MRSA: Where Do We Go From Here?
- Volume 18 - Issue 3 - March 2005
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When One Should Emphasize Antibiotic Therapy
Following necessary debridement and other surgical interventions, such as bone resection and revascularization, appropriate antibiotic therapy is a cornerstone of managing diabetic foot infections. One may manage most of these infections with initial broad-spectrum antibiotic therapy and, in many cases, follow it with a more specific therapy. However, the increasing prevalence of antibiotic resistance can be a significant barrier to successfully treating these infections.
Moderate-to-severe diabetic foot infections generally require hospitalization and parenteral antibiotic therapy. Since these infections are frequently polymicrobial, one should emphasize treatment that provides coverage against both gram-positive and gram-negative bacteria as well as anaerobes. Keep in mind that MRSA may be present in both polymicrobial and monomicrobial infections.
The most important pathogen involved in diabetic foot infections is S. aureus, whether it is alone or part of a mixed infection.28 Given that the increasing incidence of MRSA infections is often associated with previous antibiotic therapy for treating foot ulcers, patients at risk for developing an MRSA infection should be treated with an antimicrobial agent with activity against this pathogen.
What You Should Know About Vancomycin
Vancomycin has been traditionally recommended for treating MRSA infections but it can be problematic. Its efficacy in treating patients with osteomyelitis caused by S. aureus is less than optimal and patients on vancomycin therapy have higher rates of infection recurrence compared to those treated with ceftriaxone and cefazolin.29 Vancomycin also appears to be less effective than beta-lactams in treating bone infections.30 It also must be given parenterally, thus making outpatient treatment more difficult and increasing both the expense and risk of complications.
Vancomycin is associated with relatively frequent and occasionally severe adverse events. Also be aware that the incidence of vancomycin-resistant Staphylococcus aureus, while still relatively rare, is growing. A recent study suggests that S. aureus isolates that are completely resistant to vancomycin may become a major problem much sooner than anticipated.31
A Closer Look At Quinupristin/Dalfopristin
Investigators have been developing new agents with activity against gram-positive cocci, particularly against MRSA. Three new agents with demonstrated activity against MRSA are currently available. They include quinupristin/dalfopristin, linezolid and daptomycin. A fourth agent, dalbavancin, has also shown activity against several strains of gram-positive bacteria, including several resistant strains.
Quinupristin/dalfopristin is the first formulation of a class of antibiotics known as the streptogramins.32 It was approved for the treatment of serious or life-threatening infections, and complicated skin and skin structure infections (cSSTIs) caused by gram-positive cocci. Like vancomycin, quinupristin/dalfopristin can only be given by intravenous infusion.
Nichols, et. al., reported on the results of two studies that compared the safety, efficacy and tolerance of quinupristin/dalfopristin with that of cefazolin, oxacillin or vancomycin in the treatment of hospitalized adult patients with cSSTIs caused by gram-positive organisms.33 These two randomized, open-label trials enrolled a total of 893 patients (450 in the quinupristin/dalfopristin group, 443 in the comparator group).