What is the best treatment for an infected large abscess on the back?

Treatment of Large Infected Abscess on the Back

The best treatment for a large infected abscess on the back is immediate incision and drainage with multiple counter-incisions if needed, followed by selective antibiotic therapy based on the patient's systemic signs of infection. 1

Primary Treatment: Surgical Drainage

Incision and drainage is mandatory and should never be delayed for any abscess, regardless of size—this is the most important therapeutic intervention. 1

Surgical Technique for Large Abscesses

• Use multiple counter-incisions rather than a single long incision to prevent step-off deformity and delayed wound healing. 1
• Thoroughly evacuate all pus and probe the cavity to break up loculations. 1
• Simply covering the surgical site with a dry dressing is usually effective, though some clinicians pack with gauze. 1
• Packing may be omitted without compromising outcomes, as recent evidence shows no difference in recurrence rates, and it eliminates painful packing removal. 2
• However, for abscesses >5 cm, packing may reduce recurrence and complications. 3

Critical Timing

• Do not delay drainage while waiting for laboratory results—drainage is the priority. 1
• Obtain culture of the drained fluid to adapt antibiotic therapy according to microbiological results. 1

Antibiotic Therapy Decision Algorithm

When Antibiotics Are NOT Needed (Simple Abscess)

Skip antibiotics if ALL of the following criteria are met after drainage: 1

• Temperature <38.5°C
• White blood cell count <12,000 cells/µL
• Heart rate <100 beats/minute
• Erythema and induration extending <5 cm from the abscess

When Antibiotics ARE Indicated (Complex Abscess)

Administer antibiotics if ANY of the following are present: 1

• Temperature >38.5°C or signs of SIRS (temperature >38°C or <36°C, tachycardia >90 bpm, tachypnea >24 breaths/min, WBC >12,000 or <4,000 cells/µL)
• Immunocompromised status
• Incomplete source control
• Significant surrounding cellulitis (>5 cm extension)

Antibiotic Selection for Back Abscesses

First-Line Oral Regimen (Trunk Location)

For immunocompetent patients with adequate drainage and mild systemic signs: 1

• Cephalexin 500 mg every 6 hours OR
• Dicloxacillin 500 mg every 6 hours

Alternative for MRSA or Penicillin Allergy

• Clindamycin 300-450 mg every 6-8 hours 1, 4
• Note: Clindamycin has higher adverse event rates (21.9%) compared to other options but reduces new infection rates at 1 month (6.8% vs 12-13%). 5

For Complex/Severe Cases Requiring IV Therapy

If critically ill, immunocompromised, or inadequate source control: 6

• Piperacillin/tazobactam 4 g/0.5 g IV every 6 hours (first-line for broad coverage)
• Consider adding vancomycin or linezolid if MRSA is suspected or documented

Duration of Antibiotic Therapy

Base duration on clinical response and patient risk factors: 1, 6

• 4-7 days for immunocompetent patients with adequate drainage and minimal systemic signs
• Up to 7 days for immunocompromised or critically ill patients with adequate source control
• 2-6 weeks for complex cases or inadequate drainage

Laboratory Evaluation

Obtain the following tests: 1

• Culture of drained fluid (mandatory for all drained abscesses)
• Blood cultures if bacteremia or sepsis suspected
• CBC and CRP to assess infection severity (CRP >100 mg/L indicates severe infection requiring increased surveillance)
• Consider liver and kidney function if prolonged antibiotic therapy planned

Critical Pitfalls to Avoid

• Never attempt needle aspiration—it has a low success rate of 25% and <10% with MRSA infections. 1
• Never treat with antibiotics alone without drainage, even if inflammatory markers are elevated—source control is essential. 1
• Do not use inadequate antibiotic coverage after drainage of complex abscesses, as this results in a six-fold increase in readmission rates for recurrence. 7
• Persistent fever, bacteremia, or failure to improve beyond 7 days indicates inadequate source control requiring repeat imaging and potential reoperation. 1, 6

Evidence Quality Note

The recommendation prioritizes the 2025 World Journal of Emergency Surgery guidelines 1 and Infectious Diseases Society of America recommendations 1, which provide the most comprehensive and recent evidence. The 2017 NEJM trial 5 demonstrated that antibiotics (clindamycin or TMP-SMX) improve cure rates from 68.9% to 81-83% for abscesses ≤5 cm, but this benefit must be weighed against side effects in simple cases meeting criteria for observation alone.