The analysis looked at data from two earlier studies comparing linezolid and vancomycin, with a total of 160 patients with Methicillin-resistant Staphylococcus aureus (MRSA) hospital-acquired, or nosocomial, pneumonia. MRSA nosocomial pneumonia is the number one single microorganism that causes pneumonia in hospitalized patients, according to lead investigator Richard Wunderink, M.D.
"MRSA isn't treated well by common drugs that we use to treat infections," said Dr. Wunderink, Director of Research at Methodist University Hospital in Memphis, and Clinical Associate Professor of Medicine at the University of Tennessee in Memphis. "In the past, just about the only drug we had to treat it was vancomycin."
Dr. Wunderink found that in patients with MRSA pneumonia, those who received linezolid were more than twice as likely to survive compared with those receiving vancomycin. "This held true even after we adjusted for factors such as how sick the patients were, and if they had other health problems such as heart disease or kidney failure," he said.
He noted that currently, vancomycin is still considered standard treatment for MRSA pneumonia. "This is the first study done in a randomized, controlled way that shows a survival advantage of one appropriate antibiotic over another appropriate antibiotic. This study calls into question whether vancomycin should still be the standard treatment."
MRSA pneumonia usually develops in hospitalized patients who are elderly or very sick. The most common setting is patients who are on mechanical ventilation for other reasons. However, MRSA pneumonia is becoming more common in nursing home patients admitted to the hospital. MRSA can also cause other types of infections, many of which can be severe. The U.S. Centers for Disease Control and Prevention says that according to some estimates, as many as 100,000 persons are hospitalized each year with MRSA infections.
The two studies Dr. Wunderink analyzed were submitted to the U.S. Food and Drug Administration and European drug agencies as part of the approval process for linezolid, which was approved by the FDA in April 2000 and is sold under the brand name Zyvox. He noted that the studies were almost identical protocols, done to a large extent by the same investigators. "By combining two studies, we were able to look at a larger number of patients," he said.
He noted that because vancomycin is excreted by the kidneys and one of its side effects is kidney failure, doctors who prescribe vancomycin tend to underdose patients with kidney problems or those taking drugs that affect the kidneys. For these patients in particular, linezolid would be a more appropriate treatment for MRSA pneumonia, he said. "In general, we found that sicker patients, with more complex illnesses who had MRSA pneumonia, did better with linezolid," he said. The major drawback to linezolid, he noted, is its cost, compared with the generic vancomycin.