By Ed Susman, UPI Science News
SAN FRANCISCO, Sept. 26 (UPI) -- Even when laboratory tests show
bacteria have become resistant to some antibiotics, the medication may
still be successful in clearing these bugs from humans.
On Sunday, researchers said studies show that, for example, the common
antibiotic clarithromycin remains potent against infections in people
despite laboratory evidence that predicts it should fail in 20 percent
of cases.
At a symposium held in conjunction with an infectious disease
conference of the American Society for Microbiology in San Francisco,
doctors suggested the new findings are good news for scientists and
patients concerned about growing resistance of bacteria to antibiotics
-- but it doesn't mean that growing resistance to antibiotics can be
dismissed.
''We are telling doctors about all this resistance and they aren't
seeing clinical failures,'' said Dr. Donald Low, professor of medicine
and infectious diseases at the University of Toronto. Although there
are some cases in which laboratory tests are accurate in predicting
treatment results, other tests fail to give useable results.
''Many patients are responding to antibiotics despite telling them
there is resistance,'' Low said. Experts at the symposium said more
than 90 percent of patients given clarithromycin to clear bacterial
infections respond to the drug.
Researchers focused on the treatment of Streptococcus pneumoniae
infections -- one of the most frequent causes of pneumonia and other
respiratory infections. For years, the use of macrolide antibiotics -- a
group including clarithromycin -- has been the preferred treatment of
these infections.
Gary Doern, professor of pathology at the University of Iowa, Iowa
City, said about 70 percent of antibiotic use is offered to people for
respiratory infections.
Doern said recent reports indicated that as many as 20 percent of the
strains of S. pneumoniae bacteria are resistant to macrolides. But he
said those figures may overestimate the actual resistance.
He said use of outmoded laboratory tests and difficulty in getting
reproducible results from various laboratories make resistance data
hard to evaluate. ''It is a crap shoot,'' he said.
''What we find in the laboratory doesn't always correlate with clinical
outcomes in regard to macrolides,'' agreed Dr. Thomas Hooton, professor
of medicine at the University of Washington, Seattle.
However, Hooton said highly resistant strains of bacteria such as
Staphylococcus aureus and enterococci do correspond to what is found in
tests. Dr. Ronald Grossman, professor of medicine at the University of
Toronto, said that despite concerns about growing resistance to the
class of antibiotics known as macrolides, the new Canadian guidelines
for treatment of respiratory infections which will be published later
this year will still call for use of macrolide antibiotics in first
line treatment of respiratory infections.
