Preferred Antibiotic for Infected Cyst
Primary Management: Incision and Drainage First
For an infected epidermoid or sebaceous cyst in a healthy adult, incision and drainage is the definitive treatment, and antibiotics are often unnecessary if there are no systemic signs of infection. 1
- Most infected cysts (47% in one study) will not grow pathogenic bacteria on culture, making empiric antibiotics potentially unnecessary 2
- Incision and drainage alone achieves cure rates of approximately 90% even when MRSA is present 3
When Antibiotics Are Indicated
Add antibiotic therapy to incision and drainage when any of the following are present:
- Systemic inflammatory response syndrome (SIRS): Temperature >38°C or <36°C, heart rate >90 bpm, respiratory rate >24/min, or WBC >12,000 or <4,000 cells/µL 1
- Significant surrounding cellulitis extending beyond the abscess borders 4
- Immunocompromised host 1
- Incomplete source control after drainage 4
First-Line Antibiotic Selection
In Areas with Low MRSA Prevalence (<10%):
- Cephalexin (first-generation cephalosporin) or dicloxacillin (penicillinase-resistant penicillin) targeting methicillin-susceptible Staphylococcus aureus 1, 5
- These remain the antibiotics of choice for serious MSSA infections 5
In Areas with High MRSA Prevalence or Suspected MRSA:
- Trimethoprim-sulfamethoxazole (TMP-SMX) 4, 1
- Doxycycline 4, 1
- Clindamycin (if local resistance rates <10%) 4, 1
Note: TMP-SMX should not be used as monotherapy if streptococcal cellulitis is suspected, as streptococci have intrinsic resistance 4
For Penicillin-Allergic Patients:
- Clindamycin, TMP-SMX, or doxycycline are appropriate alternatives 1, 5
- Avoid cephalosporins in patients with immediate-type penicillin hypersensitivity (urticaria, angioedema, bronchospasm, anaphylaxis) 5
Treatment Duration
- 5-7 days is typically sufficient for uncomplicated infections 1
- Extend duration based on clinical response if systemic symptoms persist 1
Critical Pitfalls to Avoid
- Never treat with antibiotics alone without performing incision and drainage - this is the most common error and leads to treatment failure 1
- Do not prescribe antibiotics reflexively for all infected cysts; reserve them for cases with systemic symptoms or significant cellulitis 1, 2
- In high MRSA prevalence areas, avoid beta-lactams (cephalexin, dicloxacillin) as empiric monotherapy until susceptibility is confirmed 1, 3
- Always obtain culture if antibiotics are prescribed, as nearly half of inflamed cysts may be culture-negative or grow only normal flora 2
- Linezolid should be reserved for severe cases or treatment failures due to cost, as it offers no superiority over less expensive alternatives 4