What is the dosing regimen for Keflex (cephalexin) in postoperative incisional drainage?

Keflex (Cephalexin) Dosing for Postoperative Incisional Drainage

Direct Answer

For postoperative incisional surgical site infections (SSIs) requiring drainage, cephalexin should be dosed at 500 mg orally four times daily (or 500 mg every 6 hours) for adults when systemic signs of infection are present. 1, 2

When Antibiotics Are Indicated

Antibiotics are NOT routinely needed for simple incisional drainage alone. The key decision point is whether systemic signs of infection are present: 1

• Antibiotics ARE indicated when incisional SSIs present with:

  • Any SIRS (Systemic Inflammatory Response Syndrome) criteria 1
  • Signs of organ dysfunction (hypotension, oliguria, decreased mental alertness) 1
  • Immunocompromised status 1

• Antibiotics may NOT be needed for:

  • Simple superficial incisional SSIs without systemic signs after adequate drainage 1
  • Uncomplicated abscesses after incision and drainage (cure rates of 90.5% without antibiotics in one trial) 3

Standard Dosing Regimen

Adults

• Standard dose: 500 mg orally every 6 hours (four times daily) 2
• Alternative for less severe infections: 500 mg every 12 hours 2
• Severe infections: May require up to 1-4 grams daily in divided doses 2
• Duration: Typically 7-10 days depending on clinical response 4, 2

Pediatric Patients

• Standard dose: 25-50 mg/kg/day in divided doses 2
• Severe infections: Dosage may be doubled 2

Critical Timing Considerations

Important distinction: The question asks about treatment of established postoperative infection, NOT prophylaxis. The following applies to prophylaxis only (not your scenario): 1

• Prophylactic antibiotics should be given within 60-120 minutes before incision 1
• Prophylactic antibiotics should NOT be continued postoperatively - this is explicitly not recommended and potentially harmful 1

Clinical Pitfalls and Caveats

Major Limitations of Cephalexin

Cephalexin has NO activity against MRSA - if community-acquired MRSA is suspected or confirmed, alternative agents (trimethoprim-sulfamethoxazole, doxycycline, or clindamycin) must be used instead. 4, 3 In one trial, 87.8% of skin/soft tissue isolates were MRSA, and cephalexin showed no benefit over placebo. 3

When to Avoid or Modify Treatment

• Cross-reactivity concern: Use caution in patients with immediate hypersensitivity reactions to penicillin (anaphylaxis, angioedema, urticaria) 1, 4
• Renal impairment: Reduce dosage proportionally when creatinine clearance <30 mL/min 5
• Limited spectrum: Cephalexin has poor activity against Pasteurella multocida and anaerobes 4

Monitoring Response

• If no improvement within 5 days: Extend treatment duration and consider broadening coverage 4
• If systemic signs develop or worsen: Consider broader antimicrobial coverage, imaging for deeper infection, or repeat surgical intervention 1, 4

Practical Administration

• Cephalexin is absorbed in the upper intestine (not stomach), achieving rapid tissue distribution 5
• Urinary concentrations reach 500-1000 mcg/mL after 250-500 mg doses 5
• 70-100% excreted unchanged in urine within 6-8 hours 5
• Low protein binding and no metabolism in body fluids 5