Aminopenicillins vs non-aminopenicillins for treatment of enterococcal lower urinary tract infections

Aminopenicillins (APs) achieve urinary concentrations that exceed typical minimum inhibitory concentrations for enterococcal lower urinary tract infection (UTI). The local clinical microbiology laboratory discontinued routine susceptibilities on enterococcal urine isolates, and reports that 'APs are predictably reliable for uncomplicated enterococcal UTI'. The objective of this study was to compare outcomes of APs with non-APs (NAPs) for enterococcal lower UTIs. This was an institutional-review-board-approved, retrospective cohort of adults hospitalized with symptomatic enterococcal lower UTIs from 2013 to 2021. The primary endpoint was composite clinical success at 14 days, defined as resolution of symptoms without new symptoms and no repeat culture growth of the index organism. A non-inferiority analysis was utilized with a 15% margin, and logistic regression evaluated characteristics associated with 14-day failure. In total, 178 subjects were included: 89 AP patients and 89 NAP patients. Vancomycin-resistant enterococci (VRE) were identified in 73 (82%) AP patients and 76 (85%) NAP patients (P=0.54); in total, 34 (38.2%) AP patients and 66 (74.2%) NAP patients had confirmed Enterococcus faecium (P<0.001). Amoxicillin (n=36, 40.5%) and ampicillin (n=36, 40.5%) were the most commonly used APs, and linezolid (n=41, 46%) and fosfomycin (n=30, 34%) were the most commonly used NAPs. Fourteen-day clinical success rates for APs and NAPs were 83.1% and 82.0%, respectively [1.1% difference, 97.5% confidence interval (CI) -0.117 to 0.139]. Among the E. faecium subgroup, 14-day clinical success was observed in 27/34 (79.4%) AP patients and 53/66 (80.3%) NAP patients (P=0.916). On logistic regression, APs were not associated with 14-day clinical failure (adjusted odds ratio 0.84, 95% CI 0.38-1.86). APs were non-inferior to NAPs for treating enterococcal lower UTIs, and may be considered irrespective of susceptibility results.