Proof of the drug's efficacy adds a new weapon to the dwindling arsenal of antibiotics against these difficult-to-treat infections. Treating S. aureus infections is difficult because many strains have developed resistance to all penicillin-related antibiotics.
S. aureus now causes up to 2m infections and 90,000 deaths per year worldwide, most of them in health-care settings.
The FDA has approved the drug, Daptomycin, in 2003 for treating S. aureus-related skin infections. In this latest study, the research team tested daptomycin's ability to combat two specific types of infection caused by S. aureus, including MRSA strains.
The first type was bacteraemia, or bloodstream infection. The second was infective endocarditis, which is an infection of the inside lining of the heart.
The randomised, controlled trial enrolled 246 patients with bacteraemia, with or without endocarditis. Patients were randomly assigned to one of two treatment groups. One group received six milligrams of daptomycin per kilogram of body weight, administered intravenously once daily.
The other group received standard antibiotic therapy, which consisted of an initial four-day course of the antibiotic gentamicin plus a full course of either an antistaphylococcal penicillin or vancomycin, depending on bacterial susceptibilities.
The results showed Daptomycin was more successful at eliminating drug-resistant S. aureus, at 44.4 per cent success versus 31.8 per cent. However, the standard therapy slightly outperformed daptomycin for S. aureus without drug resistance, at 48.6 per cent success versus 44.6 per cent. Neither of these differences was statistically significant.
Additonally, both types of treatment took roughly eight or nine days to clear an MRSA infection.
"The rising prevalence of S. aureus infections and the organism's increasing resistance to drugs make these bacteria a growing threat to medical care throughout the world," said Ralph Corey, a professor of infectious diseases who participated in the study.
S. aureus bacteria are common in the environment. People whose immune systems have been weakened by disease or certain medical treatments, including surgery or receiving intravenous catheters, are at greater risk of infection.
For patients in hospitals, S. aureus is a leading cause of bloodstream infection and infection at surgical sites, among other problems.
For highly resistant strains, called methicillin-resistant S. aureus, or MRSA, the drug vancomycin has been the only consistently reliable treatment alternative. Recently, however, MRSA strains with resistance to vancomycin have appeared.
"Having another drug in our armamentarium against S. aureus not only will give physicians a new treatment option, but also may help slow the current troubling spread of drug resistance among these bacteria," said Vance Fowler, an associate professor of infectious diseases who participated in the study.
The researchers published their findings in the August 17, 2006, issue of the New England Journal of Medicine.