Antimicrobial locks (AML) decrease the incidence of catheter-related bloodstream infections in hemodialysis (HD) patients, but they may result in the emergence of problematic pathogens, according to British investigators.

In a retrospective study, John J. Dixon, MD, and colleagues at St. Helier Hospital in Carshalton, Surrey, found that AML containing vancomycin and gentamicin significantly decreased the incidence of catheter-related bloodstream infections from 8.50 to 3.80/1,000 catheter-days. However, the proportion of Gram-positive bacteria, notably Staphylococcus aureus, increased significantly with AML use, although the proportion of methicillin-resistant S. aureus and vancomycin resistance did not, the researchers reported online ahead of print in Nephrology Dialysis Transplantation.

The study also found that AML use was associated with increased gentamicin and ciprofloxacin resistance among Enterobacter species, but not among Pseudomonas species or Escherichia coli.

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Dr. Dixon’s team noted that catheter-related bloodstream infections caused by S. aureus are highly pathogenic, with studies showing that it associated with 22% in-hospital mortality, rising to 32% at 90 days. Enterobacter bacteremia has a mortality rate of 5%-20%, increasing to 44% in patients who develop endocarditis. “It seems logical that resistant Enterobacter will be harder to treat with consequent higher mortality,” the authors stated.

“Given the prevalence of S. aureus and resistant Enterobacter, there is a need for a trial directly comparing the effectiveness of AML with non-antibiotic locks (e.g. citrate) in reducing CR-BSI,” they wrote. Non-antibiotic locks do not promote antimicrobial resistance and may be more cost-effective, they noted.

The study included 927 hemodialysis patients, of whom 662 received vancomycin and gentamicin systemically as well as in an AML. The other 265 patients received only systemic vancomycin and gentamicin and served as a control group.

The proportion of S. aureus cultures was 37.7% in the AML group compared with only 28.6% of the control arm. In the AML group, 29.4% of Enterobacter isolates were resistant to gentamicin, 23.5% were resistant to ciprofloxacin, and 15.7% were resistant to both drugs. In the control group, none of the Enterobacter isolates were resistant to gentamicin and 2.9% were resistant to ciprofloxacin. None of the isolates was resistant to both drugs.