What is the treatment for Methicillin-Sensitive Staphylococcus Aureus (MSSA) bacteremia using Flucloxacillin?

Treatment of MSSA Bacteremia with Flucloxacillin

Flucloxacillin is a first-line treatment option for methicillin-sensitive Staphylococcus aureus (MSSA) bacteremia, administered at 2g IV every 6 hours. 1, 2

First-Line Treatment Options for MSSA Bacteremia

• Antistaphylococcal beta-lactams are the preferred first-line treatment for MSSA bacteremia due to their superior efficacy compared to vancomycin 1, 3
• Flucloxacillin (2g IV every 6 hours) is considered equivalent to other antistaphylococcal penicillins like nafcillin and oxacillin for treating MSSA bacteremia 4, 2
• Cefazolin (1-2g IV every 8 hours) is an effective alternative to flucloxacillin with comparable outcomes 5, 6
• Continuous infusion flucloxacillin (8-12g/day) may be considered after initial intermittent dosing, particularly for home-based parenteral therapy 7

Clinical Considerations

• For MSSA bacteremia with brain abscess or CNS involvement, flucloxacillin is preferred over cefazolin due to better blood-brain barrier penetration 4, 1
• Gentamicin should not be added to flucloxacillin therapy as it increases nephrotoxicity without improving clinical outcomes 4, 1
• Duration of therapy depends on the clinical scenario:
  • Uncomplicated bacteremia: minimum 2 weeks 2
  • Complicated bacteremia: 4-6 weeks 2
  • Infective endocarditis: 6 weeks 4

Monitoring and Follow-up

• Obtain follow-up blood cultures 2-4 days after initial positive cultures to document clearance of bacteremia 1, 2
• Persistent bacteremia (>48-72 hours) is a poor prognostic sign requiring investigation for metastatic foci of infection 2, 3
• Echocardiography is recommended for all adult patients with S. aureus bacteremia to rule out endocarditis 1, 2

Special Situations

• For patients with severe beta-lactam allergies, vancomycin (15-20 mg/kg IV every 8-12 hours) is the recommended alternative 1, 2
• Source control is critical for successful treatment of MSSA bacteremia, including removal of infected intravascular devices and drainage of abscesses 2, 3
• Flucloxacillin has demonstrated similar efficacy to nafcillin/oxacillin in observational studies, with no significant difference in 30-day mortality 5, 8

Potential Pitfalls

• Empiric vancomycin should be switched to flucloxacillin once MSSA is confirmed, as beta-lactams have superior outcomes for MSSA infections 4, 3
• The oxacillin MIC level (≥1 μg/mL vs <1 μg/mL) does not appear to affect treatment outcomes with flucloxacillin or cefazolin 6
• Piperacillin/tazobactam is associated with higher mortality compared to antistaphylococcal penicillins or cefazolin when used as monotherapy for MSSA bacteremia 8