Management of uncomplicated urinary tract infections (UTIs) has traditionally been based on 2 important principles: the spectrum of organisms causing acute UTI is highly predictable (Escherichia coli accounts for 75% to 90% and Staphylococcus saprophyticus accounts for 5% to 15% of isolates), and the susceptibility patterns of these organisms have also been relatively predictable. As a result, empiric therapy with short-course trimethoprim-sulfamethoxazole (TMP-SMX) has been a standard management approach for uncomplicated cystitis.

However, antibiotic resistance is now becoming a major factor not only in nosocomial complicated UTIs, but also in uncomplicated community-acquired UTIs. Resistance to TMP-SMX now approaches 18% to 22% in some regions of the United States, and nearly 1 in 3 bacterial strains causing cystitis or pyelonephritis demonstrate resistance to amoxicillin. Fortunately, resistance to other agents, such as nitrofurantoin and the fluoroquinolones, has remained low, at approximately 2%. Preliminary data suggest that the increase in TMP-SMX resistance is associated with poorer bacteriologic and clinical outcomes when TMP-SMX is used for therapy. As a result, these trends have necessitated a change in the management approach to community-acquired UTI. The use of TMP-SMX as a first-line agent for empiric therapy of uncomplicated cystitis is only appropriate in areas where TMP-SMX resistance prevalence is <10% to 20%. In areas where resistance to TMP-SMX exceeds this rate, alternative agents need to be considered.