the American College of Radiology Manual on Contrast Media at www.acr.org/contrast-manual.
“Five things to know about …” is a new series that presents key statements on topics of interest to physicians. For author instructions, go to cmaj.ca.
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- All contrast agents are not equal
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- Avoid oral administration of ionic contrast media
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