Shares of Cubist Pharmaceuticals ( CBST) were rising Tuesday, a day after a panel of medical experts recommended new uses for the company's Cubicin antibiotic. However, the recommendation by an advisory committee of the Food and Drug Administration wasn't a clear-cut endorsement. The panel agreed unanimously that Cubicin could be used to treat a dangerous bacterial blood infection known as bacteremia. But it only voted 5-4 to support Cubicin as a treatment for infective endocarditis, a potentially fatal disease caused by bloodstream bacteria attacking heart valves. The FDA isn't bound by recommendations by advisory committees, but it usually agrees. The agency may act late this month. The split vote on endocarditis presents a dilemma for the FDA: Does it reject a drug for which there is limited clinical trial support? Or does it approve the drug for a disease for which there are few existing treatments? Cubicin was approved by the FDA in September 2003 as a treatment for skin infections caused by certain bacteria, including some strains that have become resistant to a class of drugs that includes penicillin. Cubist began selling Cubicin in the U.S. in November 2003. The European Union granted approval for Cubicin as a skin- and soft tissue-infection treatment in January. Chiron ( CHIR) has the license to market Cubicin in the EU. Shares of Cubist rose $1.22, or 5.2%, to $24.66 Tuesday. Trading volume was nearly triple the daily average for the past three months. Shares were halted by Nasdaq on Monday while the FDA advisory panel reviewed Cubicin. Cubist's effort to expand the scope of Cubicin represents not only a time-honored R&D strategy but also an attempt to build doctors' arsenal against bacterial infections that have few treatments. Securing more uses of Cubicin "can offer physicians a much-needed therapeutic alternative for patients with these serious infections," Dr. Ralph Corey, a Duke University Medical Center infectious disease specialist, said Monday. Corey chaired the independent medical group that assessed the results of the Cubist-sponsored trial.