What is the recommended prophylactic antibiotic regimen for a leg hematoma?

Prophylactic Antibiotics for Leg Hematoma

Prophylactic antibiotics are NOT recommended for simple closed leg hematomas without an associated open wound or fracture. Hematomas alone, even if large, do not meet criteria for antibiotic prophylaxis as they represent clean, closed soft tissue injuries without communication to the external environment.

When Antibiotics ARE Indicated in Leg Injuries

Antibiotic prophylaxis or therapy is only warranted in specific traumatic leg injuries:

Open Fractures

• Start antibiotics immediately upon presentation, as delays beyond 3 hours significantly increase infection risk 1
• First-generation cephalosporin (cefazolin) is the first-line agent for most cases 2
  • Adult dosing: 1-2 grams IV 3
  • Redose every 4 hours during prolonged procedures 2
• Duration depends on fracture severity 1:
  • Gustilo-Anderson Grade I and II: 3 days
  • Gustilo-Anderson Grade III: 5 days
• Add aminoglycoside for severe injuries requiring enhanced gram-negative coverage 1
• Add penicillin for soil contamination or tissue ischemia to cover anaerobes, particularly Clostridium species 1

Surgical Procedures on Closed Fractures

• Single preoperative dose of cefazolin given within 60 minutes before incision 1
• Continue for maximum 24 hours postoperatively 1, 4
• Longer courses do not reduce infection rates and increase antibiotic resistance 1, 5

Why Hematomas Do NOT Require Antibiotics

The available guidelines specifically address contaminated or potentially contaminated wounds 1, 5, 4. A closed hematoma represents:

• Class I (clean) injury without breach of skin integrity 1
• No bacterial contamination from external environment 5
• Brief, undefined contamination period - prophylaxis only works when contamination is "brief, defined and predictable" 5

Prophylactic antibiotics do not prevent infection in situations with continuing contamination or when there is no initial contamination 5. Using antibiotics without indication only promotes antibiotic-resistant infections 5.

Critical Pitfalls to Avoid

• Do not prescribe antibiotics for closed soft tissue injuries including hematomas, as this increases resistance without benefit 5
• Do not confuse hematoma with open fracture - only open wounds communicating with bone require antibiotics 2
• Do not extend prophylaxis beyond 24 hours for surgical procedures on closed injuries 1, 4
• Do not delay antibiotics if truly indicated (open fractures) - the 3-hour window is critical 1, 2