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CHICAGO -- Patients who underwent abdominal or pelvic CT imaging with a low-osmolar contrast agent reported more discomfort during the exam than patients who received an iso-osmolar agent, researchers said here.

In a prospective, randomized, double-blind study, patients given iopamidol experienced nearly double the rate of moderate to severe discomfort compared with patients who received iodixanol (67.3% versus 35.1%, P<0.0001), reported Frederick Weiland, MD, from Sutter Roseville Medical Center in Roseville, Calif., and colleagues at the Radiological Society of North American annual meeting.

The use of the low-osmolar iopamidol also caused more heat sensation compared with iso-osmolar iodixanol (64% versus 29.1%, P<0.0001), the group added.

Iodixanol (Visipaque) is an iso-osmolar contrast agent with an osmolality equal to that of blood at 290 mOsm/kg of water. Iopamidol (Isovue) has an osmolality of 796 mOsm/kg of water.

Previous clinical research has demonstrated that iso-osmolar contrast agents cause less patient discomfort than low osmolar agents during CT scans, but the contrast was delivered by intra-arterial injection in those studies, the authors pointed out.

"It is not clear if data are still relevant to today's clinical practice, particularly to intravenous contrast-enhanced CT procedures using a power injector," they wrote.

Among 299 evaluable patients (mean age 58) enrolled in Europe and the U.S., 51 patients received iodixanol (320 mgI/mL) and 149 received iopamidol (370 mgI/mL) for contrast-enhanced CT of the abdomen and/or pelvis. Patients were excluded if they had a history of adverse reactions to contrast agents or if they were on dialysis.

The study's primary endpoint was the presence and intensity of discomfort as verbally rated by patients on a scale of zero (no pain) to 10 (severe) within 10 minutes of contrast agent injection. The secondary endpoint was the impact of patient discomfort on image quality.

The patients who received iopamidol reported more severe discomfort (16.3% versus 2.6%, P=0.0004) and severe heat (15% versus 2.6%, P=0.0008) compared with iodixanol.

There was a trend for more patients who received iodixanol to report less or no discomfort versus those who got iopamidol, although the result did not reach statistical significance (21.2% versus 7.5% ), the authors stated.

There was also a trend for iodixanol administration leading to better image quality (P=0.0508) with 95.4% of iodixanol-enhanced images rated as excellent versus 89.9% of iopamidol-enhanced scans.

"We believe this study demonstrates that contrast media composition and osmolality may be key determinants of patient comfort," Weiland said, adding that less discomfort translated into less movement during the scanning procedure, which allowed for better imaging.

"Reactions to iodinated contrast agents occur uncommonly and are typically classified into allergic-like and physiologic," commented session moderater, Peter Liu, MD, of the University of Michigan Medical Center in Ann Arbor.

"The authors of this study looked more at patient comfort and safety, that is, subjective complaints associated with the contrast administration, rather than true reactions," he told 番茄社区app in an email.

"The comparison agent was iopamidol (Isovue-370) which has a higher iodine content and viscosity than used for many routine CT scans of the abdomen and pelvis. It is possible that these characteristics contributed to the subjective feelings that were reported in the iopamidol group from this study," Liu wrote.

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