What are the recommended antibiotics (Abx) for treating Methicillin-resistant Staphylococcus aureus (MRSA) in a wound?

Treatment of MRSA Wound Infections

For non-severe MRSA wound infections, incision and drainage plus oral trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets twice daily or doxycycline 100 mg twice daily for 5-10 days is the recommended first-line approach. 1

Initial Management: Drainage is Essential

• Surgical debridement and drainage of abscesses is the mainstay of therapy and must be performed whenever feasible—antibiotics alone will fail without adequate source control. 1
• Obtain cultures from purulent drainage before starting antibiotics to confirm MRSA and guide definitive therapy. 1
• For simple abscesses or boils, incision and drainage alone may be adequate without antibiotics, but additional antibiotics are recommended for more extensive infections. 1

Antibiotic Selection Based on Severity

Outpatient Oral Therapy (Non-Severe Infections)

First-line oral agents:

• TMP-SMX 4 mg/kg/dose (TMP component) twice daily is the preferred first-line choice. 1
• Doxycycline 100 mg twice daily or minocycline 100 mg twice daily are equally effective alternatives. 1
• Clindamycin 600 mg orally three times daily should only be used if local MRSA resistance rates are below 10%. 1

Critical caveat: TMP-SMX and tetracyclines have excellent MRSA coverage but poorly defined activity against β-hemolytic streptococci. 2 If you suspect both MRSA and streptococcal infection (purulent cellulitis with surrounding erythema), use clindamycin alone (if resistance <10%) or combine TMP-SMX/tetracycline with a β-lactam like cephalexin 500 mg four times daily. 1

Inpatient IV Therapy (Severe or Complicated Infections)

Indications for hospitalization and IV therapy:

• Severe or extensive local infection with multiple sites involved 1
• Signs of systemic illness (fever, hypotension, altered mental status, SIRS) 2, 1
• Rapidly progressive infection with associated cellulitis 2
• Comorbidities, immunosuppression, or extremes of age 2
• Concurrent bacteremia 1

First-line IV agents:

• Vancomycin 15-20 mg/kg IV every 8-12 hours is the gold standard for hospitalized patients requiring MRSA coverage. 2, 1
• Daptomycin 4-6 mg/kg IV once daily is the first-line alternative when vancomycin cannot be used. 1, 3
• Linezolid 600 mg IV twice daily is another excellent option with proven efficacy (79% cure rate for MRSA skin infections in FDA trials). 1, 4

Second-line IV alternatives:

• Ceftaroline 600 mg IV every 12 hours has shown efficacy in complicated MRSA skin infections. 1
• Clindamycin 600 mg IV three times daily if local resistance is low (<10%). 2, 1

Treatment Duration

• For uncomplicated MRSA skin infections: 5-10 days of therapy, individualized based on clinical response. 1
• For complicated skin and soft tissue infections: 7-14 days. 1
• For MRSA bacteremia with skin/soft tissue source: minimum 2 weeks for uncomplicated bacteremia, 4-6 weeks for complicated bacteremia. 1

Transitioning to Oral Therapy

• After clinical improvement and if the patient can tolerate oral medications, transition to oral options (TMP-SMX, doxycycline/minocycline, or linezolid 600 mg orally twice daily). 1
• Most patients in clinical trials switched to oral therapy around day 4 (range day 1-14). 4

Special Considerations for Bacteremia

• If concurrent bacteremia is present, repeat blood cultures 2-4 days after initial positive cultures to document clearance. 1
• For MRSA bacteremia, vancomycin dosed by area-under-the-curve (AUC) targeting 400-600 mcg·h/mL is recommended, though trough-based dosing (targeting 15-20 mg/L) remains acceptable. 5, 6

Prevention of Recurrence

• Keep draining wounds covered with clean, dry bandages. 1
• Maintain good personal hygiene with regular handwashing. 1
• Consider decolonization with mupirocin (nasal) and chlorhexidine (body) for recurrent infections. 1
• Evaluate and potentially treat household contacts if recurrent infections persist. 1

Common Pitfalls to Avoid

• Never use β-lactam antibiotics alone for MRSA—they have zero activity against methicillin-resistant organisms. 2, 1
• Never fail to drain abscesses when present—this leads to treatment failure regardless of antibiotic choice. 1
• Never use rifampin as monotherapy or add it routinely to other antibiotics for skin infections, as resistance develops rapidly. 2, 1
• Do not use clindamycin for serious infections if inducible resistance is detected on susceptibility testing. 2