(Recasts; adds details on safety issues, effectiveness, background on competitors; updates shares)

By Lisa Richwine

WASHINGTON, July 25 (Reuters) - Roche Holding AG's <ROG.VX> drug Actemra appears to help adults with rheumatoid arthritis, U.S. drug reviewers said in a summary released on Friday ahead of a key meeting on the product.

Abnormal liver enzymes were relatively common but most cases were mild to moderate, Food and Drug Administration staff said. The drug's effects on liver enzymes and blood fats known as lipids were not associated with health problems in the clinical trials, the summary said.

The FDA staff said they would ask an advisory panel that meets Tuesday whether the benefits of Actemra, which Roche bills as a potential blockbuster, outweigh known and potential risks and whether the intravenous drug should be approved.

The risk of infections appeared similar to other drugs that suppress the immune system, the FDA reviewers said.

Cancer was reported in some Actemra patients but the rate seemed consistent with the expected level for people with rheumatoid arthritis, they added.

Gastrointestinal perforations "may be slightly elevated" but were "uncommon," the reviewers said.

Roche shares gained 3.5 percent in Swiss trading.

The company is seeking FDA approval to sell Actemra for adults with moderate to severe rheumatoid arthritis.

Actemra is sold in Japan by Roche's partner Chugai Pharmaceutical Co Ltd <4519.T> but has yet to reach the market in the United States or Europe.

Known generically as tocilizumab, the drug works differently than other drugs on the market. It blocks interleukin-6 (IL-6), a protein involved in inflammation.

"The clinical trial experience has been extensive, but may not capture the full extent of safety concerns that may arise with long-term IL-6 inhibition," the FDA staff said.

Roche, in a separate summary, said Actemra was "generally well tolerated" and the potential side effects were "recognizable, reversible and usually not treatment-limiting."

Rheumatoid arthritis, or RA, is a joint inflammation that causes pain, stiffness, swelling and joint damage. More than 21 million people worldwide, including 2.5 million Americans, are estimated to have the disease, Roche said.

In company-funded studies, more patients treated with Actemra reported at least a 20 percent improvement in symptoms after 24 weeks of treatment. About 26 percent of placebo patients saw that level of benefit, compared with 59 percent treated with the highest Actemra dose. Patients in the studies also were given older drugs for the disease.

"Treatment with tocilizumab appears to be effective for patients with moderate to severely active RA," the FDA staff wrote.

The FDA will make the final decision on whether to approve Actemra in the coming months after hearing the advisory panel's recommendation. The agency usually clears drugs that win support from one of its panels of outside advisors.

The drugs widely used now for treating rheumatoid arthritis block tumor necrosis factor (TNF), another protein linked with inflammation. These drugs sharply improve treatment for the disease but up to 40 percent of patients do not adequately respond to them, Roche said.

The TNF drugs in use now include Abbott Laboratories Inc's <ABT.N> Humira and Enbrel, sold by Amgen Inc <AMGN.O> and Wyeth <WYE.N>. Both drugs had more than $3 billion each in 2007 sales. (Reporting by Lisa Richwine; Editing by Tim Dobbyn and Gerald E. McCormick)

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