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Antibiotic Prophylaxis

Definition

  • Administration of antibiotics to patients undergoing surgery without clinical evidence of infection in operative field

Objectives

  • 1. Prevent naturally occurring organisms in one site from proliferating at normally sterile site
  • 2. Prevent organisms contaminating normally sterile site from producing disease
  • 3. Prevent infection by exogenous organisms

Indications

  • Unacceptably high incidence of infection
  • Low incidence of infection where infection devastating or lethal

The Ideal Agent

  • Active against typical infecting bugs
  • Long serum T½
  • Non-toxic
  • Inexpensive
  • Each institution should individualize prophylaxis
    • Based on susceptibility patterns
  • Cefazolin extensively studied
  • Consider Vancomycin if high rates of MRSA infection

Cefazolin

  • Broad spectrum activity against common pathogens
    • Effective against Staphylococcus, Streptococcus & Gram negative organisms
  • Long serum T½
  • High concentration in bone & soft tissue
  • Relatively non-toxic & inexpensive
  • Studied extensively
  • Criticized as high rates of ß-lactam resistance in community
  • Cefazolin theoretically best due to
    • Longer half life
    • Tds dosage
    • Higher bone concentrations
    • Dosage
      • 2g preoperatively
      • 1g post-op
    • Timing
      • Immediate preop
      • Peak levels reached 20-40 mins post IV bolus
      • Before tourniquet inflated
      • Give second dose if prolonged surgery
      • Adequate levels maintained for 2 hours with cephalothin & 4 hours with cefazolin
    • Duration
      • 24 hours sufficient
        • Nelson
          • No difference between 1 day & 7 days
        • Wymenga
          • No difference between 1 dose & 3 doses
        • Probably don’t need to continue until removal of drains
          • Shorter duration
          • Less expensive
          • Lower side effects
          • Less resistant organisms

Vancomycin

  • Effective against MRSA
  • Poor activity against Gram negative organisms
  • Need additional Gram negative cover
  • Expensive agent & relatively toxic

Timing of Prophylaxis

  • Need minimum of 5 minutes to achieve bactericidal levels in bone & fat from administration to tourniquet inflation
  • Classen 1992 N Eng J Med
    • Prospective trial
    • 2 847 patients
    • Infections lower if prophylaxis given 2 hours prior to skin incision

Duration of Prophylaxis

  • Not definitely established
  • Studies suggest 1 dose = 3 doses
    • But lack statistical power
  • Most authorities recommend 1 preoperative dose with 2-3 doses postoperative

Efficacy

  • Charnley
    • Initial infection rates of 9% in first 190 hips & reduced to 1.7% with laminar flow & body exhaust
  • Lidwell MRC trial
      • 1974-79
      • 8000 patients
    • Control infection rate 3.4%
    • Reduced to
      • 0.85% with antibiotics
      • 1.7% with ultraclean air
      • 0.4% with AB + ultraclean air
      • 0.2% with addition of body exhaust

Specific Uses

  • Prosthetic Joints
    • Reduction from 4% to < 1% with prophylactic antibiotics
  • Femoral Fractures
    • Shown to be effective
    • Boyd 1973
      • Reduced from 5% to 1% in hip pinning
  • Clean Orthopaedic Surgery
    • No adequate trials
    • Often useful in laminectomy & surgery > 2 hours
    • Probably not routinely justified

Summary of Antibiotic Prophylaxis

  • Appropriate Antiobiotic
    • 1st generation Cephalosporin
  • Timing of prophylaxis
    • Aim for 4x MIC in bone & fat
    • Need minimum 5min to achieve bacteriocidal levels in bone & fat from administration to tourniquet inflation
    • Infections lower if prophylaxis given 2 hours prior to skin incision
  • Duration of prophylaxis
    • not established but most authorities recommend 1 preoperative dose with 2-3 doses postoperative

 

 

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