Oral Amoxicillin-Clavulanic Acid Treatment in Urinary Tract Infections Caused by Extended-Spectrum Beta-Lactamase–Producing Organisms

BACKGROUND Extended-spectrum β-lactamases (ESBLs) are increasing problems. The involvement of ESBL-producing organisms is associated with higher rates of carbapenem usage in urinary tract infections (UTIs). Though some strains are susceptible to amoxicillin-clavulanic acid (AMC) in vitro, there is very less data about the consequences of AMC usage for such infections. OBJECTIVES The purpose of this study was to evaluate the clinical and microbiological outcomes of AMC treatment in UTIs caused by AMC-susceptible ESBL-producing organisms. PATIENTS AND METHODS A retrospective cohort study was conducted in a tertiary care hospital. Forty-six out of 652 patients (F/M ratio: 32/14; mean age: 43.9 years) with ESBL-positive UTIs were eligible for this study. These patients had cystitis (n = 23), vesicoureteral reflux (n = 7), hyperactive bladder (n = 6), and prostatitis (n = 10). Data was collected via chart review and was statistically analyzed. RESULTS AMC-susceptible ESBL-producing Escherichia coli, Klebsiella pneumoniae and K. oxytoca were identified as the causative agents in 31, 14, and 1 patients, respectively. Thirty-nine (84.7%) out of 46 patients were successfully treated with oral AMC. Additionally, 2 (4.3%) patients' urine cultures turned to be negative, though their clinical complaints and leukocyturia had continued. In the remaining 5 (10.8%) patients, no positive clinical and microbiological response was obtained. Increased minimum inhibitory concentration levels of AMC (from 4 to > 256 µg/mL) were detected in these patients and the treatment failures were attributed to this developing resistance. We found that therapeutic failure was significantly more frequent in Klebsiella spp. than in E. coli (33.3% vs 6.5%, P = 0.029). Furthermore, no treatment failure was observed in pathogens with minimum inhibitory concentrations (MICs) ≤ 2 mg/mL, and the high AMC MIC (8 mg/mL) was associated with resistance development and therapeutic failure (71.4% vs. 5.1%, P = 0.0001). CONCLUSIONS Our results suggested that amoxicillin-clavulanic acid may be a good oral antimicrobial which can be used for treatment of ESBL-positive UTIs, if the causative agent is susceptible to this antibiotic. However, some strains may develop resistance during therapy, especially in those exhibiting high AMC MICs.