CHICAGO -- The use of trimethoprim/sulfamethoxazole in women with uncomplicated urinary tract infections caused by resistant organisms is likely to lead to both microbiologic and clinical failure, Raul Colodner said at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy sponsored by the American Society for Microbiology
TMP-SMX is the drug of choice in the treatment of uncomplicated community-acquired UTIs in areas where the resistance rate is less than 10%. However, some physicians in higher-resistance areas continue to prescribe it, reasoning that "in vitro" resistance does not necessarily reflect "in vivo" resistance, especially with a drug like TMP-SMX that achieves high urinary levels, said Mr. Colodner, deputy director of the microbiology laboratory at Ha'Emek Medical Center, Afula, Israel.
Urine cultures were positive in 544 of 618 healthy nonpregnant premenopausal women with UTI symptoms, all of whom had been prescribed 160 mg TMP-800 mg SMX twice daily for 5 days at the time the culture was taken.
Sensitive organisms grew in 71% of the 544, while 29% had a TMP-SMX--resistant strain. Es-cherichia coli was the most common organism in both groups, accounting for 77% of the TMP-SMX--susceptible organisms and 81% of the resistant ones, he said.
At 5-9 days after initiation of treatment, microbiologic cure had been achieved in 86% of 353 of the TMP-SMX--susceptible UTIs, compared with just 42% of 151 resistant ones. The remaining 40 patients dropped out, experienced adverse events, or were lost to follow-up. At 28-42 days, microbiologic cure rates were 93% of 285 TMP-SMX--susceptible UTIs vs. 70% of 76 resistant ones.
Clinical cure rates were similarly different: 88% vs. 54% at 59 days, and 93% vs. 70% at 28-42 days. Susceptibility to other antibiotics remained high: 89% of the TMP-SMX--resistant strains were susceptible to ciprofloxacin, 88% to ofloxacin, 85% to macrodantin, and 84% to augmentin. Only 54% were susceptible to cephalexin, however.
In Israel, where this study was conducted, 30%-40% of community-acquired uropathogens are resistant to TMP-SMX. Rates in the United States aren't quite that high but still exceed 10% in many areas. In a recent study, 16.8% of E. coli strains in the United States were resistant to TMP-SMX, ranging from 7.4% in Pennsylvania to 33.3% in Iowa (Int. J. Antimicrob. Agents 18:121-27, 2001).
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