What is the antibiotic of choice for an open fracture?

Antibiotic of Choice for Open Fractures

For open fractures, administer a first-generation cephalosporin (cefazolin 2g IV) as the antibiotic of choice, with treatment stratified by Gustilo-Anderson classification: Type I/II fractures require cephalosporin alone for 24 hours, while Type III fractures require the addition of an aminoglycoside (gentamicin) for 48-72 hours. 1, 2

Classification-Based Antibiotic Selection

Type I and II Open Fractures

• First-line agent: Cefazolin 2g IV slow, with re-injection of 1g if surgical duration exceeds 4 hours 3, 2
• This regimen effectively targets Staphylococcus aureus, streptococci, and aerobic gram-negative bacilli 1, 4
• Duration: Limited to operative period with maximum 24 hours after initial injury 3, 4
• Cefazolin achieves sustained concentrations above the minimum inhibitory concentration for S. aureus at the fracture site for 100% of the 24-hour period 5

Type III Open Fractures

• Combination therapy required: First-generation cephalosporin (cefazolin 2g IV) PLUS aminoglycoside (gentamicin 5 mg/kg/day) 3, 1
• This combination provides enhanced gram-negative coverage necessary for severe injuries 1, 4
• Duration: Continue for 48-72 hours after initial injury but no more than 24 hours after wound closure 4, 6
• The Surgical Infection Society specifically recommends against extending therapy beyond 24 hours post-injury in the absence of active infection 3

Special Contamination Scenarios

• Farm-related injuries or gross contamination: Add penicillin to cover anaerobic organisms including Clostridium species 1, 4
• This addition is warranted even for lower-grade fractures when contamination risk is high 1

Critical Timing Considerations

Antibiotics must be administered within 3 hours of injury to minimize infection risk, as delays beyond this window significantly increase infectious complications 1, 2, 4

For surgical intervention, ensure administration within 60 minutes before incision 1, 7

Beta-Lactam Allergy Alternatives

• First alternative: Clindamycin 900mg IV slow (600mg re-injection if duration exceeds 4 hours) 3, 2
• Severe allergy or MRSA concern: Vancomycin 30mg/kg over 120 minutes 3, 2
• For Type III fractures with beta-lactam allergy, combine clindamycin with gentamicin 3

Adjunctive Local Antibiotic Strategies

Local antibiotic delivery systems serve as valuable adjuncts, particularly in Type III fractures with bone loss 3, 1:

• Antibiotic-impregnated beads (tobramycin or gentamicin) 1
• Gentamicin-coated implants have demonstrated safety in clinical application 3
• Vancomycin powder may be beneficial 1

These local strategies supplement—but do not replace—systemic antibiotic therapy 1, 7

Alternative Regimen: Ceftriaxone

Ceftriaxone offers a practical alternative with 24-hour dosing and single-agent coverage even for Grade 3 fractures 8:

• Provides broader gram-negative coverage than cefazolin 8
• Reduces dosing frequency concerns and potential under-dosing based on weight 8
• Demonstrates equivalent efficacy to cefazolin without increased infectious complications 8

Common Pitfalls to Avoid

• Do not delay antibiotics beyond 3 hours post-injury, as this dramatically increases infection risk 1, 2, 7
• Do not use initial wound cultures to guide prophylactic antibiotic selection, as organisms cultured immediately post-injury do not correlate with infecting pathogens 4
• Do not add aminoglycosides for Type I/II fractures—reserve this for Type III injuries only 2
• Do not use antiseptics or soap additives for wound irrigation—simple saline solution is equally effective 1, 2
• Do not extend antibiotic duration beyond recommended timeframes (24 hours for Type I/II, 48-72 hours for Type III) without evidence of active infection 3, 7
• Adjust cephalosporin dosing based on patient weight and renal function to ensure adequate tissue concentrations 1, 7

Dosing Adjustments

Standard cefazolin dosing (2g IV) should be increased for patients weighing >120kg, and all dosing requires adjustment for renal impairment 1