Cephalon Inc. has failed to win a U.S. panel's backing to expand marketing of its painkiller Fentora to include patients without cancer because of concern that the narcotic would be misused.

Outside advisers to the Food and Drug Administration voted 17-3 Tuesday against wider use of Fentora, saying Cephalon lacked proof that its proposed safeguards to restrict access to the drug would work. The FDA usually follows the recommendations of its panels, though it isn't required to do so.

Fentora, a fast-acting tablet that dissolves in the mouth, is approved to relieve sudden episodes of cancer pain in adults already taking other opioids, morphine-like drugs, around the clock. Overdose and use in patients without a tolerance for narcotics has led to at least five deaths since Fentora was approved in September 2006.

"It's very scary to release this amount of very, very potent opioid to the American population," said panel member Charles Cortinovis, a clinical assistant professor at the Veterans Affairs Medical Center in Pittsburgh. "I'm sure there are some people who would benefit from this. But I think the number in the population would be very, very small."

Fentora brought in $135 million in sales for Cephalon, based in Frazer, Pa., last year, or 7.6 percent of the company's revenue. While doctors already prescribe the drug predominantly to patients without cancer, expanded approval may add $70 million, or 52 percent, to Fentora sales by 2010, according to Natixis Bleichroeder analyst Corey Davis.

"It's clearly a setback for the company," Davis said Tuesday in an e-mail. "The company emerged looking like a model corporate citizen for their proposal of a novel risk management plan that's in society's best interest, but that probably won't help the stock anytime soon."

Cephalon, which produces several products in Salt Lake City, was halted Tuesday in composite trading on the Nasdaq Stock Market and has fallen 24 percent in the past 12 months.

Once a drug is approved by the FDA, doctors are free to prescribe it for other purposes. Drugmakers can't promote such "off-label" uses, and insurers sometimes limit coverage. Lack of training for physicians increases the risk of misuse and medication errors, Eric Floyd, Cephalon's vice president of regulatory affairs, told the panel, meeting in Gaithersburg, Md., Tuesday.

"There is no other way to control it than to educate the patients and physicians," which the company is barred from doing for uses that aren't FDA-approved, Floyd said. "That's why we're here today."