Cefazolin Dosing for Open Fractures
For open fractures in adults with normal renal function, administer cefazolin 2 grams IV within 1 hour of presentation, then 1 gram IV every 8 hours for 24 hours after injury for Type I/II fractures, or 48-72 hours (but no more than 24 hours after wound closure) for Type III fractures, with additional gram-negative coverage required for Type III injuries. 1, 2
Timing of Initial Dose
The first dose must be given within 1 hour of presentation to the emergency department, and ideally 30-60 minutes before surgical incision 1, 2. Early antibiotic delivery is critical to lower deep infection risk 1.
Dosing by Fracture Grade
Type I and II Open Fractures
- Initial dose: 2 grams IV cefazolin
- Maintenance: 1 gram IV every 8 hours
- Duration: 24 hours after initial injury 1, 3
- Alternative if penicillin allergy: Clindamycin 1
Type III Open Fractures
- Initial dose: 2 grams IV cefazolin PLUS gram-negative coverage (gentamicin or ceftriaxone)
- Maintenance: 1 gram cefazolin IV every 8 hours
- Duration: 48-72 hours after injury, but discontinue within 24 hours after wound closure 1, 3
- Additional coverage: Add penicillin for farm-related injuries or gross contamination with soil 1, 3
Weight-Based Dosing Considerations
Standard dosing may be inadequate for larger patients. Weight-based cefazolin dosing should be:
- <80 kg: 1 gram per dose
- 80-120 kg: 2 grams per dose
- >120 kg: 3 grams per dose 4
Under-dosing is common (33% in one study) and significantly increases gram-positive infections susceptible to cefazolin 4. Five of seven (71%) gram-positive non-MRSA infections occurred in under-dosed patients 4.
Intraoperative Redosing
For lengthy procedures (≥2 hours), administer an additional 1 gram IV cefazolin intraoperatively 2. This maintains adequate tissue levels throughout the surgical exposure.
Critical Pitfalls to Avoid
- Don't use initial wound cultures to guide prophylactic antibiotic choice—infecting organisms don't correlate with initial cultures 3
- Don't continue antibiotics beyond 24 hours after wound closure for Type III fractures, even if continuing for 48-72 hours post-injury 1
- Don't forget weight-based dosing in patients ≥80 kg—standard 1-gram doses are insufficient 4
- Don't omit gram-negative coverage for Type III fractures—cefazolin alone is inadequate 1
Pharmacokinetic Evidence
Recent microdialysis studies demonstrate that 2-gram cefazolin dosing achieves sustained concentrations above the MIC for S. aureus (100% of time over 24 hours) at open fracture sites, despite delayed time to maximum concentration (2.7 hours injured vs 1.7 hours uninjured limb) 5. This validates current dosing recommendations for Type II and IIIA fractures 5.
Renal Dosing Adjustments
For patients with renal impairment:
- CrCl 35-54 mL/min: Full dose every 8 hours minimum
- CrCl 11-34 mL/min: Half dose every 12 hours after loading dose
- CrCl <10 mL/min: Half dose every 18-24 hours after loading dose 2