To date, with the exception of linezolid, no randomized, prospective clinical trials clearly demonstrate the efficacy of the oral agents that are commonly used for the outpatient treatment of cellulitis.20
When patients require hospitalization for the optimal treatment of cellulitis, it is important to select a parenteral antibiotic that provides coverage for MRSA.8 Vancomycin, daptomycin, linezolid, and tigecycline are the most commonly used agents.6
In the inpatient setting, failure to initiate appropriate medical therapy can result in longer hospital admissions, which significantly increase inpatient costs. Inadequate antibiotic therapy creates a significant financial burden and has been associated with increased mortality.4 Historically, vancomycin is used whenever a MRSA infection is suspected. However, there is concern about the declining efficacy of vancomycin related to a gradual increase in the rate of relative resistance—a minimal inhibitory concentration (MIC) increase—in MRSA strains. This MIC creep is noted in some medical centers and can lead to a failure to respond to vancomycin.13,20
Daptomycin is rapidly bactericidal against MRSA; in some institutions, its use may be preferred over vancomycin because the former antibiotic is associated with a significantly more rapid clinical response, which may shorten the required length of hospitalization.21 The once-daily dosing requirement for daptomycin allows for ease of use in both hospital and outpatient settings, and therefore may facilitate early hospital discharge or prevent the need for hospitalization altogether. Clinical experience also suggests potential economic advantages with the use of daptomycin.22
Tigecycline is a bacteriostatic antibiotic that achieves low serum concentrations. However, it penetrates the skin well and has a similar effectiveness to combination therapy with vancomycin and aztreonam. Thus far, tigecycline is not widely used for the treatment of MRSA infections, and it has been suggested that it may be preferred for polymicrobial infections or for patients who exhibit allergies to more commonly used agents.8
When selecting an antibiotic therapy, cost considerations play an important role in the decision-making process. For intravenous agents commonly used to treat CA-MRSA infections, the 2008 cost for 10 days of treatment with generic vancomycin was $182.80; daptomycin cost $1,660.80. For tigecycline and linezolid, the same duration of treatment cost $1,362 and $1,560, respectively.8
Back to the Case
Our patient, an otherwise healthy female, presented with no apparent risk factors for developing a CA-MRSA SSTI. However, more detailed history revealed that she regularly used sports equipment at her local fitness center. Based on her clinical presentation and concerns about the high local prevalence of CA-MRSA, an incision and drainage procedure was performed, and she was started empirically on IV vancomycin. She had a positive clinical response to this treatment.
Wound culture results confirmed CA-MRSA abscess and cellulitis, susceptible to trimethoprim/sulfamethoxazole. She was discharged on the oral formulation of this antibiotic to complete a 10-day course of treatment, including the days she received intravenous antibiotics.
Few well-designed trials have compared different lengths of cellulitis therapy. Most authorities recommend five to 10 days of treatment; however, longer courses might be required for more severe or complicated diseases.
Bottom line
Because of the high prevalence of CA-MRSA, initial antibiotic therapy for the treatment of community-acquired cellulitis must provide coverage for this organism. TH
Dr. Clarke is a hospitalist and clinical instructor at Emory University School of Medicine, Atlanta. Dr. Dressler is associate professor and director of education, section of hospital medicine, and associate program director of the J. Willis Hurst Internal Medicine Residency Program. Dr. Purohit is an instructor in clinical medicine at Emory University School of Medicine.