List of products in the National Drug Code with proprietary name . This medication is an antibiotic used to treat bladder infections (such as acute cystitis or lower urinary tract infections) in women. It works by stopping the growth of bacteria. This antibiotic treats only bacterial infections. It will not work for viral infections (such as common cold, flu). Using any antibiotic when it is not needed can cause it to not work for future infections. Fosfomycin should not be used to treat infections outside the bladder (such as kidney infections).