Staff from the U.S. Food and Drug Administration questioned whether Humira had a real benefit for people with the inflammatory bowel disease who had already tried other treatments. The FDA review comes ahead of an advisory panel, which will vote on whether to recommend the drug on Tuesday, August 28.

Humira, one of the world's top-selling drugs with projected sales of $9 billion this year, is already approved for six conditions, including rheumatoid arthritis. Abbott hopes to expand its use to people with moderate to severe ulcerative colitis, a chronic disease that causes ulcers in the colon and affects about 700,000 Americans.

The FDA rejected Abbott's first application for ulcerative colitis last November, saying results from clinical trials did not conclusively show the drug helped stop the symptoms of the disease, which include diarrhea, rectal bleeding, incontinence, abdominal pain, fever, fatigue and weight loss.

The reviewers on Friday said Abbott had submitted more analyses of the data in a second application, but they were "of questionable value."

As Humira already has known safety risks that include serious infections, the FDA staff said it was unclear if the injectable drug's modest benefits justify giving it to patients instead of other approved drugs, such as Johnson & Johnson's Remicade.

Humira met its main goal in two clinical trials, but FDA reviewers questioned whether a difference of less than 10 percent between Humira and a placebo was meaningful.

"Additional evidence could help support the evaluation of the benefit-risk assessment for a Humira (ulcerative colitis) indication," the FDA staff said in documents posted online on Friday. They said the company could consider increasing the dose, or proving that people who failed other drugs had more success with Humira.

Humira, first approved in 2003, will form the heart of a planned spin-off of Abbott's branded pharmaceutical business, to be called AbbVie. When completed late this year, it would be the largest-ever separation transaction in the healthcare sector.

Abbott has said new uses for Humira could add more than $1 billion in sales, though it did not specify projections for the drug's use in ulcerative colitis. Abbott is also testing Humira in other conditions, such as pediatric Crohn's disease.

If approved for ulcerative colitis, Humira would be the first biologic drug that people could inject themselves. Remicade, which works in a similar way to Humira, must be given intravenously in the hospital.

Shares of Abbott were up 13 cents to $65.46 in morning trading on the New York Stock Exchange.

(Reporting by Anna Yukhananov; Editing by Lisa Von Ahn and John Wallace)

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