We may have enlisted some unreliable allies in the battle
against E coli and acute cystitis, according to
research in the February 23 issue of the Journal of
the American Medical Association (JAMA) which suggests
that not all antibiotics are created equal when it comes
to clearing such infections.
Amoxicillin-clavulanate, an increasingly
popular treatment option for cystitis, "should be considered
only when use of other first and secondline antibiotics
is not feasible," the researchers said in their study.
The race to keep ahead of increasing
antibiotic resistance sometimes demands that antibiotics
be pressed into service on a less than perfect evidence
base. E coli's resistance is greatest, of course,
to the standard treatment, trimethoprim-sulfamethoxazole,
which means that docs have to turn to fluoroquinolone
drugs such as ciprofloxacin.
But because we don't want to see
E coli develop resistance to ciprofloxacin, there's
been a move towards other antibiotics, notably amoxicillin-clavulanate.
The drug is safe and its properties are well known,
but it has been little studied in acute cystitis.
To correct this deficiency, researchers,
led by the University of Washington's Dr Thomas Hooton,
enlisted 370 women with acute uncomplicated cystitis.
Subjects were randomized to receive either amoxicillin-clavulanate
(500mg/125mg twice daily) or ciprofloxacin (250mg twice
daily) for three days and were followed up for four
months.
GREAT
HOPES DASHED
Of the women taking ciprofloxacin, 77% were clinically
cured at the study's end. But of those taking amoxicillin-clavulanate,
only 58% saw the infection disappear. In fact, amoxicillin-clavulanate
was not even as effective as ciprofloxacin in combating
strains known to be susceptible to amoxicillin, curing
only 60% of such infections, compared to a 77% cure
rate with ciprofloxacin.
The findings of this study will
surprise few specialists as a 2001 study in Infections
in Medicine found that more E coli strains
associated with cystitis were resistant to amoxicillin-clavulanate
than to fluoroquinolones. But then nobody ever claimed
that amoxicillin-clavulanate was more effective than
ciprofloxacin. Rather, the rationale for using the weaker
drug was that we have wasted too many antibiotics by
using them for trivial complaints so in an effort to
limit the use of stronger drugs, vital fluoroquinolones
are reserved for use in life-and-death situations.
Nothing in the new research changes
that equation, and the authors of the JAMA study
responsibly refrain from calling for the firstline use
of ciprofloxacin. Rather, they turn back to the humble
trimethoprim-sulfamethoxazole.
"Trimethoprim-sulfamethoxazole
should continue to be the firstline treatment for acute
cystitis if the woman has no history of allergy to the
drug and if the likelihood of trimethoprim-sulfamethoxazole
resistance is low," they concluded in their study. "In
areas where the likelihood of trimethoprim-sulfamethoxazole
resistance is high (greater than 20%) or in women who
have risk factors for trimethoprim-sulfamethoxazole
resistance, nitrofurantoin or a fluoroquinolone is an
appropriate choice."
JAMA Feb 23, 2005;293:949-55
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