Introduction
Surgical site infection (SSI) is one of the commonest complications of surgery. Surgical antibiotic prophylaxis (SAP) is proven to reduce it, but only when given correctly: for the right operations, with the right drug, at the right time and for a short time.
Indications
Benefit varies: NNT about 4 in colorectal surgery, 11 in appendicectomy, 57 for joint infection in arthroplasty.
Choice of drug
- Bactericidal, covering the likely skin and site organisms, good tissue penetration, safe and cheap.
- Cefazolin (1st-generation cephalosporin) 2 g IV (3 g if > 120 kg) is the drug of choice for most operations.
- Add metronidazole 500 mg IV when anaerobes are likely (colorectal, appendix, gynaecological).
- Alternatives: co-amoxiclav 1.2 g, cefuroxime; if high local resistance, a 2nd or 3rd generation cephalosporin.
- β-lactam allergy: clindamycin or vancomycin, combined with gentamicin, ciprofloxacin or metronidazole as needed.
- Known MRSA carriers: add vancomycin (and decolonise beforehand).
Timing, dose and duration
- A single IV dose within 60 minutes before the skin incision (30–60 min; vancomycin and fluoroquinolones 60–120 min), so tissue levels are high when the wound is open.
- Repeat the dose if the operation lasts longer than 2 half-lives of the drug (about 4 hours for cefazolin), or after major blood loss (> 1,500 ml) or large fluid infusions.
- Stop at the end of the operation (at most 24 hours). Longer courses do not lower SSI but increase resistance, C. difficile and cost.