What antibiotic is recommended for outpatient treatment of a wound infection following a knee replacement?

Antibiotic Treatment for Wound Infection Following Knee Replacement

For outpatient treatment of a wound infection following knee replacement, first-line therapy should be oral cloxacillin, cephalexin, or amoxicillin-clavulanic acid, with vancomycin added if MRSA is suspected. 1

Pathogen Considerations

The choice of antibiotic should be guided by the most likely pathogens involved in prosthetic joint infections:

• Staphylococcus aureus (including MSSA and MRSA) is the predominant pathogen in surgical site infections following knee replacement
• Streptococcus species are also common
• Gram-negative organisms may be involved in some cases

Antibiotic Selection Algorithm

First-line therapy (empiric treatment):

• MSSA coverage options:
  • Cephalexin 500 mg PO QID 1
  • Cloxacillin 500 mg PO QID 1
  • Amoxicillin-clavulanic acid 875/125 mg PO BID 1

When MRSA is suspected or confirmed:

• Add or switch to:
  • Vancomycin (dosed by weight) 1
  • Linezolid 600 mg PO BID 1
  • Sulfamethoxazole-trimethoprim DS 1-2 tabs PO BID 1
  • Doxycycline 100 mg PO BID 1

For surgical site infections with systemic signs:

• Consider initial parenteral therapy with:
  • Cefazolin 1-2 g IV q8h 1, 2
  • Vancomycin 15 mg/kg IV q12h (if MRSA suspected) 1, 3

When to Suspect MRSA

Add MRSA coverage when:

• Prior history of MRSA colonization or infection
• High local prevalence of MRSA
• Clinically severe infection
• Failed initial beta-lactam therapy
• Risk factors (recent hospitalization, recent antibiotic use) 1, 3

Duration of Therapy

• For superficial wound infections: 7-14 days of antibiotics
• For deeper infections involving the prosthesis: consultation with orthopedic surgery and infectious disease is required, as longer courses (often 4-6 weeks) may be necessary 1

Important Clinical Considerations

• Surgical intervention: Incision and drainage should be performed for all surgical site infections in addition to antibiotic therapy 1
• Culture before antibiotics: When possible, obtain deep tissue specimens (not surface swabs) before starting antibiotics 3
• Adjust therapy: Once culture and sensitivity results are available, narrow therapy to the most appropriate agent 3
• Monitor for treatment failure: Persistent fever, increasing pain, wound drainage, or systemic symptoms may indicate treatment failure requiring hospitalization and surgical intervention 1

Pitfalls to Avoid

1. Do not rely on surface swabs: Surface swab cultures often represent colonization rather than the true pathogen causing deep infection 1, 3
2. Do not continue antibiotics indefinitely: Prolonged antibiotic use should be avoided unless there is evidence of prosthetic joint involvement 3
3. Do not miss MRSA: Failure to cover MRSA when risk factors are present can lead to treatment failure 1, 3
4. Do not neglect surgical management: Antibiotics alone are often insufficient; surgical debridement is frequently necessary 1

For wound infections following knee replacement, prompt and appropriate antibiotic therapy combined with surgical management when indicated is essential to prevent progression to deeper prosthetic joint infection, which would significantly increase morbidity and potentially require prosthesis removal.