Establishing Safeguards for the Use of Imaging-Related Drugs

Thomas J. Barrs

Am J Health Syst Pharm. 2002;59(8) 

In This Article


Radiopaque agents are used to enhance visualization of selected anatomical features during radiographic studies.[1] Iodinated compounds, constituting one category of these, are administered by various routes, including injection and administration into the gastrointestinal tract. Iodinated radiopaque medications are also called radiographic, angiographic, contrast, and radiocontrast agents and sometimes dyes and are usually referred to as agents or media rather than as drugs, medications, or pharmaceuticals. However, for intravascular iodinated radiocontrast agents, I prefer the term "intravascular iodinated radiopaque medications" (IIRMs). This descriptor is derived from nomenclature in Drug Facts and Comparisons, which, along with Micromedex, is one of the few commonly available sources of information on these medications. It is specifically IIRMs administered intravenously or intraarterially that are associated with nephrotoxity.[2,3] Furthermore, I prefer "medications" to "agents" to emphasize their pharmaceutical nature.

A recent case report described the use of N-acetylcysteine as a renoprotective agent in a patient at risk for IIRM-induced renal impairment.[4] The patient, an 84-year-old man with chronic renal insufficiency, underwent coronary angiography. N-acetylcysteine 600 mg was administered orally every 12 hours for two doses before and two doses after the infusion of 125 mL of iohexol (Omnipaque 350, Nycomed), a low-osmolality contrast agent. The patient was hydrated with 5% dextrose and 0.45% sodium chloride injection before the procedure. The serum creatinine concentration was unchanged at 2 mg/dL 48 hours after the administration of iohexol. For me, two features of the case report stood out. First, no mention was made of the route of administration of iohexol. Second, although the subject of nephrotoxicity induced by contrast media was discussed, nothing was said to indicate that this drug-induced renal impairment is specifically caused by IIRMs.

Another example of the inattention demonstrated toward these drugs comes from Drug Facts and Comparisons, which divides radiopaque agents into three categories on the basis of osmolality (high-osmolality contrast media [HOCM] and low-osmolality contrast media [LOCM]), structure (monomeric and dimeric), and ionic status.[5] While this classification is accurate for iodinated compounds, it excludes barium sulfate, a separate category in and of itself.[6] In addition, paramagnetic agents are improperly included in this classification. Although these agents enhance magnetic resonance imaging, they are not considered radiopaque medications.

Correctly, there are two categories of radiopaque drugs. One comprises various preparations of barium sulfate for alimentary-tract administration. The other includes numerous iodinated organic compounds for alimentary-tract and parenteral administration. Iodinated compounds are subdivided into LOCM for intravascular administration (IIRMs) and HOCM for alimentary-tract, intravascular, and nonintravascular parenteral use. Examples of nonintravascular administration are intraductally with endoscopic retrograde cholangiopancreatography and intraarticularly with arthrographic imaging. Examples of LOCM are iohexol (nonionic), ioxaglate meglumine and ioxaglate sodium (ionic), and iodixanol (nonionic). HOCM are ionic compounds -- for example, diatrizoate sodium and diatrizoate meglumine.