What is the appropriate antibiotic (Abx) treatment for an infected skin cyst?

Antibiotic Treatment for Infected Skin Cysts

For infected skin cysts (inflamed epidermoid cysts), incision and drainage is the primary treatment, and antibiotics are NOT routinely recommended unless systemic signs of infection are present. 1

Primary Management Approach

Incision and drainage alone is the recommended treatment for most infected skin cysts without the need for antibiotics. 1 The decision to add antibiotics should be based on the presence of systemic inflammatory response syndrome (SIRS) criteria 1:

• Temperature >38°C or <36°C
• Tachycardia >90 beats per minute
• Tachypnea >24 breaths per minute
• White blood cell count >12,000 or <4,000 cells/µL

When Antibiotics ARE Indicated

Antibiotics directed against Staphylococcus aureus should be added when patients present with:

• SIRS criteria as listed above 1
• Markedly impaired host defenses 1
• Failed initial drainage 1
• Multiple lesions or surrounding cellulitis 1

Antibiotic Selection

For Methicillin-Susceptible S. aureus (MSSA):

First-line oral options:

• Cephalexin 500 mg four times daily 1
• Dicloxacillin 500 mg four times daily 1

Alternative for penicillin allergy:

• Clindamycin 300-450 mg four times daily 1

For Suspected or Confirmed MRSA:

Oral options include:

• Trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily 1
• Doxycycline 100 mg twice daily 1
• Clindamycin 300-450 mg four times daily (if local resistance <10%) 1
• Linezolid 600 mg twice daily (expensive, reserve for resistant cases) 1

For severe infections requiring IV therapy:

• Vancomycin 30 mg/kg/day in 2 divided doses 1
• Linezolid 600 mg every 12 hours IV 1
• Daptomycin 4 mg/kg every 24 hours IV 1

Duration of Therapy

When antibiotics are used, treat for 5-7 days, extending therapy only if the infection has not improved within this timeframe. 1

Critical Pitfalls to Avoid

Do NOT routinely culture inflamed epidermoid cysts - cultures are not recommended for typical cases. 1 However, cultures should be obtained for carbuncles and abscesses if antibiotics will be used. 1

Do NOT use beta-lactams empirically in areas with high community-acquired MRSA prevalence - studies show that cephalexin provides no additional benefit over placebo after adequate drainage when MRSA is the causative organism (87.8% of isolates in one study). 2 The cure rate with drainage alone was 90.5% versus 84.1% with cephalexin plus drainage. 2

Do NOT pack the wound routinely - simply covering with sterile gauze is as effective and causes less pain compared to packing. 1

Pediatric Considerations

For children, the same principles apply:

• Cephalexin 25-50 mg/kg/day in 3-4 divided doses 1, 3
• Clindamycin 20-30 mg/kg/day in 3 divided doses (important option for children) 1
• Avoid tetracyclines in children <8 years of age 1