Side Effects of Radiographic Contrast Media: Pathogenesis, Risk Factors, and Prevention

Table 2

Iodinated contrast media commonly used in clinical practice.

Name	Type	Iodine content (mg/mL)	mOsm/kg	Osmolality type
Ionic
Diatrizoate (Hypaque 50)	Monomer	300	1,550	HOCM
Metrizoate Isopaque (Conray 370)	Monomer	370	2,100	HOCM
Ioxaglate (Hexabrix)	Dimer	320	580	LOCM
Nonionic
Iopamidol (Isovue-370)	Monomer	370	796	LOCM
Iohexol (Omnipaque 350)	Monomer	350	884	LOCM
Iodixanol (Visipaque 320)	Dimer	320	290	IOCM

Ionic and nonionic contrast media may be monomeric or dimeric; 3 iodine atoms are present on each benzene ring of the contrast medium: if a contrast molecule contains only 1 benzene ring, it is called a monomer; if it contains 2 benzene rings, it is called a dimer. In solution, ionic contrast media break up into their anion and cation components, thereby increasing osmolality, while nonionic contrast media do not break up in solution. Nonionic dimers are the ideal contrast media as they deliver the most iodine with the least effect on osmolality.
The osmolality of contrast media is compared with the osmolality of plasma. HOCM: high-osmolar contrast media have the highest osmolality, that is, 5–8 times the osmolality of plasma. LOCM: low-osmolar contrast media have an osmolality still higher than plasma, that is, 2-3 times the osmolality of plasma. IOCM: iso-osmolar contrast media have the same osmolality as plasma.