What is the recommended oral antibiotic regimen for treating a skin abscess caused by Staphylococcus aureus (S. aureus)?

Oral Antibiotic Treatment for Staphylococcus aureus Skin Abscess

For methicillin-susceptible S. aureus (MSSA) skin abscesses, prescribe dicloxacillin 500 mg four times daily or cephalexin 500 mg four times daily for 7 days; for methicillin-resistant S. aureus (MRSA), prescribe trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets (160/800 mg) twice daily for 7-10 days. 1

Critical First Step: Incision and Drainage

• Incision and drainage is mandatory for any abscess and must be performed before or concurrent with antibiotic therapy. 1
• Obtain cultures from purulent drainage before starting antibiotics to confirm the pathogen and guide definitive therapy. 1
• For abscesses <5 cm in immunocompetent patients, incision and drainage alone may be sufficient without antibiotics, though recent evidence suggests antibiotics improve outcomes across all lesion sizes. 2, 3

Treatment Algorithm Based on Methicillin Susceptibility

For MSSA (Methicillin-Susceptible S. aureus):

• First-line: Dicloxacillin 500 mg orally four times daily for 7 days 4, 1
• Alternative: Cephalexin 500 mg orally four times daily for 7 days 4, 1
• For penicillin allergy (non-immediate): Cephalexin 500 mg orally four times daily 4
• For immediate penicillin hypersensitivity: Clindamycin 300-450 mg orally three times daily 4, 1

For MRSA (Methicillin-Resistant S. aureus):

• First-line: TMP-SMX 1-2 double-strength tablets (160/800 mg) twice daily for 7-10 days 4, 1

  • TMP-SMX demonstrates superior outcomes across all lesion sizes and patient subgroups 3
  • Treatment effect is greatest in patients with history of MRSA infection, fever, or positive MRSA culture 3

• Second-line alternatives:

  • Doxycycline 100 mg twice daily for 7-10 days (when TMP-SMX fails or is contraindicated) 4, 1
  • Minocycline 200 mg once, then 100 mg twice daily (may be more reliable than doxycycline for community-acquired MRSA) 1, 5
  • Clindamycin 300-450 mg three times daily (preferred when coverage for both MRSA and β-hemolytic streptococci is needed, but use only if local resistance <10%) 4, 1

• Advanced option for complicated infections:

  • Linezolid 600 mg twice daily for 10-14 days (highly effective but expensive; reserve for treatment failures) 1, 6

Pediatric Dosing

• MRSA in children: Clindamycin 10-13 mg/kg/dose every 6-8 hours is preferred 4, 1
• TMP-SMX: 8-12 mg/kg/day (based on trimethoprim component) in 2 divided doses 4
• Avoid doxycycline in children <8 years old due to tooth discoloration and bone growth effects 4, 1

Important Caveats and Pitfalls

• Do not use rifampin as single agent or adjunctive therapy for skin infections—resistance develops rapidly 1, 7
• TMP-SMX is bactericidal but has limited streptococcal coverage; if streptococcal infection is suspected, use clindamycin or add beta-lactam coverage 4
• Clindamycin has potential for cross-resistance with erythromycin-resistant strains and inducible resistance in MRSA—check local resistance patterns 4
• Tetracyclines (doxycycline, minocycline) are bacteriostatic and contraindicated in pregnancy and lactation 4, 1
• Treatment duration is typically 5-10 days but should be extended if infection has not improved 4, 1

When to Consider Antibiotics Essential

• Abscess cavity or erythema diameter ≥5 cm 2, 3
• Systemic signs of infection (fever, tachycardia) 4, 1
• Immunocompromised state 4
• Multiple lesions or history of recurrent MRSA infection 4, 1
• Failed initial incision and drainage alone 1

Recurrent Abscess Management

• After obtaining cultures, treat with a 5- to 10-day course of an antibiotic active against the pathogen 4
• Consider a 5-day decolonization regimen: intranasal mupirocin twice daily, daily chlorhexidine washes, and daily decontamination of personal items (towels, sheets, clothes) for recurrent S. aureus infection 4