The spread of antimicrobial resistance challenges the empirical treatment of
urinary tract infections (UTIs). Among others,
nitrofurantoin is recommended for first-line treatment, but acceptance among clinicians is limited due to chronic
nitrofurantoin-induced lung toxicity and insufficient coverage of Enterobacteriaceae other than Escherichia coli.
Nitroxoline appears to be an alternative to
nitrofurantoin owing to its favourable safety profile, however data on its current in vitro susceptibility are sparse. In this study, susceptibility to
nitroxoline was tested against 3012 urinary clinical isolates (including multidrug-resistant bacteria and Candida spp.) by disk diffusion test and/or broth microdilution. At least 91% of all Gram-negatives (n = 2000), Gram-positives (n = 403) and yeasts (n = 132) had inhibition zone diameters for
nitroxoline ≥18 mm. Except for Pseudomonas aeruginosa,
nitroxoline MIC90 values were ≤16 mg/L and were 2- to >16-fold lower compared with
nitrofurantoin. In extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae and methicillin-resistant Staphylococcus aureus (MRSA), MIC90 values of
nitroxoline were two-fold higher compared with non-ESBL-producing enterobacteria and
methicillin-susceptible S. aureus (MSSA). The in vitro efficacies of
nitroxoline and
nitrofurantoin against ATCC strains of E. coli, Enterococcus faecalis and Proteus mirabilis were compared by time-kill curves in Mueller-Hinton broth and artificial urine.
Nitroxoline was non-inferior against E. coli, P. mirabilis and E. faecalis in artificial urine. In conclusion,
nitroxoline showed a broad antimicrobial spectrum, with inhibition zone diameters and MICs of
nitroxoline well below the EUCAST breakpoint for E. coli for most organisms, and thus may also be a target for
therapy of uncomplicated UTIs.