Manipulating antibiotic use patterns may lower VRE
Mathematical model awaits clinical trials
Simply reducing overall vancomycin use may not necessarily reduce prevalence of vancomycin-resistant enterococci (VRE) in a patient population, but refining such bug-drug interactions by looking at other combinations of antibiotics may ultimately yield reduced VRE infections, researchers are finding.
A mathematical model developed by clinicians at the University of Maryland Medical System in Baltimore predicts that sharply decreasing use of vancomycin, clindamycin, and metronidazole could greatly reduce VRE. The model also suggests that simultaneously increasing the use of other antibiotics such as cefazolin, cefoxitin, and cefotetan can reduce VRE even further.
"It is not vancomycin that acts alone to cause VRE infections," says Beulah E. Perdue, PharmD, BCPS, antimicrobial coordinator and a clinical specialist in infectious diseases in the department of pharmacy services at the medical system. "And I don’t think you can do broad, general cuts of all antibiotics across the board for all services. Within a subset of patients, you may need to do different restrictions of antibiotics. That is one of the things that came out of this model."
The research was presented recently in Toronto at the meeting of the Interscience Conference on Antimicrobial Agents and Chemotherapy. The study included 15 medical services at the hospital, with researchers trying to determine whether manipulation of antibiotic use could predict increases or decreases in VRE. For example, reducing the amount of vancomycin used, along with clindamycin and metronidazole, was predictive of a 15% to 45% decrease in the number of VRE infections per 1,000 patient days. Increasing the use of other antibiotics, such as cefazolin, cefoxitin, and cefotetan at the same time would lower VRE infections by 19% to 65%.
"This is a model and we are in the process of trying to decide how, where, and when we are going to test it by picking specific areas or services within the hospital," she says. "But it is a jumping-off point for looking at different antibiotic usage patterns for different services. We are already talking about reassessing the model for other bug/drug combinations."
Reducing vancomycin alone had a more modest impact of decreasing the number of VRE infections in the model, from 3% to 34%. That prediction has been borne out by experience in the facility, where stringent vancomycin restrictions did not greatly reduce levels of VRE colonization in the patient population. That may be because increasing use of other drugs such as third-generation cephalosporins may "wipe out" most other organisms in the patient gut flora except enterococcus, allowing them to selectively "sample" the vancomycin still being administered and gradually develop resistance, she notes.
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