Fosfomycin tromethamine is a broad-spectrum antibiotic approved by the U.S. Food and Drug Administration for single-dose oral treatment of uncomplicated urinary tract infections in women. Consultants for The Medical Letter on Drugs and Therapeutics summarize the data comparing fosfomycin with other antibiotics used in the treatment of urinary tract infections.

Fosfomycin is moderately active in vitro against Escherichia coli and other common urinary tract pathogens, including most strains of enterococci. When fosfomycin is used in multiple-dose regimens, resistance to the drug emerges rapidly, but cross-resistance with other antimicrobials is uncommon. Fosfomycin is excreted unchanged in the urine, where it reaches high concentrations that persist for 24 hours or longer.

In three randomized trials comparing a single 3-g dose of fosfomycin with nitrofurantoin given for seven days, norfloxacin for five days and cephalexin for five days, treatment with fosfomycin eradicated bacteriuria in 91 to 94 percent of women. Cultures were obtained once about five days after the start of treatment and again approximately one month after treatment. Bacteriuria was eradicated one month later in 73 to 81 percent of patients treated with fosfomycin. The eradication rates for fosfomycin were similar to those for norfloxacin and nitrofurantoin but were superior to those for cephalexin.

In two unpublished trials, a single dose of fosfomycin was less effective in eradicating bacteriuria than seven days of treatment with ciprofloxacin or 10 days of treatment with trimethoprim-sulfamethoxazole.

Although fosfomycin is generally well tolerated, diarrhea developed in 9 percent of patients participating in clinical trials. Vaginitis occurred in a lower percentage of patients.

Medical Letter consultants advise that a single dose of fosfomycin is moderately effective in the treatment of acute cystitis in women. Although single-dose therapy with fosfomycin may improve compliance, it is a relatively expensive treatment.