Oct. 27, 2008 (Washington, D.C.) -- Call it an outbreak of the "superbug of superbugs." For what researchers believe is the first time, there's been a small cluster of methicillin-resistant Staphylococcus aureus (MRSA) that failed to respond to Zyvox. That's an antibiotic that can be used as a last resort when others fail.
The report of 12 such cases at a Spanish hospital comes at a time when new treatments for resistant MRSA infections are desperately needed, says Michael Scheld, MD, of the University of Virginia School of Medicine in Charlottesville.
At a major medical meeting here, researchers reported on several experimental antibiotics that appear to be safe and effective against MRSA. "What we need is a very potent anti-MRSA drug that can be taken orally," Scheld says. "Zyvox doesn't fit that bill."
MRSA is a bacterium that causes infections in different parts of the body, including the skin, bloodstream, lungs, and urinary tract. About 94,000 Americans get serious MRSA infections each year and 19,000 die, according to the CDC.
The new research was presented here at a joint meeting of the American Society for Microbiology and the Infectious Diseases Society of America. Scheld is co-chair of the committee that chose which studies to highlight at the meeting.
Zyvox-Resistant MRSA Outbreak
Miguel Sanchez, MD, of the Hospital Clinico San Carlos in Madrid, says the 12 cases of Zyvox-resistant MRSA occurred in the hospital's intensive care unit during a two-month period this spring. Half of the patients died.
While doctors have reported isolated cases of Zyvox-resistant MRSA, "this is the first clinical outbreak to the best of our knowledge," he says.
Nine patients had the same mutation of resistant MRSA, which suggests the superbug spread from patient to patient, Sanchez says.
The outbreak was controlled by ensuring that health care workers donned gowns, gloves, and other protective gear in the ICU and by slashing the use of Zyvox, according to Sanchez. Resistance can develop when a bug is exposed to, but not completely wiped out, by an antibiotic.
Fortunately, all of the strains were susceptible to treatment with antibiotics other than Zyvox, he says. No new cases have been reported since the end of June.
One of "the message[s] is that we were capable of controlling [the outbreak] relatively quickly," Sanchez says.
The cluster of cases should serve as another reminder not to take antibiotics unless they are absolutely needed, says Robert Daum, MD, of the University of Chicago. Resistance to Zyvox "has been very infrequent" in the eight years since it came on the market, he tells WebMD. But "the [bug] will figure out this drug if it's exposed to it."
Experimental Drugs Fight MRSA
In other research presented at the meeting, the experimental antibiotic ceftaroline cured skin infections caused by MRSA in 95% of patients. That was the same success rate observed with the older combination of the antibiotics vancomycin and aztreonam. All the treatments were given intravenously.
"Most of the patients came into the study with wounds or abscesses. After treatment, their infection was cured," says Tanya Baculik, MD, of Cerexa Inc., a division of Forest Labs. Forest Labs funded the study.
Ceftaroline fights bugs other than MRSA, too. "Most other common pathogens are also killed" by the drug, she tells WebMD.
The study pitted ceftaroline against vancomycin plus aztreonam in about 700 patients. The portion of people who experienced side effects was similar in both groups.
The data will be submitted to the FDA in an effort to gain marketing approval for the new drug in the near future, according to Baculik.
In a second study, the experimental drug PTK 0796 wiped out MRSA infections in 98% of patients, compared with 93% of those treated with Zyvox.
There were no serious adverse events associated with use of the new drug, says Robert Arbeit, MD, of Paratek Pharmaceuticals in Boston. Paratek makes the drug and sponsored the research.
The study involved 188 people with MRSA who were given either PTK 0796 or Zyvox intravenously for four days and then orally for about six days.
The next step is a larger study pitting PTK 0796 against Zyvox, says Paratek.
The antibiotic Iclaprim also proved effective against skin infections caused by MRSA and other bugs, other research showed. It cured infections in 93% of patients vs. 98% of those given Zyvox.
The intravenous drug, which is currently awaiting FDA review, was studied in about 1,000 patients. Manufacturer Arpida AG of Reinach, Switzerland, funded the work.