Preferred Oral Antibiotic for MSSA Abscess
For an uncomplicated MSSA abscess, dicloxacillin 250-500 mg orally every 6 hours or cephalexin 500 mg orally every 6 hours for 5-7 days is the preferred treatment, but only after incision and drainage has been performed. 1, 2
Critical First Step: Incision and Drainage is Mandatory
- Incision and drainage must be performed before or concurrent with antibiotic therapy for any abscess—this is the mainstay of treatment, not antibiotics. 1, 2
- For simple abscesses without systemic signs of infection (fever, tachycardia, spreading erythema beyond 5 cm), incision and drainage alone may be adequate without antibiotics. 2
- Obtain culture from purulent drainage before starting antibiotics to confirm MSSA and guide definitive therapy. 1, 2
First-Line Oral Antibiotic Options for MSSA
When antibiotics are indicated after drainage:
- Dicloxacillin 250-500 mg orally every 6 hours provides excellent MSSA coverage and is the preferred penicillinase-resistant penicillin. 1, 3
- Cephalexin 500 mg orally every 6 hours is equally effective and often better tolerated than dicloxacillin. 1, 3, 4
- Both agents provide bactericidal activity against MSSA with 96% success rates for uncomplicated skin and soft tissue infections. 5
Treatment Duration
- Treat for 5-7 days if clinical improvement occurs (resolution of warmth, tenderness, and fever). 5, 1
- Extend treatment only if symptoms have not improved within this timeframe—do not reflexively extend to 10-14 days based on residual erythema alone. 5
Alternative for Penicillin/Cephalosporin Allergy
- Clindamycin 300-450 mg orally every 6 hours provides single-agent coverage for both MSSA and streptococci, making it ideal for penicillin-allergic patients. 1, 6, 3
- Use clindamycin only if local MRSA clindamycin resistance rates are <10%, as resistance develops through inducible mechanisms. 1, 2, 6
- The FDA label confirms clindamycin is indicated for serious skin and soft tissue infections caused by susceptible staphylococci, particularly in penicillin-allergic patients. 6
When Antibiotics Are Actually Needed
Add systemic antibiotics to incision and drainage when:
- Temperature ≥38°C, tachycardia, tachypnea, or abnormal white blood cell count is present. 2
- Spreading cellulitis extends >5 cm beyond the abscess margin. 2
- Patient is immunocompromised, has diabetes, or has failed drainage alone. 2
- Multiple abscesses or systemic inflammatory response syndrome (SIRS) is present. 5
Common Pitfalls to Avoid
- Never use beta-lactams alone if MRSA is suspected—they have zero activity against methicillin-resistant organisms. 2
- Do not prescribe antibiotics without performing adequate drainage—antibiotics cannot penetrate purulent collections effectively. 1, 2
- Avoid using rifampin as monotherapy or routinely adding it to other antibiotics, as resistance develops rapidly. 2
- Do not use fluoroquinolones as monotherapy due to high MRSA resistance rates, even if the isolate is MSSA. 2
If MRSA Cannot Be Excluded
- If culture results are pending or MRSA risk factors exist (injection drug use, known MRSA colonization, purulent drainage), use trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily or doxycycline 100 mg twice daily instead of beta-lactams. 1, 2
- Once MSSA is confirmed by culture, switch to dicloxacillin or cephalexin for optimal bactericidal activity. 1, 3