What is the recommended antibiotic regimen for surgical site infections?

Surgical Site Infection Antibiotic Treatment

For established surgical site infections, incision and drainage is the primary treatment, with antibiotics indicated only when systemic signs are present (temperature ≥38.5°C, heart rate ≥110 bpm, WBC >12,000/μL) or cellulitis extends >5 cm from the wound edge. 1, 2

Primary Management Principle

• Surgical drainage must be performed first—antibiotics alone are insufficient and represent the most common treatment error. 2, 3
• Suture removal plus incision and drainage should be performed for all surgical site infections. 1
• Obtain wound cultures before initiating antibiotics to guide definitive therapy. 2, 3

When Antibiotics Are Indicated

Add systemic antibiotics to surgical drainage when ANY of the following are present:

• Temperature ≥38.5°C 1, 2
• Heart rate ≥110 beats/minute 3
• White blood cell count >12,000/μL 3
• Erythema and induration extending >5 cm from wound edge 1, 2
• Systemic inflammatory response syndrome (SIRS) criteria present 1
• Deep tissue involvement or inability to completely drain the abscess 2

Antibiotic Selection by Surgical Site Location

Surgery of Trunk or Extremity (Away from Axilla/Perineum)

First-line options targeting S. aureus and streptococci:

• Cefazolin 1-2g IV every 8 hours (preferred agent) 1, 4
• Oxacillin or nafcillin 2g IV every 6 hours 1
• Cephalexin 500 mg PO every 6 hours (oral option) 1, 5
• Sulfamethoxazole-trimethoprim 160-800 mg PO every 6 hours 1

For MRSA (suspected or confirmed):

• Vancomycin 15 mg/kg IV every 12 hours 1, 2
• Linezolid (alternative) 1
• Clindamycin 900 mg IV or 300-450 mg PO three times daily 1, 2, 5
• Doxycycline 1

Surgery of Axilla or Perineum

Requires coverage for gram-negatives and anaerobes:

• Metronidazole 500 mg IV every 8 hours PLUS one of the following: 1
  • Ciprofloxacin 400 mg IV every 12 hours or 750 mg PO every 12 hours 1, 5
  • Levofloxacin 750 mg IV/PO every 24 hours 1, 5
  • Ceftriaxone 1g IV every 24 hours 1

Surgery of Intestinal or Genitourinary Tract

Single-drug broad-spectrum regimens:

• Piperacillin-tazobactam 3.375g IV every 6 hours or 4.5g IV every 8 hours 1, 3
• Ertapenem 1g IV every 24 hours 1, 3
• Meropenem 1g IV every 8 hours 1, 3
• Imipenem-cilastatin 500 mg IV every 6 hours 1

Combination regimens:

• Ceftriaxone 1g IV every 24 hours + metronidazole 500 mg IV every 8 hours 1
• Ciprofloxacin 400 mg IV every 12 hours + metronidazole 500 mg IV every 8 hours 1
• Levofloxacin 750 mg IV every 24 hours + metronidazole 500 mg IV every 8 hours 1

Duration of Antibiotic Therapy

• For simple SSIs with adequate drainage: 24-48 hours only 2
• For uncomplicated infections after adequate drainage: 5-7 days 3, 5
• For moderate to severe infections or immunocompromised patients: 7-10 days 2, 3, 5
• For deep tissue involvement or retained hardware: 4-6 weeks IV therapy 2

Critical Pitfalls to Avoid

• Do not prescribe antibiotics for simple abscesses without systemic signs—drainage alone is adequate. 2
• Do not extend prophylactic antibiotics beyond 24 hours postoperatively, as this does not prevent SSIs and promotes resistance. 1, 2, 3
• Do not use beta-lactam monotherapy if the surgical site involves the axilla, GI tract, perineum, or female genital tract—these require coverage for gram-negatives and anaerobes. 1, 5
• Do not rely on antibiotics alone without surgical drainage—this is the most common error leading to treatment failure. 2, 3, 5
• Always obtain wound cultures before starting antibiotics and adjust empiric therapy based on culture results. 2, 3

Special Considerations for Hernia Repair

For clean hernia repair SSIs:

• Cephalexin 500 mg PO every 6 hours provides excellent coverage for S. aureus and streptococci 5
• Dicloxacillin 500 mg PO four times daily (alternative) 5
• For MRSA: sulfamethoxazole-trimethoprim 1-2 double-strength tablets PO twice daily (preferred oral agent) 5