What is the first‑line oral antibiotic for an infected lipoma in a healthy adult without MRSA colonization or drug allergies?

First-Line Oral Antibiotic for an Infected Lipoma

For an infected lipoma in a healthy adult without MRSA risk factors or drug allergies, cephalexin (a first-generation cephalosporin) 500 mg four times daily for 5–10 days is the recommended first-line oral antibiotic. 1

Rationale for Beta-Lactam Selection

• Infected lipomas are soft tissue infections typically caused by methicillin-susceptible Staphylococcus aureus (MSSA) and beta-hemolytic streptococci, the same pathogens responsible for most cellulitis and superficial soft tissue infections. 1

• First-generation cephalosporins (cephalexin) or antistaphylococcal penicillins provide optimal coverage against these Gram-positive organisms in patients without MRSA colonization or risk factors. 1

• Beta-lactams are preferred because they are highly effective, well-tolerated, and cost-effective for community-acquired skin infections when CA-MRSA is not suspected. 1

When Surgical Drainage Is Required

• Incision and drainage is the primary treatment if the infected lipoma has formed an abscess or purulent collection; antibiotics serve as adjunctive therapy only. 2

• Antibiotics should be added to drainage when any of the following are present: extensive cellulitis (>5 cm from wound edge), systemic signs (fever >38.5°C, tachycardia >110 bpm, WBC >12,000/µL), immunosuppression, or failure of drainage alone. 1, 2

Alternative Regimens for Penicillin Allergy

• For non-IgE-mediated penicillin allergy: Clindamycin 300–450 mg orally every 6–8 hours is the preferred alternative, provided local clindamycin resistance rates are <10%. 1, 2

• For IgE-mediated penicillin allergy: Doxycycline 100 mg twice daily can be used, though it has slightly less reliable streptococcal coverage and requires close monitoring. 2

When to Add MRSA Coverage

• MRSA-active antibiotics are NOT indicated in a healthy adult without MRSA colonization, prior MRSA infection, recent hospitalization, or recent antibiotic use. 1

• If MRSA risk factors are present or if the patient fails initial beta-lactam therapy, switch to trimethoprim-sulfamethoxazole (TMP-SMX) 1–2 double-strength tablets twice daily, which has 95–100% susceptibility against CA-MRSA. 1, 2, 3

• Critical pitfall: TMP-SMX must never be used as monotherapy for soft tissue infections because it lacks reliable activity against beta-hemolytic streptococci; if used, it must be combined with amoxicillin 500 mg three times daily. 2, 3

Treatment Duration

• A 5–10 day oral course is recommended for uncomplicated infected lipomas after adequate drainage or for cellulitis without abscess formation. 2

• Shorter 5-day courses are appropriate for rapidly responding infections; extend to 10 days for extensive cellulitis or slower clinical improvement. 2

Criteria for Escalation to IV Therapy

• Hospitalization and IV vancomycin (15–20 mg/kg every 8–12 hours) are indicated when: systemic toxicity (fever >38.5°C, hypotension, altered mental status), rapid progression despite oral antibiotics, failure of outpatient management after 48–72 hours, or deep tissue involvement. 2

Practical Management Algorithm

1. Assess for abscess formation: If present, perform incision and drainage as the definitive primary step. 2
2. Obtain wound cultures if drainage is performed to guide antimicrobial selection.
3. Start cephalexin 500 mg four times daily (or amoxicillin-clavulanate 875 mg twice daily as an alternative). 1, 2
4. Reassess at 48–72 hours: If no clinical improvement, consider treatment failure and either switch to MRSA-active therapy or escalate to IV antibiotics. 2
5. Complete 5–10 days of therapy based on severity and response. 2