What is the recommended dose and duration of Keflex (Cephalexin) for antibiotic prophylaxis in a patient with normal renal function undergoing minor amputation?

Keflex Dosing for Minor Amputation

For antibiotic prophylaxis in minor amputation, administer cephalexin (Keflex) 500 mg orally every 6 hours, with a typical duration of 2-5 days postoperatively, though single-dose or 24-hour prophylaxis may be sufficient for clean procedures. 1, 2

Recommended Dosing Protocol

Standard Prophylactic Regimen

• Cephalexin 500 mg orally every 6 hours (q6h) is the established dose for perioperative prophylaxis in surgical procedures 1
• For minor amputations, this oral first-generation cephalosporin provides adequate coverage against the primary pathogens: S. aureus, S. epidermidis, and Streptococcus species 1, 3

Duration Considerations

• 2-day prophylaxis is as effective as 5-day regimens for contaminated traumatic wounds requiring closure, with infection rates of 8.57% versus 7.14% respectively (no statistical difference, P=0.31) 2
• Current surgical prophylaxis guidelines emphasize limiting duration to 24 hours maximum for most procedures to minimize antibiotic resistance 1, 4
• In practice, foot and ankle surgeons commonly prescribe 5-7 days of prophylaxis (50% of users), though this exceeds evidence-based recommendations 5

Clinical Decision Algorithm

For clean minor amputations (no active infection):

• Single preoperative dose or 24-hour prophylaxis is appropriate 1
• Cephalexin 500 mg q6h for 24 hours postoperatively 1

For contaminated wounds or high-risk patients:

• Extend to 2 days of cephalexin 500 mg q6h, which provides equivalent protection to longer courses 2
• Consider up to 5 days only if significant contamination or patient-specific risk factors exist 2, 5

High-Risk Indications for Extended Prophylaxis

Surgeons most commonly extend prophylactic antibiotics for: 5

• Previous infection at the surgical site (71% of surgeons cite this indication)
• Medical comorbidities such as diabetes, peripheral vascular disease, or immunosuppression (65%)
• Previous wound-healing difficulties (56%)

Pharmacologic Rationale

• Cephalexin achieves urinary concentrations of 500-1000 mcg/mL after 250-500 mg oral doses, far exceeding MIC for common pathogens 3
• The drug is rapidly and completely absorbed from the upper intestine, with 70-100% recovered in urine within 6-8 hours 3
• Tissue penetration is adequate even in ischemic limbs, with both cephalosporins and other agents reaching therapeutic levels equivalent to MIC50 for vascular surgery pathogens 6

Alternative Regimens

For patients with beta-lactam allergy:

• Clindamycin 900 mg IV as single dose, or 600 mg IV every 8 hours for extended prophylaxis 1
• Fluoroquinolones (ciprofloxacin 500 mg PO q12h or levofloxacin 500 mg PO single dose) are alternatives, though typically reserved for specific urologic indications 1

Comparative evidence from lower limb amputations:

• Penicillin G and cefuroxime showed equivalent efficacy (13% vs 17% wound sepsis rates, P>0.05) in below-knee and above-knee amputations 7
• This suggests first-generation cephalosporins like cephalexin are appropriate choices 7

Critical Pitfalls to Avoid

• Do not routinely extend prophylaxis beyond 24-48 hours unless specific high-risk factors are present, as this increases antibiotic resistance without improving outcomes 1, 2
• Do not assume ischemic tissue has inadequate antibiotic penetration—studies confirm therapeutic levels are achieved even in severely ischemic limbs 6
• Adjust dosing in renal impairment: patients with creatinine clearance <30 mL/min require dose reduction proportional to renal function 3
• The presence of surgical drains does not justify extending prophylaxis duration 1

Renal Dosing Adjustment

• For patients with creatinine clearance <30 mL/min, reduce cephalexin dosage proportionally based on measured creatinine clearance or serum creatinine 3
• Standard dosing applies to patients with normal renal function 3