What is the first-line treatment for Staphylococcus (Staph) aureus skin infections?

First-Line Treatment for Staphylococcus Aureus Skin Infections

For methicillin-susceptible Staphylococcus aureus (MSSA) skin infections, dicloxacillin or cephalexin is the first-line treatment, while for methicillin-resistant Staphylococcus aureus (MRSA), trimethoprim-sulfamethoxazole, doxycycline, or clindamycin should be used as first-line therapy. 1, 2

Treatment Algorithm Based on Infection Type

1. Purulent Skin Infections (Abscesses)

• Primary treatment: Incision and drainage (I&D) 1
• Antibiotic therapy needed if:
  • Severe or extensive disease
  • Rapid progression with cellulitis
  • Signs of systemic illness
  • Immunosuppression
  • Significant comorbidities
  • Extremes of age
  • Difficult-to-drain locations
  • Lack of response to I&D alone 2

2. Non-Purulent Skin Infections (Cellulitis/Erysipelas)

• Mild infection: Antimicrobial agent active against streptococci 1
• Moderate infection with systemic signs: Coverage for both streptococci and MSSA 1
• Severe infection: Coverage for both MRSA and streptococci 1

Antibiotic Selection Based on Suspected Pathogen

For MSSA Infections:

• First-line:
  • Dicloxacillin 500 mg PO QID or
  • Cephalexin 500 mg PO QID 1, 3
• Alternatives (penicillin allergy):
  • Clindamycin 300-450 mg PO TID
  • First-generation cephalosporins (if non-anaphylactic allergy) 3

For Suspected or Confirmed MRSA:

• First-line oral options:
  • Trimethoprim-sulfamethoxazole 1-2 double-strength tablets BID
  • Doxycycline 100 mg PO BID (not for children <8 years)
  • Clindamycin 300-450 mg PO TID (if local resistance <10%) 1, 2
• For severe infections requiring IV therapy:
  • Vancomycin IV
  • Linezolid 600 mg IV/PO BID
  • Daptomycin 4 mg/kg IV daily
  • Telavancin 10 mg/kg IV daily 1, 4

Duration of Therapy

• 5-7 days for uncomplicated infections
• 7-14 days for complicated infections, based on clinical response 1, 2

Special Considerations

Pediatric Patients

• For MSSA: Cephalexin or dicloxacillin (weight-based dosing)
• For MRSA: Clindamycin (10-13 mg/kg/dose PO every 6-8 hours)
• Avoid tetracyclines in children <8 years of age 1, 5

Recurrent Infections

1. Obtain cultures of recurrent abscesses
2. Treat with 5-10 day course of antibiotics active against the pathogen
3. Consider 5-day decolonization regimen:
   • Intranasal mupirocin twice daily
   • Daily chlorhexidine washes
   • Daily decontamination of personal items 1

Important Caveats

• Cultures are recommended for purulent infections when antibiotic therapy is initiated 2
• Incision and drainage alone may be sufficient for simple abscesses without antibiotics 6
• Check local resistance patterns before using clindamycin empirically 2
• Consider combination therapy with TMP-SMX or tetracycline plus a beta-lactam if coverage for both MRSA and streptococci is needed 2
• Beta-lactams remain effective for many community-acquired skin infections despite increasing MRSA prevalence 6, 7

Treatment Failure Considerations

• Reassess diagnosis and consider surgical consultation
• Obtain cultures if not previously done
• Consider switching to alternative antibiotic based on susceptibility results
• Evaluate for complications or underlying conditions