UPDATE 2-US FDA sees varying risk from MRI agents

* Risk seen highest with GE’s Omniscan, Bayer’s Magnevist

* FDA to bring issue to December advisory panel

* FDA staff want labels to reflect varying risk levels (Recasts first paragraph to emphasize some agents carry higher risk; adds company comments)

WASHINGTON, Nov 17 (Reuters) - Some contrast agents used with magnetic resonance imaging scans appear to carry a higher risk of a potentially fatal skin disease than others, U.S. drug reviewers said in documents released on Tuesday.

The Food and Drug Administration said a staff review found the highest risk of the skin disease, nephrogenic systemic fibrosis (NSF), was associated with GE Healthcare's GE.N Omniscan, Bayer AG's BAYGn.DE Magnevist and Covidien's COV.N Optimark.

The lowest risk was associated with Prohance and Multihance, made by Bracco Diagnostics, the agency said, adding “the data do not appear to rule out an NSF risk for each of the agents.”

The agency said the staff review that found variations among the drugs had limitations and it would take the issue to a panel of outside experts that meets in December.

The products, used to help make MRI scans easier to read, have been given to millions of patients. They are members of a family known as gadolinium-based imaging agents. The FDA announced in 2007 it was requiring a strong “black box” warning on all of the drugs to alert physicians that patients with certain kidney and liver conditions were at risk for for NSF.

Staff in the FDA’s drug safety unit said the magnitude of the risk “does not compel removal of specific (imaging agents) from the U.S. market” but recommended that the drug labels note the varying levels of risks with each product.

NSF triggers thickening of the skin, organs and other tissues that makes it difficult to move and can lead to broken bones, although the exact cause is unclear. There is no effective treatment.

FDA reviewers said the extent of risk from any of the agents was unknown. One study of Omniscan estimated the chances of developing NSF was 4 percent among patients with severe kidney impairment.

Covidien spokeswoman Erica Abbett said the company had voluntarily modified the Optimark label to say it should not be used in patients with severe kidney impairment, which affects less than 0.5 percent of the U.S. population.

The company decided “it was prudent to act now, rather than wait for a causal link... to be established” between the imaging drugs and NSF, Abbett said.

“We have concluded that Optimark contrast agent should be reserved for the vast majority of patients - more than 99 percent - where the benefits are well established,” she said.

Bayer spokeswoman Marcy Funk said the company’s product, Magnevist, was the most widely used and widely studied MRI contrast agent on the market.

She said the safety issues were “complex” and Bayer “looks forward to the opportunity to participate in a scientific discussion” at the FDA panel meeting.

Magnevist has “a well-documented safety profile,” she said.

GE Healthcare spokesman Ryan Fitzgerald said the strong warning about NSF on Omniscan had made an impact and the company had not received any reports of the problem since late 2007.

He said the company had been “extremely proactive with physicians getting the word out. We feel very comfortable that the current labeling has reduced the risk of NSF.” (Reporting by Lisa Richwine; Editing by Gunna Dickson and Tim Dobbyn)