Effect of prophylactic, low dose cephalexin on fecal and vaginal bacteria.

Effective prophylactic antimicrobial therapy for recurrent urinary tract infections depends upon the creation of minimal antimicrobial resistance in the fecal and vaginal flora. Cephalexin is known to be useful for prophylaxis clinically but substantial resistance has been reported in vaginal and rectal Escherichia coli at doses of 2 gm. per day. The effect of 250 mg. cephalexin nightly was studied in 23 women with recurrent bacteriuria who were treated for 6 months. Of the 23 patients 22 remained free of infection for 132 months of observation. Despite heavy carriage of Escherichia coli in the rectal and vaginal reservoirs during therapy, Escherichia coli resistant to 32 micrograms per ml. cephalexin did not occur. These observations explain the prophylactic effectiveness of cephalexin when used in small amounts of single nightly dosages.