By Toni Clarke

(Reuters) - The effectiveness of Cempra Inc's antibiotic to treat community-acquired pneumonia outweighs the risk of liver injury, an advisory panel to the U.S. Food and Drug Administration narrowly concluded on Friday.

The panel voted 7-6 that the drug, solithromycin, should be approved to treat the kind of pneumonia that recently affected U.S. presidential candidate Hillary Clinton. The FDA is not obliged to follow the recommendations of its advisory panels but typically does so.

Panelists voted unanimously that the drug works as well as the potent antibiotic moxifloxacin. But most said the company had not fully characterized the potential risk of liver injury.

Clinical trials showed a greater number of patients taking solithromycin developed elevated liver enzymes than those taking moxifloxacin. Elevated liver enzymes can be a sign of underlying liver damage.

In Cempra's clinical trials the elevations were transient and there were no cases of acute liver injury. Even so, panelists recommended the company be required to conduct additional studies to further assess the potential liver risk after the drug has been approved.

"I feel we could wait if the bugs would just slow down," said Ellen Andrews, executive director of the Connecticut Health Policy Project.

Solithromycin is descended from a notorious drug made by Sanofi SA called Ketek, or telithromycin. Ketek was approved by the FDA in 2004 but later linked to dozens of serious or fatal liver problems. It was eventually discontinued.

The Ketek episode prompted congressional investigations and accusations that the agency stifled concerns over the drug voiced by its own reviewers. On Friday agency reviewers stated that "there is a very clear signature of hepatic injury" in the solithromycin clinical trial data.

Solithromycin belongs to a class of antibiotics known as macrolides that include erythromycin, clarithromycin and azithromycin and are used to treat a wide range of bacterial infections. Roughly 50 percent of the most common bacterium, the pneumococcus that cause chest and other infections, are resistant to macrolides, making the quest for new antibiotics pressing.

Community-acquired pneumonia develops in people with limited or no contact with medical institutions or settings.

(Reporting by Toni Clarke in Washington; Editing by Meredith Mazzilli and Dan Grebler)