UPDATE 2-FDA staff question wider use of Lilly's Cymbalta

* Drugmaker seeks U.S. approval to sell Cymbalta for pain

* FDA to ask outside advisers about safety with wider use

* FDA's advisers to weigh possible new use Thursday

* Shares down 2.5 pct after another Lilly drug halted (Adds details from documents, share price, analyst comment)

By Susan Heavey

WASHINGTON, Aug 17 (Reuters) - U.S. government scientists raised safety concerns about using Eli Lilly and Co's (LLY.N) blockbuster antidepressant Cymbalta to treat pain, also noting that approval of the new use would likely cause "a substantial increase" in prescriptions among the wider population.

Food and Drug Administration staff, in documents released on the agency's website on Tuesday, said they would ask a panel of outside advisers about the potential for liver toxicity and whether broadening use of the drug would be appropriate.

The FDA released the documents ahead of a public meeting on Thursday to discuss the potential new use of the drug to treat conditions such as low back pain and osteoarthritis.

Shares of Eli Lilly were down 2.5 percent to $34.68 in afternoon trading on the New York Stock Exchange. Earlier on Tuesday the company said it had halted development of an experimental Alzheimer's disease treatment. [ID:nN17120793]

Cymbalta is already approved for depression, anxiety, diabetes-related pain and fibromyalgia, but Eli Lilly also wants permission to market it for chronic pain.

More than 50 million Americans experience chronic pain, according to the company. Treating such patients could help boost sales before Cymbalta loses its U.S. patent exclusivity in mid-2013.

Analysts expect the antidepressant to garner worldwide sales of $3.4 billion in 2010 and $3.7 billion in 2011, according to consensus forecast data from Thomson Reuters. It was unclear if the figures include approval of Cymbalta for chronic pain.

At the Thursday meeting, an FDA panel of outside experts will decide whether to back wider use of the drug. It was unclear how the FDA staff's review would affect the advisory panel's recommendation. The FDA will make the final decision, but it usually follows panel recommendations.

In nearly 200 pages of analysis, FDA staff said no new side effects cropped up in Lilly's pain studies and that the drug's risks were already pretty well characterized on its label.

Known side effects with Cymbalta, also know as duloxetine and first approved in 2004, include dizziness, nausea and drowsiness. Like other antidepressants, the drug already carries a strong "black box" warning about possible suicidal tendencies in children, teenagers and young adults.

At issue is how those risks might increase given potentially millions more users.

"Keep in mind that the approval of Cymbalta for the treatment of chronic pain will likely result in a substantial increase in the prescribing of the product in the general population," Bob Rappaport, head of the FDA division that oversees pain-related drugs, advised panelists in a memo.

Separately, Eli Lilly said current painkillers such as opioids and nonsteroidal anti-inflammatory drugs also carry risks, and that the company has a substantial risk-monitoring program already in place to help monitor Cymbalta's safety.

FDA staff also said Eli Lilly's clinical trials were well designed with an adequate mix and number of patients. But reviewers evaluating efficacy data identified "several key points" as "problematic," the FDA wrote in its review.

The drugmaker withdrew its earlier bid for pain use in November 2008 to add more data. It is unclear when the FDA may act as the new deadline for the agency's decision has already passed, Lilly's spokeswoman, Sonja Kay Popp-Stahly, said. (Reporting by Susan Heavey; additional reporting by Ransdell Pierson in New York; editing by John Wallace)