Abstract:
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.
