Effect of trimethoprim and trimethoprim-sulfamethoxazole on development of drug-resistant vaginal and fecal floras.

Trimethoprim-sulfamethoxazole (TMP-SMX) or trimethoprim (TMP) alone was given on a random double-blind basis to 26 young women to treat urinary tract infections. Fecal and introital aerobic bacterial floras were identified at 1, 7, 14, and 42 days to analyze changes in these floras or development of resistance to TMP or TM-SMX. Neither TMP alone nor the TMP-SMX combination administered for 2 weeks selected a resistant fecal or introital flora. In the few individuals who had strains resistant to TMP or TMP-SMX before initiation of therapy, these organisms did not persist once therapy began. Both programs effectively cleared the introitus and rectal areas of Enterobacteriaceae. Concentrations of TMP adequate to inhibit the majority of Escherichia coli strains causing urinary tract infections were found in the vaginal secretions.