Empiric use of trimethoprim-sulfamethoxazole (TMP-SMX) to treat uncomplicated UTIs may be contributing to both TMP-SMX resistance and multidrug resistance, it was revealed at the recent Infectious Diseases Society of America meeting in San Diego.

New findings from a national database suggest that high levels of resistance to TMP-SMX (>20%) have developed in six out of nine regions of the United States among Escherichia coli UTI isolates, with the highest levels generally in the South. No clear correlation was found between TMP-SMX resistance and fluoroquinolone resistance rates among E. coli isolates, however.

The investigators found similar trends among other enteric gram-negative UTI isolates, but these tended to be more susceptible to TMP-SMX than E. coli. “Clinicians in their offices don’t usually have laboratory results to guide therapy for UTIs, so they treat empirically with TMP-SMX,” said Clyde Thornsberry, PhD, chief research advisor at Eurofins Medinet in Herndon, Va. “Some communities are now seeing resistance rates greater than 20%, indicating that they need to think about using another empiric agent because of the increased risk of failures with TMP-SMX. More often, these alternative agents are either levofloxacin, ciprofloxacin, or nitrofurantoin.”

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Increased resistance to TMP-SMX among E. coli and its variability in different regions emphasize the importance of local surveillance to guide management and treatment of uncomplicated UTIs, the researchers concluded.