Cephalexin Dosing for Post-Traumatic Amputation
Cephalexin is not the recommended antibiotic for post-traumatic amputation prophylaxis; cefazolin 2g IV is the guideline-recommended agent, with prophylaxis limited to a maximum of 24 hours postoperatively. 1
Why Cephalexin Is Not Appropriate
Post-traumatic amputations are classified as contaminated or dirty procedures, particularly when associated with infected gangrene, and require IV antibiotic prophylaxis rather than oral agents. 1 The 2019 surgical prophylaxis guidelines specifically address vascular surgery amputations and trauma scenarios but do not include oral cephalexin as an option for these high-risk procedures. 1
Recommended Antibiotic Protocol
First-Line Therapy
- Cefazolin 2g IV slow infusion should be administered within 60 minutes before surgical incision 1, 2
- Redose with 1g IV if surgical duration exceeds 4 hours 1, 2
- Discontinue within 24 hours after surgery—extending prophylaxis beyond this provides no additional benefit and increases antimicrobial resistance risk 1, 3, 4
For Beta-Lactam Allergy
- Clindamycin 900 mg IV slow infusion plus gentamicin 5 mg/kg/day for contaminated wounds 1
- Alternatively, vancomycin 30 mg/kg over 120 minutes (infusion must be completed 30 minutes before incision) 1, 2
If Oral Cephalexin Must Be Used (Suboptimal)
If clinical circumstances absolutely require oral therapy after the immediate perioperative period (which is not guideline-supported), the FDA-approved dosing would be:
- Adults: 250-500 mg every 6 hours (standard dosing range 1-4g daily in divided doses) 5
- For severe infections: up to 4g daily in divided doses 5
- Cephalexin achieves urinary concentrations of 500-1000 micrograms/mL but has limited tissue penetration and does not enter host cells 6
Critical Clinical Caveats
Timing is everything: The antibiotic must be administered within 60 minutes before incision—earlier administration results in inadequate tissue levels, and later administration is less effective. 3, 4
Avoid prolonged prophylaxis: Continuing antibiotics beyond 24 hours postoperatively does not reduce infection rates and promotes resistance. 1, 3, 4 This is a common pitfall in trauma surgery.
Cephalexin has poor bone penetration: Studies show bone concentrations of only 3.2-10.6 micrograms/g with IV cefazolin, and cephalexin (oral) would achieve even lower levels. 7 For post-traumatic amputations involving bone, IV therapy is essential.
Renal adjustment: If the patient develops renal impairment (creatinine clearance <30 mL/min), cephalexin dosing must be reduced proportionally, though this is moot since IV cefazolin remains the preferred agent. 6, 8
Algorithm for Antibiotic Selection
- Is this perioperative prophylaxis? → Use cefazolin 2g IV, not cephalexin 1
- Is there beta-lactam allergy? → Use clindamycin + gentamicin or vancomycin 1
- Is surgery prolonged (>4 hours)? → Redose cefazolin 1g IV 1, 2
- Is it >24 hours postoperatively? → Stop all prophylactic antibiotics 1, 3, 4
- Is there established infection requiring treatment (not prophylaxis)? → This requires therapeutic dosing and culture-directed therapy, not prophylaxis protocols
Bottom line: Cephalexin has no role in post-traumatic amputation prophylaxis. Use IV cefazolin as outlined above.