Community-Acquired MRSA
The recent rapid increase in community-acquired MRSA soft tissue infections has forced physicians to reconsider their approach to routine SSTIs. Recent reports of antimicrobial resistance patterns have found that community-acquired MRSA is responsible for up to 60 percent of SSTIs in U.S. emergency departments.10,11 These rates are higher in certain populations, including ethnic minorities, children, intravenous drug users, patients who have received recent antibiotic treatment, men who have sex with men, residents of long-term care facilities and prisons, and patients receiving hemodialysis.5,12,13 In addition to purulent SSTIs, community-acquired MRSA is associated with other infectious processes, such as necrotizing pneumonia and sepsis.10 Although many patients with community-acquired MRSA infections describe the initial presentation as resembling a spider bite, there are no reliable signs and symptoms to distinguish community-acquired MRSA infections from other purulent SSTIs.13,14
Diagnosis and Assessment of SSTIs
SSTIs in the presence of comorbid infections, such as
diabetes,
neutropenia,
or cirrhosis, are more likely to be severe and caused by uncommon organisms (e.g., Pseudomonas species, Klebsiella species, yeast, fungi).7
Complicated and potentially life-threatening SSTIs are characterized by fever,
widespread or a rapidly spreading area of involvement, firm and hard feel of subcutaneous tissues, pain disproportionate to examination, skin sloughing, cutaneous bleeding with or without bullae, and skin crepitus.15 Additionally, patients with necrotizing infections may be lethargic or disorientated.7 Rapidly progressive and life-threatening infections warrant urgent surgical referral.3,7,16
Hospitalization should be considered in patients with the following laboratory findings:
left shift in complete blood count with differential,
elevated serum creatinine level,
reduced serum bicarbonate level,
elevated creatine kinase level, or
C-reactive protein level greater than 13 mg per L (123.81 nmol per L).7
wound cultures of purulent secretions should be performed in patients with multiple or extensive lesions,
fever or other evidence of systemic illness,
prior treatment failure, immunocompromise, trauma, water contact, or animal or human bites.7 If wound cultures are indicated, fluid or tissue specimens should be collected using aseptic technique via needle aspiration or tissue biopsy.
Antimicrobial Treatment
When indicated, antimicrobial therapy for uncomplicated SSTIs is usually initiated empirically. Familiarity with common pathogens and with local flora and resistance patterns is essential in choosing initial agents.
Oral antibiotics that have been shown to be effective against community-acquired MRSA include
trimethoprim/sulfamethoxazole (Bactrim, Septra),
tetracyclines, and
Local patterns of sensitivity may vary, however. In one study, patients with uncomplicated cellulitis who received five days of antibiotic treatment had similar outcomes to those who were treated for 10 days.26 In patients with widespread or systemic infection, comorbidities, or an inability to tolerate oral treatment, vancomycin is the first-line parenteral anti-MRSA agent, although clindamycin, quinolones, linezolid (Zyvox), tigecycline (Tygacil), and daptomycin (Cubicin) may also be used.3
If clindamycin therapy is considered,
a D-zone test should be performed to
identify patients with inducible clindamycin resistance.
LINEZOLID
Linezolid is effective against methicillin-sensitive S. aureus (MSSA) and MRSA, and the nearly equal bioavailability of oral and intravenous preparations makes it a convenient alternative to vancomycin. Because of cost (approximately $1,700 for a 10-day oral course) and the potential for the development of additional drug resistance, linezolid should be reserved for patients with MRSA who do not respond to other agents and for patients with complicated SSTIs in whom alternative treatment has been inferior.
1.As a weak monoamine oxidase inhibitor, linezolid may be associated with an increase in blood pressure.
2. Serotonin syndrome has been reported in patients taking selective serotonin reuptake inhibitors with line-zolid.
3.Linezolid also should be used with caution in patients with chronic kidney disease because it is renally excreted.26
TIGECYCLINE
Tigecycline is indicated for the treatment of complicated SSTIs caused by MSSA and MRSA infections.
The drug is metabolized in the liver; therefore, dosing adjustments are
needed in patients with severely impaired liver function (i.e., those with Child-Pugh classification C cirrhosis).
No dosing adjustment is needed in patients with renal impairment,
and tigecycline does not alter the effectiveness of warfarin (Coumadin) therapy.31
Tigecycline is administered intravenously.
The most common adverse effects are nausea and vomiting.
As with tetracyclines,
tigecycline is not recommended
for use in children.31
DAPTOMYCIN
Daptomycin exhibits bactericidal activity against most gram-positive organisms, including MRSA and vancomycin-resistant enterococci. This unique medication disrupts the ionic electric potentials of the cell membrane by promoting rapid calcium-dependent efflux of potassium from the cell.32,33 In a prospective, open-label study comparing daptomycin with vancomycin for the treatment of complicated SSTIs with risk of MRSA, both groups had complete clinical resolution, with the daptomycin-treated group demonstrating a significantly reduced duration of intravenous therapy and reduced median number of days to achieve clinical cure.34
Daptomycin is administered intravenously.
Potential adverse effects include myopathy and gastrointestinal effects,
such as nausea, vomiting, and diarrhea.
Daptomycin may elevate the prothrombin time and, therefore,
should be used with caution in patients taking warfarin.33
RETAPAMULIN
Retapamulin (Altabax) is a topical antibiotic that has been investigated for use in the treatment of impetigo.
cally significant improvement in outcomes after seven days of retapamulin therapy, compared with placebo.35 Retapamulin has not been compared with topical mupirocin, however.
Prevention of SSTIs
Standard infection control precautions should be implemented and encouraged for all patients in ambulatory and inpatient settings, including
proper and frequent handwashing,
use of gloves when managing wounds, and
contact precautions (e.g., use of gowns and gloves, grouping patients with similar infections) for patients with known or suspected MRSA infections.12 To prevent SSTIs, current consensus guidelines support proper foot care among patients with diabetes, tinea pedis, or pedal edema from venous insufficiency or lymphedema.
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