990
a pathogen in only a small number of cases compared to the number of total cases in which vancomycin is used as an empiric agent. These results are supported by other studies showing that MRSA is not a prevalent pathogen for infections for which van- comycin is often used. For example, Self et al4 found that only 0.7% of patients admitted for community-acquired pneumonia had confirmed MRSA, even though vancomycin or linezolid was administered to almost 30% of these patients. In addition, the most common indication for vancomycin use, as confirmed by the results of this study, is SSTI. Most nonpurulent cellulitis is thought to be caused by β-hemolytic streptococci.5,6 Guidelines published by the Infectious Diseases Society of America recom- mend agents with activity against MRSA for SSTIs if there is cellulitis associated with “penetrating trauma, evidence of MRSA infection elsewhere, nasal colonization with MRSA, injection drug use, purulent drainage, or SIRS”.6 Empiric therapy for suspected MRSA infection should be
guided by geographic location. Rates of MRSA infection are dif- ferent in different areas of the United States. For example, Moran et al7 found that rates of MRSA in patients with SSTI presenting to the emergency department are higher in the southern region and lower in the northeastern and central parts of the United States. Considering these data, clinicians should use their best judgment in determining whether vancomycin would be an appropriate empiric therapy. All cultures in the Moran et al study that were positive for MRSA were from purulent wounds or abscesses and cellulitis with purulent exudate. This finding sup- ports the argument that cellulitis or wounds with purulence should include antibiotic therapy with activity against MRSA.7 The results of this study suggest that vancomycin is over-
utilized to treat empiric infections and that MRSA infection is relatively rare compared to the frequency with which vancomycin is prescribed. Based on the results of this study, providers in some areas should expect to discontinue vancomycin therapy in up to 90% of patients for whom cultures are negative at 48 hours after initiation of vancomycin therapy. Many data have been published regarding the early attainment
of therapeutic vancomycin serum concentrations, which the most appropriate way to obtain therapeutic trough concentrations, to obtain appropriate pharmacodynamic and pharmacokinetic parameters by which to monitor vancomycin therapy, and to ensure that nephrotoxicity is minimized.8,9 Perhaps, however, there should be a shift in the research to determine how to most efficiently utilize stewardship efforts to ensure that vancomycin therapy is stopped when it is not indicated. Antimicrobial stew- ardship efforts regarding vancomycin should continue and should not only focus on pharmacodynamic or pharmacokinetic mon- itoring but also should encourage providers to discontinue van- comycin therapy when culture data or clinical presentation suggest that an MRSA infection is unlikely. Our study has several limitations. First, this was only an observational study conducted in a geographically limited area.
C. Dustin Waters and Joshua Caraccio
Also, rates of MRSA may differ throughout the United States (and world); therefore, rates of MRSA in this study may not reflect rates of MRSA in other geographic locations. Second, lack of culture data for conditions such as cellulitis may have skewed the data for culture positivity and the use of antibiotics in this patient population. As previously mentioned, SSTIs were the most common source of culture positivity and were likely the most common indication for use of vancomycin, although indication was not directly assessed in the current study. Another limitation is that the definition of “appropriate” use of vancomycin is somewhat arbitrary, even in the case of negative cultures. Some patients may not have had abscesses drained for culture or may have had cultures performed elsewhere, and culture data may not have been available. Also, some use of vancomycin beyond 48 hours may have been due to failure of other antibiotic therapy for which culture data were not available. In conclusion, vancomycin continues to be the most commonly
used antibiotic to empirically treat infections in the inpatient setting. The results of the current study show that vancomycin continues to be used often in many cases in which the risk for MRSA (or other infection necessitating vancomycin therapy) is low.
Financial support. No financial support was provided relevant to this article.
Conflicts of interest. All authors report no conflicts of interest relevant to this article.
References 1. Dantes R, Mu Y, Belflower R, et al. National burden of invasive methicillin- resistant Staphylococcus aureus infections, United States, 2011. JAMA Intern Med 2013;173:1970–1978.
2. Magill SS, Edwards JR, Beldavs ZG, et al. Prevalence of antimicrobial use inUS acute care hospitals,May–September 2011. JAMA 2014;312:1438–1446.
3. Kim NH, Koo HL, Choe PG, et al. Inappropriate continued empirical vancomycin use in a hospital with a high prevalence of methicillin-resistant Staphylococcus aureus. Antimicrob Agents Chemother 2015;59:811–817.
4. Self WH, Wunderink RG, Williams DJ, et al. Staphylococcus aureus community-acquired pneumonia: prevalence, clinical characteristics, and outcomes. Clin Infect Dis 2016;63:300–309.
5. Jeng A, Beheshti M, Li J, Nathan R. The role of beta-hemolytic streptococci in causing diffuse, nonculturable cellulitis: a prospective investigation. Medicine (Baltimore) 2010;89:217–226.
6. Stevens DL, Bisno AL, Chambers HF, et
al.Practiceguidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis 2014;59:e10–e52.
7. Moran GJ, Krishnadasan A, Gorwitz RJ, et al. Methicillin-resistant S. aureus infections among patients in the emergency department. N Engl J Med 2006;355:666–674.
8. Kullar R, Leonard SN, Davis SL, et al. Validation of the effectiveness of a vancomycin nomogram in achieving target trough concentrations of 15–20 mg/L suggested by the vancomycin consensus guidelines. Pharmacotherapy 2011;31:441–448.
9. Neely MN, Youn G, Jones B, et al. Are vancomycin trough concentrations adequate for optimal dosing? Antimicrob Agents Chemother 2014;58:309–316.
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