Infections Now Resistant to Old Antibiotic
Polymyxin B Joining List of Antibiotics That Are Facing Resistance From Infections
Oct. 30, 2009 (Philadelphia) -- An old antibiotic, largely abandoned after
causing kidney ailments some 50 years ago, has become the treatment of last
resort for some drug-resistant infections.
But now there are signs that bacteria are developing resistance to this
antibiotic, called polymyxin B, as well, says Jason Kessler, MD, of Columbia
University in New York.
Polymyxin B is active against a variety of bacteria that cause respiratory
and urinary tract infections, Kessler says.
It acts like a detergent, destroying cell membranes and killing the
bacteria, he says. But that proved "quite toxic," particularly to the kidney,
As a result, many doctors stopped using it shortly after it was introduced
But the fact that it has not been widely used has an upside: Many bacteria,
such as Pseudomonas aeruginosa and Klebsiella pneumonia, which
are resistant to other classes of antibiotics, have not developed resistance to
polymyxin B, Kessler says.
For the study, Kessler and colleagues looked at blood samples and other
patient specimens tested in their microbiology lab between 2005 and 2008.
"Over 30% had resistance to at least five classes of antibiotics, meaning
they could probably only be treated with polymyxin B," he says. While the
portion of specimens that showed resistance to polymyxin B in 2008 was still
low, at 6%, that's a 50% increase from 2006, Keller reports.
He presented the findings at the annual meeting of the Infectious Diseases
Society of America.
“Our current experience has been that the drug is relatively
well-tolerated,” Kessler adds.
That could be because lower doses are used or because doctors can now better
manage kidney problems, says Neil Fishman, MD, of the University of
Pennsylvania. Fishman moderated a news conference at which the findings were
Fishman says that when he went to medical school in the early 1980s,
polymyxin B was never mentioned, except for this warning: "They’re toxic and
you’ll never have to use them."
"Then, about two and one-half years ago, I did have to use them,” he tells
"Because they are old antibiotics, there aren’t a lot of companies making
them and their use in increasing," Fishman adds. "It's getting increasingly
difficult to get them."