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

Treatment of Methicillin-Sensitive Staphylococcus Aureus (MSSA) Bacteremia

For MSSA bacteremia, antistaphylococcal beta-lactams such as nafcillin, oxacillin, or cefazolin are the first-line treatments due to superior clinical outcomes compared to vancomycin or other alternatives. 1, 2

First-Line Treatment Options

Preferred Agents

• Nafcillin or oxacillin: 2g IV every 6 hours for 2-6 weeks 1, 2
• Cefazolin: 1-2g IV every 8 hours for 2-6 weeks 1, 2, 3

Important Considerations

• Beta-lactams are superior to vancomycin for MSSA bacteremia 4, 3
• In a study comparing hemodialysis patients with MSSA bacteremia, those treated with vancomycin had a 3.5 times higher risk of treatment failure compared to cefazolin 4
• No significant difference in mortality has been observed between nafcillin/oxacillin and cefazolin in comparative studies 3

Special Clinical Scenarios

Brain Abscess/CNS Involvement

• Nafcillin is preferred over cefazolin due to better blood-brain barrier penetration 1
• If patient cannot tolerate nafcillin, use vancomycin 1

Reported Penicillin Allergy

1. Evaluate allergy history - most patients reporting penicillin allergy are not truly allergic 5
2. If no history of anaphylaxis: Consider cefazolin 5
3. If severe allergy: Use vancomycin 15 mg/kg IV every 12 hours 1, 2

Duration of Therapy

Clinical Scenario	Duration
Uncomplicated bacteremia	Minimum 14 days [2,6]
Complicated bacteremia (endocarditis, metastatic infection)	4-6 weeks [2,6]

Source Control

• Identify and remove any potential source of infection (intravascular devices, abscesses) 6
• Retention of infected devices (e.g., hemodialysis access) is associated with nearly 5 times higher risk of treatment failure 4

Monitoring

• Follow blood cultures until clearance of bacteremia
• Persistent bacteremia (≥48 hours) is associated with 39% mortality risk at 90 days 6
• Perform transthoracic echocardiography for all patients with S. aureus bacteremia 6
• Consider transesophageal echocardiography for patients with:
  • Persistent bacteremia
  • Persistent fever
  • Metastatic infection foci
  • Implantable cardiac devices 6

What NOT to Do

• Avoid vancomycin for MSSA bacteremia when beta-lactams can be used 4, 3
• Avoid gentamicin combination therapy - it does not reduce mortality or cardiac complications and increases nephrotoxicity 1
• Avoid once-daily regimens like ceftriaxone - insufficient evidence supports their use for MSSA bacteremia 7
• Avoid piperacillin/tazobactam as monotherapy - associated with higher mortality compared to nafcillin/oxacillin/cefazolin 3

Common Pitfalls

1. Inadequate duration of therapy - treat for at least 14 days for uncomplicated cases
2. Failure to identify and address metastatic foci - occurs in more than one-third of cases 6
3. Using vancomycin when beta-lactams are appropriate - significantly worse outcomes 4
4. Not removing infected devices - associated with treatment failure 4
5. Inadequate follow-up - failure to monitor for clearance of bacteremia

By following these evidence-based recommendations, you can optimize outcomes for patients with MSSA bacteremia and reduce the risk of treatment failure, recurrence, and mortality.