Gilead Sciences (NASDAQ:GILD) couldn't convince the Food and Drug Administration last year to approve its inhaled antibiotic treatment for cystic fibrosis-related infections, but now it's got a panel of experts on its side.

Yesterday an FDA advisory committee voted 15 to 2 that the Gilead's aztreonam lysine was safe and effective at killing bacteria that cause lung infections in cystic fibrosis patients. The panel also voted 17 to 0 that Gilead was proposing the right dose.

Even with the backing from the FDA advisory committee, the approval isn't a slam dunk. The briefing documents to the committee brought up several issues with the antibiotic's clinical trials. The advisory committee seems to have shrugged them off, but the FDA makes the final decision, and it's been hard on antibiotics, recently turning down candidates made by Theravance (NASDAQ:THRX), Pfizer (NYSE:PFE), and Johnson & Johnson (NYSE:JNJ).

On the plus side, Gilead has experience changing the minds of regulators. The EU's Committee for Medicinal Products for Human Use originally said no to the drug, but reversed course after Gilead appealed. The PDUFA date for the drug is Feb. 13, 2010, so Gilead and investors won't have to wait too long to find out if the FDA will do the same.

The "aztreonam" part of aztreonam lysine is the active ingredient in Elan's (NYSE:ELN) injected antibiotic Azactam, which was originally developed by Bristol-Myers Squibb (NYSE:BMY). If the FDA signs off on the drug, it'll compete directly with Novartis' (NYSE:NVS) Tobi, which is inhaled like aztreonam lysine.

The approval isn't a do-or-die situation for Gilead; its drugs to kill HIV are a lot more important than its efforts to kill bacteria. Still, an approval in the U.S. would move the drugmaker closer to its goal of becoming more diversified.