Context: The high prevalence of resistance to trimethoprim-sulfamethoxazole and other antimicrobials among Escherichia coli causing acute cystitis in women has led to increased use of alternative antibiotics. One such antibiotic, amoxicillin-clavulanate, has not been well studied.
Objective: To compare the efficacy of a 3-day regimen of amoxicillin-clavulanate to that of a 3-day regimen of ciprofloxacin in the treatment of acute cystitis in women. The primary study hypothesis was that the amoxicillin-clavulanate and ciprofloxacin treatment groups would differ in clinical cure.
Design, setting, and patients: Randomized, single-blind treatment trial of 370 women, aged 18 to 45 years, with symptoms of acute uncomplicated cystitis and a urine culture with at least 10(2) colony-forming units of uropathogens per milliliter from a university student health center or a health maintenance organization.
Interventions: Women were randomly assigned to receive amoxicillin-clavulanate (500 mg/125 mg twice daily) or ciprofloxacin (250 mg twice daily) for 3 days and were followed up for 4 months.
Main outcome measures: The main outcome measure was clinical cure. Secondary study outcomes of interest were microbiological cure and vaginal E coli colonization at the 2-week follow-up visit.
Results: Clinical cure was observed in 93 (58%) of 160 women treated with amoxicillin-clavulanate compared with 124 (77%) of 162 women treated with ciprofloxacin (P<.001). Amoxicillin-clavulanate was not as effective as ciprofloxacin even among women infected with strains susceptible to amoxicillin-clavulanate (65 [60%] of 109 women in the amoxicillin-clavulanate group vs 114 [77%] of 149 women in the ciprofloxacin group; P = .004). The difference in clinical cure rates occurred almost entirely within the first 2 weeks after therapy. Microbiological cure at 2 weeks was observed in 118 (76%) of 156 women treated with amoxicillin-clavulanate compared with 153 (95%) of 161 women treated with ciprofloxacin (P<.001). At this visit, 45% of women in the amoxicillin-clavulanate group compared with 10% in the ciprofloxacin group had vaginal colonization with E coli (P<.001).
Conclusions: A 3-day regimen of amoxicillin-clavulanate is not as effective as ciprofloxacin for the treatment of acute uncomplicated cystitis, even in women infected with susceptible strains. This difference may be due to the inferior ability of amoxicillin-clavulanate to eradicate vaginal E coli, facilitating early reinfection.