TMP-SMX use often fails with resistant organisms. (Uncomplicated Urinary Tract Infections).

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, ...