WASHINGTON – Government experts narrowly backed a Johnson & Johnson antibiotic as a treatment against pneumonia Wednesday, despite serious concerns about how the company studied the drug.

A Food and Drug Administration panel of antibiotic experts voted 7-6 that Doribax is effective at treating hospital-acquired pneumonia, a new use sought by the New Brunswick, N.J.-based manufacturer. A majority of panelists also said the drug seems safe for patients.

“I can't come up with a clear difference that would make doripenem different from all the other 'me-too' drugs that came before it,” said panelist James Leggett, a professor at Oregon Health Sciences University, referring to the drug by it's generic name.

But the panel also voted 9-4 against accepting studies the company submitted to support its application, complaining they were not statistically rigorous enough to prove the drug works as well as older therapies.

The group's recommendations are nonbinding, though the FDA often follows its advice.

Pneumonia is the most fatal infection associated with hospitals, according to the FDA. Strains found in hospitals are generally more virulent than others.

J&J based its application for Doribax on two studies designed to show that it worked at least as well as two older antibiotic therapies. But FDA scientists said before the meeting there were a number of problems with the research.

J&J evaluated Doribax's performance based on chest X-rays of pneumonia patients before and after they received the injectable drug. But the government's review of the application “revealed cases in which patients with worsening chest X-rays were evaluated as cures.”

Some panelists said J&J should have shown evidence that its drug actually saved at least as many lives as existing therapies. But the panel's one industry representative argued such an approach would require excessively large, lengthy trials.

“If you want new drugs and want new tools, it's important for us to identify practical compromises that will let us move down the road,” said John Rex, a vice president with AstraZeneca.

Fellow panelist Thomas Fleming said the FDA should not lower the bar simply because larger trials would require more work from companies.

“If we introduce antibiotics that aren't effective because they haven't been rigorously tested, I don't see how that benefits patients,” said Fleming, a professor of biostatistics at the University of Washington.

Doribax is already approved to treat infections of the inner-abdomen and urinary tract.

FDA is expected to make its decision on the new use of Doribax before the end of the month.

If the agency rejects Doribax, it could signal a tough standard for other companies developing hospital-acquired pneumonia drugs, including Theravance Inc., according to a note from Cowen & Co. analyst Rachel McMinn.

Shares of Johnson & Johnson rose 49 cents to close at $68.19.