What is the recommended treatment for an outpatient with a Methicillin-resistant Staphylococcus aureus (MRSA) skin infection?

Treatment of Outpatient MRSA Skin Infections

For outpatient MRSA skin infections, perform incision and drainage when feasible, then prescribe trimethoprim-sulfamethoxazole (1-2 double-strength tablets twice daily) or doxycycline (100 mg twice daily) for 5-10 days. 1, 2

Initial Management: Drainage First

• Surgical drainage of abscesses is the mainstay of therapy and should be performed whenever feasible before or concurrent with antibiotics. 1, 2
• Obtain cultures from purulent drainage before starting antibiotics to confirm MRSA and guide therapy. 1, 2
• For simple abscesses without surrounding cellulitis or systemic symptoms, incision and drainage alone may be adequate without antibiotics. 1, 2

When Antibiotics Are Required

Add antibiotic therapy when any of the following are present:

• Severe or extensive disease involving multiple sites 2
• Signs of systemic illness (fever, tachycardia, hypotension) 2
• Immunosuppression or significant comorbidities 2
• Surrounding cellulitis beyond the abscess 1

First-Line Oral Antibiotic Options

Trimethoprim-sulfamethoxazole (TMP-SMX):

• Dose: 1-2 double-strength tablets twice daily 1, 2, 3
• Excellent MRSA coverage but limited activity against beta-hemolytic streptococci 1, 3
• Most cost-effective first-line option 1

Doxycycline:

• Dose: 100 mg twice daily 1, 2, 3
• Equally effective as TMP-SMX with similar streptococcal coverage limitations 1, 3
• Alternative: Minocycline 200 mg loading dose, then 100 mg twice daily 1, 3

Clindamycin:

• Dose: 300-450 mg three times daily 1, 3
• Only use if local MRSA resistance rates are below 10% due to inducible resistance concerns. 1, 3
• Advantage: Covers both MRSA and beta-hemolytic streptococci 1

Linezolid:

• Dose: 600 mg twice daily 4, 1
• Highly effective but significantly more expensive than alternatives 1
• Reserve for treatment failures or when other options are contraindicated 4

Treatment Duration

• 5-10 days for uncomplicated MRSA skin infections 1, 2
• Extend to 7-14 days for complicated infections 4, 1, 2
• Reassess clinically within 48-72 hours to ensure appropriate response 1

Critical Decision: Purulent vs Non-Purulent Cellulitis

For purulent cellulitis with drainage/abscess (high MRSA likelihood):

• Start with TMP-SMX or doxycycline immediately 1, 3

For non-purulent typical cellulitis (streptococci more likely):

• Start with beta-lactam (cephalexin 500 mg four times daily) 3
• Add MRSA coverage only if no response within 48-72 hours or systemic toxicity present 3

For dual coverage when both organisms are suspected:

• Clindamycin alone (if resistance <10%) 1, 3
• OR combine TMP-SMX or doxycycline with a beta-lactam (cephalexin or amoxicillin) 4, 3

Pediatric Dosing

• Clindamycin: 10-13 mg/kg/dose orally every 6-8 hours 1, 2
• TMP-SMX: 4-6 mg/kg/dose (trimethoprim component) every 12 hours 1
• Never use tetracyclines in children under 8 years of age 1

Common Pitfalls to Avoid

• Never use beta-lactam antibiotics alone when MRSA is suspected—they have zero activity against methicillin-resistant organisms. 3
• Do not use TMP-SMX or tetracyclines alone for typical non-purulent cellulitis, as they will miss streptococcal coverage. 3
• Failure to drain associated abscesses leads to treatment failure regardless of antibiotic choice. 3
• Do not use clindamycin for serious infections if inducible resistance is detected on susceptibility testing. 3
• Never use rifampin as monotherapy or add it routinely—resistance develops rapidly with no proven benefit. 3

When to Hospitalize for IV Therapy

Admit patients with any of the following high-risk features:

• Systemic signs of illness or rapidly progressive infection 3
• Multiple sites of infection 3
• Abscess in difficult-to-drain locations 3
• Significant comorbidities or extremes of age 3
• Septic phlebitis 3

For hospitalized patients, vancomycin 15-20 mg/kg IV every 8-12 hours remains the gold standard. 1, 2, 3