What is the best treatment approach for a skin infection in an adult patient?

Treatment of Skin Infections in Adults

For most uncomplicated skin infections, incision and drainage alone is adequate for simple abscesses, with antibiotics reserved only for patients with specific risk factors such as systemic illness, extensive disease, rapid progression with cellulitis, immunosuppression, or failure of drainage alone. 1

Initial Assessment and Management Approach

The cornerstone of treating skin infections depends on proper classification:

• Simple abscesses achieve 85-90% cure rates with incision and drainage alone, without antibiotics 2, 1
• Small furuncles may respond to moist heat application to promote drainage 2, 1
• Topical mupirocin 2% ointment applied three times daily is appropriate for limited superficial infections like impetigo 2, 1

When to Add Antibiotics to Drainage

Antibiotics should be added to incision and drainage only when specific risk factors are present 1:

• Severe or extensive disease with multiple lesions 2, 1
• Rapid progression with associated cellulitis 2, 1
• Signs of systemic illness (fever, tachycardia, hypotension) 2, 1
• Immunosuppression or diabetes 2, 1
• Extremes of age 1
• Difficult-to-drain locations (face, hands, genitals) 1
• Lack of response to drainage alone after 48 hours 2, 1

Outpatient Oral Antibiotic Selection

For Non-Purulent Cellulitis (No Abscess or Drainage)

Empirical therapy targeting β-hemolytic streptococci is recommended, as the role of CA-MRSA in non-purulent cellulitis remains unclear 2:

• Cephalexin 500 mg four times daily for 5-10 days is first-line when MRSA is not suspected 2, 1, 3
• Amoxicillin-clavulanate 875/125 mg twice daily provides broader coverage 2, 1
• If no response to β-lactam therapy within 48-72 hours, add MRSA coverage 2

For Purulent Infections or Suspected MRSA

When MRSA coverage is needed 2, 1:

• Clindamycin 300-450 mg three times daily (first-line option with excellent MRSA and streptococcal coverage) 2, 1
• Trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets twice daily (MRSA coverage but misses streptococci—combine with amoxicillin if streptococcal coverage needed) 2, 1
• Doxycycline 100 mg twice daily (MRSA coverage but some streptococci resistant—combine with β-lactam if needed) 2, 1
• Linezolid 600 mg twice daily (expensive but covers both MRSA and streptococci) 2, 1

Critical caveat: When using TMP-SMX or doxycycline for suspected mixed infections, always add a β-lactam like amoxicillin for streptococcal coverage 2.

Hospitalized Patients with Complicated SSTI

For patients requiring IV therapy with deeper infections, surgical/traumatic wounds, major abscesses, or infected ulcers 2:

• Vancomycin 15-20 mg/kg IV every 8-12 hours (first-line for MRSA) 2
• Linezolid 600 mg IV/PO twice daily 2
• Daptomycin 4 mg/kg IV once daily 2
• Clindamycin 600-900 mg IV every 8 hours (if local resistance <10%) 2

For mixed necrotizing infections requiring emergency surgical debridement, use vancomycin PLUS piperacillin-tazobactam 3.375 g IV every 6-8 hours, or a carbapenem 2.

Duration of Therapy

• Topical therapy: 5-7 days 1
• Oral therapy for uncomplicated infections: 5-10 days based on clinical response 2, 1
• Most bacterial SSTIs: 7-14 days 2
• Treatment duration should be guided by clinical improvement rather than arbitrary timeframes 1

Special Situations

Animal or Human Bites

Amoxicillin-clavulanate 875/125 mg twice daily is the treatment of choice for bite wounds, covering Pasteurella, streptococci, staphylococci, Eikenella corrodens, and anaerobes 2:

• Alternative: Moxifloxacin 400 mg daily (monotherapy with anaerobic coverage) 2
• Alternative for β-lactam allergy: Ciprofloxacin 500-750 mg twice daily PLUS metronidazole 500 mg three times daily 2
• Tetanus toxoid required if >10 years since last dose (Tdap preferred over Td if not previously given) 2
• Primary wound closure NOT recommended except for facial wounds, which require copious irrigation, cautious debridement, and preemptive antibiotics 2

Diabetic Patients and Injection Drug Users

• Clinically uninfected wounds require no antibiotics 1
• Mild infections require targeted narrow-spectrum antibiotics 1
• Moderate-severe infections require broad-spectrum coverage for aerobic and anaerobic organisms, with MRSA coverage if suspected 2
• Rule out foreign bodies with radiography and vascular complications with duplex ultrasound in injection drug users 2

Common Pitfalls to Avoid

• Do not use rifampin as monotherapy or adjunctive therapy for SSTI 2
• Avoid tetracyclines in children <8 years of age 2, 1
• Do not prescribe antibiotics for simple abscesses that can be adequately drained 1
• Clindamycin resistance varies by region—verify local resistance patterns before empiric use 2
• TMP-SMX and doxycycline lack reliable streptococcal coverage—must add β-lactam for non-purulent cellulitis 2